JP5265404B2 - Nitride semiconductor light emitting device and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a light emission spectrum with a full width at half maximum by an LED. <P>SOLUTION: A nitride semiconductor light emitting element has an AlInGaN layer 101 formed of an Al<SB>X</SB>In<SB>Y</SB>Ga<SB>1-X-Y</SB>N (0&le;X&lt;1, 0&le;Y&lt;1, and 0&le;X+Y&lt;1) crystal and spreading in a direction parallel to an (m) plane as the ä1-100} plane of the crystal, and an InGaN light emission layer 102 located on the AlInGaN layer 101 and formed of an In<SB>Z</SB>Ga<SB>1-Z</SB>N (0&lt;Z&lt;1) crystal. The upper surface of the AlInGaN layer 101 includes at least one first inclined plane 101a inclined in a [0001] direction from the (m) plane and at least one second inclined plane 101b inclined in a [000-1] direction from the (m) plane. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a nitride semiconductor light emitting device using an InGaN light emitting layer capable of emitting light from the ultraviolet region to the red region, and a method for manufacturing the same.

A nitride semiconductor having nitrogen (N) as a group V element is considered promising as a material for a short-wavelength light-emitting element because of its large band gap. Among them, gallium nitride-based compound semiconductors (GaN-based semiconductors: Al _x Ga _y In _z N (0 ≦ x, y, z ≦ 1, x + y + z = 1)) are actively studied, and blue light emitting diodes (LEDs). In addition, green LEDs and semiconductor lasers made of GaN-based semiconductors have been put into practical use, and white LEDs have been actively developed for applications such as lighting.

  In a white LED (Light-Emitting Diode) that has already been put to practical use, a method of obtaining a pseudo white color by exciting a YAG (Yttrium Aluminum Garnet) phosphor using a blue LED fabricated from a GaN-based semiconductor as an excitation light source is generally used. It has been.

The GaN-based semiconductor has a wurtzite crystal structure. FIG. 1 schematically shows a unit cell of GaN. In a crystal of Al _x Ga _y In _z N (0 ≦ x, y, z ≦ 1, x + y + z = 1), a part of Ga shown in FIG. 1 can be substituted with Al and / or In.

FIG. 2 shows the primitive translation vectors a ₁ , a ₂ , a ₃ of the wurtzite crystal structure. The basic translation vector a ₃ extends in the [0001] direction, and this direction is called “c-axis”. A plane perpendicular to the c-axis is called “c-plane” or “(0001) plane”. The c-plane is a “polar plane”, but the (1-100) plane shown in FIG. 2 is a nonpolar plane and is referred to as an “m-plane”.

  The blue LED serving as the excitation light source has the following problems.

  (1) The emission wavelength fluctuates due to variations in manufacturing processes and the influence of heat generation.

  (2) Since the full width at half maximum (FWHM) of the emission spectrum is narrow, it is difficult to excite the phosphor with light of an appropriate wavelength, and the excitation efficiency of the phosphor is significantly attenuated.

  (3) Conventionally, the c-plane ({0001} plane) of a gallium nitride based semiconductor is used as an underlayer for crystal growth. Since the c-plane of a gallium nitride semiconductor is a polar plane, electrons and holes are spatially separated due to spontaneous polarization and the influence of a large piezoelectric field, and the recombination probability is lowered, so that the internal quantum efficiency is lowered. .

  In order to solve these problems, Patent Document 1 and Non-Patent Document 1 disclose white LEDs that obtain a plurality of different emission wavelengths from one blue LED. FIG. 15 is a cross-sectional view showing a light emitting layer in a conventional blue LED described in Non-Patent Document 1. The upper surface of the nitride layer 1201 shown in FIG. 15 has a c-plane that is a polar surface and a plurality of inclined surfaces that are inclined from the c-plane. These inclined surfaces are nonpolar surfaces or semipolar surfaces. The InGaN light emitting layer 1202 is formed on the top surface of the nitride layer 1201 having such irregularities. Specifically, InGaN light-emitting layers are formed on five surfaces, the (11-22) plane, the (-1-122) plane, the (11-20) plane, and the (-1-120) plane. Thus, in Non-Patent Document 1, the In composition of the light emitting layer on each surface is changed by growing InGaN on a plurality of non-equivalent surfaces.

  On the other hand, in order to realize high efficiency of LEDs, in recent years, as disclosed in Patent Document 2 and Non-Patent Document 2, an LED in which an InGaN light-emitting layer is formed with a nonpolar surface or a semipolar surface as a main surface is provided. Has been developed. FIG. 16 is a cross-sectional view showing a light emitting layer formed on a nitride layer having a nonpolar surface as a surface described in Non-Patent Document 2.

In FIG. 16, the InGaN light emitting layer 1302 has a nonpolar surface with an off-angle as a main surface. The nitride layer 1301 has a non-polar surface having the same off-angle as the light emitting layer 1302 as a main surface.
Japanese Patent Laid-Open No. 11-289108 JP-A-11-112029 Applied PhysiCs Express 1, 011106 (2008). Journal of Crystal Growth, 310, 4968 (2008).

  However, in the conventional LED structure that realizes light emission of a plurality of wavelengths from one element on the c-plane (Non-Patent Document 1), in order to obtain various emission wavelengths, a plurality of non-equivalent surfaces are selected and InGaN light emission is performed. It was necessary to change the In composition in the layer. However, the (11-22) plane and the (-1-122) plane are equivalent to each other in the atomic arrangement. Similarly, the (11-20) plane and the (-1-120) plane are also in the mutual atomic arrangement. Are equivalent planes, so that the amounts of In taken in are equal in the (11-22) plane and the (-1-122) plane, the (11-20) plane and the (-1-120) plane, and as a result, the same light emission Wavelength. That is, in the case of Non-Patent Document 1, five surfaces are formed, but only three types of wavelengths of light are obtained. This is because in the light emitting layer on the c-plane, the crystal symmetry is strong around the c-axis, so that the atomic arrangement on the inclined plane tends to be equivalent.

  This problem also applies to the element of Patent Document 2.

  Therefore, when the full width at half maximum of the emission spectrum is widened using the methods of Non-Patent Document 1 and Patent Document 2, it is necessary to select and form a plurality of non-equivalent surfaces, and the manufacturing method becomes complicated. there were.

  In addition, in the conventional LED configuration disclosed in Patent Document 2 in which the semipolar plane is the inclined surface of the InGaN light emitting layer, the inclination angle is as large as at least 10 °, and thus it is difficult to manufacture the light emitting element. There was a problem. This problem is also present in Non-Patent Document 1.

  Further, the structure of a conventional LED that emits different emission wavelengths from one light emitting element disclosed in Patent Document 1 utilizes nonuniformity of the In composition by deteriorating the crystallinity of the light emitting layer. Such a technique has a problem that the internal quantum efficiency is not improved in addition to the difficulty of controlling the In composition.

  Furthermore, in the structure of the conventional LED disclosed in Non-Patent Document 2 having a nonpolar surface with an off angle on the main surface, the peak wavelength of the emission spectrum is shifted, but there is a change in the full width at half maximum. There is no problem.

  The present invention solves the conventional problems, effectively widens the full width at half maximum of the emission spectrum of the LED, improves the excitation efficiency to the phosphor absorption line, and at the same time effectively improves the color rendering of the white LED. In addition, an object of the present invention is to provide a nitride semiconductor light emitting device in which a decrease in internal quantum efficiency due to a piezoelectric field is improved, and a manufacturing method thereof.

The nitride semiconductor light emitting device of the present invention is formed of Al _x In _Y Ga _1-XY N (0 ≦ X <1, 0 ≦ Y <1, 0 ≦ X + Y <1) crystal, and {1-100 of the crystal } surface and AlInGaN layer extending in a direction parallel to the m-plane is located on the AlInGaN layer, nitride and a _{in Z Ga 1-Z N (} 0 <Z <1) InGaN light-emitting layer formed from a crystalline In the semiconductor light emitting device, the upper surface of the AlInGaN layer has at least one first inclined surface inclined in the [0001] direction from the m plane and at least one inclined in the [000-1] direction from the m plane. Two second inclined surfaces.

  In a preferred embodiment, the InGaN light emitting layer has a first inclined portion located on the first inclined surface of the AlInGaN layer and a second inclined portion located on the second inclined surface of the AlInGaN layer. The emission wavelength of the first inclined part is different from the emission wavelength of the second inclined part.

In a preferred embodiment, when the entire area of the first inclined portion is S ₁ and the entire area of the second inclined portion is S _{2 on} the surface of the InGaN light emitting layer, S ₁ and S _{2 are} substantially equal to each other. equal.

In a preferred embodiment, 0.5 ≦ S ₂ / S ₁ ≦ 2 is satisfied.

  In a preferred embodiment, the absolute value of the angle formed by the first inclined surface and the m plane of the AlInGaN layer and the absolute value of the angle formed by the first inclined surface and the m surface are both 0. It is in a range greater than 5 degrees and less than 5 degrees.

  In a preferred embodiment, the first inclined surface and the second inclined surface of the AlInGaN layer are alternately arranged along the [0001] direction.

  In a preferred embodiment, the first inclined surface and the second inclined surface of the AlInGaN layer are each composed of a plane.

  In a preferred embodiment, the AlInGaN layer includes a plurality of the first inclined surfaces and the second inclined surfaces, and an absolute value of an angle formed by the plurality of first inclined surfaces and the m-plane. Are equal to each other, and the absolute values of the angles formed by the plurality of second inclined surfaces and the m-plane are also equal to each other.

  In a preferred embodiment, the AlInGaN layer includes a plurality of the first inclined surfaces and the second inclined surfaces, and an absolute value of an angle formed by the plurality of first inclined surfaces and the m-plane. The absolute values of the angles formed by the plurality of second inclined surfaces and the m-plane are different from each other.

  In a preferred embodiment, the upper surface of the AlInGaN layer has at least one horizontal plane parallel to the m-plane, and the InGaN light emitting layer has a horizontal portion located on the horizontal plane of the AlInGaN layer. Yes.

  In a preferred embodiment, the first inclined surface, the horizontal surface, and the second inclined surface of the AlInGaN layer are alternately arranged along the [0001] direction.

  In a preferred embodiment, each of the first inclined surface, the horizontal surface, and the second inclined surface of the AlInGaN layer is a flat surface.

The method for manufacturing a nitride semiconductor light emitting device according to the present invention is formed of Al _x In _Y Ga _1-XY N (0 ≦ X <1, 0 ≦ Y <1, 0 ≦ X + Y <1) crystals, An AlInGaN layer extending in a direction parallel to the m-plane which is a 1-100} plane, wherein the upper surface has at least one first inclined plane inclined in the [0001] direction from the m-plane, and [000- 1] Step (A) of forming an AlInGaN layer having at least one second inclined surface inclined in the direction, and In _Z Ga _{1 -Z} N (0 <Z <1) on the AlInGaN layer. And (B) forming an InGaN light emitting layer formed of crystals.

In a preferred embodiment, the step (A) is formed of Al _x In _Y Ga _1-XY N (0 ≦ X <1, 0 ≦ Y <1, 0 ≦ X + Y <1) crystal, with the m-plane as the surface. A step (a1) of preparing a flat layer having the step, and a step (a2) of forming the AlInGaN layer having the first inclined surface and the second inclined surface from the flat layer by processing the surface of the flat layer. Including.

  In a preferred embodiment, the step (a2) includes at least one of a step of changing the surface shape of the flat layer by etching and a step of changing the surface shape of the flat layer by epitaxial growth.

  According to the present invention, the full width at half maximum of the InGaN light-emitting layer can be expanded as compared with the prior art. Therefore, even if the emission wavelength fluctuates due to manufacturing process variations, usage environment variations, heat generation effects, etc., phosphor absorption The excitation efficiency to the line can be kept high, and the color rendering properties of the white LED can be improved. Furthermore, internal quantum efficiency can be improved by using a nonpolar surface.

  Such a phenomenon that the emission wavelength shifts to the long wave side and the short wave side depending on the tilt angle of the light emitting layer is a phenomenon peculiar on the nonpolar plane of the gallium nitride based semiconductor. This is a phenomenon that cannot be obtained on the polar surface of a conventionally used gallium nitride based semiconductor as disclosed in Document 1.

  The technology for widening the full width at half maximum of the emission spectrum according to the present invention has a function of improving the excitation efficiency of the phosphor absorption line and at the same time improves the color rendering property of the white LED. It is useful to do. Further, since the emission wavelength can be arbitrarily controlled by controlling the indium composition in the light emitting layer, it can be applied to a light emission source of RGB (red, green, blue) three-wavelength type white illumination.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment)
A first embodiment of a nitride semiconductor light emitting device according to the present invention will be described with reference to FIGS. 3A to 3D.

  First, refer to FIG. 3A and FIG. 3B. FIG. 3A is a cross-sectional view schematically showing a basic configuration of the nitride semiconductor light emitting device of this embodiment, and FIG. 3B is a perspective view showing a part thereof.

As shown in FIG. 3A, the nitride semiconductor light emitting device of this embodiment is made of Al _X1 In _Y1 Ga _{1 -X1-Y1} N (0 ≦ X1 <1, 0 ≦ Y1 <1, 0 ≦ X1 + Y1 <1) crystal. The n-type AlInGaN layer 101 formed, the InGaN light emitting layer 102 located on the AlInGaN layer 101 and made of In _Z Ga _{1 -Z} N (0 <Z <1) crystal, and the InGaN light emitting layer 102 And a p-type AlInGaN layer 103 formed of Al _X2 In _Y2 Ga _{1 -X2-Y2} N (0 ≦ X2 <1, 0 ≦ Y2 <1, 0 ≦ X2 + Y2 <1) crystal. Further, this nitride semiconductor light emitting device includes an n-type electrode 104 in contact with the n-type AlInGaN layer 101 and a p-type electrode 105 in contact with the p-type AlInGaN layer 103.

  As shown in FIG. 3B, the n-type AlInGaN layer 101 as a whole extends in a direction parallel to the m-plane, which is the {1-100} plane of the crystal, but the upper surface of the AlInGaN layer 101 extends from the m-plane [ A first inclined surface 101a inclined in the [0001] direction and a second inclined surface 101b inclined in the [000-1] direction from the m-plane. The magnitude of the tilt angle is indicated by “θ” in FIG. 3A.

  As described with reference to FIG. 2, the m-plane is composed of a (1-100) plane parallel to the c-axis and is a nonpolar plane. Spontaneous polarization and piezoelectric fields are not formed in the light emitting layer formed on the non-polar surface of the AlInGaN layer, so that the internal quantum efficiency can be increased compared to the light emitting layer formed on the c surface. Such an effect can be similarly obtained even when the light emitting layer is formed on a surface slightly inclined from the m-plane.

  In this specification, “a plane inclined in the [0001] direction from the m plane” means that the normal of the plane has a component in the c-axis [0001] direction. It is preferable that the normal of such a surface (inclined surface) does not include a component in the a-axis [11-20] direction.

  Next, the configuration of the InGaN light emitting layer 102 will be described in detail with reference to FIGS. 3C and 3D. FIG. 3C is a cross-sectional view showing a main part centering on the InGaN light emitting layer 102, and FIG. 3D is a top view of the InGaN light emitting layer 102.

  As shown in FIG. 3C, the InGaN light emitting layer 102 includes a first inclined portion 102a located on the first inclined surface 101a of the AlInGaN layer 101 and a second inclined surface located on the second inclined surface 101b of the AlInGaN layer 101. Part 102b. The emission wavelength of the first inclined portion 102a is different from the emission wavelength of the second inclined portion 102b. The reason why the emission wavelength is different depending on the light emitting portion in spite of the single InGaN light emitting layer 102 is that the In composition is different between the first inclined portion 102a and the second inclined portion 102b. The In composition depends on the plane orientation on the surface of the n-type AlInGaN layer 101 which is the base for crystal growth, and the growth conditions of the InGaN light emitting layer 102, such as the growth rate, the In incorporation rate, temperature, pressure, raw material flow rate, It can be controlled by conditions such as the molar ratio of the Group 15 element and the Group 13 element contained in the raw material. Even if these growth conditions are the same, if the surface of the underlying crystal is tilted, the In composition differs depending on the tilt direction and tilt angle θ. As a result, even in the InGaN light-emitting layer 102 formed under the same growth conditions, the In composition differs between the first inclined portion 102a and the second inclined portion 102b. Since the difference in In composition causes a difference in the band gap of the crystal, the emission wavelength is changed.

  As will be described later, by adjusting the inclination angle θ from the m-plane, the emission wavelength from the InGaN emission layer 102 can be changed, for example, in the range of 435 nm to 475 nm. In a preferred embodiment (described later) of the present invention, a wavelength shift of about 5 nm could be realized by changing the tilt angle θ by 1 °. In this embodiment, since a plurality of inclined portions 102a and 102b having different emission wavelengths are formed in the InGaN light emitting layer 102 in one light emitting element, the spectrum of light obtained from the light emitting element as a whole is as follows. The emission spectrum obtained from each of the inclined portions 102a and 102b is synthesized. Therefore, it is possible to obtain light emission having a spectrum width (full width at half maximum) larger than that of a conventional light emitting element.

  The first inclined surface inclined in the [0001] direction from the m-plane and the second inclined surface inclined in the [000-1] direction from the m-plane are related to the In incorporation rate of the InGaN layer grown on these inclined surfaces. Are not equivalent to each other. For this reason, when two types of inclined surfaces inclined in the positive and negative directions of the c-axis are formed as shown in FIG. 3C, the emission wavelength can be shifted to both the short wavelength side and the long wavelength side. Such an effect cannot be obtained by using a substrate having a c-plane as a main surface.

  Next, another configuration example in the present embodiment will be described with reference to FIGS. 3E to 3H.

  As shown in FIG. 3E, the upper surface of the AlInGaN layer 101 may have at least one horizontal plane 101c parallel to the m-plane. In this case, the InGaN light emitting layer 102 has a horizontal portion 102c parallel to the m-plane on the horizontal plane 101c of the AlInGaN layer 101, separately from the first inclined portion 102a and the second inclined portion 102b. Since the In composition in the horizontal portion 102c of the InGaN light emitting layer 102 is different from the In composition of the first inclined portion 102a and the second inclined portion 102b, the emission wavelength obtained from the InGaN light emitting layer 102 is three according to the part. Become. According to such a configuration, since three types of emission spectra are synthesized, the full width at half maximum of the entire emission spectrum can be further expanded.

  As shown in FIG. 3F, only one first inclined surface 101a and second inclined surface 101b may be formed in one light emitting element. However, for example, as shown in FIG. 3C, it is preferable that the plurality of inclined surfaces 101a and 101b are alternately arranged along the [0001] direction. This is because, by alternately arranging the inclined surfaces 101a and 101b, individual light emitting regions having different wavelengths can be reduced, and the synthesis of the emission spectrum can be made spatially uniform. Moreover, as shown to FIG. 3G, the 1st inclined surface 101a, the horizontal surface 101c, and the 2nd inclined surface 101b may be alternately arranged along the [0001] direction. As shown in FIG. 3E, the inclined surfaces 101a or 101b and the horizontal surface 101c may be alternately arranged along the [0001] direction.

  When a plurality of first inclined surfaces 101a and second inclined surfaces 101b are formed in one light emitting element, the inclination angles between the inclined surfaces 101a, 101b and the m-plane (in FIG. 3H, inclination angles θ1 to θ3). May have mutually different sizes, or all may have the same angle. If the inclination angles θ are the same, there is an advantage that the manufacture becomes easy. When the inclination angle θ differs depending on the inclined surface, manufacturing becomes difficult, but emission spectra having different wavelengths can be obtained from the light emitting layer located on the inclined surface, so that a broad spectrum with little peak separation can be obtained as a whole. There are advantages.

  The upper surface of the AlInGaN layer 101 is preferably a flat surface rather than a curved surface. This is because if the upper surface of the AlInGaN layer 101 includes a curved surface, not only the layer thickness controllability of the InGaN light emitting layer 102 grown on the AlInGaN layer 101 is deteriorated, but also the steepness of the light emitting layer interface is impaired. It is.

  Hereinafter, an example of a method for manufacturing the nitride semiconductor light emitting device shown in FIG. 3A will be described with reference to FIGS. 4A to 4G.

In the present embodiment, crystal growth of a nitride semiconductor is performed using a MOVPE method (Metal-Organic Vapor Phase Epitaxy Method). The growth pressure may be any of negative pressure, atmospheric pressure (1 atm), and positive pressure higher than atmospheric pressure, and may be switched to an optimum pressure in each crystal growth layer. The carrier gas for supplying the raw material to the substrate is preferably a gas containing at least an inert gas such as nitrogen (N ₂ ) or hydrogen (H ₂ ).

  The nitride semiconductor growth method in the present invention is not limited to the MOVPE method, but can be applied to all methods for growing compound semiconductor crystals, such as a hydride vapor phase growth method (HVPE method) and a molecular beam epitaxy method (MBE method). be able to.

First, as shown in FIG. 4A, a substrate 1400 is prepared. As the substrate 1400, an m-plane GaN substrate, m-plane 4H—SiC substrate, m-plane 6H—SiC substrate, a-plane sapphire substrate, MgAl ₂ O ₄ (spinel) substrate, Ga ₂ O ₃ substrate, or the like can be used. As described above, the surface (main surface) of the substrate itself does not have to be an m-plane, and may be any substrate on which a nitride semiconductor having the m-plane as a surface grows.

After the surface of the substrate 1400 is cleaned with an organic solvent or acid, the substrate 1400 is placed on the susceptor in the reaction chamber in the MOVPE apparatus. After sufficiently replacing the reaction chamber with N ₂ , the carrier gas is switched to H ₂ and ammonia (NH ₃ ) is supplied at the same time. The reaction chamber is heated to about 850 ° C., and the surface of the substrate 1400 is cleaned for about 10 minutes.

Thereafter, the temperature is further increased to 950 to 1050 ° C., and then trimethylgallium (TMG) and SiH ₄ are supplied to grow an n-type m-plane GaN layer 1401 having a thickness of about 2 μm on the main surface of the substrate 1400.

  Next, as shown in FIG. 4B, a resist 1410 having a thickness of about 500 to 1000 nm is uniformly applied to the surface of the n-type m-plane GaN layer 1401. Thereafter, a resist pattern having a triangular cross section is formed by a gray scale exposure method in which exposure is performed while changing the amount of light according to the position (FIG. 4C). Such exposure can be performed by, for example, a maskless exposure apparatus (Nano System Solutions Co., Ltd.).

  Next, the surface of the n-type m-plane GaN layer 1401 is etched using chlorine-based dry etching. As an etching gas, chlorine or hydrogen chloride can be used. As the etcher, a parallel plate type plasma or an inductively coupled plasma can be suitably used.

  In the above dry etching process, as shown in FIG. 4D, the surface of the resist 1410 is also etched in the process of etching the surface of the n-type m-plane GaN layer 1401. As the etching progresses, the edge of the resist 1410 recedes (moves in the horizontal horizontal direction in the drawing), so that the region covered with the resist 1410 in the surface of the n-type m-plane GaN layer 1401 is reduced.

Here, the speed at which the edge of the resist 1410 recedes in the horizontal horizontal direction is E _L , and the speed at which the surface of the n-type m-plane GaN layer 1401 is etched in the vertical direction is E _V. In this case, a portion of the surface of the n-type m-plane GaN layer 1401 that is initially exposed due to the recession of the edge of the resist 1410 is etched and deeper than a portion that is exposed later. Inclination angle θ of the inclined surfaces thus formed, will satisfy the relationship tanθ = E _L / E _V.

The speed E _{L at} which the edge of the resist 1410 recedes in the horizontal and lateral directions depends on the etching speed of the resist 1410 and the cross-sectional shape of the resist 1410. The etching rate of the resist 1410 can be adjusted by the supply amount of oxygen added to the etching gas.

  In the anisotropic etching, if the etching rate of the resist 1410 and the etching rate of the n-type m-plane GaN layer 1401 are substantially equal, the cross-sectional shape corresponding to the cross-sectional shape of the resist 1410 is changed to that of the n-type m-plane GaN layer 1401. It can be applied to the surface.

  In the example shown in FIGS. 4C to 4E, the inclination angle θ of the inclined surface formed on the surface of the n-type m-plane GaN layer 1401 is substantially equal to the inclination angle of the inclined surface of the resist 1410 after grayscale exposure.

  If etching is stopped at the stage shown in FIG. 4D and the resist 1410 is removed, both the plane parallel to the m-plane and the inclined plane can be formed on the surface of the n-type m-plane GaN layer 1401. If the cross-sectional shape of the resist 1410 after gray scale exposure has a surface parallel to the m-plane, a surface parallel to the m-plane is finally formed also on the surface of the n-type m-plane GaN layer 1401. Can do. In addition, if the resist 1401 has an opening with a predetermined width and the surface of the n-type m-plane GaN layer 1401 is exposed at the opening at the start of etching, the portion is in a state parallel to the m-plane. Deeply etched.

  As described above, various shapes can be imparted to the surface of the m-plane GaN layer 1401 by adjusting the shape of the resist 1410 and the etching conditions.

After the etching step, oxygen ashing and substrate cleaning are performed to remove the resist. After the surface of the n-type m-plane GaN layer 1401 is cleaned with an organic solvent or acid, the substrate 1400 is placed again on the susceptor of the reaction chamber in the MOVPE apparatus. After sufficiently replacing the reaction chamber with N ₂ , the carrier gas is switched to H ₂ and ammonia (NH ₃ ) is supplied at the same time. The temperature of the reaction chamber is increased to 850 ° C. at a temperature increase rate of 1 ° C./1 second, and the surface of the substrate 1400 is cleaned for 10 minutes. Thereafter, the carrier gas is switched to N ₂ , the temperature is lowered to about 750 to 800 ° C. and stabilized, and then TMG and trimethylindium (TMI) are supplied.

In this way, an InGaN light emitting layer 1402 made of In _0.1 Ga _0.9 N / GaN-MQWs is grown as shown in FIG. 4F. The In _0.1 Ga _0.9 N well layer thickness is 3 nm, the GaN barrier layer thickness is 7 nm, and the number of well layers is 3. The InGaN light emitting layer 1402 is not intentionally doped.

  The growth conditions of the light emitting layer 1402 are not limited to the specific conditions described above, and other conditions can be adopted. According to this embodiment, due to the surface structure provided on the base, portions having different In compositions can be formed in the InGaN light-emitting layer 1402 grown on the surface structure under normal crystal growth conditions.

After the InGaN light emitting layer 1402 is formed, the temperature is raised to 1000 ° C., the carrier gas is switched to H ₂ , and after the growth temperature reaches 1000 ° C., biscyclopentadienyl magnesium (Cp ₂ Mg) is added as an Mg raw material. To do. Thus, as shown in FIG. 4F, a p-type m-plane GaN layer 1403 having a thickness of about 500 nm doped with Mg is grown.

  Next, after exposing a part of the n-type m-plane GaN layer 1401, as shown in FIG. 4G, an n-type electrode 1404 and a p-type electrode 1405 are formed, and the nitride semiconductor light emitting device of this embodiment is completed. To do.

  In the above manufacturing method, an inclined surface is formed on the surface of the n-type m-plane GaN layer 1401 by etching, but the present invention is not limited to such a manufacturing method. It is also possible to form an inclined surface on the surface of the n-type m-plane GaN layer 1401 by selective epitaxial growth. In addition, a structure having an inclined surface may be formed by performing both etching and epitaxial growth.

  The structures shown in FIGS. 3E to 3H can also be manufactured by the same method as described above.

  FIG. 5 is a graph showing an emission spectrum obtained from an InGaN light emitting layer having an inclined portion inclined from the m-plane in an embodiment of the present invention. The horizontal axis of the graph is wavelength λ (Wavelength: unit nm), and the vertical axis is emission intensity (Intensity: arbitrary unit).

  In the graph of FIG. 5, a broken line indicates an emission spectrum having a center wavelength of 450 nm and a full width at half maximum of 20 nm, which is obtained from an InGaN light emitting layer that is formed on the m-plane and does not have an inclined portion. The thin solid line shows two emission spectra obtained by shifting the emission spectrum represented by the broken line to the long wave side and the short wave side by 7 nm, respectively. A thick solid line indicates an emission spectrum having a central wavelength of 450 nm obtained by synthesizing two emission spectra represented by the thin solid line.

As can be seen from FIG. 5, the emission spectrum obtained from the entire InGaN emission layer can be obtained simply by forming inclined portions with different In contents in the InGaN emission layer and shifting the emission wavelength by 7 nm from the long wavelength side to the short wavelength side. The full width at half maximum increases to 30 nm. This full width at half maximum is about 1.5 times as large as the full width at half maximum in the emission spectrum of the InGaN light emitting layer consisting only of a portion parallel to the main surface having no inclined structure.

  FIG. 6 is a graph showing an emission spectrum of a white LED using a YAG phosphor in the embodiment of the present invention. The horizontal axis of the graph is wavelength λ (Wavelength: unit nm), and the vertical axis is emission intensity (Intensity: arbitrary unit).

  In the graph of FIG. 6, the broken line indicates the emission spectrum of a white LED using a conventional blue LED having a full width at half maximum of the emission spectrum of 20 nm. On the other hand, the solid line is the emission spectrum of a white LED using a blue LED in which the full width at half maximum of the emission spectrum in the embodiment of the present invention extends to 30 nm. As can be seen from FIG. 6, the light emission intensity between the blue component and the yellow component was improved by increasing the full width at half maximum of the blue LED, and it was confirmed that color rendering was improved.

  FIG. 7 is a graph showing the relationship between the wavelength shift Δλ (unit: nm) from the phosphor absorption line and the excitation efficiency (unit%) for the phosphor absorption line in the embodiment of the present invention. In FIG. 7, the broken line is plotted for a conventional blue LED having a full width at half maximum of the emission spectrum of 20 nm, and the solid line is plotted for the blue LED in the embodiment of the present invention in which the full width at half maximum of the emission spectrum is expanded to 30 nm. As can be seen from FIG. 7, since the full width at half maximum of the emission spectrum is widened, the excitation efficiency is not easily attenuated even when the peak wavelength deviates from the phosphor absorption line.

  FIG. 8 is a graph showing the difference between the inclination angle from the m-plane and the shift amount of the peak wavelength of the InGaN light emitting layer due to the inclination in the embodiment of the present invention. The horizontal axis of the graph is the inclination angle θ (Slope Angle: unit degree) of the surface inclined in the [0001] direction and [000-1] direction from the m plane, and the vertical axis is formed on the inclined surface of the inclination angle θ. The difference between the peak wavelength of the formed InGaN light emitting layer and the peak wavelength of the InGaN light emitting layer formed on the m-plane (wavelength shift: unit nm).

  In order to obtain the data of FIG. 8, a plurality of GaN substrates having inclined surfaces with different inclination angles θ are prepared, and crystal growth conditions with an emission wavelength of 450 nm when the inclination angle θ is 0 ° are formed on the substrate. The InGaN light emitting layer was crystal grown. In this experiment, the emission wavelength from the InGaN light emitting layer could be changed in the range from 435 nm to 475 nm depending on the tilt angle θ.

  According to the data of FIG. 8, a wavelength shift of about 5 nm was confirmed by changing the tilt angle θ by 1 °. However, the amount of wavelength shift per unit inclination angle depends on the growth conditions of the light emitting layer (for example, growth rate, In incorporation rate, temperature, pressure, raw material flow rate, molar ratio of Group 5 element to Group 3 element contained in the material, etc. Condition). The effect of the present invention is exhibited even under any growth conditions obtained by changing these parameters.

  FIG. 9 is a diagram schematically illustrating the cathode luminescence (CL) mapping measurement result of the light emitting layer formed on the inclined surface and the structure of the inclined surface in the embodiment of the present invention.

  Here, after forming a mountain-shaped GaN layer on the surface of the m-plane GaN substrate, crystal growth of the InGaN light emitting layer was performed. In FIG. 9, the surfaces inclined in the [0001] direction and the [000-1] direction are both inclined by 0.23 ° from the m-plane which is the main surface.

  An emission wavelength of 400.0 nm is obtained from the inclined portion of the light emitting layer inclined in the [0001] direction, and an emission wavelength of 398.5 nm is obtained from the inclined portion of the light emitting layer inclined in the [000-1] direction.

  FIG. 10A is a graph showing the results of performing CL measurement along Line-A shown in FIG. 9 according to the embodiment of the present invention, and FIG. 10B shows the measurement results along Line-B. It is a graph. The horizontal axis of the graph represents the CL measurement position on Line-A or Line-B in FIG.

  As can be seen from the graph of FIG. 10A, a constant emission wavelength is obtained at about 400.0 nm from the inclined portion inclined in the [0001] direction, and about 398.5 nm from the surface inclined in the [000-1] direction. A constant emission wavelength was obtained. On the other hand, as can be seen from the graph of FIG. 10B, a constant emission wavelength of about 399.5 nm was obtained from the inclined portion inclined in the <11-20> direction. Thus, the emission wavelength can be shifted by inclining the inclined portion of the light emitting layer in a specific direction.

  FIG. 11 is a graph showing an emission spectrum obtained from the light emitting layer formed on the inclined surface shown in FIG. In the graph of FIG. 11, two broken lines are emission spectra obtained from inclined portions inclined by 0.23 ° in the [0001] direction and the [000-1] direction, respectively, from the main surface. A solid line is an emission spectrum obtained from the entire light emitting layer formed on the inclined surface. The full width at half maximum of about 13.5 nm was obtained from the emission spectrum indicated by the broken line, and the full width at half maximum of about 16.0 nm was obtained from the emission spectrum indicated by the solid line. According to the embodiment of the present invention, it is confirmed that the full width at half maximum of the emission spectrum of the entire light emitting layer can be improved by about 20% by providing the light emitting layer with an inclined structure having an inclination angle of 0.23 °. It was done.

Here, with reference to the emission wavelength obtained from the light emitting layer formed on the plane parallel to the m-plane, the shift amount of the emission wavelength obtained from the inclined portion is | Δλ |, and the emission spectrum obtained from the inclined portion is Let the full width at half maximum be F _slope . At this time, (shift amount of the emission wavelength obtained from the inclined portion) / (full width at half maximum of the emission spectrum obtained from the inclined portion) is represented by | Δλ | / F _slope .

FIG. 12 is a graph showing the relationship between the emission intensity (PeakIntensity) obtained from the entire light emitting layer and | Δλ | / F _{slope in} the embodiment of the present invention. In FIG. 12, characteristic phenomena occur when | Δλ | / F _slope has values of 0.35, 0.425, and 0.5, and each will be described below.

First, consider a light emitting layer having two inclined portions (same area) inclined by an inclination angle θ in the [0001] direction and the [000-1] direction from the m-plane {1-100}, respectively. The full width at half maximum of the emission spectrum of one inclined part is F _slope [nm], and the difference between the peak wavelength of the emission spectrum of the emission layer parallel to the m-plane {1-100} and the peak wavelength of the emission spectrum of the inclined part is Δλ [nm]. The ratio of Δλ to the inclination angle θ from the m-plane is Δλ / θ, and this ratio is α.

In the range satisfying Δλ / F _slope > 0.35, the full width at half maximum of the emission spectrum obtained from the entire light emitting layer including the inclined portion is obtained from the light emitting layer parallel to the m-plane {1-100} having no inclined portion. It becomes 1.5 times or more of the full width at half maximum of the emission spectrum. For example, when F _slope = 30 nm and | α | = 3 nm / degree, | θ |> 3.50 °, for example, when F _slope = 10 nm and | α | = 8 nm / degree, | θ |> 0.438 °.

In a range satisfying | Δλ | / F _slope <0.425, a light emitting layer in which the peak wavelength of an emission spectrum obtained from the entire light emitting layer including the inclined portion is parallel to the m-plane {1-100} having no inclined portion Is not deviated from the peak wavelength of the emission spectrum obtained. For example, when F _slope = 30 nm and | α | = 3 nm / degree, | θ | <4.25 °. For example, when F _slope = 10 nm and | α | = 8 nm / degree, | θ | <0.531 °.

In a range satisfying | Δλ | / F _slope <0.5, the peak intensity of the emission spectrum obtained from the entire light emitting layer including the inclined portion exceeds the peak intensity of the emission spectrum obtained from one inclined portion. For example, when F _slope = 30 nm and | α | = 3 nm / degree, | θ | <5.00 °, for example, when F _slope = 10 nm and | α | = 8 nm / degree, | θ | <0.625 °.

FIG. 13 is a graph showing the effect of the shift amount of the emission wavelength obtained from the inclined portion on the emission spectrum obtained from the entire light emitting layer in the embodiment of the present invention. The horizontal axis of the graph is | Δλ | / F _slope , and the vertical axis is the effect (Peak shift effect: arbitrary unit) that the shift amount of the emission wavelength obtained from the inclined portion has on the emission spectrum obtained from the entire light emitting layer. is there. In the graph of FIG. 13, the characteristic phenomenon that occurs when | Δλ | / F _slope has values of 0.35, 0.425, and 0.5 is as described above.

“Peak shift effect”, which is the vertical axis of FIG. 13, is defined by the following equation.
(F _whole / F _slope ) ^ I _C

Here, F _slope is the full width at half maximum of the emission spectrum obtained from the inclined portion, F _whole is the full width at half maximum of the emission spectrum obtained from the entire light emitting layer, and the normalized emission intensity of the emission spectrum obtained from the entire I _C light emitting layer. The value defined here relatively indicates the excitation efficiency of the phosphor, and as this value increases, the absorption efficiency of the phosphor increases. The symbol “^” indicates a power.

As can be seen from FIG. 13, the condition for obtaining the maximum effect of the present invention is when | Δλ | / F _slope = 0.45. For example, when F _slope = 30 nm and | α | = 3 nm / degree, | θ | <4.50 °. For example, when F _slope = 10 nm and | α | = 8 nm / degree, | θ | < 0.563 °.

  From the above facts, in order to obtain the maximum effect of the present invention, a surface inclined in the [0001] direction and the [000-1] direction from the m-plane {1-100} which is the main surface is set at an inclination angle θ. It is preferable to design so that the absolute value | θ |

  In addition, although the inclination angle may be a value that varies depending on the inclined surface, the surface area of the entire light emitting layer including the inclined surface is preferably designed to be 1.01 times or less of the surface area of the substrate based on the above guidelines. . If the value exceeds this value, the inclination angle of the inclined surface becomes 5 degrees or more, and the effect of the present invention is weakened, and the smoothness of the multilayer film formed on the light emitting layer cannot be maintained.

FIG. 14A shows the ratio S ₂ of the total area S ₂ of the surface inclined in the [000-1] direction from the m surface to the total area S ₁ of the surface inclined in the [0001] direction from the m surface in the embodiment of the present invention. / and S _1, it is a graph showing the relationship between the full width at half maximum F _whole of the emission spectra obtained from the whole light emitting layer. On the other hand, FIG. 14B is a graph showing the relationship between S ₂ / S ₁ and (F _whole / F _slope ) · I _C in the embodiment of the present invention. 14A and 14B, in all the data, the full width at half maximum F _slope of the emission spectrum obtained from the inclined portion is 20 nm, and | Δλ | is 5 nm, 7 nm, and 9 nm.

As can be seen from FIG. 14A and FIG. 14B, when S ₂ / S ₁ has a value away from 1, the peak of the emission spectrum obtained from the entire light emitting layer is not only shifted, but the effect of the present invention is weakened. . Therefore, the total area S _{1 of the} surfaces inclined in the [0001] direction from the m plane and the total area S _{2 of the} surfaces inclined in the [000-1] direction from the m plane should be designed to be substantially equal. Is preferred. In addition, even when there is a difference between S ₁ and S ₂ , it is desirable to design so that 0.5 ≦ S ₂ / S ₁ ≦ 2.

  The present invention makes it possible to widen the full width at half maximum of the emission spectrum, so that the excitation efficiency of the phosphor absorption line is improved and the color rendering property of the white LED is also improved. For this reason, it is useful to apply this invention to the light emission source of high efficiency white LED.

  In addition, since the present invention can arbitrarily control the emission wavelength by controlling the indium composition in the light emitting layer, the present invention is also applicable to a light source for RGB (red / green / blue) three-wavelength white illumination. Can be applied.

It is a perspective view which shows typically the unit cell of GaN. FIG. ₃ is a perspective view showing basic translation vectors a ₁ , a ₂ , and a ₃ of a wurtzite crystal structure. It is sectional drawing which shows embodiment of the nitride semiconductor light-emitting device by this invention. It is a perspective view which shows the principal part of FIG. 3A. It is sectional drawing which shows the arrangement | sequence of the inclined surface in embodiment of FIG. 3A. It is a top view which shows the arrangement | sequence of the inclined surface in embodiment of FIG. 3A. It is sectional drawing which shows the other structure of the nitride semiconductor light-emitting device by this invention. It is sectional drawing which shows other structure of the nitride semiconductor light-emitting device by this invention. It is sectional drawing which shows other structure of the nitride semiconductor light-emitting device by this invention. It is sectional drawing which shows other structure of the nitride semiconductor light-emitting device by this invention. It is process sectional drawing which shows the manufacturing process of the nitride semiconductor light-emitting device by this invention. It is process sectional drawing which shows the manufacturing process of the nitride semiconductor light-emitting device by this invention. It is process sectional drawing which shows the manufacturing process of the nitride semiconductor light-emitting device by this invention. It is process sectional drawing which shows the manufacturing process of the nitride semiconductor light-emitting device by this invention. It is process sectional drawing which shows the manufacturing process of the nitride semiconductor light-emitting device by this invention. It is process sectional drawing which shows the manufacturing process of the nitride semiconductor light-emitting device by this invention. It is process sectional drawing which shows the manufacturing process of the nitride semiconductor light-emitting device by this invention. It is a graph which shows the emission spectrum obtained from the InGaN light emitting layer which provided the inclined surface in embodiment of this invention. It is a graph which shows the emission spectrum of white LED using YAG type | system | group fluorescent substance in embodiment of this invention. It is a graph which shows the relationship between the wavelength shift from a fluorescent substance absorption line, and the excitation efficiency to a fluorescent substance absorption line in embodiment of this invention. In the embodiment of the present invention, the relationship between the inclination angle of the inclined portion included in the InGaN light emitting layer and the difference between the peak wavelength of the emission spectrum obtained from the main surface without the inclined structure and the peak wavelength of the emission spectrum obtained from the inclined portion. It is a graph to show. It is a figure which shows typically the mapping measurement result of the cathodoluminescence (CL) of the light emitting layer containing an inclination part, and the inclination part in embodiment of this invention. It is a graph which shows CL intensity | strength measured along Line-A of FIG. It is a graph which shows CL intensity | strength measured along Line-B of FIG. It is a graph which shows the emission spectrum obtained from the light emitting layer which provided the inclination part shown by FIG. 9 in embodiment of this invention. FIG. 5 is a graph showing a relationship between (shift amount of emission wavelength obtained from an inclined portion) / (full width at half maximum of emission spectrum obtained from an inclined portion) and (emission intensity obtained from the entire light emitting layer) in an embodiment of the present invention. is there. In the embodiment of the present invention, (shift amount of emission wavelength obtained from the inclined portion) / (full width at half maximum of emission spectrum obtained from the inclined portion) and (shift amount of emission wavelength obtained from the inclined portion are from the entire light emitting layer) It is a graph which shows the relationship of the effect on the emission spectrum obtained. In an embodiment of the present invention, it is a graph showing the relationship between the full width at half maximum F _whole and S ₂ / S ₁ of the emission spectra obtained from the whole light emitting layer. In an embodiment of this invention, it is a graph showing the relationship between the shift amount of the emission wavelength derived from the slope portion to the effect and the S ₂ / S ₁ exerted to emission spectrum obtained from the whole light emitting layer. It is a figure which shows the light emitting layer containing the conventional nonpolar surface and the semipolar surface described in patent document 1 and nonpatent literature 1. FIG. It is a figure which shows the light emitting layer containing the conventional nonpolar surface and semipolar surface described in the nonpatent literature 2. FIG.

101 n-type nitride layer 101a first inclined surface 101b second inclined surface 101c horizontal surface 102 InGaN light emitting layer 102a first inclined portion;
102b Second inclined portion 102c Horizontal portion 103 p-type nitride layer 104 n-electrode 105 p-electrode 1201 nitride layer 1202 InGaN light-emitting layer 1301 nitride layer 1302 InGaN light-emitting layer 1400 substrate 1401 n-type nitride layer 1402 InGaN light-emitting layer 1403 p Type nitride layer 1404 n-electrode 1405 p-electrode 1410 resist

Claims (15)

A direction formed from an Al _X In _Y Ga _1-XY N (0 ≦ X <1, 0 ≦ Y <1, 0 ≦ X + Y <1) crystal and parallel to the m-plane which is the {1-100} plane of the crystal An AlInGaN layer extending to
An InGaN light-emitting layer located on the AlInGaN layer and formed of In _Z Ga _1-Z N (0 <Z <1) crystal;
A nitride semiconductor light emitting device comprising:
The upper surface of the AlInGaN layer is
At least one first inclined surface inclined in the [0001] direction from the m-plane;
A nitride semiconductor light emitting device having at least one second inclined surface inclined in the [000-1] direction from the m-plane. The InGaN light emitting layer is
A first inclined portion located on the first inclined surface of the AlInGaN layer;
A second inclined portion located on the second inclined surface of the AlInGaN layer,
2. The nitride semiconductor light emitting device according to claim 1, wherein an emission wavelength of the first inclined portion is different from an emission wavelength of the second inclined portion. The surface of the InGaN light-emitting layer, the entire area of the first inclined portion and S _1, when the entire area of the second inclined portion and S _2, are approximately equal S ₁ and S _2, according to claim 1 The nitride semiconductor light-emitting device according to 1. The nitride semiconductor light-emitting device according to claim 3, wherein 0.5 ≦ S ₂ / S ₁ ≦ 2. The absolute value of the angle formed by the first inclined surface and the m-plane of the AlInGaN layer and the absolute value of the angle formed by the second inclined surface and the m-plane are both greater than 0 degree and 5 degrees. The nitride semiconductor light-emitting device according to claim 1, which is in the following range.   2. The nitride semiconductor light emitting element according to claim 1, wherein the first inclined surface and the second inclined surface of the AlInGaN layer are alternately arranged along a [0001] direction.   2. The nitride semiconductor light emitting element according to claim 1, wherein each of the first inclined surface and the second inclined surface of the AlInGaN layer is formed of a flat surface. In the AlInGaN layer, a plurality of the first inclined surface and the second inclined surface exist,
The absolute values of the angles formed by the plurality of first inclined surfaces and the m-plane are equal to each other,
2. The nitride semiconductor light emitting element according to claim 1, wherein absolute values of angles formed by the plurality of second inclined surfaces and the m-plane are also equal to each other. In the AlInGaN layer, a plurality of the first inclined surface and the second inclined surface exist,
The angle formed by one of the first inclined surfaces and the m-plane is θ1, the angle formed by one of the second inclined surfaces and the m-plane is θ2, and another first inclined surface different from the first inclined surface. The nitride semiconductor light-emitting element according to claim 1, wherein θ1, θ2, and θ3 have different sizes, where θ3 is an angle formed by the m-plane . An upper surface of the AlInGaN layer has at least one horizontal plane parallel to the m-plane;
The nitride semiconductor light emitting device according to claim 1, wherein the InGaN light emitting layer has a horizontal portion located on the horizontal plane of the AlInGaN layer. 11. The nitride semiconductor light emitting element according to claim 10, wherein the first inclined surface, the horizontal surface, and the second inclined surface of the AlInGaN layer are arranged in this order along a [0001] direction.   11. The nitride semiconductor light emitting element according to claim 10, wherein each of the first inclined surface, the horizontal surface, and the second inclined surface of the AlInGaN layer is configured by a plane. A direction formed from an Al _X In _Y Ga _1-XY N (0 ≦ X <1, 0 ≦ Y <1, 0 ≦ X + Y <1) crystal and parallel to the m-plane which is the {1-100} plane of the crystal An at least one first inclined surface whose upper surface is inclined in the [0001] direction from the m-plane and at least one second inclined surface inclined in the [000-1] direction from the m-plane A step (A) of forming an AlInGaN layer having:
And (B) forming an InGaN light emitting layer formed of In _Z Ga ₁ -ZN (0 <Z <1) crystal on the AlInGaN layer. The step (A)
A step (a1) of preparing a flat layer formed of Al _X In _Y Ga _1-XY N (0 ≦ X <1, 0 ≦ Y <1, 0 ≦ X + Y <1) crystal and having an m-plane on the surface;
Forming the AlInGaN layer having the first inclined surface and the second inclined surface from the flat layer by processing the surface of the flat layer;
The method for manufacturing a nitride semiconductor light emitting device according to claim 13, comprising:   The nitride semiconductor light emitting element according to claim 14, wherein the step (a2) includes at least one of a step of changing a surface shape of the flat layer by etching and a step of changing the surface shape of the flat layer by epitaxial growth. Manufacturing method.

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