JP2001028457A - GaN-BASED SEMICONDUCTOR LIGHT-EMITTING DEVICE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the influence of the radiation of light to a substrate side, and to stabilize a beam pattern by providing a photoabsorption layer for absorbing the light being emitted by an active layer between the active layer and a substrate. SOLUTION: A GaN-based semiconductor light-emitting diode 30 becomes an SLD for emitting a blue light beam with a wavelength of 488 nm by optical waveguide structure consisting of layer structure and ridge-type refractive index structure, and light reflection structure being formed by both light emission end faces. Then, in the GaN-based semiconductor light-emitting diode 30, a light absorption layer 31 is provided between an active layer 7 and a sapphire c surface substrate 1, thus absorbing light being radiated to the side of the substrate 1 from the active layer 7 even when the light is not sufficiently confined by a clad layer 5 by the absorption layer 31, or reflecting the light by the photoabsorption layer 31 for turning. Even when the GaN-based semiconductor-light emitting diode 30 is driven by current being lower than an oscillation threshold, a beam pattern with superior symmetry for a direction being vertical to a pn junction surface is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a GaN-based semiconductor light emitting device having an active layer made of a GaN-based semiconductor and a stripe structure, and more specifically, to an SLD (Super Luminescent Diode).
ode) and a semiconductor laser.

[0002]

2. Description of the Related Art Conventionally, various optical scanning recording apparatuses for scanning and exposing a color photosensitive material with recording light of three colors and recording a color image thereon have been provided. This type of optical scanning recording apparatus is of a type that exposes a color photosensitive material for ordinary visible light exposure using recording light of three colors of red, green, and blue, and a wavelength range that is not restricted to the three colors. Each recording light of three wavelengths (for example, red to infrared) is modulated based on image information carrying red, green, and blue information, respectively, and three types of light having sensitivity to the wavelength of each recording light are modulated by the recording light. The photosensitive layer is broadly classified into a type of scanning exposure.

The former type of these optical scanning recording apparatuses has the advantage that the recording cost can be kept low since general color photosensitive materials having stable characteristics and being inexpensive can be used. Having. In this type of optical scanning recording apparatus, a light source that emits red, green, and blue light is required. However, to reduce the size and weight of the apparatus, it is advantageous to use a semiconductor laser that is smaller than a gas laser or the like. is there.

As a semiconductor laser suitable for such an application, an active layer is composed of a GaN-based semiconductor such as InGaN, InGaNAs or GNAAs, and emits a blue laser beam.
GaN-based semiconductor lasers are exemplified. Such semiconductor lasers have been actively researched recently, and are approaching practical use.

FIG. 6 shows an example of this type of GaN semiconductor laser. This semiconductor laser 20 is composed of an n-GaN low-temperature buffer layer 2, a striped SiO ₂ mask 14, an n-GaN buffer layer 3, and an n-InG
aN buffer layer 4, n-AlGaN cladding layer 5, n-GaN light guide layer 6, undoped active layer 7, p-GaN light guide layer 8, p-GaN
It has an AlGaN cladding layer 9 and a p-GaN cap layer 10, and has a SiN film 11, a p-side electrode 12 formed thereon, and an n-side electrode 13 formed on the n-GaN buffer layer 3.
It is provided with.

Further, as disclosed in Japanese Patent Application Laid-Open No. 11-74559, for example, a light emitting diode having an active layer made of a GaN-based semiconductor and having a stripe structure, so-called SL
D (Super Luminescent Diode) is also known.
Although this SLD does not oscillate laser light, it can output green light or blue light with a small light emission diameter and a narrow beam emission angle because the light emitting region is limited by a narrow stripe structure.

[0007]

However, in the SLD made of the GaN-based semiconductor, there is a problem that a beam radiation pattern becomes unstable. Hereinafter, this point will be described in detail.

In this type of SLD, GaN as a buffer layer material and sapphire or SiC as a substrate material are transparent to the emission wavelength. On the other hand, since the AlGaN cladding layer, which becomes a light confinement layer with a lower refractive index than the active layer region, is cracked when the thickness is approximately 1 μm or more, it is difficult to have a sufficient thickness for light confinement. Has become. Further, since it is difficult to reduce the resistance of the clad layer, the resistance is surely increased when the thickness is increased.

In a GaN-based semiconductor laser actually provided, a superlattice cladding layer of AlGaN and GaN is used. However, the thickness of the cladding layer is set to 1 μm or less due to the above-mentioned circumstances. At the time of laser oscillation, even if the cladding layer is so thin, there is little adverse effect, and an interference fringe due to the radiation mode of the laser beam to the substrate is seen in the beam pattern in the direction perpendicular to the pn junction surface. is there. FIG. 7 shows an example of this beam pattern. The semiconductor laser used for this measurement has the basic configuration shown in FIG.

In FIG. 7, the horizontal axis represents pn from the center of the light emitting point.
An angle in a direction perpendicular to the bonding surface is shown, and a vertical axis shows a light intensity relative value. In the figure, a curve a shows a state when laser oscillation is performed at a drive current of 5 mW, and curves b and c respectively show the drive current as 0.77 times the laser oscillation threshold current (Ith),
Similarly, the state when the magnification is 0.58 is shown. from here,
When operating as an SLD with a low drive current, the coherency is reduced, the effect of the radiated light on the substrate side is increased, and the beam pattern is deteriorated.

When the above-mentioned SLD is configured as a monolithic array in which a plurality of light-emitting portions are arranged on the same substrate, GaN as a common buffer layer material, sapphire or SiC as a substrate material emits light as described above. Since it is transparent to the wavelength, light is guided in the direction in which the plurality of light emitting units are arranged (the direction parallel to the pn junction surface). If so, reflection or refraction occurs at the edge of the substrate or at an uneven portion of the device, and light is radiated outside from unnecessary portions other than the light emitting portion, and optical crosstalk occurs.

In view of the above circumstances, the present invention provides a GaN-based semiconductor light-emitting device (more specifically, an SLD and a semiconductor laser) whose beam pattern is stabilized by reducing the influence of light radiation on the substrate side. The purpose is to provide.

Further, the present invention relates to a Ga
An object is to reduce optical crosstalk in an N-based semiconductor light emitting device.

[0014]

SUMMARY OF THE INVENTION One GaN according to the present invention
In the GaN-based semiconductor light emitting device, which has an active layer made of a GaN-based semiconductor and a stripe structure, a light absorption layer for absorbing light emitted from the active layer is provided between the active layer and the substrate. It is characterized by having.

Another GaN-based semiconductor light-emitting device according to the present invention is a GaN-based semiconductor light-emitting device having an active layer made of a GaN-based semiconductor and a stripe structure, wherein the active layer is provided between the active layer and the substrate. A light reflection layer for reflecting emitted light is provided.

Still another GaN-based semiconductor light-emitting device according to the present invention is an array-shaped GaN-based light-emitting device having a plurality of light-emitting portions having an active layer made of a GaN-based semiconductor and a stripe structure arranged in parallel on a common substrate. In a system semiconductor light emitting device, a light absorbing layer for absorbing light emitted by the active layer is provided between each active layer of the light emitting portion and the substrate, and between each of the light emitting portions, the substrate is also provided. A light separating groove that reaches is formed.

Still another GaN-based semiconductor light-emitting device according to the present invention is an array-like GaN-based semiconductor light-emitting element in which a plurality of light-emitting portions having an active layer made of a GaN-based semiconductor and a stripe structure are arranged in parallel on a common substrate. In the system semiconductor light emitting device, a light reflecting layer for reflecting light emitted from the active layer is provided between each active layer of the light emitting portion and the substrate, and between each of the light emitting portions, the substrate is provided. A light separating groove that reaches is formed.

Preferably, a light absorbing material for absorbing light emitted from the active layer is embedded in the light separating groove.

[0019]

In the GaN-based semiconductor light emitting device according to the present invention, the light absorption layer or the light reflection layer as described above is provided between the active layer and the substrate, so that the light confinement by the cladding layer is sufficient. The light emitted to the substrate side without
The light is absorbed by the light absorbing layer or reflected by the light reflecting layer to be folded. Therefore, even if this GaN-based semiconductor light emitting device is driven with a current lower than the oscillation threshold, the beam pattern does not become the one shown by the curves b and c in FIG. 7, but the stable beam pattern shown by the curve a in FIG. Is obtained.

In particular, when the above-mentioned light reflection layer is provided, a so-called photon recycling effect is obtained in which the reflected light returns to the active layer and the gain is increased, so that a semiconductor laser or SLD having high light use efficiency is realized. .

Therefore, according to the GaN-based semiconductor light emitting device of the present invention, it is possible to realize a light source with a stable beam pattern that emits light with a small emission diameter and a narrow beam emission angle in the visible short wavelength region of green and blue. As a result, the present element can be applied to color image recording using three primary color lights of red, green and blue, exposure of a high-gradation silver halide photograph, and further to a laser display or the like.

The GaN-based semiconductor light-emitting device of the present invention can be used in place of a conventional light source in many other laser application fields, such as a light source for excitation of fluorescence analysis using a conventional gas laser.

In the array-like GaN-based semiconductor light-emitting device according to the present invention, in addition to the above-described effects, a light separating groove reaching the substrate is formed between each of the plurality of light-emitting portions. As a result, light guided in the direction in which the light emitting portions are arranged (the direction parallel to the pn junction surface) cannot be guided from the groove to the end, and the above-described optical crosstalk is also prevented.

When a light absorbing material for absorbing the light emitted from the active layer is embedded in the light separating groove, light guided in the direction in which the light emitting portions are arranged is absorbed there.
The effect of preventing optical crosstalk is higher.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic side sectional shape of a GaN-based semiconductor light emitting device 30 according to a first embodiment of the present invention. This semiconductor light emitting device 30 includes an active layer 7 having a cladding layer 6 similar to a general stripe type semiconductor laser.
8 has a double hetero structure sandwiched by 8, and has a stripe-shaped current injection window for confining light (portion of the cap layer 10)
Is provided. The cleavage surface of the element is a reflection surface, and a light reflection structure is formed.

Hereinafter, the layer structure of the semiconductor light emitting device 30 will be briefly described together with the manufacturing method. Sapphire c-plane substrate 1
After the n-GaN low-temperature buffer layer 2 is grown thereon by MOCVD, a striped SiO ₂ mask 14 is formed. Next, an n-GaN buffer layer 3 (Si-doped, 5
μm), n-In _0.05 Ga _0.95 N buffer layer 4 (Si-doped, 0.
1 μm), n-light absorption layer 31, n-Al _0.1 Ga _0.9 N clad layer 5
(Si-doped, 0.5 μm), n-GaN optical guide layer 6 (Si-doped, 0.1 μm), undoped active layer 7, p-GaN optical guide layer 8 (Mg-doped, 0.1 μm), p-Al _0.1 Ga _0.9 N Cladding layer 9 (Mg doped, 0.5 μm) and p-GaN cap layer 10
(Mg-doped, 0.3 μm). After that, the p-type impurity is activated by heat treatment in a nitrogen gas atmosphere.

The active layer 7 is made of undoped ln _0.05 Ga _0.95
N (10 nm), undoped In _0.28 Ga _0.72 N quantum well layer (2.5 nm, wavelength 488 nm), undoped In _0.05 Ga _0.95 N
(5 nm), undoped In _0.28 Ga _0.72 N quantum well layer (2.5
nm), undoped ln _0.05 Ga _0.95 N (5 nm), undoped In _0.28 Ga _0.72 N quantum well layer (2.5 nm), undoped ln _0.05 Ga _0.95 N (5 nm), undoped Al _0.1 Ga _0.9 N
(10 nm).

The n-light absorbing layer 31 is made of undoped ln _0.05 Ga
_0.95 N (5 nm), undoped In _0.4 Ga _0.6 quantum well layer (10 nm), undoped In _0.05 Ga _0.95 N (5 nm), undoped In _0.4 Ga _0.6 quantum well layer (10 nm), undoped l
It has a double quantum well structure made of n _0.05 Ga _0.95 N (5 nm).

Next, in order to form a ridge stripe having a width of 6 μm, the epitaxial layer other than the ridge stripe portion is removed from the cap layer 10 to the middle of the cladding layer 9 by reactive ion beam etching (RIBE) using chlorine ions. Next, an SiN film 11 is formed on the exposed surface including the upper portion of the ridge stripe portion by plasma CVD. After that, in order to form an n-side electrode, the epitaxial layer other than the light emitting region including the ridge stripe is removed by etching until the n-GaN buffer layer 3 is exposed by photolithography and RIBE using chlorine. At this time, a resonator end face is formed.

Thereafter, a stripe window (10 μm width) for current injection is formed in the SiN film 11 on the upper surface of the ridge portion, and Ni / Au is used as the p-side electrode 12 so as to cover the stripe window. Ti / A as an n-side electrode 13 on the exposed portion of the buffer layer 3
After vacuum deposition of l, annealing is performed in nitrogen to form an ohmic electrode.

After manufacturing the above device, the front and rear end faces of the element are formed by cleavage, and the rear end face is coated with a multilayer reflective film made of SiO ₂ and TiO ₂ to have a high reflectance of 50% or more. When the front end face is coated with SiO ₂ and has a low reflectance of 10% or less, the GaN-based semiconductor light emitting device 30 is completed.

Although the GaN-based semiconductor light emitting device 30 does not oscillate laser, it has a so-called super radiance (Super Radiance) due to a layer structure, an optical waveguide structure composed of a ridge type refractive index waveguide structure, and a light reflection structure formed by both light emitting end faces. Ra
SLD that emits a blue light beam with a wavelength of 488 nm
Becomes

In the GaN-based semiconductor light emitting device 30, since the light absorbing layer 31 is provided between the active layer 7 and the sapphire c-plane substrate 1, light emitted from the active layer 7 toward the substrate 1 is provided. Is absorbed by the light absorbing layer 31. Therefore,
Even when the GaN-based semiconductor light-emitting element 30 is driven with a current lower than the oscillation threshold, a beam pattern with good symmetry in a direction perpendicular to the pn junction plane can be obtained as shown in FIG.
The beam pattern shown in FIG. 2 is shown in the same manner as in FIG. 6 described above.

While the embodiment configured to obtain a blue light beam having a wavelength of 488 nm has been described above, the GaN-based semiconductor light emitting device of the present invention can be configured to have a wavelength of about 430 to 600 nm by changing the In composition of the InGaN active layer. Can be emitted at an arbitrary wavelength within a wide wavelength range. In such a case, light may be effectively absorbed by the light absorbing layer 31, for example, by increasing the In composition of the light absorbing layer 31 in accordance with the composition of the active layer 7.

Next, a second embodiment of the present invention will be described with reference to FIG. In FIG. 3, elements that are the same as the elements in FIG. 1 are given the same reference numerals, and overlapping descriptions thereof will be omitted (hereinafter the same).

The GaN semiconductor light emitting device 4 of the second embodiment
0 is also the same SLD as that of the first embodiment. This G
The aN-based semiconductor light-emitting device 40 is different from the GaN-based semiconductor light-emitting device 30 of the first embodiment in that an n-light reflection layer 41 is provided instead of the n-light absorption layer 31. n-light reflection layer
41 is, for example, n-GaN and n-Al _0.1 Ga _0.9 N respectively 1 /
The Bragg reflection structure is obtained by alternately laminating the layers with a thickness of four wavelengths.

In the GaN-based semiconductor light emitting device 40, since the light reflecting layer 41 is provided between the active layer 7 and the sapphire c-plane substrate 1, light emitted from the active layer 7 toward the substrate 1 is The light is reflected by the light reflection layer 41 and turned back to the active layer 7 side. Therefore, even if the GaN-based semiconductor light emitting device 40 is driven with a current lower than the oscillation threshold, a beam pattern having relatively good symmetry with respect to a direction perpendicular to the pn junction surface can be obtained.

Further, in this case, a so-called photon recycling effect in which the light reflected by the light reflection layer 41 returns to the active layer 7 to increase the gain is obtained, and an SLD with high light use efficiency is realized.

Next, a third embodiment of the present invention will be described with reference to FIG. The GaN-based semiconductor light-emitting device 50 according to the third embodiment includes a sapphire c-plane substrate 1, an n-GaN low-temperature buffer layer 2 sequentially formed thereon, a SiO ₂ mask 1
4. The buffer layer 3 is shared with the n-GaN buffer layer 3.
Is an array-shaped SLD in which a plurality of light-emitting portions 51 are formed in a single row.

Each light emitting portion 51 constituted by a portion above the n-In _0.05 Ga _0.95 N buffer layer 4 is the same as the portion above the buffer layer 4 shown in FIG. And the light emitting section
A light separation groove 52 reaching from the surface of the buffer layer 3 to the substrate 1 is formed between the light emitting portion 51 and the light emitting portion 51.

In the above configuration, the provision of the light reflecting layer 41 provides the same effect as that of the second embodiment shown in FIG. Further, since the light separation groove 52 is formed as described above, light guided in the direction in which the light emitting portions 51 are arranged (the direction parallel to the pn junction surface) is guided from the groove 52 to the end. This prevents optical crosstalk between the light emitting units 51.

Next, a fourth embodiment of the present invention will be described with reference to FIG. The GaN-based semiconductor light emitting device 60 according to the fourth embodiment also includes a sapphire c-plane substrate 1, an n-GaN low-temperature buffer layer 2, and an SiO ₂ mask 1 sequentially formed thereon.
4. The buffer layer 3 is shared with the n-GaN buffer layer 3.
Is an array-shaped SLD in which a plurality of light emitting portions 61 are formed in a single row.

Each light emitting portion 61 constituted by a portion above the n-In _0.05 Ga _0.95 N buffer layer 4 is the same as the portion above the buffer layer 4 shown in FIG. And the light emitting section
A light separation groove 52 extending from the surface of the buffer layer 3 to the substrate 1 is formed between the light emission portion 61 and the light emission portion 61.
A light absorbing material 62 for absorbing the light emitted from the active layer 7 is embedded in 52.

In the above configuration, the provision of the light absorbing layer 31 provides the same effects as in the first embodiment shown in FIG. Then, the light separation groove 52
Since the light absorbing material 62 is embedded in the
(In the direction parallel to the pn junction surface) is absorbed by the light absorbing material 62 and cannot be guided further therefrom, and optical crosstalk between the light emitting portions 61 is prevented. . When embedding the light absorbing material 62 in the light separating groove 52 as described above,
Optical crosstalk is more reliably prevented as compared with the case where it is not embedded.

As described above, the embodiment in which the present invention is applied to the SLD has been described. However, the present invention can also be applied to a semiconductor laser, and in this case, the effects as described above can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic side sectional view showing a GaN-based semiconductor light emitting device according to a first embodiment of the present invention;

FIG. 2 is a graph showing an emission beam pattern in the GaN-based semiconductor light emitting device.

FIG. 3 is a schematic side sectional view showing a GaN-based semiconductor light emitting device according to a second embodiment of the present invention;

FIG. 4 is a schematic sectional side view showing a GaN-based semiconductor light emitting device according to a third embodiment of the present invention;

FIG. 5 is a schematic side sectional view showing a GaN-based semiconductor light emitting device according to a fourth embodiment of the present invention;

FIG. 6 is a schematic side sectional view showing an example of a conventional GaN-based semiconductor light emitting device.

FIG. 7 is a graph showing an emission beam pattern in a conventional GaN-based semiconductor light emitting device.

[Explanation of symbols]

Reference Signs List 1 sapphire c-plane substrate 2 n-GaN low-temperature buffer layer 3 n-GaN buffer layer 4 n-In _0.05 Ga _0.95 N buffer layer 5 n-Al _0.1 Ga _0.9 N clad layer 6 n-GaN optical guide layer 7 undoped active layer 8 p-GaN optical guide layer 9 p-Al _0.1 Ga _0.9 N clad layer 10 p-GaN cap layer 11 SiN film 12 p-side electrode 13 n-side electrode 14 SiO ₂ mask 30, 40, 50, 60 semiconductor light emitting device 31 light absorption Layer 41 Light reflection layer 51, 61 Light emitting part 52 Light separation groove 62 Light absorbing material

Claims (5)

[Claims] 1. A GaN-based semiconductor light emitting device having an active layer made of a GaN-based semiconductor and a stripe structure, wherein a light-absorbing layer that absorbs light emitted by the active layer is provided between the active layer and a substrate. A GaN-based semiconductor light-emitting device, characterized in that: 2. A GaN-based semiconductor light-emitting device having an active layer made of a GaN-based semiconductor and a stripe structure, wherein a light reflection layer for reflecting light emitted by the active layer is provided between the active layer and a substrate. A GaN-based semiconductor light-emitting device, characterized in that: 3. A GaN-based semiconductor light-emitting device in which a plurality of light-emitting portions having an active layer made of a GaN-based semiconductor and a stripe structure are arranged in parallel on a common substrate, wherein each active layer of the light-emitting portion and the substrate are A light-absorbing layer for absorbing light emitted from the active layer is provided between the light-emitting portions; and a light separation groove reaching the substrate is formed between each of the light-emitting portions. Light emitting element. 4. In a GaN-based semiconductor light-emitting device in which a plurality of light-emitting portions having an active layer made of a GaN-based semiconductor and a stripe structure are juxtaposed on a common substrate, each active layer of the light-emitting portion and the substrate A light reflection layer that reflects light emitted by the active layer is provided between the light emitting portions; and a light separation groove that reaches the substrate is formed between each of the light emitting portions. Light emitting element. 5. The GaN-based semiconductor light emitting device according to claim 3, wherein a light absorbing material that absorbs light emitted from the active layer is embedded in the light separating groove.