JP2019160974A - Semiconductor light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor light emitting device in a deep ultraviolet region, which suppresses an early decrease in output and has high luminous efficiency. SOLUTION: An n-type semiconductor layer 12 having an AlGaN composition, an active layer region 13 formed on the n-type semiconductor layer 12 and having an AlGaN composition, and an AlGaN or AlN formed on the active layer region 13. A p-type semiconductor having a composition and having an electron block layer 14 having a band gap larger than that of the n-type semiconductor layer 12 and the active layer region 13, and a p-type semiconductor formed on the electron block layer 14 and having a band gap of the electron block layer 14 or less. The p-type semiconductor layer has a composition of AlzGa1-zN (0 <z≤1) and gradually from the interface with the electron block layer 14 along the direction perpendicular to the electron block layer 14. It has a composition gradient layer 15A in which the Al composition z is reduced. [Selection diagram] Fig. 3

Description

  The present invention relates to a semiconductor light emitting device, and more particularly to a semiconductor light emitting device that emits light in the deep ultraviolet region.

  In recent years, semiconductor light-emitting devices having a light emission wavelength band in the deep ultraviolet region (for example, a peak wavelength of 200 nm to 300 nm) have attracted attention as a new light source having a sterilizing action for air or water. For example, Patent Document 1 discloses a light-emitting element made of a nitride semiconductor having an active layer between an n-type layer and a p-type layer and having a peak wavelength of 200 nm to 300 nm.

JP-A-2014-154597

  Semiconductor light-emitting elements having an emission wavelength in the deep ultraviolet region have problems in terms of extending their lifetime and increasing output. In particular, when a relatively large current (for example, a current of 100 mA or more) is applied in order to obtain a high light output, the device is often deteriorated at an early stage, and the output is often rapidly decreased.

  The present invention has been made in view of the above points, and provides a semiconductor light emitting device in the deep ultraviolet region having a high light emission efficiency, in which an early output decrease is suppressed in a semiconductor light emitting device particularly requiring a high injection current amount. The purpose is to do.

A semiconductor light emitting device according to the present invention includes an n-type semiconductor layer having an AlGaN composition, an active layer region having an AlGaN composition, an active layer region having an AlGaN composition, and an AlGaN or AlN layer. An electron block layer having a composition and a larger band gap than the n-type semiconductor layer and the active layer region, and a p-type semiconductor layer formed on the electron block layer and having a band gap equal to or smaller than the electron block layer. and, p-type semiconductor _{layer, Al z Ga 1-z N} (0 <z ≦ 1) has the composition and gradually Al composition z from the interface along a direction perpendicular to the electron blocking layer between the electron blocking layer It has the characteristic that it has a composition gradient layer which decreases.

1 is a top view of a semiconductor light emitting element according to Example 1. FIG. 1 is a cross-sectional view of a semiconductor light emitting element according to Example 1. FIG. 1 is a band diagram of a semiconductor light emitting element according to Example 1. FIG. 3 is a diagram illustrating a current path in a semiconductor light emitting device according to Example 1. FIG. It is a figure which shows the electric current path | route in the semiconductor light-emitting device which concerns on a comparative example. 6 is a diagram showing a relationship between a composition change rate of a composition gradient layer and a light output in the semiconductor light emitting device according to Example 1. FIG. 6 is a diagram showing a relationship between a layer thickness of a composition gradient layer and a deterioration rate in a semiconductor light emitting element according to Example 1. FIG. 6 is a band diagram of a semiconductor light emitting element according to Modification 1 of Example 1. FIG. 6 is a band diagram of a semiconductor light emitting element according to Modification 2 of Example 1. FIG.

  Examples of the present invention will be described in detail below.

  FIG. 1 is a top view of a semiconductor light emitting device (hereinafter simply referred to as a light emitting device) 10 according to a first embodiment. 2 is a cross-sectional view of the light-emitting element 10 and is a cross-sectional view taken along the line WW in FIG. FIG. 3 is a band diagram of the light-emitting element 10. A configuration of the light-emitting element 10 will be described with reference to FIGS. 1 to 3.

  First, the structure of the light emitting element 10 will be described. In this embodiment, the light emitting element 10 is made of a nitride-based semiconductor having an emission wavelength band in the deep ultraviolet region (for example, in the range of 200 to 300 nm).

  The light emitting element 10 includes an n-type semiconductor layer 12, an active layer region 13, an electron block layer 14 and a p-type semiconductor layer 15 formed on a substrate 11. The n-type semiconductor layer 12 to the p-type semiconductor layer 15 function as a light emitting structure layer in the light emitting element 10. The light emitting element 10 includes an n electrode 16 and a p electrode 17 connected to the n type semiconductor layer 12 and the p type semiconductor layer 15, respectively.

  First, in this embodiment, the substrate 11 is a growth substrate for crystal growth of the n-type semiconductor layer 12 to the p-type semiconductor layer 15. The substrate 11 is made of, for example, an AlN substrate, a GaN substrate, a sapphire substrate, a SiC substrate, or a Si substrate. In this embodiment, the substrate 11 is an AlN substrate.

In consideration of growing the n-type semiconductor layer 12 to the p-type semiconductor layer 15 having high crystal quality, the substrate 11 preferably has a relatively low dislocation density. For example, the dislocation density of the substrate 11 is preferably 10 ⁸ cm ⁻² or less, and more preferably 10 ⁷ cm ⁻² or less. The dislocation density can be measured by using a known method such as measuring the number of dislocations from a transmission electron microscope image and measuring the number of etch pits measured after being immersed in a heated acid mixed solution. .

  In this embodiment, the substrate 11 is made of AlN having a + C plane as a crystal growth plane. Therefore, the n-type semiconductor layer 12 to the p-type semiconductor layer 15 grown on the substrate 11 have a C plane as a crystal growth plane. However, the crystal growth surface of the substrate 11 is not limited to the C plane. For example, a surface inclined (off) from the C plane may be used as the crystal growth surface. When a plane inclined from the C plane is used as the crystal growth plane, the inclination angle (off angle) is preferably in the range of 0.1 to 0.5 °, and in the range of 0.3 to 0.4 °. More preferably, it is within. Further, the crystal growth surface of the substrate 11 may be an M plane or an A plane.

  The thickness of the substrate 11 can be determined in consideration of reducing the light absorption coefficient, ease of handling (yield), and the like. The thickness of the substrate 11 is preferably in the range of 50 to 1000 μm, for example.

  Note that a buffer layer (not shown) may be provided between the substrate 11 and the n-type semiconductor layer 12. When the buffer layer is provided, the buffer layer is made of, for example, a single AlN layer, a superlattice structure made of an AlN layer and an AlGaN layer, or a superlattice structure made of AlGaN layers having different compositions. Is preferred. The buffer layer is preferably made of an AlGaN layer having an Al composition higher than that of the n-type semiconductor layer 12, for example. However, the buffer layer only needs to have a composition that contributes to improving the yield of the crystal growth process of the n-type semiconductor layer 12 to the p-type semiconductor layer 15.

  Moreover, when providing a buffer layer, when considering the productivity, for example, the buffer layer preferably has a layer thickness in the range of 1 to 1000 nm, and more preferably has a layer thickness in the range of 10 to 100 nm.

  Referring to FIGS. 2 and 3, the n-type semiconductor layer 12 is formed on the substrate 11. The n-type semiconductor layer 12 plays a role of injecting electrons into the active layer region 13. The n-type semiconductor layer 12 functions as a cladding layer.

In the present embodiment, the n-type semiconductor layer 12 has a composition of Al _x Ga _1-x N (0.5 ≦ x ≦ 1, preferably 0.5 ≦ x ≦ 0.9). In the present embodiment, the n-type semiconductor layer 12 has a composition of Al _0.7 Ga _0.3 N. For example, the n-type semiconductor layer 12 preferably has a layer thickness of 100 nm or more. The n-type semiconductor layer 12 preferably has a low dislocation density.

The n-type semiconductor layer 12 includes, for example, Si as an n-type dopant and has an n-type conductivity type. The dopant concentration of the n-type semiconductor layer 12 is not particularly limited and may be appropriately determined according to the purpose. For example, in view of obtaining high conductivity, the dopant concentration of the n-type semiconductor layer 12 is preferably in the range of 1 × 10 ^{15 to} 5 × 10 ¹⁹ cm ⁻³ .

The n-type semiconductor layer 12 may be composed of a plurality of semiconductor layers exhibiting n-type conductivity. In this case, each of the semiconductor layers preferably has a dopant concentration in the range of 1 × 10 ^{15 to} 5 × 10 ¹⁹ cm ⁻³ .

The active layer region 13 is formed on the n-type semiconductor layer 12 and has a band gap equal to or smaller than that of the n-type semiconductor layer 12. The active layer region 13 functions as a light emitting layer. In this embodiment, the active layer region 13 has a composition of Al _y Ga _1-y N (0 <y ≦ 1). The active layer region 13 emits light in the deep ultraviolet region. Note that the active layer region 13 is preferably formed directly on the n-type semiconductor layer 12, that is, in contact with the n-type semiconductor layer 12.

In the present embodiment, as shown in FIG. 3, the active layer region 13 has a multiple quantum well (MQW) structure. In this embodiment, the active layer region 13 includes a plurality of well layers 13A each having a composition of Al _y1 Ga _{1 -y1} N, and each of the well layers having a composition of Al _y2 Ga _{1 -y2} N. A plurality of barrier layers 13B having a larger band gap.

In this embodiment, each of the well layers 13A has a composition of Al _0.5 Ga _0.5 N, and each of the barrier layers 13B has a composition of Al _0.65 Ga _0.35 N. In the present embodiment, the Al composition y2 of the barrier layer 13B is smaller than the Al composition x of the n-type semiconductor layer 12. Therefore, the barrier layer 13 </ b> B has a smaller band gap than the n-type semiconductor layer 12. Therefore, in this embodiment, a band gap step is provided between the n-type semiconductor layer 12 and the barrier layer 13B.

  The configuration of the active layer region 13 is not limited to this. For example, the active layer region 13 is not limited to having a multiple quantum well structure. For example, the active layer region 13 may have a single quantum well structure or a single layer.

The electron block layer 14 is formed on the active layer region 13 and has a larger band gap than the active layer region 13. The electron block layer 14 has a composition of Al _s Ga _1-s N (0.8 <s ≦ 1). The electron blocking layer 14 functions as a layer that suppresses overflow of electrons injected into the active layer region 13 into the p-type semiconductor layer 15. In this embodiment, the electron block layer 14 has a larger band gap than the n-type semiconductor layer 12. In this embodiment, the electron block layer 14 has the same composition as that of the substrate 11, that is, the composition of AlN (corresponding to the case of s = 1).

  In this embodiment, the electron blocking layer 14 includes Mg as a p-type dopant and has a p-type conductivity. However, the electron block layer 14 may not include the p-type dopant, and may include the p-type dopant in a part thereof. Further, the electron block layer 14 may not be provided. That is, the p-type semiconductor layer 15 may be formed on the active layer region 13.

  The p-type semiconductor layer 15 has a band gap equal to or smaller than the electron block layer 14. The p-type semiconductor layer 15 includes, for example, Mg as a p-type dopant, and has a p-type conductivity type. The p-type semiconductor layer 15 functions as a cladding layer together with the n-type semiconductor layer 12.

  The p-type semiconductor layer 15 includes a composition gradient layer 15A whose composition changes along the direction perpendicular to the electron block layer 14 (the layer thickness direction of each layer) from the interface with the electron block layer 14, and the composition gradient layer 15A. And a contact layer 15B that forms an ohmic contact with the p-electrode 17. In the present embodiment, the composition gradient layer 15A functions as a cladding layer.

The composition gradient layer 15 </ b> A has a larger band gap than the active layer region 13. In this embodiment, the composition gradient layer 15A has a band gap larger than that of the n-type semiconductor layer 12 and not more than the electron block layer 14. In the present embodiment, the composition gradient layer 15A has a composition of Al _z Ga _1-z N (0.5 <z ≦ 1).

In the present embodiment, the composition gradient layer 15A is configured such that the Al composition z decreases monotonously and linearly from the interface with the electron blocking layer 14 to the interface with the contact layer 15B. In this embodiment, the composition gradient layer 15A has an AlN composition (corresponding to the case of z = 1 and the same composition as the electron block layer 14) at the interface with the electron block layer 14, and the contact layer 15B The interface has a composition of Al _0.8 Ga _0.2 N (corresponding to the case of z = 0.8). That is, in the composition gradient layer 15A, the Al composition z decreases from 1.0 to 0.8 as the distance from the electron block layer 14 increases.

The contact layer 15B has a band gap equal to or less than the interface portion with the contact layer 15B in the composition gradient layer 15A. The contact layer 15B has a composition of Al _t Ga _1-t N (0 ≦ t <0.8, preferably 0 ≦ t <0.1). In this embodiment, the contact layer 15B has a smaller band gap than the n-type semiconductor layer 12 and the active layer region 13 (each of the well layer 13A and the barrier layer 14B). In this embodiment, the contact layer 15B has a GaN composition (corresponding to the case of t = 0).

  In this example, the band gaps of the n-type semiconductor layer 12, the active layer region 13, the electron block layer 14, and the p-type semiconductor layer 15 (composition gradient layer 15A and contact layer 15B) are as shown in FIG. Have a good relationship.

  Referring to FIGS. 1 and 2, the n-electrode 16 is formed on the n-type semiconductor layer 12, and the p-electrode 17 is formed on the p-type semiconductor layer 15 (contact layer 15B). For example, the n-electrode 16 is composed of a laminate of a Ti layer, an Al layer, and an Au layer. The p-electrode 17 is composed of a stacked body of, for example, a Ni layer and an Au layer.

  In the present embodiment, the surface of the p-type semiconductor layer 15 penetrates the p-type semiconductor layer 15, the electron blocking layer 14, and the active layer region 13 to reach the n-type semiconductor layer 12, and has a comb-teeth shape in a top view. The recessed part (mesa structure part) which has is formed. The n-electrode 16 is formed in a comb shape on the surface of the n-type semiconductor layer 12 exposed at the bottom of the recess.

  The p electrode 17 is formed in a comb shape on the surface of the p-type semiconductor layer 15 where the concave portion is not formed, and is arranged so that the comb tooth portion meshes with the comb tooth portion of the n electrode 16 in a top view. Has been.

  Although not shown, in this embodiment, the light emitting element 10 has a pad electrode on the upper surface on the n electrode 16 and p electrode 17 side, and is solder-bonded to the mounting substrate via the pad electrode. It has a flip chip type mounting structure. The light emitted from the active layer region 13 passes through the n-type semiconductor layer 12 and is extracted to the outside through the substrate 11. That is, the surface of the substrate 11 opposite to the n-type semiconductor layer 12 functions as a light extraction surface in the light emitting element 10.

  The configurations of the n-type semiconductor layer 12 to the p-type semiconductor layer 15 and the configurations of the n-electrode 16 and the p-electrode 17 are merely examples. For example, the n electrode 16 may be in contact with the n-type semiconductor layer 12. Further, for example, the p-electrode 17 may be in contact with the p-type semiconductor layer 15. That is, for example, the configuration of the light emitting element 10 shown in FIGS. 1 and 2 (for example, electrode shape) is merely an example.

  FIG. 4 is a diagram illustrating a current path between the n-type semiconductor layer 12 and the p-type semiconductor layer 15 in the light emitting element 10. FIG. 4 is a cross-sectional view taken along the line W-W in FIG. 1, but only a part thereof is shown. For clarity of illustration, hatching is omitted in FIG. 4, and the contact layer 15B and the p-electrode 17 are omitted. The light emitting operation of the light emitting element 10 and the function of the composition gradient layer 15A will be described with reference to FIG.

  As shown in FIG. 4, the current C1 applied from the p-electrode 17 passes through the contact layer 15B, the composition gradient layer 15A, the electron block layer 14, the active layer region 13, and the n-type semiconductor layer 12 to the n-electrode 16. It flows toward.

  Here, by providing the composition gradient layer 15A in the p-type semiconductor layer 15, the inventors of the present application can improve the light emission efficiency while suppressing one mode leading to the early deterioration of the light emitting element 10. I found out that I can do it.

  Specifically, the inventors of the present application apply a phenomenon in which a current flows concentrically in a part of an element (current cloudy) when a voltage that generates a large forward current (for example, about 400 mA) is applied in the element. (Current crowding) has occurred. The inventors of the present application have found that this current crowding has a great influence on early deterioration and that the current crowning can be suppressed by providing the composition gradient layer 15A.

  The current crowding will be described with reference to FIG. FIG. 5 is a cross-sectional view similar to FIG. 4 in the light emitting device 100 of the comparative example. The light emitting device 100 has the same configuration as that of the light emitting device 10 except that instead of the composition gradient layer 15A, the cladding layer 101 has an AlGaN layer whose composition does not change.

  When the light emitting device 100 is driven, a triangular potential well is formed at the interface between the cladding layer 101 and the electron blocking layer 14, and holes are accumulated at this interface (also referred to as generation of a two-dimensional hole gas). When the two-dimensional hole gas is generated, the current C2 tends to flow in a direction parallel to the cladding layer 101 (hereinafter referred to as a lateral direction) at the interface between the cladding layer 101 and the electron blocking layer 14 and flows in the electron blocking layer 14. It becomes difficult to flow in the direction (hereinafter referred to as the vertical direction).

  As a result, as shown in FIG. 5, most of the current C2 flows laterally toward the n-electrode 16 at the interface between the cladding layer 101 and the electron blocking layer 14, and then the electron blocking layer 14 and the active layer. It flows toward the n-type semiconductor layer 12 through the region 13. In other words, in the light emitting element 100, the current C2 flows in a concentrated manner in the portion (mesa structure portion) of the n-type semiconductor layer 12 in the vicinity of the n electrode 16. In this way, current crowding occurs in the light emitting element 100.

  When the current crowding occurs, the current concentration portion where the current crowding occurs rapidly deteriorates. Therefore, in the light emitting element 100, it is expected that the output is rapidly reduced and destabilized at an early stage, that is, the lifetime is short. In addition, when current crowding occurs, it becomes difficult for current to flow through the entire light emitting region, that is, the active layer region 13. Therefore, it is expected that the light emission efficiency is lowered.

  On the other hand, in the light emitting element 10, the p-type semiconductor layer 15 has a composition gradient layer 15A in which the Al composition z gradually increases toward the electron block layer 14 (that is, the band gap gradually approaches the electron block layer 14). Have This suppresses the formation of a potential between the composition gradient layer 15 </ b> A and the electron block layer 14. Accordingly, generation of two-dimensional hole gas and generation of current crowding are suppressed.

  Therefore, as shown in FIG. 4, in the light emitting element 10, the current C <b> 1 tends to flow in the vertical direction from the most region of the composition gradient layer 15 </ b> A and flows widely in the n-type semiconductor layer 12. . Therefore, early deterioration of the element can be suppressed and high luminous efficiency can be obtained.

  In particular, in a light-emitting element having a light emission band in the deep ultraviolet region, such as the light-emitting element 10, element degradation in a short time during a large current drive is one of the major problems. The inventors of the present application confirmed that the deterioration rate was about 23% when a predetermined number of light-emitting elements 100 were driven at 400 mA. On the other hand, the inventors of the present application confirmed that the deterioration rate under the same condition was improved to at least about 10% by providing the composition gradient layer 15 </ b> A in the light emitting element 10. Here, the deterioration rate is defined as the ratio of the light output that has decreased after 100 hours of driving time with the light output immediately after driving as a reference (100%).

  In this embodiment, the composition gradient layer 15A has a larger band gap than the n-type semiconductor layer 12 as a whole. In the present embodiment, the composition gradient layer 15A has an Al composition z larger than the Al composition x of the n-type semiconductor layer 12 even in the portion on the contact layer 15B side, which is the portion having the smallest band gap. Thereby, the composition gradient layer 15A has a high resistance. It is considered that the increase in resistance of the composition gradient layer 15A contributes to effective suppression of current crowding and improvement of the deterioration rate.

  FIG. 6 is a diagram showing the relationship between the layer thickness D of the composition gradient layer 15A (see FIG. 2 for the layer thickness D) and the deterioration rate. FIG. 7 is a diagram showing the relationship between the change rate of the Al composition z in the composition gradient layer 15A (change rate of the Al composition z per 1 nm in the layer thickness direction) and the light output. A preferable range of the layer thickness D of the composition gradient layer 15A and the Al composition z will be described with reference to FIGS.

  First, FIG. 6 is a diagram showing experimental results of deterioration rates in light emitting elements in which the layer thickness D of the composition gradient layer 15A is different in units of 5 nm from 40 nm to 60 nm. Each of the data points in FIG. 6 corresponds to a deterioration rate for each layer thickness D when the Al composition z of the composition gradient layer 15A is changed from 1.0 to 0.8. Considering that the deterioration rate of the light emitting element 100 that does not have the composition gradient layer 15A is 20% or more, when the composition gradient layer 15A has a layer thickness D of 50 nm or more, confirm a clear improvement of the deterioration rate. Can do.

  In addition, it is considered that the effect of suppressing the deterioration rate is caused by the current crowding being suppressed by setting the layer thickness D of the composition gradient layer 15A within a preferable range. The inventors of the present application have developed a light emission pattern from the light emitting element 10 having the composition gradient layer 15A having various layer thicknesses D (exactly, the contact layer 15B is excited by the light emitted from the active layer region 13 and the contact layer 15B is excited). The emitted PL light) was observed. As a result, a preferable result could be obtained if the layer thickness D of the composition gradient layer 15A was 40 nm or more.

  More specifically, when the layer thickness D of the composition gradient layer 15A is 40 nm, the light emission pattern from the light emitting element 10 is slightly biased toward the outer peripheral portion of the p-electrode 17 in top view, but the layer thickness D is increased. The light emission pattern spreads to the inner region, and light having a stable intensity could be observed over the entire region of the p-electrode 17 in the top view. Considering these, the layer thickness D of the composition gradient layer 15A is preferably 40 nm or more, more preferably 50 nm or more, and further preferably 60 nm or more.

  From the results shown in FIG. 6, it is estimated that the deterioration rate is almost 0% when the layer thickness D of the composition gradient layer 15A is 60 nm or more, and further 80 nm or more. Therefore, if the layer thickness D of the composition gradient layer 15A is, for example, 80 nm or less, it is considered that a sufficient effect of suppressing the deterioration rate can be obtained.

  Next, FIG. 7 shows the result of simulating the light output of each of the light emitting elements in which the layer thickness D of the composition gradient layer 15A is fixed to 60 nm and the Al composition z is changed at different gradient rates in the composition gradient layer 15A. Indicates. The data points in FIG. 7 are respectively obtained when the Al composition z is decreased from 1.0 to 0.8, from 1.0 to 0.7, and from the interface with the electron blocking layer 14, and This corresponds to the output value corresponding to the composition gradient layer 15 </ b> A when decreased from 1.0 to 0.6.

As shown in FIG. 7, the inclination rate of the Al composition z, that is, the reduction rate of the Al composition z per nm in the direction perpendicular to the electron blocking layer 14 of the composition gradient layer 15A, contributes to the improvement in light output. Recognize. That is, it can be seen that it is preferable that the Al composition z varies greatly in the composition gradient layer 15A. For example, the inclination rate (change rate) of the Al composition z is preferably 0.003 nm ⁻¹ or more from the viewpoint of improving the light output.

In consideration of the experimental results of FIG. 6, the simulation results of FIG. 7, and the composition range described above, the composition gradient layer 15A has a reduction rate of at least 0.0025 to 0.007 nm ⁻¹ and the electron blocking layer 14. It is preferable to have an Al composition z that gradually decreases along the direction perpendicular to the electron blocking layer 14 from the interface or a layer thickness D of 40 nm or more.

Further, according to the experimental results of FIG. 6, it is possible to expect an improvement effect of the deterioration rate when the layer thickness D is 40 nm or more. When this is applied to the simulation results of FIG. 7, when the Al composition z is changed from 1.0 to 0.6 in the composition gradient layer 15A having a layer thickness D of 40 nm, the gradient ratio of the Al composition z is 0.01 nm. ^-1 . Therefore, the change rate (decrease rate) of the Al composition z in the composition gradient layer 15A is preferably in the range of 0.0025 to 0.01 nm ⁻¹ .

Moreover, the result of FIG. 6 is based on the experiment performed with respect to the composition inclination layer 15A when the Al composition z is inclined from 1.0 to 0.8. When the result of FIG. 6 is converted into the slope ratio of the Al composition z, for example, when the layer thickness D is 40 nm, the slope ratio is 0.005 nm ⁻¹ , and similarly when the layer thickness D is 50 nm and 60 nm, the slope is The rates are 0.004 nm ⁻¹ and 0.003 nm ⁻¹ , respectively. Moreover, from the result of FIG. 7, the improvement effect of the light output has been confirmed within the range of 0.0033 to 0.0067 nm ⁻¹ .

Therefore, the gradient rate of the Al composition z in the composition gradient layer 15A is preferably in the range of 0.003 to 0.0066 nm ⁻¹ , for example. Moreover, as a tilt rate expected to obtain the highest effect in consideration of the results of FIGS. 6 and 7, for example, a range of 0.0033 to 0.005 nm ⁻¹ may be mentioned.

  In addition, a preferable layer thickness D of the composition gradient layer 15A in consideration of the suppression of the deterioration rate and the increase in light output is, for example, in the range of 40 to 160 nm. The layer thickness D is more preferably in the range of 40 to 135 nm, and further preferably in the range of 40 to 120 nm.

  For example, in this embodiment, the Al composition y1 of the well layer 14A in the active layer region 13 is 0.5. In this case, for example, the Al composition z on the contact layer 15B side in the composition gradient layer 15A (the lower limit value of the Al composition z in the composition gradient layer 15A) is preferably 0.5 or more.

In this embodiment, the electron block layer 14 has an AlN composition (corresponding to s = 1), and the contact layer 15B has a GaN composition (corresponding to t = 0). Therefore, in this case, for example, the composition gradient layer 15A has an Al composition z between the electron block layer 14 and the contact layer 15B, that is, Al _z Ga _1-z N (0 ≦ z ≦ 1). You may have a composition. That is, the Al composition z may be inclined from 1.0 to 0 (that is, with the maximum change amount) in the composition gradient layer 15A.

  Note that when the Al composition z is configured to be inclined from 1.0 to 0 in the composition gradient layer 15A, the formation of potential is also suppressed at the interface between the composition gradient layer 15A and the contact layer 15B. Therefore, an improvement effect of the deterioration rate can be expected. In addition, the inventors of the present application also performed a simulation for this configuration, and confirmed that the light output was improved. Accordingly, it is expected that the light output is improved when the change rate of the Al composition z is increased by increasing the change amount of the Al composition z in the composition gradient layer 15A.

  On the other hand, when the light emitting device 10 is manufactured using the n-type semiconductor layer 12 to the p-type semiconductor layer 15 grown on the substrate 11 made of AlN as in this embodiment, the Al composition z of the composition gradient layer 15A is set to When changing to the Al composition s of the contact layer 15B (when changing in the range of 0 ≦ z <s), there is a possibility that the crystallinity deteriorates, such as lattice relaxation in the composition gradient layer 15A. The inventors of the present application confirmed the light output of the light emitting element 10 when the Al composition z of the composition gradient layer 15A is inclined from 1.0 to 0. As a result, the light emitting element 10 having the band configuration shown in FIG. The light output was about half.

  Therefore, considering the crystallinity, the Al composition z of the composition gradient layer 15A is, for example, in a range larger than the middle between the electron block layer 14 and the contact layer 15B, that is, in a range of ((t + s) / 2 <z <s). It is preferable to be within.

  Further, from the viewpoint of both the improvement of the deterioration rate and the improvement of the light output, the Al composition z of the composition gradient layer 15A is larger than the Al composition x of the n-type semiconductor layer 12, that is, (x <z <s). Preferably there is. In consideration of forming a clear band gap difference with the electron blocking layer 14, the Al composition z is preferably 0.05 or more, and more preferably 0.1 or more.

  Note that these preferable Al composition z ranges, for example, ((t + s / 2) <z <s) and (x <z <s) are limited to the case where an AlN single crystal substrate is used as the substrate 11. is there. For example, when the light emitting element 10 is formed so that the n-type semiconductor layer 12 to the p-type semiconductor layer 15 are grown while the lattice is relaxed on the sapphire substrate as the substrate 11, the n-type grown on the heterogeneous substrate is used. The light emitting element 10 having the semiconductor layer 12 to the p-type semiconductor layer 15 is not limited to this.

  In the present embodiment, the contact layer 15B has a layer thickness of 270 nm. In this embodiment, the contact layer 15B is the thickest layer among the layers to which the p-type dopant is added. However, the layer thickness of the contact layer 15B can be arbitrarily designed in consideration of a desired driving voltage, formation of a transparent electrode, and the like.

  In the present embodiment, the case where the electron block layer 14 has an AlN composition and the composition gradient layer 15A has an Al composition z that gradually decreases from 1.0 corresponding to the same composition as AlN has been described. . However, the configuration of the electron blocking layer 14 and the composition gradient layer 15A is not limited to this.

  First, the electron block layer 14 is not limited to having an AlN composition, and may have an AlGaN composition. Further, the Al composition z on the electron blocking layer 14 side in the composition gradient layer 15A is not limited to the above. The composition gradient layer 15 </ b> A may have a composition different from that of the electron block layer 14 at the interface with the electron block layer 14, that is, an Al composition z different from the Al composition s of the electron block layer 14. In consideration of suppressing the generation of the two-dimensional hole gas, the Al composition z and the Al composition s preferably satisfy the relationship (s−z) <0.05, and (s−z) <0. More preferably, the relationship of 05 is satisfied.

  Further, the preferred range of the layer thickness D of the composition gradient layer 15A and the preferred range of the reduction rate of the Al composition z are merely examples. The composition gradient layer 15 </ b> A only needs to be composed of an AlGaN layer in which the Al composition z gradually decreases along the direction perpendicular to the electron block layer 14 from the interface with the electron block layer 14.

  In the present embodiment, the case where the Al composition z of the composition gradient layer 15A changes linearly and exhibits the band gap shown in FIG. 3 has been described. However, the aspect in which the Al composition z of the composition gradient layer 15A changes is not limited to this. The composition gradient layer 15 </ b> A only needs to be composed of an AlGaN layer in which the Al composition z decreases monotonously from the interface with the electron block layer 14.

  FIG. 8 is a band diagram of the light-emitting element 20 according to the first modification of the first embodiment. The light emitting element 20 has the same configuration as the light emitting element 10 except for the configuration of the p-type semiconductor layer 21. The p-type semiconductor layer 21 has the same configuration as that of the p-type semiconductor layer 15 except for the configuration of the composition gradient layer 21A.

  In this modification, the decreasing rate of the Al composition z in the composition gradient layer 21A gradually decreases from the interface with the electron blocking layer 14. The composition gradient layer 21A has the same composition on the electron blocking layer 14 side and the contact layer 15B side as the composition gradient layer 15A. Therefore, the composition gradient layer 21A exhibits a band gap as shown in FIG.

  As in the present modification, the two-dimensional hole gas and current at the interface between the electron block layer 14 and the composition gradient layer 21A are also reduced by decreasing the Al composition z while gradually decreasing the reduction rate toward the contact layer 15B. Generation of crowding can be suppressed.

  FIG. 9 is a band diagram of the light-emitting element 30 according to the second modification of the first embodiment. The light emitting element 30 has the same configuration as the light emitting element 10 except for the configuration of the p-type semiconductor layer 31. The p-type semiconductor layer 31 has the same configuration as that of the p-type semiconductor layer 15 except for the configuration of the composition gradient layer 31A.

  In this modification, the decreasing rate of the Al composition z in the composition gradient layer 31A gradually increases from the interface with the electron blocking layer 14. Note that the composition on the electron blocking layer 14 side and the composition on the contact layer 15B side in the composition gradient layer 31A are the same as those in the composition gradient layer 15A. Therefore, the composition gradient layer 31A exhibits a band gap as shown in FIG.

  As in this modification, the two-dimensional hole gas and current at the interface between the electron block layer 14 and the composition gradient layer 21A are also reduced by gradually increasing the decrease rate toward the contact layer 15B. Generation of crowding can be suppressed.

  Like the composition gradient layers 21A and 31A of Modifications 1 and 2, the composition gradient layer 15A may be configured such that the Al composition z gradually decreases while the decrease rate changes.

  Further, the Al composition z of the composition gradient layer 15A may be continuously changed or may be changed stepwise as long as it monotonously decreases. However, when the Al composition z is changed stepwise, the generation of two-dimensional hole gas in the composition gradient layer 15A needs to be suppressed. Therefore, the amount of change of the Al composition z at the step is preferably within 5%, and preferably within 3%. When the Al composition z changes stepwise, the decrease rate of the Al composition z may be, for example, an average decrease rate of the Al composition z in the composition gradient layer 15A.

  Thus, in this embodiment, the light emitting element 10 is formed on the substrate 11 (for example, an AlN single crystal substrate), the n-type semiconductor layer 12 having the composition of AlGaN, and the n-type semiconductor layer 12, and is made of AlGaN. An active layer region 13 having a composition, an electron blocking layer 14 formed on the active layer region 13, having a composition of AlGaN or AlN, and having a larger band gap than the n-type semiconductor layer 12 and the active layer region 13; A p-type semiconductor layer 15 formed on the electron block layer 14 and having a band gap equal to or smaller than the electron block layer 14.

In addition, for example, the p-type semiconductor layer 15 has a composition of Al _z Ga _{1 -zN} (0 <z ≦ 1) and extends in a direction perpendicular to the electron block layer 14 from the interface with the electron block layer 14. It has a composition gradient layer 15A in which the Al composition z gradually decreases. Therefore, it is possible to provide the light emitting element 10 in the deep ultraviolet region that has an early output reduction and has high luminous efficiency.

10, 20, 30 Semiconductor light emitting device 13 n-type semiconductor layer 14 active layer region 15 electron block layers 16, 21, 31 p-type semiconductor layers 16A, 21A, 31A Composition gradient layer

Claims (10)

An n-type semiconductor layer having a composition of AlGaN;
An active layer region formed on the n-type semiconductor layer and having an AlGaN composition;
An electron blocking layer formed on the active layer region, having an AlGaN or AlN composition, and having a larger band gap than the n-type semiconductor layer and the active layer region;
A p-type semiconductor layer formed on the electron block layer and having a band gap equal to or smaller than the electron block layer;
The p-type semiconductor _{layer, Al z Ga 1-z N} (0 <z ≦ 1) has the composition and gradually Al composition along a direction perpendicular from the interface between the electron blocking layer in the electron blocking layer A semiconductor light emitting device comprising a composition gradient layer in which z decreases.   The semiconductor light emitting element according to claim 1, wherein the composition gradient layer has a layer thickness of 40 nm or more.   3. The semiconductor light emitting element according to claim 1, wherein the n-type semiconductor layer is formed on a single crystal AlN substrate.   4. The semiconductor light emitting device according to claim 1, wherein the composition gradient layer has a larger band gap than the n-type semiconductor layer on a surface opposite to the electron blocking layer. 5. element. 5. The semiconductor light emitting element according to claim 1, wherein a decreasing rate of the Al composition z in the composition gradient layer is in a range of 0.0025 to 0.01 nm ⁻¹ . The electron blocking layer has a composition of AlN,
6. The p-type semiconductor layer according to claim 1, further comprising a contact layer formed on the composition gradient layer and having an AlGaN or GaN composition having a smaller Al composition than the composition gradient layer. The semiconductor light emitting element as described in any one. The semiconductor light emitting element according to claim 5, wherein the decreasing rate of the Al composition z in the composition gradient layer is in a range of 0.003 to 0.008 nm ⁻¹ . The semiconductor light emitting element according to claim 7, wherein the decreasing rate of the Al composition z in the composition gradient layer is in a range of 0.003 to 0.006 nm ⁻¹ .   9. The semiconductor light emitting element according to claim 1, wherein a decreasing rate of the Al composition z in the composition gradient layer gradually decreases from the interface with the electron blocking layer.   The semiconductor light emitting element according to claim 1, wherein a decreasing rate of the Al composition z in the composition gradient layer gradually increases from the interface with the electron blocking layer.

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