JP2014192274A - HIGH-OUTPUT GaN-BASED SEMICONDUCTOR LIGHT-EMITTING ELEMENT - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor light-emitting element that allows obtaining a high-linearity radiation output corresponding to fluctuations in current density while suppressing reduction in light-emitting efficiency corresponding to an increase in the current density of the semiconductor light-emitting element, and allows obtaining a high radiation output even when the current density is increased.SOLUTION: A semiconductor light-emitting device composed of at least an n-type semiconductor layer, a light-emitting layer, and a p-type semiconductor layer includes: a P-type AlGaN layer, which is the p-type semiconductor layer on the light-emitting layer, having a magnesium (Mg) concentration of 1.0×10to 6.0×10atoms/cm; a first p-type GaN layer having a higher concentration of Mg than the p-type AlGaN layer on the p-type AlGaN layer; and a second p-type GaN layer having a similar extent of Mg as the p-type AlGaN layer on the first p-type GaN layer.

Description

The present invention relates to a nitride semiconductor light emitting device, and relates to a structure of a p-type nitride layer that suppresses a decrease in light emission efficiency corresponding to an increase in current density.

  In recent years, semiconductor light-emitting elements, that is, LEDs (Light Emitting Diodes), have been remarkably improved in light emission efficiency and have been used for lighting applications. By the way, the semiconductor light emitting device has a phenomenon in which the light emission efficiency is lowered in response to an increase in operating current. More specifically, this is a phenomenon in which the luminous efficiency decreases in response to an increase in operating current density (hereinafter referred to as current density), which is a value obtained by dividing the operating current by the light emitting area of the semiconductor light emitting device.

  This phenomenon causes various problems in the use of the semiconductor light emitting device. For example, there is a problem that a radiation output with high linearity corresponding to increase / decrease in current density cannot be obtained. Further, there is a problem that a high radiation output cannot be obtained even if the current density is increased.

  For example, as an attempt to improve the light emission efficiency of a semiconductor light emitting device, Patent Document 1 discloses that “a first nitride semiconductor layer containing a p-type impurity is formed on an active layer, and the first nitride semiconductor layer is formed on the first nitride semiconductor layer. And a second nitride semiconductor layer having a p-type impurity concentration that gradually decreases as the distance from the first nitride semiconductor layer increases. The second nitride semiconductor layer is formed on the second nitride semiconductor layer. Discloses a method of improving the light emission efficiency by having a structure having a third nitride semiconductor layer containing a p-type impurity in a larger amount than the average p-type impurity concentration.

  However, although the method disclosed in Patent Document 1 improves the light emission efficiency, there is a problem that a radiation output with high linearity corresponding to the increase or decrease of the current density cannot be obtained. Even if the current density is increased, a high radiation output is obtained. Problems that cannot be obtained have not been improved.

Japanese Patent Laid-Open No. 11-068155

Accordingly, an object of the present invention is to provide a semiconductor light emitting device capable of obtaining a radiation output with high linearity corresponding to increase / decrease in current density while suppressing a decrease in light emission efficiency corresponding to an increase in current density of the semiconductor light emitting device. Another object of the present invention is to provide a semiconductor light emitting device that can obtain a high radiation output even when the current density is increased.

A semiconductor light-emitting device comprising at least an n-type semiconductor layer, a light-emitting layer, and a p-type semiconductor layer, and the magnesium (Mg) concentration of the p-type semiconductor layer on the light-emitting layer is 1.0 × 10 ^{19 to} 6.0 × 10 A p-type AlGaN layer of ¹⁹ atoms / cm ³ ; a first p-type GaN layer having a higher concentration of Mg than the p-type AlGaN layer on the p-type AlGaN layer; and the first p-type GaN. A semiconductor light emitting device having a second p-type GaN layer having Mg on the same level as the p-type AlGaN layer on the layer.

  The light emitting layer has a multiple quantum well structure in which a plurality of well layers and barrier layers are alternately stacked, wherein the multiple well layer has a structure in which the barrier layers are stacked, and the band gap of the first barrier layer is A semiconductor light emitting device, which is narrower than the band gap of the other barrier layer, wider than the band gap of the well layer, and is a GaN-based crystal containing at least indium (In).

A semiconductor light emitting device having a structure in which the well layer and the barrier layer of the light emitting layer are formed as one unit, and are stacked at least 6 units and 16 units or less.

A p-type AlGaN layer having a Mg concentration of 1.0 × 10 ^{19 to} 6.0 × 10 ¹⁹ atoms / cm ³ is disposed on the light emitting layer, and a first p-type having a higher Mg concentration than the p-type AlGaN layer. The semiconductor light emitting device having a structure in which GaN is disposed and the second p-type GaN having the same Mg concentration as the p-type AlGaN layer is disposed, the light emission efficiency at a low current density is suppressed, and the light emission efficiency at a high current density is reduced. Reduction can be suppressed. That is, a radiation output with high linearity corresponding to the increase / decrease in current density can be obtained. Further, even if the current density is increased, a high radiation output can be obtained.

FIG. 1A is a relationship diagram between current density and radiation output, and FIG. 1B is a relationship diagram between current density and external quantum efficiency. FIG. 2 is a schematic diagram of a semiconductor light emitting device of an example. FIG. 3 is a schematic view of a light emitting layer of the semiconductor light emitting device of the example. FIG. 4 is a schematic view of the MOCVD apparatus. FIG. 5A is a diagram showing a procedure for crystal growth, and FIG. 5B is a diagram showing a procedure for device formation. FIG. 6 is a graph plotting the external quantum efficiencies of the example and the comparative example. FIG. 7 is an analysis diagram of SIMS analysis in Example 2.

  First, the radiation output (P), external quantum efficiency (ηext), and efficiency droop of the semiconductor light emitting device will be described. FIG. 1A shows a relationship between current density and radiation output, and FIG. 1B shows a relationship between current density and external quantum efficiency.

  The radiation output (P) of the semiconductor light emitting device increases corresponding to the increase of the current density (J). For example, as indicated by the solid line in FIG. 3A, the radiation output also increases in the order of P0, Pstd, P1, and P2 as the current density increases in the order of JD0, Jstd, JD1, and JD2. That is, to obtain a high radiation output, the current density should be increased. However, it is not known whether the radiation output is high or low at the current density.

  There is an external quantum efficiency (ηext) as an evaluation value indicating the luminous efficiency of the semiconductor light emitting device. The external quantum efficiency is a value obtained by dividing the emitted light quantum number of the semiconductor light emitting device by the number of injected electrons, and represents the conversion ratio from electrons to photons. That is, it is possible to determine whether the radiation output at a certain current density is high or low by using the external quantum efficiency. Hereinafter, the light emission efficiency in the description of the present invention indicates the external quantum efficiency.

  For example, a solid line in FIG. 1A which is a correlation curve between a current density and a radiation output of a certain semiconductor light emitting element is a solid line in FIG. 1B when represented by a correlation curve between the current density and the external quantum efficiency. Corresponding to increasing the current density in the order of JD0 and Jstd, the external quantum efficiency increases in the order of ηD0 and ηstd. Further, in response to increasing the current density in the order of Jstd, JD1, and JD2, the external quantum efficiency decreases in the order of ηstd, ηD1, and ηD2. As described above, the external quantum efficiency of the semiconductor light emitting device has a maximum value on the low current density side, and has a feature of decreasing as the current density becomes higher. Therefore, it can be seen that a high external quantum efficiency can be achieved with a high current density in order to obtain a high radiation output.

  The efficiency droop is a value obtained by subtracting the external quantum efficiency at a certain operating current density from the maximum value of the external quantum efficiency and dividing the result by the maximum value of the external quantum efficiency, and represents a reduction ratio of the external quantum efficiency. As this value is smaller, a radiation output with higher linearity corresponding to the current density can be obtained.

As described above, it is understood that the efficiency droop is small to obtain a radiation output with high linearity corresponding to the increase / decrease of the current density, and that the external quantum efficiency is high to obtain a high radiation output in a region where the current density is high. .

  Next, the structure of the semiconductor light emitting device of the present invention will be described with reference to FIG.

  The structure of the semiconductor light emitting device of the invention is composed of an n-type nitride layer 210, a light emitting layer 206, and a p-type nitride layer 211, which are GaN-based crystals, on a substrate 201. The n-type nitride layer 210 includes a low-temperature GaN layer 202, a high-temperature GaN layer 203, an n-type GaN layer 204, and an SLS (Super Lattice Structure) layer 205. The p-type nitride layer 211 includes a p-type AlGaN layer 207, a first p-type GaN layer 208a, a second p-type GaN layer 208b, and a contact p-type GaN layer 209.

The n-type GaN layer 204 is doped with silicon (Si) as an n-type impurity. The p-type nitride layer 211 is doped with magnesium (Mg) as a p-type impurity. The Mg concentration of the p-type AlGaN layer 207 is 1.0 × 10 ^{19 to} 6.0 × 10 ¹⁹ atoms / cm ³ . The Mg concentration of the first p-type GaN layer 208 a is higher than that of the p-type AlGaN layer 207 and lower than that of the contact p-type GaN layer 209. The Mg concentration of the second p-type GaN layer 208b is set to the same Mg concentration as that of the p-type AlGaN layer 207. The Mg concentration of the contact p-type GaN layer 209 is the highest in the p-type nitride layer 211.

The n-side electrode 214 is disposed on the n-type GaN layer 204. The p-side transparent electrode 212 is disposed on the contact p-type GaN layer 209, and the p-side electrode 213 is disposed thereon.

  Next, details of the layers characterizing the structure of the semiconductor light emitting device of the present invention will be described. In particular, the structure of the p-type AlGaN layer 207, the first p-type GaN layer 208a, and the second p-type GaN layer 208b has a high linearity radiation output corresponding to the increase and decrease of the current density, and a region where the current density is high. This makes it possible to obtain high radiation output.

The p-type AlGaN layer 207 is an AlGaN-based crystal layer and has an Mg concentration of 1.0 × 10 ¹⁹ atoms / cm ³ or more and 6.0 × 10 ¹⁹ atoms / cm ³ or less. By setting this Mg concentration range, the generation of crystal defects (such as disorder of element arrangement) in the p-type AlGaN layer 207 can be suppressed, and hole mobility can be increased.

If the Mg concentration is less than 1.0 × 10 ¹⁹ atoms / cm ³ , the hole concentration is insufficient, and if it exceeds 6.0 × 10 ¹⁹ atoms / cm ³ , the crystal defect density becomes extremely high, and the first p-type GaN 208a The activation rate of holes is reduced. Further, the thickness is preferably about 10 nm to 40 nm, preferably about 15 nm to 30 nm, which can suppress the overflow of electrons and can reduce the specific resistance. For the same reason, the aluminum composition is preferably 0.07 to 0.2, and most preferably about 0.1 to 0.15.

  The first p-type GaN layer 208 a is a GaN-based crystal layer, and the Mg concentration is higher than that of the p-type AlGaN layer 207. With this structure, the hole concentration of the first p-type GaN layer 208 a can be made higher than the hole concentration of the p-type AlGaN layer 207.

  In particular, since the first p-type GaN layer 208a has a narrower band gap than the p-type AlGaN layer 207, the activation rate of Mg as a p-type impurity is high, and the crystal defect density of the p-type AlGaN layer 207 is suppressed. Since the GaN crystal is a binary crystal and the generation of crystal defects can be suppressed, a much higher hole concentration than that of the p-type AlGaN layer 207 can be obtained.

The Mg concentration is preferably 6.0 × 10 ¹⁹ atoms / cm ³ or more and 2.0 × 10 ²⁰ atoms / cm ³ or less, preferably 7.0 × 10 ¹⁹ atoms / cm ³ or more and 1.5 × 10 ²⁰ atoms. / Cm ³ or less is preferable. If the Mg concentration is less than 6.0 × 10 ¹⁹ atoms / cm ³ , the hole concentration is insufficient, and if it exceeds 2.0 × 10 ²⁰ atoms / cm ³ , the crystal defect density increases and the hole activation rate decreases. As a result, the specific resistance increases. Further, the film thickness is preferably 5 nm or more and 50 nm or less that can supply a sufficient hole concentration to the p-type AlGaN layer 207, and preferably about 15 nm to 35 nm. If the film thickness is less than 5 nm, a sufficient hole concentration cannot be supplied to the p-type AlGaN layer 207, and if it exceeds 50 nm, the specific resistance increases.

  The second p-type GaN layer 208b is a GaN-based crystal layer, and the Mg concentration is approximately the same as that of the p-type AlGaN layer 207. With this structure, extremely higher hole mobility than that of the p-type AlGaN layer 207 can be obtained, and the specific resistance can be reduced.

  Since the second p-type GaN layer 208b has a narrower band gap than the p-type AlGaN layer 207, the activation rate of Mg, which is a p-type impurity, is high, and the crystal defect density of the p-type AlGaN layer 207 is suppressed. Since the crystal defect density of the single p-type GaN layer 207a can be suppressed and the generation of crystal defects can be suppressed because the GaN crystal is a binary crystal, a specific resistance much lower than that of the p-type AlGaN layer 207 can be obtained.

The Mg concentration is preferably in the range of 1.0 × 10 ¹⁹ atoms / cm ³ or more and 6.0 × 10 ¹⁹ atoms / cm ³ or less. If the Mg concentration is less than 1.0 × 10 ¹⁹ atoms / cm ³ , the hole concentration becomes insufficient, and if it exceeds 6.0 × 10 ¹⁹ atoms / cm ³ , the hole mobility decreases. Resistance increases. The film thickness may be about 30 nm or more as long as holes can be uniformly supplied from the contact p-type GaN layer 209 to the first p-type GaN layer 208a.

  The contact p-type GaN layer 209 is a GaN-based crystal layer, and the Mg concentration is the highest in the p-type nitride layer 211. With this structure, holes are efficiently injected from the p-side transparent electrode 212 into the contact p-type GaN layer 209.

With the structure of the p-type nitride layer 211 described above, when the current density is about 25 A / cm ² or less, the efficiency of hole injection into the light emitting layer 206 can be suppressed, and when the current density is about 25 A / cm ² or more. In addition, a decrease in the efficiency of hole injection into the light emitting layer 206 can be suppressed.

In other words, the semiconductor light emitting device structure of the present invention suppresses external quantum efficiency when the current density is about 25 A / cm ² or less (for example, Jηstd in FIG. 1B becomes Jηstd *), and the current density is 25 A / cm2. It is possible to suppress a decrease in external quantum efficiency at about cm ² or more (for example, Jη2 in FIG. 1B becomes Jη2 *). At the same time, the efficiency droop can be reduced. That is, the solid external quantum efficiency curve in FIG. 1B is a one-dot chain external quantum efficiency curve, and the solid line radiation output curve in FIG. 1A is a one-dot chain radiation output curve.

  As described above, the semiconductor light emitting device structure of the present invention can obtain a high linearity radiation output corresponding to the increase or decrease of the current density, and can obtain a high radiation output even if the current density is increased. It was excellent.

  Next, the structure and operation of the light emitting layer 206 of the present invention will be described with reference to FIG.

  The light emitting layer 206 has a multiple quantum well structure, and an electron storage layer 206e in which a first barrier layer 206a and a first well layer 206b are arranged on the SLS layer 205 is formed, and a barrier layer 206c is formed thereon. A plurality of unit radiation layers 206f each having a well layer 206d are disposed, and finally a barrier layer 206c is disposed.

  The first barrier layer 206a is a GaN-based crystal layer containing indium (In), and its band gap is narrower than the band gaps of the other barrier layers 206c and wider than the band gaps of the first well layer 206b and the well layer 206d. The first well layer 206b is a GaN-based crystal layer containing indium (In), and its band gap is narrower than the band gap of the other well layer 206d. With this structure, the first barrier layer 206a and the first well layer 206b serve as an electron storage layer 206e that can store electrons.

The electron storage layer 206e improves the efficiency with which the electrons supplied from this layer and the holes supplied from the p-type nitride layer 211 are radiatively recombined by the plurality of radiation unit layers 206f. However, it is possible to suppress a decrease in external quantum efficiency at a high current density (for example, 35 A / cm ² or more).

The barrier layer 206c is a GaN-based crystal layer, and its band gap is wider than that of the first barrier layer 206a. The well layer 206d is a GaN-based crystal layer containing indium (In), and its band gap is wider than that of the first well layer 206b. The barrier layer 206c and the well layer 206d are unit radiating layers 206f, and 5 to 15 units are stacked. When the unit radiation layer 206f is less than 5 units, it is impossible to suppress a decrease in external quantum efficiency at a high current density (for example, 35 A / cm ² or more). On the other hand, when the unit is 15 units or more, the resistance increases, and the efficiency also decreases.

  Since the semiconductor light-emitting device of the present invention can obtain a radiation output with high linearity corresponding to the current density, for example, if it is used in a lighting fixture, dimming can be performed with a simple drive circuit (power supply circuit). In addition, since a high radiation output can be obtained even at a high current density, for example, it is possible to reduce the size and energy of a lighting fixture that requires a large amount of light (a large luminous flux). Furthermore, it is possible to manufacture a lighting device with high emission brightness.

  Examples of the present invention will be described below. In the semiconductor light emitting device of the present invention, the semiconductor light emitting device layer was crystal-grown by the procedure shown in FIG. Further, the device was formed by the procedure shown in FIG.

[MOCVD equipment]
First, an MOCVD apparatus used for crystal growth of a semiconductor light emitting device will be described with reference to FIG. In the MOCVD apparatus 100, a material gas supply pipe 102 for supplying a material gas and a pressure supply pipe 104 for supplying a pressure gas are connected to corresponding material gas nozzles 103 and pressure gas nozzles 105 arranged in an airtight reaction vessel 101. In this structure, the material gas and the pressing gas are sprayed onto the substrate 110 placed on the susceptor 107. The substrate 110 is heated to a predetermined temperature by the heater 108 through the susceptor 107. The substrate 110 is rotated at 10 revolutions per minute by a rotation shaft 109 connected to the susceptor 107. The used material gas is exhausted through the exhaust pipe 106.

[Procedure for crystal growth]
1. Substrate heat treatment (P11)
As the substrate 110, a 2 inch single crystal sapphire substrate having a c-plane main surface was set on the susceptor 107 and rotated at 10 times per minute. Subsequently, the internal pressure of the reaction vessel 101 was set to atmospheric pressure. The subsequent pressure inside the reaction vessel was maintained at atmospheric pressure. Next, 10 SLM (L / min, 0 ° C., 1 atm) of hydrogen gas was supplied from the material gas nozzle 103, and 10 SLM of hydrogen gas was supplied from the presser gas nozzle 105. Then, the substrate temperature was raised to 1150 ° C., and the substrate was heat-treated in a hydrogen atmosphere for 10 minutes.

2. Formation of low-temperature GaN layer (P12)
After the substrate temperature is lowered to 700 ° C., 1 SLM of hydrogen gas, 5 SLM of ammonia (NH ₃ ) gas, and 5 SCCM (cc / min, 0 ° C., 1 atm) of trimethyl gallium (TMGa) gas are supplied from the material gas nozzle 103. The GaN crystal layer was formed as the low temperature GaN layer 202 by growing for 200 seconds.

3. Formation of high-temperature GaN layer (P13)
After raising the substrate temperature to 1200 ° C., 2 SLM of hydrogen gas, 4 SLM of ammonia gas, and 15 SCCM of TMGa gas were supplied from the material gas nozzle 103 and grown for 20 minutes to form a GaN crystal layer as the high temperature GaN layer 203. .

4). Formation of n-type GaN layer (P14)
With the substrate temperature maintained at 1200 ° C., 2 SLM of hydrogen gas, 4 SLM of ammonia gas, 15 SCCM of TMGa gas, and 0.2 SCCM of disilane gas (Si ₂ H ₆ ) as an n-type impurity source are supplied from the reaction gas nozzle 103, Growing for 90 minutes, a GaN crystal layer containing Si was formed as an n-type GaN layer 204 having a thickness of about 6 m.

5. Nitrogen gasification of holding gas (P15)
After forming the n-type GaN layer, the supply gas from the presser gas nozzle 105 was changed from 10 LSM for hydrogen gas to 10 SLM for nitrogen gas.

6). Formation of SLS (Super Lattice Structures) layer (P16)
After the substrate temperature is lowered to 900 ° C., 2 SLM of hydrogen gas, 4 SLM of ammonia gas, and 35 SCCM of triethylgallium (TEGa) gas are supplied from the material gas nozzle 103 and grown for 50 seconds, and a GaN crystal is formed as a first SLS layer. A layer was formed.
With the substrate temperature kept at 900 ° C., 2 SLM of hydrogen gas, 4 SLM of ammonia gas, 35 SCCM of TEGa gas, and 50 SCCM of trimethylindium (TMIn) gas are supplied from the material gas nozzle 103, and the second SLS layer is grown for 50 seconds. As a result, an InGaN crystal layer was formed. The SLS layer 205 was formed by alternately growing the first SLS layer and the second SLS layer in four layers, and finally growing the first SLS layer.

7). Formation of light emitting layer (P17)
After the substrate temperature is lowered to 850 ° C., the material gas nozzle 103 supplies 2 SLM of nitrogen gas, 4 SLM of ammonia gas, 5 SCCM of TEGa gas, and 50 SCCM of TMIn gas, and grows for 150 seconds, the first barrier having a thickness of about 5 nm An InGaN crystal layer was formed as the layer 206a. With the substrate temperature kept at 850 ° C., 2 SLM of nitrogen gas, 4 SLM of ammonia gas, 5 SCCM of TEGa gas, and 90 SCCM of TMIn gas are supplied from the material gas nozzle 103, grown for 150 seconds, and the first well layer 206b having a thickness of about 4 nm. An InGaN crystal layer was formed as the well layer 206d. With the substrate temperature kept at 850 ° C., 2 SLM of nitrogen gas, 4 SLM of ammonia gas, and 5 SCCM of TEGa gas were supplied from the material gas nozzle 103 and grown for 150 seconds to form a GaN layer as a barrier layer 206c having a thickness of about 5 nm. The light emitting layer 206 was formed by growing the first barrier layer 206a and the first well layer 206b, then growing the barrier layer 206c and the well layer 206d alternately eight layers, and finally growing the barrier layer 206c. The indium (In) composition of the first well layer 206b becomes higher than the indium composition of the other well layers 206d by growing on the first barrier layer 206a.

8). Hydrogen gas of holding gas (P18)
After forming the light emitting layer, the supply gas from the presser gas nozzle 105 was changed from 10 LSM for nitrogen gas to 10 SLM for hydrogen gas.

9. Formation of p-type AlGaN layer (P19)
After raising the substrate temperature to 1000 ° C., hydrogen gas is 3 SLM, ammonia gas is 4 SLM, TMGa gas is 1 SCCM, trimethylaluminum (TMAl) gas is 1 SCCM, and biscyclopentadiene as a p-type impurity source from the material gas nozzle 103. An enilmagnesium (Cp ₂ Mg) gas was supplied at 30 SCCM and grown for 500 seconds to form an AlGaN crystal layer containing Mg having a thickness of about 30 nm and an Al composition of about 0.15 as the p-type AlGaN layer 207. Mg concentration was ^{2.4 × 10 19 atoms / cm 3} ~4.3 × 10 19 atoms / cm 3.

10. Formation of p-type GaN layer (P20)
With the substrate temperature kept at 1000 ° C., 3SLM for hydrogen gas, 4SLM for ammonia gas, 3.5SCCM for TMGa gas, and 80SCCM for Cp2Mg gas are supplied from the material gas nozzle 103, grown for 40 seconds, and the first p-type GaN layer 208a is grown. As a result, a GaN crystal layer containing Mg having a thickness of about 8 nm was formed. Mg density | concentration was 7.0 * 10 < ¹⁹ > atoms / cm < ³ > -1.0 * 10 < ²⁰ > atoms / cm < ³ >.

With the substrate temperature kept at 1000 ° C., 3SLM for hydrogen gas, 4SLM for ammonia gas, and 3.5SCCM for TMGa gas and 30SCCM for Cp2Mg gas are supplied from the material gas nozzle 103 to grow for 360 seconds, and the second p-type GaN layer 208b is grown. As a result, a GaN crystal layer containing Mg having a thickness of about 72 nm was formed. Mg concentration was ^{2.4 × 10 19 atoms / cm 3} ~4.3 × 10 19 atoms / cm 3.

11. Formation of contact p-type GaN layer (P21)
With the substrate temperature kept at 1000 ° C., hydrogen gas 3SLM, ammonia gas 4SLM, TMGa gas 1.75 SCCM and Cp2Mg gas 200 SCCM are supplied from the material gas nozzle 103 and grown for 20 seconds to form a contact p-type GaN layer 209. A GaN crystal layer containing Mg having a thickness of about 3 nm was formed.

  Through the above procedure, the semiconductor light emitting element layer is placed on the substrate 201, the low temperature GaN layer 202, the high temperature GaN layer 203, the n-type GaN layer 204, the SLS layer 205, the light emitting layer 206, the p-type AlGaN layer 207, the first The p-type GaN layer 208a, the second p-type GaN layer 208b, and the contact p-type GaN layer 209 were grown in this order.

[Elementization procedure]
First, an element partition groove 216 having a depth reaching the n-type GaN layer 204 was formed on the substrate on which the crystal of the semiconductor element layer had been grown by a photolithography technique and a dry etching technique (P21). Next, the p-side transparent electrode 212 was formed on the contact p-type GaN layer 209 by photolithography technique and sputtering technique (P22). Next, the p-side electrode 213 was formed on the p-side transparent electrode 212 by photolithography technique and metal vapor deposition technique (P23). Similarly, the n-side electrode 214 was formed on the n-type GaN layer 204 exposed by forming the element partition groove 216 by photolithography technique and metal deposition technique (P24). Finally, the elements were separated along the element partition grooves by the scribing technique and the breaking technique (P25).

  The semiconductor light emitting device 200 was formed by the above procedure. When a current is passed from the p-side electrode 213 to the n-side electrode 214 of the semiconductor light emitting device 200, holes are injected from the p-type nitride layer 211 into the light-emitting layer 206, and electrons from the n-type nitride layer 210 are emitted from the light-emitting layer 206. Then, holes and electrons are radiated and recombined in the light emitting layer 206 to emit light at a wavelength of about 440 nm to 450 nm.

The crystal growth procedure and device fabrication procedure of the semiconductor light emitting device 200 of the second embodiment are the same as those of the first embodiment. However, the growth time, film thickness, and Mg concentration of the first p-type GaN layer 208a and the second p-type GaN layer 208b are (E2-1) and (E2-2) below.
(E2-1) First p-type GaN layer • Growth time: 100 seconds • Film thickness: 20 nm
Mg concentration: 7.0 × 10 ¹⁹ atoms / cm ^{3 to} 1.0 × 10 ²⁰ atoms / cm ³
(E2-2) Second p-type GaN layer Growth time: 300 seconds Film thickness: 60 nm
Mg concentration: 2.4 × 10 ¹⁹ atoms / cm ^{3 to} 4.3 × 10 ¹⁹ atoms / cm ³

The crystal growth procedure and device fabrication procedure of the semiconductor light emitting device 200 of the third embodiment are the same as those of the first embodiment. However, the growth time, film thickness, and Mg concentration of the first p-type GaN layer 208a and the second p-type GaN layer 208b are (E3-1) and (E3-2) below.
(E3-1) First p-type GaN layer • Growth time: 150 seconds • Film thickness: 30 nm
Mg concentration: 7.0 × 10 ¹⁹ atoms / cm ^{3 to} 1.0 × 10 ²⁰ atoms / cm ³
(E3-2) Second p-type GaN layer Growth time: 250 seconds Film thickness: 50 nm
Mg concentration: 2.4 × 10 ¹⁹ atoms / cm ^{3 to} 4.3 × 10 ¹⁹ atoms / cm ³
(Comparative Example 1)

The crystal growth procedure and device fabrication procedure of the semiconductor light emitting device 200 of Comparative Example 1 are the same as those of Example 1. However, the p-type AlGaN layer 207 was used, and the p-type GaN layer 208 was configured as a single layer. The growth time, film thickness, and Mg concentration of each crystal layer are the following (C1-1) and (C1-2). Comparative Example 1 has a structure simulating the configuration of the p-type nitride layer of Patent Document 1.
(C1-1) p-type AlGaN layer Growth time: 500 seconds Film thickness: 30 nm
Mg concentration: 7.0 × 10 ¹⁹ atoms / cm ^{3 to} 1.0 × 10 ²⁰ atoms / cm ³
(C1-2) p-type GaN layer • Growth time: 400 seconds • Film thickness: 80 nm
Mg concentration: 2.4 × 10 ¹⁹ atoms / cm ^{3 to} 4.3 × 10 ¹⁹ atoms / cm ³

The semiconductor light emitting devices 200 of Examples 1 to 3 and Comparative Example 1 were manufactured by the above procedure. The crystal growth conditions and the differences in film thickness and Mg concentration are shown in Table 1.

  Next, the evaluation results of Examples 1 to 3 and Comparative Example 1 will be described. Table 2 shows the results of external quantum efficiency, current density, and efficiency droop. The current density / external quantum efficiency curve is shown in FIG. FIG. 7 shows the result of SIMS (Secondary Ion Mass Spectrometry) depth direction analysis of the semiconductor light emitting device of Example 2.

First, a spectrophotometer was used for measurement of radiation output and the like. As the sample, an element-formed substrate at the stage where the p-side electrode 213 and the n-side electrode 214 were formed (P24) was used. The radiant power was evaluated by measuring a part of the total radiant flux. Therefore, the external quantum efficiency is smaller than the value of the total radiant flux.

The maximum value of the external quantum efficiency of Example 1 and the current density at that time are 5.72% and 18.7 A / cm ^2. The external quantum efficiency and the efficiency droop when the current density is 35 A / cm ² are 5 The external quantum efficiency and the efficiency droop when the current density was 70 A / cm ² were 5.16% and 9.73%, respectively.

The maximum value of the external quantum efficiency of Example 2 and the current density at that time are 5.66% and 20.5 A / cm ² , and the external quantum efficiency and the efficiency droop when the current density is 35 A / cm ² are 5 The external quantum efficiency and the efficiency droop when the current density was 70 A / cm 2 were 5.23% and 7.51%, respectively.

The maximum value of the external quantum efficiency of Example 3 and the current density at that time are 5.59% and 22.8 A / cm ² , and the external quantum efficiency and the efficiency droop when the current density is 35 A / cm ² are 5 The external quantum efficiency and the efficiency droop when the current density was 70 A / cm 2 were 5.23% and 6.32%, and 5.23% and 6.35%, respectively.

The maximum value of external quantum efficiency of Comparative Example 1 and the current density at that time are 5.75% and 15.8 A / cm ² , and the external quantum efficiency and efficiency droop when the current density is 35 A / cm ² are 5 The external quantum efficiency and the efficiency droop when the current density was 70 A / cm 2 were 5.06% and 4.06%, respectively, 5.06% and 11.89%.

From the above results, the maximum value of the external quantum efficiency (ηext) decreases in the order of Comparative Example 1, Example 1, Example 2, and Example 3, and the current density increases in order. Thus, the external quantum efficiency at a low current density (for example, less than 25 A / cm ² ) can be reduced by using the semiconductor light emitting device structure of the present invention.

On the other hand, when the current density is 70 A / cm ² , the external quantum efficiency increases in the order of Comparative Example 1, Example 1, Example 2, and Example 3 (3 is larger than Example 2 in the third decimal place). The efficiency droop is getting smaller. Thus, by using the structure of the semiconductor light emitting device of the present invention, it is possible to suppress a decrease in external quantum efficiency at a high current density.

Thus, the effect of reducing the external quantum efficiency while shifting the maximum value of the external quantum efficiency to a high current density and the effect of suppressing the reduction of the external quantum efficiency at a high current density (for example, 70 A / cm ² ) are implemented. In the example, the Mg concentration of the p-type AlGaN layer 207 is set to 2.4 × 10 ¹⁹ atoms / cm ^{3 to} 4.3 × 10 ¹⁹ atoms / cm ^3, and the Mg concentration of the first p-type GaN layer 208a is set to 7. It was set to 0 × 10 ¹⁹ atoms / cm ^{3 to} 1.0 × 10 ²⁰ atoms / cm ^3, and the Mg concentration of the second p-type GaN layer 208b was set to 2.4 × 10 ¹⁹ atoms / cm ^{3 to} 4.3 ×. 10 ¹⁹ atoms / cm ³ is achieved. In addition, these effects can be enhanced as the thickness of the first p-type GaN layer 208a is increased to 8 nm, 20 nm, and 30 nm. As a result, the efficiency droop can be reduced. However, when the film thickness of the first p-type GaN layer 208a exceeds 50 nm, the efficiency droop can be kept small, but it becomes impossible to suppress a decrease in external quantum efficiency at a high current density (for example, 70 A / cm ² ). Further, when the second p-type GaN layer 208b is removed, the above effect disappears.

In addition, as a result of trial evaluation of many samples other than those described, when the maximum value of the external quantum efficiency is shifted to the higher current density side, the failure rate at high current density (test value is 70 A / cm ² ) (non-lighting, forward rising) The incidence of voltage failures and reverse withstand voltage failures) was halved. Specifically, the failure rate decreased when the maximum current density of the external quantum efficiency was about 18 A / cm ² or more, and the failure rate was halved at 20 A / cm ² or more.

Next, a plot of the relationship between current density and external quantum efficiency is shown in FIG. For example, the external quantum efficiency of Comparative Example 1 reaches its maximum at the CP1 point, and then decreases nonlinearly and rapidly to CP2. On the other hand, the external quantum efficiency of Example 3 reaches its maximum at the ET1 point, and gradually decreases linearly there until reaching ET2. That is, the structure of the semiconductor light emitting device of the present invention can suppress the decrease in external quantum efficiency corresponding to the increase in current density and at the same time linearize the decrease rate. When dimming with a drive circuit (power supply circuit), if the efficiency droop is close to 0 (zero), the radiation output can be proportionally controlled with respect to the drive current of the semiconductor light emitting device. Proportional control of radiation output is also possible by making the increase rate (linear) linear. In the semiconductor light emitting device of the present invention, the rate of decrease in external quantum efficiency may be linearized by setting the efficiency droop at a current density of 70 A / cm ² to 8% or less.

Regarding the radiant output, the external quantum efficiency is a comparative example at the H point (35 A / cm ² ) in FIG. 6 by suppressing the decrease in the external quantum efficiency of Example 1, Example 2, and Example 3. It is above 1. Furthermore, the difference opens with increasing current density. That is, the radiation output can be kept high at a high current density (for example, 35 A / cm ² or more). When the current density at which the external quantum efficiency is maximized is lower than the normal current density (for example, 35 A / cm ² or more) of the semiconductor light emitting device, there is no problem even if the maximum value of the external quantum efficiency is lowered.

  Next, the SIMS depth profile of the semiconductor light emitting device of Example 2 is shown in FIG. 7 (<ET2>). Since the resolution in the depth direction of SIMS is on the order of nanometers, the element component signal of the crystal layer constituting the semiconductor light emitting element is slightly broad at the interface of each crystal layer.

  In the figure, 306 corresponds to the light emitting layer 206, 307 corresponds to the p-type AlGaN layer 207, 308a corresponds to the first p-type GaN layer 208a, 308b corresponds to the second p-type GaN layer 208b, Reference numeral 309 corresponds to the second contact p-type GaN layer 209.

The Mg concentration of the p-type AlGaN layer 207 of Example 2 is in the range of 2.4 × 10 ¹⁹ atoms / cm ^{3 to} 4.3 × 10 ¹⁹ atoms / cm ³ , and the Mg concentration of the first p-type GaN layer 208a. Is in the range of 7.0 × 10 ¹⁹ atoms / cm ^{3 to} 1.0 × 10 ²⁰ atoms / cm ³ , and the Mg concentration of the second p-type GaN layer 208b is 2.4 × 10 ¹⁹ atoms / cm ³ to The range was 4.3 × 10 ¹⁹ atoms / cm ³ , which was the Mg concentration range of the semiconductor light emitting device of the present invention.

  In addition, since the first peak (Pmix in FIG. 7) of the secondary ion intensity signal of indium (In) is stronger than other indium signal peaks and has been observed widely, the first well layer 206b has other peaks. It can be seen that the indium composition is higher than that of the well layer 206d, and that the electron storage layer 206e is formed by the first barrier layer 206a and the first well layer 206b.

  Further, since there are eight signal peaks other than the first peak (Pmix in FIG. 7) of the secondary ion intensity signal of indium (In), eight units of the unit radiation layer including the barrier layer 206c and the well layer 206d are formed. I understand that

  As described above, from the result of SIMS depth analysis of the semiconductor light emitting device of Example 2, the Mg concentration and film thickness of the p-type AlGaN layer 207, the first p-type GaN layer 208a, and the second p-type GaN layer 208b ( (See FIG. 7). In addition, the existence of the electron storage layer 206e of the light emitting layer 206 and the number of unit emission layers 206f can be confirmed.

The semiconductor light emitting device structure of the present invention, a low current density (e.g., less than 25A / cm ²⁾ to suppress the external quantum efficiency, a decrease in external quantum efficiency of the high current density (e.g., 25A / cm ² greater) and allow for repression It will be apparent that this is a semiconductor light emitting device capable of obtaining a radiation output with high linearity corresponding to an increase or decrease in current density. It will be apparent that the semiconductor light emitting device can obtain a high radiation output even when the current density is increased.

Although the element structure and the manufacturing method of the present invention have been described according to the embodiments, the present invention is not limited to these. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

200 Semiconductor Light Emitting Element 201 Substrate 202 Low Temperature GaN Layer 203 High Temperature GaN Layer 12-0526 Application Document (ver1.0)
204 n-type GAN layer 205 SLS layer 206 light emitting layer (MQW)
207 p-type AlGaN layer 208 p-type GaN layer 208a first p-type GaN layer 208b second p-type GaN layer 209 contact p-type GaN layer 210 n-type layer 211 p-type layer 212 p-side transparent electrode 213 p-side electrode 214 n-side electrode

Claims (8)

A semiconductor light-emitting device comprising at least an n-type semiconductor layer, a light-emitting layer, and a p-type semiconductor layer;
A p-type AlGaN layer having a magnesium (Mg) concentration of 1.0 × 10 ^{19 to} 6.0 × 10 ¹⁹ atoms / cm ³ ;
A first p-type GaN layer having a higher concentration of Mg than the p-type AlGaN layer on the p-type AlGaN layer;
On the first p-type GaN layer, a second p-type GaN layer having the same Mg as the p-type AlGaN layer;
A semiconductor light emitting device comprising: The light emitting layer has a multiple quantum well structure in which a plurality of well layers and barrier layers are alternately stacked,
The multi-well layer is a structure laminated from the barrier layer,
A band gap of the first barrier layer is narrower than a band gap of the other barrier layer, wider than a band gap of the well layer, and is a GaN-based crystal containing at least indium;
The semiconductor light-emitting device according to claim 1. The well layer and the barrier layer of the light emitting layer are set as one unit, and are stacked at least 6 units to 16 units,
The semiconductor light-emitting device according to claim 1 or 2, wherein Mg concentration of the first p-type GaN layer is 6.0 × 10 ¹⁹ atoms / cm ³ or more and 2.0 × 10 ²⁰ atoms / cm ³ or less,
4. The semiconductor light emitting device according to claim 1, wherein: The film thickness of the first p-type GaN layer is 5 nm or more and 50 nm or less;
The semiconductor light-emitting device according to claim 1. Mg concentration of the second p-type GaN layer is 1.0 × 10 ¹⁹ atoms / cm ³ or more and 6.0 × 10 ¹⁹ atoms / cm ³ or less,
6. The semiconductor light emitting device according to claim 1, wherein: The semiconductor light emitting device according to any one of claims 1 to 6,
The operating current density that maximizes the external quantum efficiency of the radiation output when a current is passed is 18 A / cm ² or more,
A semiconductor light emitting device characterized by the above. The semiconductor light-emitting device according to any one of claims 1 to 7,
The efficiency droop when the operating current density is 70 A / cm ² is 8% or less,
A semiconductor light emitting device characterized by the above.

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