JPH08316587A - Group iii nitride semiconductor light emitting element - Google Patents

Abstract

PURPOSE: To protect a clad layer against cracking by specifying the thickness of the clad layer for emission layer composed of a group III nitride semiconduc tor having three layer structure where an active layer is sandwiched by clad layers. CONSTITUTION: Al0.1 Ga0.9 N is deposited by 4μm on high carrier concentration n<+> layer 3 of various heights and the cracking conditions are observed. No crack is observed in the Al0.1 Ga0.9 N deposited on the layer 3 of 5μm thick. Consequently, the thickness of high carrier concentration n<+> layer 3 is set in the range of 2-5μm. Thickness of the clad layer 4, 61 is preferably set in the range of 0.5-1μm thus obtaining a low balance device excellent in crack prevention performance and conductivity of n<+> layer. More preferably, the compositional ratio of Al is set at 0.1 or less for the clad layer in order to eliminate cracking. Consequently, cracking can be prevented when the thickness of clad layer is set in the range of 0.5-2μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device using a group III nitride semiconductor.

[0002]

Conventionally, AlGa has been used as a blue laser diode.
An InN-based compound semiconductor having a double heterojunction structure is known. Since the compound semiconductor is a direct transition type, it has been noted that it has high emission efficiency, and that blue, which is one of the three primary colors of light, is used as the emission color.

[0003]

However, in the conventional laser diode having the above structure, the cladding layer has a thickness of 2000.
Since it was about Å, the optical confinement efficiency was poor, and laser oscillation was difficult. The present invention has been made to solve the above problems, and an object thereof is to easily obtain laser oscillation.

[0004]

The present invention comprises a group III nitride semiconductor (including Al _x Ga _Y In _1-XY N; X = 0, Y = 0, X = Y = 0) and has an active layer. Is a light emitting device having a three-layer structure sandwiched by clad layers from both sides. The first feature is that the thickness of the clad layer is 0.5 to 2 μm, and the second feature is
That is, the three-layer structure is formed on the GaN layer formed on the buffer layer formed on the sapphire substrate. Also, the third
The feature is that the thickness of the GaN layer is 2 to 5 μm, the fourth feature is that the cladding layer is Al _x Ga _1-x N (where X ≦ 0.1), and the fifth feature is that the active layer is In. _x Ga _1-x N.

[0005]

Since the thickness of the cladding layer is determined as described above, it is possible to make the cladding layer a good quality crystal without cracks and to sufficiently confine light. Easy laser oscillation was realized.
Further, by setting the thickness of the GaN layer having the three-layer structure to 2 to 5 μm, it was possible to improve the crystal quality of the cladding layer while improving the conductivity with respect to the active layer.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, a laser diode 10 has a sapphire substrate 1, on which a buffer layer 2 of AlN 3 of 500 Å is formed. Of On the buffer layer 2, in turn, a film thickness of about 2.0 [mu] m, the electron concentration of 2 × 10 ¹⁸ / cm high carrier concentration comprising a silicon-doped GaN of ³ n ⁺ layer 3, a thickness of about 1.0 [mu] m, an electron concentration 2 × 10 ¹⁸ / c
m ³ of silicon doped Al _0.08 Ga _0.92 consisting N n conductivity type cladding layer 4, active layer 5 consisting of a thickness of about 0.05μm of In _0.08 Ga _0.92 N, a thickness of about 1.0 [mu] m, a hole concentration 5 × 10 ¹⁷ / c
Al doped with magnesium at m ³ and a concentration of 1 × 10 ²⁰ / cm ³
_A p-conduction type clad layer 61 made of _0.08 Ga _0.92 N, a contact layer 62 made of magnesium-doped GaN having a film thickness of about 0.2 μm, a hole concentration of 7 × 10 ¹⁷ / cm ³ and a magnesium concentration of 2 × 10 ²⁰ / cm ³ was formed. Has been formed. Then, the SiO ₂ layer 9 is formed on the contact layer 62, and the electrode 7 made of Ni that is bonded to the contact layer 62 through the window portion of the SiO ₂ layer 9 is formed. Further, on the high carrier concentration n ⁺ layer 3, an electrode 8 made of Ni and joined to the layer 3 is formed.

Next, a method of manufacturing the laser diode 10 having this structure will be described. The laser diode 10
Was produced by vapor phase growth by an organometallic compound vapor phase growth method (hereinafter referred to as “M0VPE”). The gas used was NH ₃ and carrier gas H ₂ or N ₂ , trimethylgallium (Ga (CH ₃ ) ₃ ) (hereinafter referred to as “TMG”), and trimethylaluminum (Al (CH ₃ ) ₃ ) (hereinafter referred to as “TMA )), Trimethylindium (In (CH ₃ ) ₃ ) (hereinafter referred to as “TMI”), silane (SiH ₄ ), and cyclopentadienyl magnesium (Mg (C ₅
H ₅ ) ₂ ) (hereinafter referred to as “CP ₂ Mg”).

First, a single crystal sapphire substrate 1 having a thickness of 100 to 400 μm, whose main surface is a surface washed by organic cleaning and heat treatment, is mounted on a susceptor placed in a reaction chamber of a M0VPE apparatus. Next, the sapphire substrate 1 was vapor-phase etched at a temperature of 1100 ° C. while flowing H ₂ into the reaction chamber at a flow rate of 2 liter / min under normal pressure.

Next, the temperature is lowered to 400 ° C. and H ₂ is added.
20 liter / min, NH ₃ 10 liter / min, TMA 1.8 × 10 ^-5
The buffer layer 2 of AlN was formed at a thickness of about 500Å by supplying at a mol / min. Next, the temperature of the sapphire substrate 1 is set to 1150.
Hold at ₂ ℃, H ₂ 20 liter / min, NH ₃ 10 liter / min,
TMG was supplied at 1.7 × 10 ^-4 L / min, and silane diluted to 0.86 ppm with H ₂ gas was supplied at 200 ml / min for 30 minutes to obtain a film thickness of about 2.2.
[mu] m, thereby forming an electron concentration of 2 × 10 ¹⁸ / cm high carrier concentration n ⁺ layer 3 made of GaN of silicon doped ^3.

Next, the temperature of the sapphire substrate 1 is maintained at 1100 ° C., N ₂ or H ₂ is 10 liter / min, and NH ₃ is 10 liter / min.
Min, TMG 1.12 × 10 ^-4 mol / min, TMA 0.47 × 10 ^-4 mol / min, and silane diluted to 0.86 ppm with H ₂ gas at 10 × 10 ^-9 mol / min for 60 min. Then, an n-conductivity type cladding layer 4 made of silicon-doped Al _0.08 Ga _0.92 N having a film thickness of about 1 μm and a concentration of 1 × 10 ¹⁸ / cm ³ was formed.

Subsequently, the temperature was maintained at 850 ° C. and N ₂ or H _{2 was} added.
20 liter / min, NH ₃ 10 liter / min, TMG 1.53 × 10
^-4 mol / min and TMI at 0.02 × 10 ^-4 mol / min for 6 minutes to form an active layer of 0.05 μm In _0.08 Ga _0.92 N 5
Was formed.

Subsequently, the temperature was maintained at 1100 ° C. and N ₂ or H _{2 was} added.
20 liter / min, NH ₃ 10 liter / min, TMG 1.12 × 10
^-4 mol / min, TMA 0.47 × 10 ^-4 mol / min, and CP ₂ Mg
Was introduced at 2 × 10 ⁻⁴ mol / min for 60 minutes to form a p-conductivity-type cladding layer 61 made of magnesium (Mg) -doped Al _0.08 Ga _0.92 N with a film thickness of about 1.0 μm. The concentration of magnesium in the clad layer 61 is 1 × 10 ²⁰ / cm ³ . In this state, the cladding layer 61 is still an insulator having a resistivity of 10 ⁸ Ωcm or more.

Subsequently, the temperature was maintained at 1100 ° C., and N ₂ or H _{2 was} added.
20 liter / min, NH ₃ 10 liter / min, TMG 1.12 × 10
^-4 mol / min and CP ₂ Mg at a rate of 4 × 10 ^-4 mol / min
After being introduced for 4 minutes, a contact layer 62 made of magnesium (Mg) -doped GaN having a film thickness of about 0.2 μm was formed. The magnesium concentration of the contact layer 62 is 2 × 10 ²⁰ / cm ³ . In this state, the contact layer 62 still has a resistivity.
It is an insulator of 10 ⁸ Ωcm or more.

Next, the contact layer 62 and the cladding layer 61 were uniformly irradiated with an electron beam by using a reflection electron beam diffractometer. Electron beam irradiation conditions are acceleration voltage of about 10KV and sample current of 1
μA, beam moving speed 0.2mm / sec, beam diameter 60μm
φ, vacuum degree is 5.0 × 10 ⁻⁵ Torr. By this electron beam irradiation, the contact layer 62 and the cladding layer 61 have hole concentrations of 7 × 10 ¹⁷ / cm ³ , 5 × 10 ¹⁷ / cm ³ , and a resistivity of 2 respectively.
It became p-conductivity type semiconductor of Ωcm and 0.8 Ωcm. In this way, a wafer having a multilayer structure was obtained.

Next, a SiO ₂ layer 9 having a thickness of 2000 Å is formed on the contact layer 62 by sputtering.
A photoresist was applied on the O ₂ layer 9. Then, by photolithography, on the contact layer 62, the photoresist at the electrode formation site for the high carrier concentration n ⁺ layer 3 was removed. Next, the SiO ₂ layer 9 not covered with the photoresist was removed with a hydrofluoric acid-based etching solution.

Next, the contact layer 62, the clad layer 61, the active layer 5 and the clad layer 4 which are not covered with the photoresist and the SiO ₂ layer 9 are vacuumed to 0.04 Torr, high frequency power 0.44 W / cm ² , BCl ₃ gas was supplied at a rate of 10 ml / min for dry etching, and then Ar was used for dry etching. In this step, the hole A for taking out the electrode for the high carrier concentration n ⁺ layer 3 was formed.

Next, the SiO ₂ layer 9 was coated with a photoresist, subjected to a photolithography process, and wet-etched to form a window at the electrode formation site of the contact layer 62 of the SiO ₂ layer 9.

Next, Ni is vapor-deposited uniformly on the entire surface of the sample, photoresist coating, photolithography process,
Through the etching process, the electrodes 8 and 7 for the high carrier concentration n ⁺ layer 3 and the contact layer 62 were formed. Then, the wafer processed as described above was cut into strips in the length direction of the laser cavity and cleaved at right angles to the direction to form laser diode chips.

High carrier concentration n ⁺ layer 3, cladding layer 4,
By setting the thicknesses of the active layer 5, the clad layer 61, and the contact layer 62 as shown in the above-mentioned examples, it was possible to obtain a good-quality epitaxial growth layer in which cracks did not occur.

The surface of the uppermost contact layer 62 was observed with a microscope while varying the thickness of each layer. First, the AlN buffer layer 2 was formed on the sapphire substrate 1, and only GaN was grown on it. The thickness limit at which no cracks were generated on the surface was 20 μm. Next, the AlN buffer layer 2 is formed on the sapphire substrate 1 and the AlN buffer layer 2 is formed thereon.
Only _0.1 Ga _0.9 N was grown. In this case, the limit of the thickness at which cracks did not occur on the surface was 7 μm. Therefore, the cladding layers 4 and 61 of the laser diode 10 are made of Al.
_{When x} Ga _1-X N (x ≦ 1) is used, the thickness of the entire epitaxial growth layer of the laser diode 10 is considered to be about 7 μm or less in order not to generate cracks. on the other hand,
The thickness of the high carrier concentration n ⁺ layer 3 cannot be set to 2 μm or less because it is necessary to reduce the resistance. Therefore, when the thickness of the high carrier concentration n ⁺ layer 3 is set to 2 μm, the thickness of the epitaxial growth layer excluding the high carrier concentration n ⁺ layer 3 is 5 μm.
If it is m or less, no crack is generated in the surface layer. The total thickness of the active layer 5 and the contact layer 62 can easily be 1 μm or less. Therefore, if the upper limit of the thickness is set to 1 μm, when the thickness of the high carrier concentration n ⁺ layer 3 is set to 2 μm, the clad layers 4 and 6 which do not generate cracks in the surface layer are formed.
The upper limit of the thickness of 1 is 2 μm, respectively. It has been confirmed that cracks do not occur in the uppermost contact layer 62 in this structure.

In order to improve the effect of confining light,
The lower limits of the thicknesses of the cladding layers 4 and 61 are 0.5 and 0.5, respectively.
μm. Therefore, at this time, assuming that the total of the active layer 5 and the contact layer 62 is 1 μm, the total thickness of the cladding layers 4, 61, the active layer 5 and the contact layer 62 is 2 μm. Therefore, the limit of the thickness of the crack formed by only Al _0.1 Ga _0.9 N is 7 μm. Therefore, if the thickness of the high carrier concentration n ⁺ layer 3 is 5 μm or less, the crack is not generated at all.

However, since the high carrier concentration n ⁺ layer 3 is made of GaN and the upper limit of the thickness at which no crack occurs in the GaN single layer is 20 μm, the high carrier concentration n ^{+
Even if the +} layer 3 has a thickness of 3 μm or more, it is predicted that the contact layer 62 of the laser diode 10 is not cracked.

Therefore, high carrier concentration n ⁺ of various thicknesses
Form a layer 3 on which 4 μm thick Al _0.1 Ga _0.9 N
Were formed, and the occurrence of cracks was observed. as a result,
Even if the thickness of the high carrier concentration n ⁺ layer 3 was set to 5 μm, no crack was generated in the Al _0.1 Ga _0.9 N formed thereon. Therefore, the thickness of the high carrier concentration n ⁺ layer 3 is 2 to 5
It can be used in the range of μm. The thickness of the clad layer is
Desirably, a device having a low balance of generation of cracks and excellent conductivity of the n ⁺ layer can be obtained at 0.5 to 1 μm. Further, desirably, the Al composition ratio x of the cladding layer
However, when it is 0.1 or less, a superior device in which cracks do not occur can be obtained.

In the above embodiment, the structure of the active layer 5 is
A single layer of In _0.08 Ga _0.92 N was used, but each had a thickness of 100
A multiple quantum well structure composed of Å In _0.08 Ga _0.92 N and GaN may be used. The thickness of the active layer 5 is 100-1000Å,
The composition ratio of In is preferably 0 to 0.15.

Further, the cladding layers 4 and 61 and the active layer 5 may be generally Al _x Ga _y In _1-xy N. Composition ratio x: y: 1-
xy is determined according to the oscillation wavelength of the laser.

The buffer layer 2 is made of Al _0.1 Ga _0.83 In _0.07 N
Etc., it may be _{Al x Ga y In 1-xy} N. The p-type conversion can be performed by electron beam irradiation, thermal annealing, heat treatment in N ₂ plasma gas, or laser irradiation.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of a laser diode according to a first specific example of the present invention.

[Explanation of symbols]

10 ... Laser diode 1 ... Sapphire substrate 2 ... Buffer layer 3 ... High carrier concentration n ⁺ layer 4 ... Clad layer 5 ... Active layer 61 ... Clad layer 62 ... Contact layer 7, 8 ... Electrode 9 ... SiO ₂ layer

Claims (5)

[Claims] 1. A Group III nitride semiconductor (Al _x Ga _Y In _1-XY N; X = 0,
Y = 0, X = Y = 0), and the clad layer has a thickness of 0.5 to 2 μm in a light emitting device having a three-layer structure in which an active layer is sandwiched by clad layers from both sides. A light emitting element characterized by. 2. The light emitting device according to claim 1, wherein the three-layer structure is formed on a GaN layer formed on a buffer layer formed on a sapphire substrate. 3. The light emitting device according to claim 1, wherein the GaN layer has a thickness of 2 to 5 μm. 4. The clad layer is made of Al _x Ga _1-x N (provided that X
≦ 0.1), The light emitting device according to claim 1. 5. The light emitting device according to claim 1, wherein the active layer is made of In _x Ga _1-x N.