JP2003055099A - Method of manufacturing gallium nitride-based compound semiconductor substrate and gallium nitride-based compound semiconductor substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a gallium nitride-based compound semiconductor having a good surface morphology nearly free of pits. SOLUTION: The gallium nitride-based compound semiconductor is obtained by growing at least a first gallium nitride-based compound semiconductor layer and a second gallium nitride-based compound semiconductor layer in this order on a substrate by using a hydride vapor phase growth method. At this time, the growth rate of the first gallium nitride-based compound semiconductor layer is adjusted to be lower than that of the second gallium nitride-based compound semiconductor layer.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a light emitting diode,
A gallium nitride-based compound semiconductor (In _x Al _y Ga) used for a light emitting element such as a laser diode, a light receiving element such as a solar cell or an optical sensor, or an electronic device.
_1-x-y N, 0≤X, 0≤Y, X + Y≤1), and a gallium nitride-based compound semiconductor substrate.

[0002]

2. Description of the Related Art Generally, when a semiconductor is grown on a substrate, it is known that if a substrate lattice-matched with the semiconductor to be grown is used, crystal defects of the semiconductor are reduced and crystallinity is improved. Therefore, when a gallium nitride compound semiconductor element used for an electronic device such as an LED element, an LD element, or a light receiving element is manufactured, if a substrate made of a gallium nitride compound semiconductor is used, there are few crystal defects on the substrate. A gallium nitride-based compound semiconductor can be grown, and the characteristics of the above device can be greatly improved.

Conventionally, since it has been difficult to prepare a single crystal substrate of gallium nitride compound semiconductor, a heterogeneous substrate such as sapphire, spinel, and silicon carbide which is not lattice-matched with the gallium nitride compound semiconductor is generally used as the substrate. .

When a heterogeneous substrate is used, a method of growing a buffer layer made of a gallium nitride compound semiconductor on the heterogeneous substrate at a low temperature of 900 ° C. or lower is used for growing a single crystal. By growing this buffer layer, it became possible to grow a flat and mirror-finished gallium nitride-based compound semiconductor layer. Thus, a gallium nitride-based compound semiconductor substrate having a gallium nitride-based compound semiconductor layer formed on a heterogeneous substrate via a buffer layer is used as a gallium nitride-based compound semiconductor substrate.

However, when the gallium nitride-based compound semiconductor layer is grown on the above-mentioned buffer layer, if grown at a temperature of 1000 ° C. or higher, which is higher than that of the buffer layer, islands grown around the growth nuclei are formed, Dislocations occur when these islands are joined together. After that, the dislocations propagate in the crystal growth direction, and as threading dislocations in the growth layer or on the surface of 10 ⁸ -1.
There are 0 ¹⁰ / cm ² . Due to the existence of the threading dislocations, the crystallinity of the gallium nitride-based compound semiconductor is lowered, and there is a problem that the electrical characteristics are lowered.

Therefore, in order to reduce threading dislocations, an ELOG (Epitaxially Lateral OverGrowth) growth method has been proposed in which a gallium nitride compound semiconductor layer is grown laterally with respect to a substrate. In the ELOG growth method, for example, a protective film such as SiO ₂ is partially formed on GaN grown on a sapphire substrate, and GaN is grown on the protective film. Since GaN does not grow directly on the SiO ₂ protective film, Ga grown from the portion (window portion) without the protective film
Ga with a low dislocation density is formed on the protective film by lateral growth of N.
N can be grown. Therefore, in the ELOG growth method, the threading dislocation density can be reduced by two digits or more as compared with the gallium nitride-based compound semiconductor grown using the buffer layer.

However, in the ELOG growth method, the number of dislocations on the window cannot be reduced, so that there are portions with many dislocations and portions with few dislocations on the substrate, and it is difficult to utilize the entire surface of the substrate. is there.

On the other hand, by using the hydride vapor phase epitaxy method, a first growth layer and a second growth layer having a growth rate smaller than that of the first growth layer are grown on a heterogeneous substrate to form gallium nitride. A method for producing a compound semiconductor substrate has been proposed (for example, Japanese Patent Laid-Open No. 2001-168045).
Hydride vapor deposition (hereinafter referred to as HVPE method)
Reacts with a group III element such as gallium, aluminum or indium, and a halogen gas such as hydrogen chloride to produce I
In this method, a halide such as a chloride, bromide, or iodide of a group II element is generated, and the halide is reacted with a nitrogen source such as ammonia or hydrazine at a high temperature to obtain a nitride semiconductor. Since the growth rate is several times faster than MOCVD (Metal Organic Chemical Vapor Deposition), a thick film can be formed in a shorter time. JP 2001-16804 A
According to the method disclosed in Japanese Patent Publication No. 5, the propagation of threading dislocations to the substrate surface is suppressed, so that the dislocation density on the entire substrate surface can be reduced.

[0009]

However, the above method using the hydride vapor phase epitaxy has the advantage that the dislocation density on the entire substrate surface can be reduced, while the pits and the pit-shaped There was a problem that a large number of growth hills were generated. Here, the growth hill refers to a hill-like growth of crystals centered on the pit. It is necessary to suppress the generation of pits and growth hills because they reduce the area that can be used as a substrate and make processing difficult. Here, as the causes of the large number of pits and growth hills, 1) a large number of dislocations are present on the original substrate, and 2) the first growth layer is formed at high speed.
Is mentioned. MOCVD on the foreign substrate as the original substrate
In many cases, a buffer layer and an underlayer formed by the method are used. In this case, once the temperature is lowered, the wafer is MOC
Since it is necessary to take it out from the VD device, dislocations are introduced into the buffer layer and the underlayer for alleviating the strain due to the difference in thermal expansion coefficient. Further, since it is taken out from the furnace, the surface may be contaminated by dust or water. Also,
It is considered that when the first growth layer is formed at a high speed on the substrate, the interface state at the initial stage of growth becomes unstable as compared with the case where the first growth layer is grown at a low speed, so that the first growth layer is more likely to be affected by dislocations and contamination.

Therefore, the present invention solves the above problems,
An object of the present invention is to provide a method for producing a gallium nitride-based compound semiconductor substrate having excellent crystallinity and a good substrate surface morphology, and a gallium nitride-based compound semiconductor substrate produced by the method.

[0011]

In order to solve the above problems, a method for manufacturing a gallium nitride compound semiconductor substrate according to the present invention uses a hydride vapor phase epitaxy method to form a gallium nitride compound semiconductor layer on a substrate. A method for manufacturing a gallium nitride-based compound semiconductor substrate, wherein the gallium nitride-based compound semiconductor layer is at least a first gallium nitride-based compound semiconductor layer formed on the substrate in this order,
A second gallium nitride-based compound semiconductor layer,
The growth rate of the gallium nitride based compound semiconductor layer is lower than the growth rate of the second gallium nitride based compound semiconductor layer.

In the manufacturing method of the present invention, HVP is formed on the substrate.
When forming a gallium nitride-based compound semiconductor layer by using the E method, at least two layers having different growth rates are formed. The first gallium nitride-based compound semiconductor layer on the side of the base substrate is grown at a lower speed than the second gallium nitride-based compound semiconductor layer to allow two-dimensional homogeneous initial growth. As a result, the first gallium nitride-based compound semiconductor layer forms a mirror surface, and the influence of the morphology on the surface of the base substrate is eliminated. Then, the second gallium nitride-based compound semiconductor layer is
By growing on the first gallium nitride-based compound semiconductor layer that is a mirror surface, crystal defects do not propagate to the surface and are not affected by the surface state of the underlying substrate,
A thick film of gallium nitride-based compound semiconductor can be formed.

In the manufacturing method of the present invention, the gallium nitride-based compound semiconductor layer further has a third gallium nitride-based compound semiconductor layer formed on the second gallium nitride-based compound semiconductor layer. In addition, the growth rate of the third gallium nitride-based compound semiconductor layer can be lower than the growth rate of the second gallium nitride-based compound semiconductor layer.

Further, according to the manufacturing method of the present invention, the growth rate of the first gallium nitride-based compound semiconductor layer is set to 60 μm / ho.
It can be less than or equal to ur.

Further, in the manufacturing method of the present invention,
A heterogeneous substrate made of a material different from that of the gallium nitride-based compound semiconductor can be used.

Further, in the manufacturing method of the present invention,
A substrate made of a gallium nitride-based compound semiconductor can be used.

In the manufacturing method of the present invention, the second gallium nitride compound semiconductor layer can be grown at substantially the same temperature as the first gallium nitride compound semiconductor layer.

Further, according to the manufacturing method of the present invention, the third gallium nitride-based compound semiconductor layer can be grown at the same temperature as or higher than that of the second gallium nitride-based compound semiconductor layer.

The gallium nitride compound semiconductor substrate of the present invention is a gallium nitride compound semiconductor substrate comprising a substrate and a gallium nitride compound semiconductor layer formed on the substrate by a hydride vapor phase epitaxy method. The gallium nitride-based compound semiconductor layer is at least a first gallium nitride-based compound semiconductor layer, a second gallium nitride-based compound semiconductor layer, and a third gallium nitride-based compound semiconductor layer formed in this order on the substrate.
And a crystal defect of the gallium nitride-based compound semiconductor layer is 1 × 10 ⁷ / cm ² or less by CL image observation.

In the gallium nitride compound semiconductor substrate of the present invention, a heterogeneous substrate made of a material different from that of the gallium nitride compound semiconductor can be used as the substrate.

The gallium nitride-based compound semiconductor substrate of the present invention may be made of a gallium nitride-based compound semiconductor.

The gallium nitride compound semiconductor device of the present invention is a gallium nitride compound semiconductor substrate comprising a substrate and a gallium nitride compound semiconductor layer formed on the substrate by a hydride vapor phase epitaxy method. At least an n-type gallium nitride compound semiconductor layer, an active layer, and a p-type gallium nitride compound semiconductor layer are formed in this order on the gallium nitride compound semiconductor layer.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. In the present invention, the substrate on which the gallium nitride-based compound semiconductor is grown may be a heterogeneous substrate made of a material different from the gallium nitride-based compound semiconductor or a substrate made of a gallium nitride-based compound semiconductor. For the heterogeneous substrate, it is possible to use sapphire or SiC (6H, 4H, 3C) whose main surface is any of the c-plane, r-plane, and a-plane, spinel, ZnS, ZnO, GaAs, and Si for the substrate. it can.

As the substrate made of a gallium nitride compound semiconductor, for example, a substrate obtained by forming a gallium nitride compound semiconductor layer on a heterogeneous substrate by the HVPE method and then removing the heterogeneous substrate can be used. In this case, it is preferable that the growth surface is the opposite surface of the gallium nitride-based compound semiconductor layer to the main surface on the side of the different substrate. This is because the main surface of the gallium nitride-based compound semiconductor substrate on the side of the different substrate is damaged when the different substrate is removed, and crystal defects are easily generated.

Further, a substrate having a buffer layer formed by MOCVD on a different type of substrate can be used as the substrate.
By forming the buffer layer on the substrate, the lattice constant mismatch with the substrate can be relaxed. Specific examples of the buffer layer include AlN, GaN, AlGaN, and InG.
Examples include aN and InAlGaN. Hydrogen is used as a carrier gas, trimethylgallium, trimethylaluminum, trimethylindium, etc. are used as a source gas, and a temperature of 300 ° C. or higher and 900 ° C. or lower on a sapphire substrate is 10 Å
The film is grown to a film thickness of 0.5 μm or less. The buffer layer may be omitted depending on the type of substrate.

Further, an underlayer can be formed on the buffer layer by the MOCVD method. The underlayer is preferably made of the same gallium nitride-based compound semiconductor as the buffer layer, and has a temperature higher than that of the buffer layer of 900 ° C. or higher 1100
Grow at a temperature of ℃ or less and a film thickness of 500 Å or more and 50 μm or less. The underlayer has an effect of reducing crystal defects.

Next, a method of growing a gallium nitride-based compound semiconductor using the HVPE method will be described. A metal such as Ga is reacted with a halogen gas to generate a halide of a group III element. This halide is reacted with ammonia gas to grow a gallium nitride-based compound semiconductor on the substrate. H ₂ and N ₂ are generally used as a carrier gas, but when stacking a gallium nitride-based compound semiconductor layer, the surface morphology deteriorates when N ₂ is used, so H ₂ is usually used. Further, a substrate in which a buffer layer and a base layer are formed can be used, and the base layer can be used as a growth surface.

It is also possible to dope n-type impurities such as Si, Sn, Ge and S during the growth of the gallium nitride compound semiconductor. As a source gas for doping,
For example, doping is performed by supplying SiH ₄ or SiH ₂ Cl ₂ to the surface of the substrate using a supply pipe.

The growth conditions for the first gallium nitride-based compound semiconductor layer may be 60 μm or less, more preferably 30 μm or less, as long as the growth rate is uniform and a mirror surface is obtained. The film thickness of the first gallium nitride-based compound semiconductor layer is 1 μm or more, 5 to 1
About 0 μm is preferable. The effect is the same even if the thickness is further increased. Further, as the first gallium nitride-based compound semiconductor layer, undoped GaN, Si as an n-type impurity,
Ga doped with at least one of Sn, Ge and S
N can be used. The first gallium nitride-based compound semiconductor layer has the effect of stabilizing the substrate temperature without decomposing the gallium nitride-based compound semiconductor substrate, or the buffer layer and the underlying layer, and stabilizing the growth interface.

As the growth conditions for the second gallium nitride-based compound semiconductor layer, the growth rate is higher than that of the first gallium nitride-based compound semiconductor layer and the growth rate is 0.5 m.
m / hour or more, more preferably 1 to 10 mm / ho
ur. The film thickness of the second gallium nitride-based compound semiconductor layer is 20 μm to 1 mm, more preferably 50 μm to 200 μm. This is because if the second gallium nitride-based compound semiconductor layer is thick, it becomes difficult to eliminate the influence of the surface shape of the second gallium nitride-based compound semiconductor layer when the third gallium nitride-based compound semiconductor layer is stacked. In addition, as the second gallium nitride-based compound semiconductor layer, undoped GaN, and n-type impurities such as Si and S
GaN doped with at least one of n, Ge and S
Can be used.

Further, it is preferable that both the first and second gallium nitride-based compound semiconductor layers are grown at substantially the same temperature, and the growth temperature is preferably 1000 ° C. or higher.

Further, the third gallium nitride-based compound semiconductor layer eliminates the influence of the surface shape of the second gallium nitride-based compound semiconductor layer and forms a mirror surface. As a growth condition, the growth rate may be lower than that of the second gallium nitride-based compound semiconductor layer and the growth rate may be uniform.
μm / hour or less, more preferably 30 to 60 μm /
Hour. The film thickness of the third gallium nitride-based compound semiconductor layer is not particularly limited as long as the upper surface is a mirror surface, and may be any thickness as long as the surface shape of the second gallium nitride-based compound semiconductor layer can be erased. When the substrate is provided, the thickness is preferably 20 μm or more, more preferably 50
It is at least μm. Further, when the heterogeneous substrate is removed and used, the third gallium nitride-based compound semiconductor layer needs to be thick to some extent in order to facilitate processing and handling. In this case, the total thickness of the first to third gallium nitride-based compound semiconductor layers is preferably 100 μm or more, more preferably 300 μm or more. Further, by forming the second and third gallium nitride-based compound semiconductor layers a plurality of times repeatedly, the required film thickness can be obtained. Further, as the third gallium nitride-based compound semiconductor, undoped GaN and GaN doped with at least one of Si, Sn, Ge, S, etc. as n-type impurities can be used.

The third gallium nitride-based compound semiconductor layer is preferably grown at the same temperature as the second gallium nitride-based compound semiconductor layer or at a temperature higher than that, and the growth temperature is preferably 1000 ° C. or higher.

To remove the heterogeneous substrate to obtain a substrate made of gallium nitride compound semiconductor, for example, the following method can be used. 1) A buffer layer is formed on a heterogeneous substrate, and a gallium nitride compound semiconductor layer is laminated on the buffer layer by MOCVD to a thickness of about 2.5 μm. Then, the heterogeneous substrate is transferred to an HVPE apparatus and heated at 1000 ° C. or higher at 50 μm / A gallium nitride-based compound semiconductor layer is stacked to a thickness of about 150 μm. Then, it is taken out from the HVPE apparatus and the foreign substrate is removed. First to third gallium nitride compound semiconductor layers are grown on the obtained gallium nitride compound semiconductor substrate. 2) A buffer layer is formed on a different type substrate. Next, the heterogeneous substrate is transferred to an HVPE apparatus, and first to third gallium nitride compound semiconductor layers are grown on the buffer layer. Then, the substrate is taken out from the HVPE device and the foreign substrate is removed. In addition, 1) above
And 2), the step of further forming the first to third gallium nitride compound semiconductor layers on the substrate made of the first to third gallium nitride compound semiconductor layers is repeated one or more times to obtain a thicker layer. A gallium nitride-based compound semiconductor substrate for the film can also be manufactured. Here, when the step of forming the three layers of the first to third gallium nitride-based compound semiconductor layers is taken as one step and this step is repeated a plurality of times in the HVPE apparatus, after the second step, the first gallium nitride compound semiconductor layer is formed. The compound semiconductor layer can be omitted. Since the reaction is carried out continuously, there is no need to lower the temperature, a large number of rearrangements are not introduced with cooling, and it is not necessary to take it out of the reactor during the reaction, and it is contaminated by dust and water in the atmosphere. This is because there is no fear. For example, the first to the third
When the three layers (referred to as the A layer) including the gallium nitride-based compound semiconductor layer are formed, the second layer includes the second and third gallium nitride-based compound semiconductor layers (this is referred to as a B layer). ) May be formed, and the B layer may be formed after the third time. Further, a method of forming the first to third gallium nitride-based compound semiconductor layers on the foreign substrate to fabricate the device and then removing the foreign substrate can also be used.

[0035]

EXAMPLES Example 1. In this example, a gallium nitride-based compound semiconductor layer was formed on a heterogeneous substrate, and this gallium nitride-based compound semiconductor layer was removed from the heterogeneous substrate to obtain a gallium nitride-based compound semiconductor substrate.

A sapphire substrate having a c-plane as the main surface and an orientation flat surface as the a-plane was used as a heterogeneous substrate, set in an MOCVD apparatus, and subjected to thermal cleaning at a temperature of 1050 ° C. for 10 minutes to remove water and deposits on the surface. .

Next, the temperature is set to 510 ° C., hydrogen is used as a carrier gas, ammonia and trimethylgallium are used as source gases, and a GaN buffer layer is set to 200 Å.
The temperature was raised to 0 ° C. and the underlayer was grown to a film thickness of 2.5 μm.

Next, a sapphire substrate was set in the HVPE device so that the above-mentioned underlayer was a growth surface. G
HCl gas is supplied to the a-metal from the halogen gas supply pipe to generate GaCl, and ammonia gas is supplied from the nitrogen source gas supply pipe to react these gases on the sapphire substrate to grow undoped GaN. The gallium nitride-based compound semiconductor layer 1 was formed. The growth temperature of the first gallium nitride-based compound semiconductor was 1000 ° C., and the growth rate was 25 μm / hour.

Subsequently, the growth temperature is 1000 ° C., the growth rate is 1 mm / hour, and the film thickness is 100 μm.
A second gallium nitride based compound semiconductor layer was grown on the first gallium nitride based compound semiconductor layer.

Next, the growth temperature is 1050 ° C., the growth rate is 45 μm / hour, and the film thickness is 300 μm.
A third gallium nitride compound semiconductor layer was grown on the second gallium nitride compound semiconductor layer.

Next, after taking out the sapphire substrate on which the first to third gallium nitride-based compound semiconductor layers were grown from the HVPE device, the sapphire substrate was removed and removed,
A gallium nitride-based compound semiconductor substrate including the first to third gallium nitride-based compound semiconductor layers was obtained.

The surface of the obtained third gallium nitride-based compound semiconductor layer was flat and mirror-like, and the CL observation revealed that the threading dislocation density was about 1.5 × 10 ⁶ / cm ² with low defects. Further, the number of pits was 10 or less per φ30 mm.

Example 2. In this example, a gallium nitride-based compound semiconductor substrate was manufactured by the same method as in Example 1 except that the step of removing the sapphire substrate was not performed. Since it is not necessary to remove the sapphire substrate, the thickness of the third gallium nitride-based compound semiconductor layer was 100 μm, which is thinner than that in Example 1.

The surface of the obtained third gallium nitride-based compound semiconductor layer was flat and mirror-like, and the threading dislocation density was about 3 × 10 ⁶ / cm ² according to CL observation. The number of pits was 10 or less per φ30.

Example 3. In this example, a gallium nitride-based compound semiconductor substrate was manufactured by the same method as in Example 1 except that the step of forming the buffer layer and the underlayer and the step of removing the sapphire substrate were not performed. Since it is not necessary to remove the sapphire substrate, the thickness of the third gallium nitride-based compound semiconductor layer was 100 μm, which is thinner than that in Example 1.

The surface of the obtained third gallium nitride-based compound semiconductor layer was flat and mirror-like, and the threading dislocation density was about 4.5 × 10 ⁶ / cm ² by CL observation. The number of pits was 10 or less per φ30.

Comparative Example 1. Example 1 except that the first gallium nitride-based compound semiconductor layer was not formed and the second first gallium nitride-based compound semiconductor layer was grown on the buffer layer.
A gallium nitride-based compound semiconductor substrate was produced by the same method as described above.

The surface of the obtained third gallium nitride-based compound semiconductor layer has a threading dislocation density of about 3 × according to CL observation.
It was 10 ⁶ / cm ² . Further, the number of pits was 100 or more per φ30.

As is clear from the results of Examples 1 to 3 and Comparative Example 1, the first gallium nitride-based compound semiconductor layer grown at a slower speed than the second gallium nitride-based compound semiconductor layer is used as a base. By providing it on the substrate side, it was possible to maintain the threading dislocation density at a low defect of the order of 10 ⁶ / cm ² and significantly reduce the number of pits.

Example 4. Using the gallium nitride-based compound semiconductor substrate obtained in Example 1, a laser device was manufactured by the following method. FIG. 1 shows a schematic sectional structure of the laser device 1.

(Undoped n-type contact layer 20) Gallium nitride compound semiconductor substrate 10 obtained in Example 1
Is a gallium nitride-based compound semiconductor substrate layer 11 and a first
Gallium nitride compound semiconductor layer 12, a second gallium nitride compound semiconductor layer 13, and a third gallium nitride compound semiconductor 14. The substrate is MOCV with the third gallium nitride compound semiconductor layer 14 as a growth surface.
It was set in the reaction vessel of the D apparatus. Ammonia and TM
Using G (trimethylgallium) and TMA (trimethylaluminum), an undoped n-type contact layer 20 made of Al _{0.0 5} Ga _0.95 N was grown to a film thickness of 1 μm. This layer plays the role of a buffer layer between the gallium nitride compound semiconductor substrate and the gallium nitride compound semiconductor layer grown thereon.

(N-Type Contact Layer 21) Next, ammonia, TMG and TMA, and silane gas as an impurity gas are used on the undoped n-type contact layer 20,
Al _0.05 Ga doped with Si at 1050 ° C.
_The n-type contact layer 21 made of _0.95 N was grown to a film thickness of 4 μm.

(Crack prevention layer 22) Next, TMG, T
A crack prevention layer 22 made of In _0.07 Ga _0.93 N was grown to a thickness of 0.15 μm at a temperature of 900 ° C. using MI (trimethylindium) and ammonia. This crack prevention layer can be omitted.

(N-type clad layer 23) Next, the temperature is raised to 10
At 50 ° C., TMA, TMG, and ammonia are used as source gases, and an A layer made of undoped Al _0.05 Ga _0.95 N is grown to a film thickness of 25 Å.
Stop, silane gas is used as impurity gas, and Si
2 × 10 ¹⁸ / cm ³ B layer of GaN
It was grown to a film thickness of 5Å. This operation was repeated 200 times to form a laminated structure of A layer and B layer, and an n-type clad layer 23 composed of a multilayer film (superlattice structure) having a total film thickness of 1 μm was grown.

(N-Type Guide Layer 24) Next, the silane gas was stopped, and the n-type guide layer 24 made of undoped GaN was grown to a thickness of 0.15 μm at 1050 ° C. The n-type guide layer may be doped with n-type impurities.

(Active layer 25) Next, the temperature was set to 900 ° C., TMI, TMG and ammonia, and silane gas was used as an impurity gas, and In _0.05 Ga _0.95 doped with Si at 5 × 10 ¹⁸ / cm ³ was used. 1 barrier layer made of N
It was grown to a film thickness of 40Å. Then, the silane gas was stopped, and a well layer made of undoped In _0.13 Ga _0.87 N was laminated in the order of barrier layer / well layer / barrier layer / well layer with a thickness of 40 Å, and finally as a barrier layer. , TMI, TM
Undoped In _0.05 G using G and ammonia
a _0.95 N was grown. The active layer 25 has a total film thickness of 50.
It becomes a multi quantum well structure (MQW) of 0Å.

(P-type cap layer 26) Next, 900 ° C.
, TMA, TMG and ammonia, and impurity gas
Cp_TwoUses Mg (cyclopentadienyl magnesium)
1 x 10 Mg¹⁹/ Cm ^ThreeDoped Al 0.3
The p-type cap layer 26 made of Ga0.7N has a thickness of 100 Å
It was grown to a film thickness.

(P-type guide layer 27) Next, the temperature is set to 105.
At 0 ° C., TMG and ammonia were used to grow a p-type guide layer 27 of undoped GaN to a film thickness of 0.15 μm. The p-type guide layer may be doped with p-type impurities.

(P-type cladding layer 28) Next, 1050 ° C.
Then, an A layer made of undoped Al _0.05 Ga _0.95 N is grown to a film thickness of 25 Å, then TMA is stopped, and Cp
₂ Mg was used to form a B layer of Mg-doped GaN 25
It is grown to a film thickness of Å and repeated 90 times to obtain a total film thickness of 0.
A p-type clad layer 28 composed of a 45 μm superlattice layer was grown. The p-type cladding layer 28 having a superlattice structure can increase the Al mixed crystal ratio of the entire cladding layer. This reduces the refractive index of the cladding layer itself and increases the bandgap energy, so that the threshold value can be lowered.

(P-type contact layer 29) at 1050 ° C.
On the p-type clad layer 28, TMG, ammonia, and
Cp _Two1 x 10 Mg with Mg²⁰/ Cm^ThreeDoe
The p-type contact layer 29 made of p-type GaN
It was grown to a film thickness of 0Å. After the reaction is complete, place it in the reaction vessel.
And anneal at 700 ° C in nitrogen to obtain p-type
The tact layer 29 has further reduced resistance.

After the annealing, the substrate on which the gallium nitride-based compound semiconductor was laminated was taken out from the reaction vessel and the uppermost p
A protective film made of SiO ₂ is formed on the surface of the mold contact layer 29, and Si is formed by RIE (reactive ion etching).
The surface of the n-type contact layer 21 on which the n-side electrode 32 is to be formed is exposed by etching with Cl ₄ gas.

Next, the SiO ₂ protective film is subjected to CF using RIE.
_A ridge stripe was formed as a stripe-shaped waveguide region by etching with ₄ gas.

Next, after forming a ridge stripe, ZrO is formed.
_An insulating film 30 of ₂ was formed to a thickness of 0.5 μm on the p-type clad layer 28 exposed by etching.

Next, on the p-type contact layer 29, Ni /
A p-side electrode 31 made of Au is formed, and Ti / A is formed on the n-type contact layer 21 exposed by etching.
The n-side electrode 32 of 1 was formed in a direction parallel to the stripe.

As described above, the gallium nitride compound semiconductor substrate of the wafer on which the n-side electrode 32 and the p-side electrode 31 are formed is polished and thinned, and then, in the direction perpendicular to the striped electrodes, the substrate side is formed. Cleaves into a bar shape, and forms a resonator on the cleavage plane. A dielectric multilayer film made of SiO ₂ and TiO ₂ was formed on the cavity facet, and separated into chips to form a laser device 1. The obtained laser device oscillates at room temperature, exhibits room temperature continuous oscillation at a threshold current density of 2.8 kA / cm ² , and 3000 at an output of 5 to 30 mW.
It showed a life of 20,000 hours or more.

[0066]

As described above, according to the method for manufacturing a gallium nitride-based compound semiconductor substrate of the present invention, the growth rate at the time of forming a gallium nitride-based compound semiconductor layer on the substrate by the HVPE method is increased. Since at least two different layers are formed and the growth rate of the first gallium nitride-based compound semiconductor layer on the base substrate side is made smaller than that of the second gallium nitride-based compound semiconductor layer, the surface condition of the base substrate It is possible to grow a gallium nitride-based compound semiconductor without being affected by.

According to the manufacturing method of the present invention, a third gallium nitride compound semiconductor layer having a growth rate smaller than that of the second gallium nitride compound semiconductor layer is formed on the second gallium nitride compound semiconductor layer. By forming it, crystal defects can be reduced. This makes it possible to provide a gallium nitride-based compound semiconductor substrate having few crystal defects and few pits and having a good surface morphology. Therefore, by growing a gallium nitride-based compound semiconductor on this substrate, an element with few crystal defects can be manufactured, and an element with long life and high reliability can be provided.

According to the manufacturing method of the present invention, the second gallium nitride-based compound semiconductor layer is grown at the same temperature as the first gallium nitride-based compound semiconductor layer. Since the warp of the substrate does not occur, the occurrence of crystal defects can be suppressed.

The gallium nitride-based compound semiconductor substrate of the present invention has the first and second gallium nitride-based compound semiconductor layers on the substrate, has a crystal defect of 1 × 10 ⁷ / cm ² or less, and has a pit Provide a substrate with less generation.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a laser device using a substrate according to an example of the present invention.

[Explanation of symbols]

1 gallium nitride based laser device, 10 gallium nitride based compound semiconductor substrate, 11 gallium nitride based compound semiconductor substrate layer, 12 first gallium nitride based compound semiconductor layer,
13 second gallium nitride-based compound semiconductor layer, 14 third gallium nitride-based compound semiconductor layer, 20 undoped n-type contact layer, 21 n-type contact layer, 22 crack prevention layer, 23 n-type cladding layer, 24 n-type guide Layer, 25 active layer, 26 p-type cap layer, 27 p
Type guide layer, 28 p-type clad layer, 29 p-type contact layer, 30 protective film, 31 p-side electrode, 32 n-side electrode.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4G077 AA03 AB01 BE15 DB05 EF01                       EH09 TC10 TC14 TC19                 5F045 AA02 AA04 AB14 AB17 AC08                       AC12 AC13 AD07 AD08 AD09                       AD10 AD11 AD12 AD13 AD14                       AD15 AF02 AF03 AF04 AF09                       BB12 CA12 DA53 DA55 DQ08                       EB13                 5F073 AA74 AA83 CA07 CB02 CB05                       CB07 CB22 DA05 DA07 DA25                       DA32 DA33 EA28

Claims (9)

[Claims] 1. A method for manufacturing a gallium nitride-based compound semiconductor substrate, comprising forming a gallium nitride-based compound semiconductor layer on a substrate by using a hydride vapor phase epitaxy method, wherein the gallium nitride-based compound semiconductor layer is at least: A first gallium nitride-based compound semiconductor layer and a second gallium nitride-based compound semiconductor layer formed in this order on the substrate, and the growth rate of the first gallium nitride-based compound semiconductor layer is the second gallium nitride-based compound semiconductor layer. 2. A method for producing a gallium nitride-based compound semiconductor having a growth rate lower than that of the gallium nitride-based compound semiconductor layer. 2. The gallium nitride-based compound semiconductor layer,
Furthermore, a third gallium nitride-based compound semiconductor layer is formed on the second gallium nitride-based compound semiconductor layer,
The method according to claim 1, wherein the growth rate of the third gallium nitride-based compound semiconductor layer is lower than the growth rate of the second gallium nitride-based compound semiconductor layer. 3. The manufacturing method according to claim 1, wherein the growth rate of the first gallium nitride-based compound semiconductor layer is 60 μm / hour or less. 4. The manufacturing method according to claim 1, wherein a heterogeneous substrate made of a material different from a gallium nitride-based compound semiconductor is used as the substrate. 5. The manufacturing method according to claim 1, wherein a substrate made of a gallium nitride-based compound semiconductor is used as the substrate. 6. The manufacturing method according to claim 1, wherein the second gallium nitride-based compound semiconductor layer is grown at substantially the same temperature as that of the first gallium nitride-based compound semiconductor layer. 7. A gallium nitride compound semiconductor substrate comprising a substrate and a gallium nitride compound semiconductor layer formed on the substrate by a hydride vapor phase epitaxy method, wherein the gallium nitride compound semiconductor layer is provided. At least a first gallium nitride-based compound semiconductor layer, a second gallium nitride-based compound semiconductor layer, and a third gallium nitride-based compound semiconductor layer formed in this order on the substrate, The crystal defect of the gallium nitride compound semiconductor layer is 1 ×
A gallium nitride-based compound semiconductor substrate having a density of 10 ⁷ / cm ² or less. 8. The gallium nitride-based compound semiconductor substrate according to claim 7, wherein the substrate is a heterogeneous substrate made of a material different from a gallium nitride-based compound semiconductor. 9. The gallium nitride compound semiconductor substrate according to claim 7, wherein the substrate is made of a gallium nitride compound semiconductor.