JPH11238935A - Gan compound semiconductor device and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the crystal property of a gallium-nitride-based compound semiconductor growing on a buffer layer at a high yield rate, by constituting a buffer layer on the side of a substrate in the two or more layers with GaAlN, and constituting the butter layer on the side of a GaN-based compound semiconductor layer by InGaN in the laminated structure. SOLUTION: On a substrate 11, GaXAl1-x (0<=x<=1) as a first buffer layer 12 and Iny Ga1-y N (0<=y<=1) as a second buffer layer 13 thereon are laminated. A gallium-nitride-based compound semiconductor crystal 14 is grown thereon. The structure of an epitaxial wafer is formed in this way. After the growing nucleus is formed of the first buffer layer 12 by introducing the second buffer layer 13, the crystal defect present in the first buffer layer 12 can be embedded without drawing the growing surface at the layer, wherein the growing speed vertical to the growing direction of the thin-film crystal is relatively high. Therefore, the defect density of the gallium-nitride compound semiconductor or growing thereon can be decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a GaN-based compound semiconductor device using a GaN-based semiconductor crystal and a method of manufacturing the same.

[0002]

2. Description of the Related Art In recent years, GaN-based compound semiconductors, for example,
A blue light-emitting device of a material represented by a general formula represented by Ga _x Al ₁ -xN (where x is in the range of 0 ≦ x ≦ 1) has attracted attention. As a method of growing a crystal of a GaN-based compound semiconductor, an organic metal compound vapor deposition method (hereinafter referred to as MOCVD)
Is widely known. In this method, an organometallic compound gas is supplied as a reaction gas into a reaction vessel in which a substrate is placed, and a crystal growth temperature is maintained at a high temperature of about 900 ° C. to 1100 ° C. to grow an epitaxial layer of a compound semiconductor crystal on the substrate. It is a way to make it. For example, when growing a GaN epitaxial layer, trimethylgallium is used as a group III gas and ammonia is used as a group V gas.

In order to manufacture a semiconductor device using an epitaxial layer of a GaN-based compound semiconductor grown as described above, it is essential to significantly improve the crystallinity.

In addition, the surface of, for example, a GaN layer directly grown on a substrate by using the MOCVD method has a hexagonal pyramid or hexagonal growth pattern, and has a myriad of irregularities, and its surface morphology is extremely high. There is a drawback that gets worse. For example, it has been very difficult to produce a blue light emitting diode using a crystal layer of a semiconductor having extremely inferior surface morphology having a myriad of irregularities on the surface, because of very low yield.

In order to solve such a problem, a method of growing an AIN buffer layer on a substrate before growing a gallium nitride compound semiconductor crystal [Appl. Phy.
t.48, (1986), 353 (Applied Physics Letters 4
8, 1986, p. 353, and JP-A-2-229.
476)] and a method of growing a GaN buffer layer [Jpn. J. Appl. Phys. 30, (1991), L1705, (Japanese Journal of Applied Physics Vol. 30, No. 1,
991, L1715, and JP-A-4-297023
Gazette)] has been proposed. In this method, a buffer layer having a growth temperature of 400 to 900 ° C. and a film pressure of 10 to 120 nm is provided on a sapphire substrate. This method is characterized in that the crystallinity and surface morphology of the GaN semiconductor layer can be improved by growing GaN on the buffer layer.

[0006]

However, in the above method, the growth conditions of the buffer layer are severely restricted and the film thickness must be set very precisely and precisely. It is difficult to form a uniform and uniform thickness on the entire surface of a substrate, for example, a sapphire substrate having a diameter of about 50 mm. Therefore, it is difficult to improve the crystallinity and surface morphology of the gallium nitride-based compound semiconductor formed on the buffer layer with a good yield, and the crystallinity is not enough to produce a practical semiconductor laser or the like. It has not been provided yet, and a remarkable improvement in crystallinity has been demanded. In particular, it is widely recognized that the presence of relatively large crystal defects, sometimes referred to as nanopipes, can cause significant damage when improving the reliability of semiconductor devices, in particular.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a semiconductor device in which the surface morphology of a GaN-based compound formed on a buffer layer has been improved to a practical level, and the crystallinity has been improved. It is intended to provide a manufacturing method for improving crystallinity to greatly reduce crystal defects, and for further stably growing a GaN-based compound semiconductor device with high yield.

[0008]

According to another aspect of the present invention, there is provided a method of manufacturing a GaN-based compound semiconductor device, comprising supplying a reaction gas into a reaction vessel and growing the first buffer layer at a temperature of 800 ° C. or less. A method for growing a GaN-based compound semiconductor crystal at a temperature of 800 ° C. or higher after growing a second buffer layer adjacent to the first buffer layer, wherein the first buffer layer is formed of Ga _x Al ₁ -xN. (0 ≦ x ≦ 1), and the second buffer layer is formed of In _y Ga _1-y N (0 <y
≦ 1).

The thickness of the second buffer layer is 2 nm or more and 200 nm or less, more preferably 10 nm to 100 n.
Adjust to the range of m. If the thickness is less than 2 nm, the effect will not be seen. If the thickness is more than 200 nm, many crystal defects will occur in the crystal of the GaN-based compound semiconductor formed on the buffer layer, and the surface morphology tends to deteriorate.

(Action) Ga _x Al ₁ -xN on the substrate 11
(0 ≦ x ≦ 1) is deposited as a first buffer layer 12, and In _y Ga _1-y N (0 <y ≦ 1) is deposited thereon as a second buffer layer 13. FIG. 1 is a cross-sectional view showing the structure of an epitaxial wafer when the compound semiconductor crystal 14 is grown, and FIG. 2 is a cross-sectional view showing the structure of a conventional epitaxial wafer without a second buffer layer. After the growth nuclei are formed in the first buffer layer by introducing the second buffer layer of the present invention, the growth rate perpendicular to the growth direction of the thin film crystal is relatively high in the first buffer layer. Since the existing crystal defects can be buried so as not to be dragged on the growth surface, the defect density of the gallium nitride-based compound semiconductor grown thereon can be greatly reduced.

A method for growing a GaN-based compound semiconductor crystal using GaN as a first buffer layer is described in Jpn.
Appl. Phys. 30, (1991), L1705 (Japanese Journal of Applied Physics Vol. 30, 1991, L1
715) and JP-A-4-297023, etc., but the operation of the buffer layer described in those documents is briefly described as follows.

The GaN buffer layer grown at a low temperature (about 600 ° C.) is polycrystalline, and when the temperature is raised to 1000 ° C. to grow an epitaxial GaN layer on the polycrystalline GaN buffer layer, The GaN buffer layer is partially monocrystallized and acts as a seed crystal for the GaN epitaxial layer. When there is no GaN buffer, the sapphire substrate itself becomes a seed crystal, so that hexagonal prism crystals of GaN with large variations in orientation grow.

As in the present invention, In _y Ga _1-y N (0 <y
≦ 1) is considered to be as follows when the case where the second buffer immediately above the first buffer is formed is compared with the case where only the conventional GaN buffer is used.

First, for example, y =
Considering the case of forming In _y Ga _1-y N of 0.15, the melting point of GaN is 1700 ° C. and the melting point of InN is 1100 ° C. Therefore, when In _y Ga _1-y N with y = 0.15 is used as the second buffer layer as compared with the first buffer layer of GaAs1N, the growth rate in the direction perpendicular to the film thickness direction is higher than that of GaN. Expected to be big.
The reason can be understood by considering the optimum growth temperature of the single crystal layer. There is a report that InN is about 550 ° C. in contrast to GaN, in which a high temperature of about 1100 ° C. is generally considered to be the optimum growth temperature. In the case of GaN at a low temperature of 550 ° C., a single crystal cannot be formed because condensed species adhere to the growth front, move on the substrate, and are taken into the solid layer in situ before reaching the kink or step. However, it can be interpreted that InN allows single crystal growth at such a low temperature because the movement of condensed species on the substrate is relatively fast. Further, since InN is easily decomposed, it means that even if it is In or N (form of whether it is in a primitive state or a radical is unknown), the time spent in the growth front is relatively long. That is, the growth rate component in the direction is sufficiently larger than that of GaN. On the other hand, the growth rate in the vertical direction of the wafer is slow. In GaN, the optimum growth temperature 11
Hexagonal columnar crystals are formed first even at around 00 ° C,
It is known that they grow and grow flat. From this, the growth rate ratio between the wafer in-plane direction and the vertical direction is different depending on the material.
It is sufficiently expected that the in-plane direction component is relatively larger than that.

Therefore, at the very early stage of growth nucleus supply, a flat growth front can be formed first. As a result, as a growth mode of, for example, a GaN epitaxial layer grown on the second buffer, the transition from island growth to two-dimensional growth is at a very early stage or
It is considered that two-dimensional growth can be realized from the beginning, and that there are advantages that a crystal with a very low dislocation density and few crystal defects can be obtained, and a large improvement in crystallinity can be realized. Can be

In order to confirm the above-mentioned prediction, In _y was formed as a second buffer layer immediately above the first buffer of GaN grown on a sapphire substrate at about 600 ° C. at about 50 nm.
A second buffer having a different In composition y of Ga _1-y N was grown so as to have a thickness of 20 nm, and a GaN epitaxial layer was grown thereon at 1100 ° C. with a thickness of 4 μn. The sample was subjected to melt KOH etching for 20 seconds and the density of the holes from the surface was measured by counting the number of hexagonal holes in a photograph of the same field taken using an optical microscope. Here, the number is called an etch pit density. Since the etch pit density is considered to be correlated with the density of crystal defects, it was selected as an index of crystallinity. A smaller amount corresponds to better crystallinity. FIG. 3 shows the relationship between the In composition of the second buffer layer and the etch pit density. Although y = 0 means GaN, it is included for comparison. However, when GaN is used for the second buffer, it is the same as in the case of only the first buffer. Also, Ga
In the case of only N buffer, holes were seen by microscopic observation without performing molten KOH etching, and when etching was performed, the whole surface of the wafer became uneven, and it became impossible to count the number of pits, so for reference only In parentheses.

As can be seen from FIG. 3, as the In composition increases, the etch pit density sharply decreases, and the crystallinity improves. Therefore, it was found that the above-described effects were obtained.

Next, Ga to be grown on the first buffer
A second buffer layer having a higher In composition was grown thicker (70 nm) immediately above N, and a GaN epitaxial layer was grown at 1100 ° C. with a thickness of 4 μn. However, contrary to willingness, the etch pit density was clearly increasing. If the In composition of the second buffer is increased, the crystallinity during the growth of the second buffer may be improved, but another phenomenon that the resistance at a high temperature of 1100 ° C. for performing GaN epitaxial growth is deteriorated. It seems that there is an optimal value in the struggle. Therefore, the preferred In composition of the second buffer layer is y =
It is desirable not to exceed 0.15.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the illustrated embodiments. However, the following examples illustrate a method for embodying the technical idea of the present invention, and the method of the present invention uses the following growth conditions, types of organometallic compound gases, and materials used. However, the present invention is not limited to this. Various modifications can be made to the crystal growth method of the present invention within the scope of the claims. FIG. 4 shows a schematic structure of the metal organic chemical vapor deposition apparatus used in this embodiment.
Reference numeral 43 denotes a reaction vessel made of quartz, which is configured to supply a raw material gas from a gas introduction pipe 45 and discharge the gas from an exhaust pipe 44. The graphite susceptor 42 is heated by a high-frequency heating coil 46, and the temperature of the susceptor 42 is W
It is measured and controlled by a thermocouple 47. The substrate 41 is placed directly on the susceptor 42 and is configured to be heated. A gallium nitride-based compound semiconductor crystal was grown using such a crystal growth apparatus.

(First Embodiment) An GaN epitaxial layer was grown to a thickness of 2 μm on a sapphire substrate in the following steps. The washed sapphire substrate 41 having a diameter of 50.8 mm is placed on the susceptor 42. After the inside of the quartz reaction vessel 43 is evacuated from the exhaust pipe 44 by a vacuum pump (not shown), the inside is further replaced with hydrogen. Thereafter, the susceptor 42 is heated by the high frequency heating coil 46 to 1060 ° C. at the indicated temperature of the thermocouple 47 while supplying hydrogen gas into the reaction vessel 43 from the reaction gas introduction pipe 45. This state is maintained for 10 minutes to increase the cleanliness of the surface of the sapphire substrate 41. Next, the temperature of the susceptor 42 is lowered to 500 ° C., and the process waits until the temperature is stabilized. Subsequently, a mixed gas of hydrogen and nitrogen is supplied from the gas introduction pipe 45, and an ammonia gas is supplied. The flow rates of the hydrogen gas and the nitrogen gas supplied from the gas introduction pipe 45 are 15.5 L / min and 5 L / min, respectively, and the flow rate of the ammonia gas is 9.5 L / min. Wait until it stabilizes at 500 ° C. Thereafter, in order to form a first buffer layer, a TMG (trimethylgallium) gas is supplied from the gas introduction pipe 45 at 3.7 × 10 ⁻⁵ mol / min for 4 minutes in addition to the ammonia gas.
Here, a GaN buffer layer having a film pressure of 50 nm was formed. Next, additional supply of TMI (trimethylindium) gas is started from the gas introduction pipe 45 to grow the second buffer layer. At this time, the TMI gas was 1.5 × 10 ^-4 mol / min and 1
Pour for minutes. Next, stop only TMG gas and TMI gas,
Stop the formation of the buffer layer. Here, In with a film pressure of 20 nm
A GaN buffer layer was formed. Further, while flowing other gases, the temperature of the susceptor 42 is increased by 10 at the indicated temperature of the thermocouple 47.
Raise to 00 ° C. After the indicated temperature of the thermocouple 47 rises to 1020 ° C., in addition to the ammonia gas and the hydrogen gas, a TMG gas is supplied at a flow rate of 1.4 × 10 ⁻⁴ mol / min for 60 minutes from the gas introduction pipe 45 to obtain GaN. An epitaxial layer is grown to a thickness of 2.0 μm. Thus, a GaN buffer layer having a thickness of 50 nm, an InGaN buffer layer having a thickness of 20 nm, and a GaN epitaxial layer having a thickness of 2 μm were further grown thereon.

(First Comparative Example) As a comparison of the first embodiment, a comparison with the following embodiment was made. That is, a 2.0 μm GaN epitaxial layer was grown on the GaN buffer layer in the same manner as in the first embodiment except that the second buffer layer was not formed.

After the growth, the hole measurement is performed at room temperature, and the GaN epitaxial layer according to the present invention and the G layer according to the first comparative example are measured.
The carrier concentration and mobility of the aN epitaxial layer were determined.

When a crystal with no addition is grown, the lower the carrier concentration and the higher the mobility, the better the crystallinity and the lower the impurity concentration. Ga according to the present invention
N has a carrier concentration of 3 × 10 ¹⁶ / cm ³ and a mobility of about 7
It shows a very good value of 00 ² / V · sec. On the other hand, the second
The GaN of the first comparative example, which did not use the buffer, had a carrier concentration of 2 × 10 ¹⁷ / cm ³ and a mobility of about 300 c
m ² / V · sec. The average dislocation density of the GaN according to the present invention is 8 × 10 ⁴ / cm ² ,
10 ⁸ / c obtained by GaN of the conventional method and the first comparative example
It can be seen that the value can be greatly reduced from the value of m ² or more. In addition, the Ga method of the conventional method and the first comparative example
In N, in the periphery of the wafer, where it is considered that the temperature distribution of the wafer cannot be avoided to some extent, many holes were thought to be generated due to deviation from the optimum temperature condition. In the case of GaN, no hole was found even without taking measures to improve the temperature distribution in the wafer surface, and it was concluded that the GaN had sufficient conditions for the problem of hole formation. Is done.

In the present embodiment, sapphire is used as a substrate material. However, the present invention is not limited to this. Even when silicon carbide, spinel, silicon or the like is used, only the conventional first buffer is used. It is confirmed by experiments of the present inventors that there is a remarkable difference as compared with the above, and that the effect is large.

(Second Embodiment) A laser diode was manufactured as follows using the conditions for growing GaN as described in the first embodiment. After lowering the growth temperature of the first buffer layer grown in the step of forming the buffer layer according to the first embodiment to a second temperature,
Is grown, the In buffer of the second buffer layer is grown.
When the composition becomes higher and the temperature is set higher, an InGaN buffer layer having a low In composition can be grown. In advance, the temperature at which the second buffer layer is grown is varied in various ways, and the optimum temperature is selected based on the surface morphology of the epitaxial GaN layer grown thereon, the mobility obtained by hole measurement, and the background carrier concentration as indexes. Was. FIG. 5 shows a process sectional view.

While supplying hydrogen from the gas inlet tube 45, the high-frequency heating coil 46 is energized to heat the sapphire substrates 41 and 501 placed on the susceptor 42, so that the thermocouple 47 indicates 1200.degree. Was adjusted. Less than,
The indication of the thermocouple 47 is simply called temperature. At this temperature 10
After the temperature was reduced to 600 ° C., the supply of TMG and ammonia gas was started when the temperature became stable.
The GaN buffer layer 502 was grown for 50 nm.
The temperature is reduced by 10 ° C. and the supply of TMI is added, and the second In
After growing the GaN buffer layer 503 to a thickness of 30 nm, the temperature was increased again to 1200 ° C.

Next, silane gas diluted with hydrogen and TM
G supply is started and the silicon-added n-type GaN layer
μm growth. Thereafter, by additionally supplying trimethylaluminum (hereinafter abbreviated as TMA), a silicon-added n-type GaAIN layer 505 was grown to 0.6 μm. T
The supply of MA was stopped, and the n-type GaN layer 506 was subsequently grown to 0.1 μm. After stopping the supply of TMG and silane, the temperature was lowered to 800 ° C.
TMG and TMI prepared by supplying MI and another system
Layer 5 composed of 7 pairs of multiple quantum wells using
07 was created. In the active layer, the quantum well layer has an In composition of 14%.
3.5 nm in thickness, and the quantum barrier layer is 3% in thickness with an In composition of 3%.
nm. After the supply of TMI was stopped, the temperature was returned to 1200 ° C., and biscyclopentadienyl magnesium (hereinafter abbreviated as Cp ₂ Mg) was obtained at a stable place.
Was supplied to grow a p-type GaN layer 508 to which magnesium was added by 0.1 μm. Then, additional TMA is supplied and p
A GaAIN layer 509 was grown to a thickness of 0.6 μm. Subsequently, the supply of TMA was stopped, and a magnesium-added p-type GaN layer 510 was grown to 1 μm as it was. Then, C
At the same time as the supply of p ² Mg was stopped, a silane gas diluted with hydrogen was supplied to grow n-type GaN 511 to 0.1 μm.

Thereafter, supply of TMG and silane gas was stopped, and power supply to the high-frequency heating coil 46 was stopped. When the temperature dropped to 350 ° C., the supply of ammonia was stopped.

The wafer obtained as described above is
A portion of the wafer is made into a magnesium-added p-type GaN layer 51 by reactive ion etching using O ² as a mask.
Digged to zero.

The following steps will be described with reference to FIG. After removing the SiO ₂ mask with hydrofluoric acid, it was once again introduced into the metalorganic vapor phase epitaxy apparatus. This time, heating was started by the high-frequency heating apparatus 46 while flowing ammonia, and when the temperature became stable at 1200 ° C. TMG and Cp ₂
Mg was supplied, but the amount of Cp ₂ Mg at this time was the same as that of the previously grown p-type GaN layer 510, and was first grown to 1 μm to grow the p-type GaN layer 61 to fill the dug hole.

Subsequently, ap ⁺ -type GaN layer 62 in which the amount of Cp ₂ Mg was suddenly increased to three times was grown. Thereafter, the supply of TMG was stopped, and the power supply to the high-frequency heating device 46 was stopped. When the temperature dropped to 850 ° C., the supply of ammonia was stopped. It was confirmed by cross-sectional electron microscope observation that the wafer obtained as described above had a structure as shown in FIG.

Further, the surface state of the outermost layer 62 was closely observed with the naked eye and an optical microscope, but no characteristic pattern such as a hole or undulation was observed. Next, as described above, n
Conditions are determined based on the distance to the n-type GaN layer 504, and a portion of the wafer is n-type G doped with magnesium by reactive ion etching using a metal mask.
It dug to the aN layer 504.

After attaching the mask, an alloy of Ti and Al for n-type was deposited. The SiO ² mask on the p ⁺ -type GaN layer 62 is removed with hydrofluoric acid, and the Pt and V are deposited by depositing a SiO ² mask on the alloy of Ti and Al on the n-type GaN layer 504. 8 after removing the SiO ² mask
By performing a heat treatment in a nitrogen atmosphere at 00 ° C. for 10 minutes, n
Ohmic electrode characteristics were obtained for both the p-type and the p-type.

The characteristics of the semiconductor laser fabricated as described above were measured at room temperature. As a result, it was confirmed that a current of 20 mA flowed under a voltage of 4.5 V and continuous oscillation was performed. In this state, the test was continued continuously, and the life until the operating current was doubled was measured. The total number of devices whose life was measured was 230, but the number of devices showing a life of 5000 hours was 212. If the method of the present invention was not used, many devices were formed on one sapphire substrate. Of these, only 30 elements continuously oscillate,
V, continuous oscillation at room temperature at 20 mA.
Significant progress was confirmed in comparison with only two elements having a long life.

As described above, according to the present embodiment, the operating voltage and the current value of the continuous oscillation of the laser at room temperature can be reduced, and the life can be drastically improved. Furthermore, no remarkable feature was observed in the characteristic distribution in the wafer plane, and it was also confirmed at the same time that it greatly contributed to an increase in the device yield.

(Third Embodiment) A laser diode was manufactured in the following manner under the conditions for growing GaN as described in the first embodiment. The second growth performed at the growth temperature of the first buffer layer grown in the step of forming the buffer layer according to the first embodiment.
The growth temperature was gradually changed to the growth temperature of the buffer layer, and the TMI that was not flown at the beginning was supplied in accordance with the temperature change, and the supply amount was gradually increased to change the TMI flow. That is, an epitaxial GaN layer was grown on a buffer layer having a portion where GaN gradually changed to InGaN without forming a clear interface between the first buffer layer and the second buffer layer. . In the subsequent steps, for example, the performance was evaluated by applying the semiconductor laser manufacturing process described in the second embodiment or the light emitting diode manufacturing process described in the fourth embodiment. was gotten. That is,
Strictly, even if the first buffer layer and the second buffer layer do not exist separately from each other, that is, even if a layer in which the In composition changes gradually is sandwiched, it is sufficient as long as each plays a role. The effect was obtained.

Fourth Embodiment In the third embodiment, the case where the boundary between the first buffer layer and the second buffer layer may be unclear has been described. A description will be given of a case where the same or more effect can be obtained even if there is another layer in a strict sense between the first buffer layer and the second buffer layer, or an extremely thin layer that can be called an altered layer. I do. In other words, in a broad sense, the same applies to rephrasing the uppermost portion of the first buffer layer. However, in various experiments conducted by the present inventors, monosilane gas was supplied at the final stage of the growth of the first buffer layer. By being introduced into the growth apparatus, the first buffer layer having a high Si concentration is provided over most of the first buffer layer where the Si concentration is hardly detectable (S only at the uppermost portion of the first buffer layer).
(Synonymous with forming a portion to which i was added) was also found to be more effective than when this portion was not introduced. This is interpreted as the result of the fact that the introduction of Si promoted the nucleation of the outermost surface of the first buffer layer and maximized the effect of flattening the second buffer layer grown thereon. doing.

(Fifth Embodiment) In the structure described in the first embodiment, the first buffer layer 502 is made of GaAl.
Although a structure with N was prepared, a surface state and device characteristics comparable to those when GaN was used for the first buffer layer were obtained.

(Sixth Embodiment) The semiconductor laser has been described as an example of a device to be manufactured. Next, a manufacturing process of a light emitting diode will be described. FIG. 4 is a schematic structural view of the metal organic chemical vapor deposition apparatus used for crystal growth. FIG. 7A shows a process sectional view.

The supply of hydrogen to the high-frequency heating coil 45 is started while supplying hydrogen from the gas introduction pipe 45, and the sapphire substrates 41 and 71 placed on the susceptor 42 are heated, and the thermocouple 4 is heated.
7 was adjusted to 1200 ° C. Hereinafter, the instruction of the thermocouple 47 is simply referred to as temperature. After maintaining at this temperature for 10 minutes, the temperature was lowered to 600 ° C., and when the temperature became stable, supply of TMG ammonia gas was started, and GaN was grown to 40 nm as the first buffer layer 72. Subsequently, TMI was additionally supplied to grow InGaN having an In composition of 10% as the second buffer layer 73 to a thickness of 20 nm. TMG
And the supply of TMI was stopped, and the temperature was raised again to 1200 ° C.

Next, silane gas diluted with hydrogen and TM
G supply is started, and the silicon-added n-type GaN
m. After stopping the supply of TMG and silane gas,
TMG and TMI after the temperature is lowered to 800 ° C and stabilized
Was supplied to form an InGaN multiple quantum well active layer 75. The supply of TMG and TMI was stopped, and the temperature was raised. The temperature was returned to 1200 ° C., and TMA and Cp ₂ Mg were supplied at a stable place to supply magnesium-added p-type GalN.
Layer 76 was grown 0.7 μm. After the supply of TMA is stopped and the p-type GaN layer 77 is grown, the supply of Cp ₂ Mg is then increased to directly add p ⁺ -type G with a large amount of magnesium.
The aN layer 78 was grown to 0.1 μm. Thereafter, supply of TMG and Cp ₂ Mg was stopped, and power supply to the high-frequency heating coil 46 was stopped. When the temperature dropped to 800 ° C., the supply of ammonia was stopped.

In this wafer, the outermost surface of the p ⁺ -type GaN layer 78 was observed with the naked eye and with an optical microscope, but no holes or characteristic patterns in the surface state were observed. Next, the n-type GaN layer 7 was observed from the outermost surface confirmed by cross-sectional electron microscope observation.
The etching conditions were determined on the basis of the distance up to 4, and a portion of the wafer was dug down to the n-type GaN layer 74 by reactive ion etching using a metal mask (FIG. 7).
(B)).

The next step will be described with reference to FIG.
Next, an alloy 79 of Ti and Al for n-type was deposited. The SiO ₂ mask on the p ⁺ -type GaN layer 78 is removed with hydrofluoric acid, a SiO ₂ mask is applied on the alloy of Ti and Al on the n-type GaN layer 74, and then Ti, Pt, and Au are removed. After depositing the laminated structure 80 and removing the SiO ₂ mask, 8
By performing a heat treatment in a nitrogen atmosphere at 00 ° C. for 10 minutes, n
Ohmic electrode characteristics were obtained for both the p-type and the p-type.

When the cross section of the semiconductor light emitting device prepared as described above was observed by an electron microscope, it was found that the thickness of each layer was as designed. Further, when the optical characteristics were measured, the peak of the emission wavelength was 420 nm, a voltage as low as 2.0 V was sufficient for applying a current of 20 mA, and the emission efficiency was as high as 13.4% in terms of external quantum efficiency. Efficiency was achieved. When the life test of this light emitting diode was performed at 40 mA, the failure rate after 1000 hours passed was 1% or less, and it was confirmed that the life was extended.

(Seventh Embodiment) In the above embodiments, only the case where sapphire is used as the substrate to be used has been described. Next, the case where the Si surface of the 6H-SiC substrate is used will be described. In this case, a better result was obtained when the composition x of the first buffer layer was closer to zero, that is, closer to AlN. However, in this case, instead of growing the second buffer layer as it is,
The present inventors have found that the key is to increase the temperature to around 00 ° C. to sufficiently nucleate the amorphous GaAlN before growing the second buffer layer. x is 1
In the case where the temperature is close to 0, such a high-temperature treatment is not required, so that the combination with the second buffer layer may not provide a sufficient effect. In the case where a 6H-SiC substrate is used, x is close to zero. It turned out to be more desirable.

(Eighth Embodiment) Next, a case where GaN is used as a substrate material will be described. Single crystal Ga
Although the N-substrate has attracted attention in recent years, a growth method characterized by a relatively high growth rate is adopted as the growth method.
Therefore, single crystal GaN has a dislocation density of 1 × 10 ³ cm
Substrates below ^-2 are very expensive or, at the very least, hardly available. That is, even when GaN having a normal dislocation density is used as the substrate material,
It has been clarified by a separate experiment conducted by the present inventors that the presence of the first buffer layer is desirable, and exhibits an effect of stopping the propagation of dislocations from the substrate.

When the manufacturing method as described above is employed, the yield of non-defective products is more than doubled as compared with the case of using the prior art as described in the first to eighth embodiments.

This is interpreted as a result corresponding to a marked improvement in the flatness of the outermost surface. In each of the embodiments described so far, some examples have been given as the p-type electrode material and the n-type electrode material. However, any electrode material and a heat treatment method exhibiting equal or higher ohmic properties and contact resistance values may be used. The present invention can be implemented with various modifications.

[0049]

As described above, by forming the second buffer layer immediately above the first buffer layer, the crystallinity of the gallium nitride-based compound semiconductor grown thereon is drastically improved. Therefore, in the semiconductor device manufactured by the method of the present invention, for example, the lifetime of the light emitting element can be significantly improved, particularly when the light emitting element is a laser.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a structure of an epitaxial wafer for explaining the gist of the present invention.

FIG. 2 is a cross-sectional view illustrating a structure of an epitaxial wafer for explaining a first comparative example and a conventional example.

FIG. 3 is a diagram for explaining the operation of the present invention, showing the relationship between the In composition of the second buffer layer and the etch pit density of the GaN epitaxial layer thereon.

FIG. 4 is a diagram for illustrating a manufacturing process of the semiconductor device according to the first to fourth embodiments, and is a diagram illustrating a schematic cross-sectional configuration of a metal organic chemical vapor deposition apparatus.

FIG. 5 is a diagram showing the first half of the manufacturing process of the semiconductor laser device according to the second embodiment.

FIG. 6 is a view showing the latter half of the manufacturing process of the semiconductor laser device according to the second embodiment, and is a cross-sectional view of the device for explaining a process following FIG. 5;

FIG. 7 is a view showing a manufacturing process of the semiconductor light emitting diode according to the fourth embodiment.

[Explanation of symbols]

11, 21 ... substrate 12, 22 ... first buffer layer _{Ga x A lx N (0 ≦} x
≦ 1) 13... Second buffer layer In _y Ga _1-y N (0 <y ≦
1) 14, 23: gallium nitride based semiconductor crystal 41, 501, 71: sapphire substrate 42: susceptor 43: reaction vessel 44: exhaust pipe 45: gas introduction pipe 46: high frequency heating coil 47: thermocouple 502, 72: first Buffer layers GaN 503, 73 ... second buffer layers InGaN 504, 74 ... n-type GaN (contact) layer 505 ... n-type GaAlN (cladding) layer 506 ... n-type GaN (guide) layer 507 ... active layer 508 ... p -type GaN (guide) layer 509 ... p-type GaAlN (cladding) layer 510,61,77 ... p-type GaN layer 511 ... n type GaN (blocks) layer 62 and 78 ... p ⁺ -type GaN (contact) layer 75 ... InGaN multiple Quantum well active layer 76: p-type GaAlN layer 79: n-type electrode 80: p-type electrode

Claims (3)

[Claims] 1. A GaN-based compound semiconductor device in which two or more buffer layers are provided on a substrate and a stacked structure composed of a GaN-based compound semiconductor layer is formed on the buffer layer. The buffer layer on the substrate side is composed of Ga _x Al ₁ -xN (0 ≦ x ≦ 1), and the buffer layer on the GaN-based compound semiconductor layer side of the laminated structure is In _y Ga
Ga constituted by _1-yN (0 <y ≦ 1)
N-based compound semiconductor device. 2. A reaction gas is supplied into a reaction vessel, a first buffer layer is grown on the substrate at a temperature of 800 ° C. or less, and a second buffer layer is grown on the first buffer layer. after a process for producing a GaN based compound semiconductor crystal is grown gallium nitride-based compound semiconductor device at 800 ° C. or higher, the first buffer layer Ga _x Al
A GaN-based compound semiconductor device represented by _1-xN (0 ≦ x ≦ 1) and wherein the second buffer layer is represented by In _y Ga _1-y N (0 <y ≦ 1). Manufacturing method. 3. The method of manufacturing a GaN-based compound semiconductor device according to claim 2, wherein the growth method is a vapor phase growth method using an organic metal.