JPS63186418A - Manufacture of compound semiconductor crystal layer - Google Patents

Abstract

PURPOSE:To enable the high substrate temperature to be made applicable by a method wherein, during MOCVD process for crystal growing, the cracking efficiency of phosphine applied for the material of phosphorus is improved by means of selecting the pressure in the reaction chamber. CONSTITUTION:A GaAs substrate 15 is arranged in a reaction furnace 11 to lead in group III material and group V material gas while heating the substrate 15 to growth-form an In1-x-yGaxAlyP layer (0<=x<=1, 0<=y<=1) on the substrate 15 by organic metal chemical vapor growing process. Phosphine is used as the group V material gas to be led in the reaction furnace 11 while specifying the pressure in reaction furnace to be 15-35 torr and the surface temperature of the substrate 15 to exceed 740 deg.C. By such a crystal growth, the upper limit growing temperature can be increased extending over all composition region of Al. Through these procedures, the InGaAlP in the high quality and the least defect can be grown.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Field of Application) The present invention relates to a method for growing and forming an InGaA or i7P layer by metal organic chemical vapor deposition (MOCVD), and particularly relates to a method for growing and forming an InGaA or i7P layer by a metal organic chemical vapor deposition method (MOCVD method). The present invention relates to a method for manufacturing a compound semiconductor crystal layer suitable for creating a compound semiconductor crystal layer.

(Prior Art) Single crystal 1nGaAnoP is an important material for obtaining short wavelength semiconductor lasers among the ■-V group compound semiconductors.

This material is produced using conventional liquid phase epitaxial method (LPE method).
In a quasi-plane growth method such as or vapor phase epitaxial method (VPE method), growth is virtually impossible because the segregation coefficient of A into the solid phase is extremely large. Therefore, recently, methods of growing the compound semiconductor crystal layer using methods such as molecular beam epitaxy (MBE) and MOCVD, which are considered to grow under conditions that are significantly deviated from the equilibrium state, have been studied.

In recent years, several room-temperature operations of semiconductor lasers using double hetero wafers grown by MBE or MOCVD have been reported. However, there are some major problems with the characteristics of these elements, as described below. The first is that the device life is short, on the order of several hundred hours, and the second is that although all devices use InGaP, which is lattice-matched to the GaAs substrate, as the active layer, the oscillation wavelength is LPE.
This is 20 to 40 nm longer than the value expected from the peak wavelength of photoluminescence of InGaP grown by the method, which is considered to be close to the ideal.

The first problem is caused by the high A composition InGaAl! used for the cladding layer! Crystal defects represented by hillocks, etc., which exist in high density in P, are considered. The second problem is due to the InGaP used as the active layer.
It is possible that the In and Ga components are incompletely mixed. However, no suitable means to solve these problems has been found so far, and therefore continuous operation at room temperature at the shortest wavelength of InGaAJP lasers is difficult.
It remains at a value that is not much different from 880 nm in a GaAlAs-based laser. This has been a major problem for realizing a long-life, short-wavelength semiconductor laser, which is the original purpose of using InGaAiP as a laser material.

(Problems to be Solved by the Invention) Conventionally, it has not been possible to eliminate the crystal defects existing in InGaAiP with a high A content and the incomplete mixing of In and Ga that constitute InGaP. It has been difficult to create a long-life semiconductor laser having an oscillation wavelength shorter than 650r+a+, which is expected from the original band gap.

The present invention has been made in consideration of the above-mentioned circumstances, and its purpose is to create an InGaA-P crystal with a theoretically expected band gap and ideal crystallinity.
It is an object of the present invention to provide a method for producing a compound semiconductor crystal layer that can be grown on a substrate with good reproducibility and is effective for producing a semiconductor laser with a short wavelength and long life.

[Structure of the Invention] (Means for Solving Problems) The gist of the present invention is to increase the decomposition efficiency of phosphine used as a raw material for phosphorus during crystal growth by MOCVD method by selecting the reaction chamber pressure, This makes it possible to use high substrate temperatures. In addition to this, G
The generation of crystal defects at the heterointerface was suppressed by devising the introduction procedure of the raw material gas when starting growth on the aAs substrate, and by setting the growth rate to a relatively large value, the structure during growth was improved. The reason is that the effect of re-evaporation of elements is reduced.

That is, the present invention provides GaAs in a reactor used for crystal growth.
A substrate is placed, gases of the group I raw material and the group V raw material are introduced into the reactor, the substrate is heated, and I n r two y Ga A is deposited on the substrate by organometallic chemical vapor deposition.
In a method for manufacturing a compound semiconductor crystal layer in which an IP layer (O≦X≦1.0≦x y y≦1) is grown and formed, phosphine is used as a group II raw material gas introduced into the reactor; Pressure inside 15-35
torr, and the surface temperature of the substrate is 740°C.
This is the method of setting as described above.

(Function) With the crystal growth method according to the present invention, the upper limit of the growth temperature can be raised over the entire composition range of A and ff. Therefore, it is possible to grow high quality InGaA nanoP with very few defects. Also, with this growth method, it is usually difficult to mix well In, Ga, A, i? Since these are ideally mixed, it is possible to grow InGaA-P having a band gap that matches the theoretical value, which has not been previously possible. Therefore, it becomes possible to create a semiconductor laser with a short wavelength and long life, which was previously impossible.

(Example) First, before describing an example, the basic principle of the present invention will be explained.

The present inventors used methyl as a raw material for growth using the MOCVD method.
3), various experiments have been repeated to form InC1aA and i2P on a GaAs substrate. As a result, I nG
It has been found that the bandgap value of aAnoP varies significantly depending on the growth conditions, especially the growth temperature, even when the mixed crystal composition is the same. FIG. 2 shows the substrate temperature dependence during the growth of InGaA-P which is lattice matched to GaAs and has been discovered by the present inventors. From this figure, it can be seen that there is a growth temperature at which the bandgap value is minimum, and LPE
Wide bandgap (1,9
It can be seen that there are two ways to obtain a crystal with a voltage of 1oV, one is to raise the substrate temperature, and the other is to lower it.

In addition, other research institutes have recently found that the bandgap of InGaP grown on a single GaAs plate by the MOC:VD method changes depending on the supply amount of PH3, which is a group V raw material.
It has been reported that when the amount of H3 supplied is reduced, the bandgap tends to become wider.

However, according to research by the present inventors, when growth is performed in a low temperature region or with a reduced amount of phosphine supplied, the photoluminescence efficiency is particularly low for In containing A).
Since the temperature decreases extremely in the case of GaA and i'P, it is difficult to expect a highly efficient light emitting device to be realized in this temperature range. In addition, in high-temperature regions, the evaporation of phosphorus, a volatile component, becomes intense, and the concentration of phosphine, a raw material for phosphorus, in the mixed raw material gas in the reaction chamber, which is required to suppress this, becomes extremely large. Until now, it has been difficult to grow crystals of good quality. Furthermore, the cladding layer of the laser is InGaAl! with a high A composition! Although P is required,
When grown using conventional methods, many defects, such as hillocks, are observed on the surface of the resulting crystal, which poses a major problem in improving the reliability of devices.

However, according to further intensive research and experiments by the present inventors, it has been found that the optimal growth temperature range is not absolute, and that the following growth conditions Under these conditions, it is possible to raise the upper limit of the substrate temperature that can be grown significantly higher than before, and under these conditions, it is possible to achieve good surface morphology and crystallinity, and a band gap equal to the theoretically expected value. InGaAJ! It has been found that P can be grown over the entire composition range of A.

■ Phosphine is used as the group material.

(2) Set the reaction chamber pressure during growth to 15 to 35 torr.

(2) Set the surface temperature of the GaAs substrate during growth to 740°C or higher.

■ Set the growth rate to a regular value rather than 2 μm/h.

(2) The time during which the surface of the GaAs substrate is exposed to the adjacent vapor, which is a group (2) source gas, is kept to 1 second or less.

Here, high-quality InGaA has a PL half-width and a PL wavelength close to the theoretical value, and has a very low surface defect density.
The reason why JP crystals can be grown is that the growth temperature can be made much higher than conventional ones, and the reason why such a high substrate temperature can be adopted is because the reaction chamber pressure is lower than usual at 15 to 35 This is because the phosphine decomposition efficiency was increased by setting the torr (■ to ■). moreover,
By setting the growth rate to a relatively fast value, the effect of crystal re-evaporation is reduced, and by limiting the exposure time of the GaAs substrate surface to phosphorus, which is the constituent element of the longest layer, within a certain value. This is due to suppressing the deterioration of the substrate surface before the start (■, ■).

FIG. 2 shows the relationship between the band gap and substrate temperature of InGaP grown on a GaAs substrate by the growth method according to the present invention over a wider growth temperature range than conventional ones. From this figure, it can be seen that a crystal having approximately the same band gap as InGaP obtained by the LPE method can be obtained at a substrate temperature of 740° C. or higher. Furthermore, FIG. 3 shows the relationship between the hillock density on the surface of InAiP grown on a GaAs substrate and the substrate temperature. From this figure, it can be seen that the defect density suddenly decreases when the substrate temperature is 730° C. or higher.

Therefore, by using a growth temperature range of 740°C or higher, where high-quality crystals could not be grown in the past due to the reasons mentioned above, it is possible to grow InGaP with a wide bandgap comparable to that of the LPE method, which could not be grown with the conventional MOCVD method. and has a high A1 composition up to InAiP.
It can be seen that it is possible to grow crystals with extremely few defects using GaAiP.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing a growth apparatus used in an embodiment of the present invention. In the figure, reference numeral 11 denotes a quartz reaction tube (reaction furnace), into which a raw material mixed gas is introduced from a gas inlet 12.

The gas within the reaction tube 11 is then exhausted from the gas exhaust port 13. A carbon susceptor 14 is arranged inside the reaction tube 11, and the GaAs substrate is placed on this susceptor 14. In addition, the susceptor 14
is heated by induction by a high frequency coil 16.

Next, a crystal growth method using the above apparatus will be explained.

First, the surface of GaAs was cleaned by chemical etching.
A substrate 15 is placed on the susceptor 14. High-purity hydrogen is introduced from the gas introduction tube 12 at 11 times per minute to replace the atmosphere inside the reaction tube 11. Next, the gas exhaust tube 13 is connected to a rotary pump, the pressure inside the reaction tube 11 is reduced, and the internal pressure is set in the range of 15 to 35 torr. Thereafter, 10% arsine gas is introduced from the gas inlet 12, and the susceptor 14 and substrate 15 are heated by the high frequency coil 16 and held at the growth temperature for 30 minutes to clean the substrate.

Next, after stopping the introduction of arsine and starting the introduction of phosphine gas, there was a pause of about 1 second in order to sufficiently replace the arsine in the reaction tube 11, and then TMA, TMG, which had been adjusted to a predetermined mixing ratio in advance, Grow by introducing TMI. At this time, dimethylzinc (DM
Z ) or cyclopentagenylmagnesium (C
p2Mg).

Hydrogen selenide (H2S e ) r Silane gas (
SiH4) etc. are introduced at the same time. The surface temperature of the removed substrate was measured using a radiation thermometer calibrated based on the eutectic temperature of silicon and aluminum.

FIG. 3 shows InAiP grown by such a procedure.
This figure shows the relationship between surface defect density and substrate temperature. From this figure, it can be seen that the defect density decreases as the substrate temperature increases. In addition, the defect density decreases as the A1 composition decreases, so in order to grow crystals with a defect density of less than 1000 per square centimeter required for device fabrication over all A1 compositions, the growth temperature must be 740°C. It turns out that the above settings need to be made.

FIG. 4 shows the relationship between growth temperature, PL, and characteristics of InGaP lattice-matched to a GaAs substrate. From this figure and the above-mentioned figure 2, in order to grow InGaP having a band gap that almost matches the theoretical value, a narrow half-width PL spectrum, and high luminous efficiency, the substrate temperature must be increased to 74°C.
It can be seen that it is necessary to set the temperature above 0°C. Furthermore, FIG. 5 shows the relationship between the mobility of a p-type 1nA node lattice-matched to a GaAs substrate and the substrate temperature. This figure shows that the hole mobility of InAiP decreases as the substrate temperature decreases. Furthermore, the mobility decreases as the A, & composition increases, so in order to grow crystals with high mobility over the entire composition range of A, it is necessary to set the substrate temperature to 700°C or higher. It turns out that there is. In particular, wide bandgap, high luminous efficiency, high A, f? It can be seen that a substrate temperature of 740° C. or higher is required to create a laser material that requires high mobility and low defect density in the composition range.

On the other hand, in order to grow InGaAfP at a high substrate temperature, it is necessary to grow the crystal in an atmosphere with a P partial pressure higher than the vapor pressure of InGaAfP, which inevitably requires a large amount of phosphine, which is a PR material. However, the actual PH3 flow rate that can be supplied is usually limited to about 10% of the total flow rate. Furthermore, the decomposition efficiency of PH3 depends on the pressure within the reaction chamber, and generally the lower the pressure, the higher the decomposition efficiency, that is, the utilization efficiency.

Figure 6 shows the PH'3 of InGaAfP, which is difficult to obtain the best morphology.
This figure shows a schematic relationship between the upper limit of the substrate temperature at which a crystal with good morphology can be grown and the reaction chamber pressure when the flow rate is 10% of the total flow rate. From this figure, it can be seen that in order to grow InGaA nanoP at a substrate temperature of 740° C. or higher, it is necessary to set the reaction chamber pressure to 15 to 35 torr. Good morphology cannot be obtained when the reaction chamber pressure is below 15 torr because of the P supplied into the reaction chamber.
This seems to be because the partial pressure of H3 becomes too low.

At a substrate temperature of 740°C or higher, which is required to grow InGaAfP with good crystallinity, the Ga substrate
Since the surface of As rapidly decomposes, in order to achieve good crystal growth, the substrate must be kept in an arsenic atmosphere until immediately before the start of growth in order to prevent deterioration of the substrate surface when the temperature rises. On the other hand, at the start of growth, the arsenic raw material in the reaction chamber must be completely replaced with phosphine, which is a phosphorus raw material, in order to prevent arsenic from being mixed into the growth layer. Although it is impossible to completely satisfy these two contradictory requirements, according to research by the present inventors, there is a certain tolerance value for the time that the GaAsM plate surface is exposed to PH3, and the substrate It has been found by X-ray diffraction of the grown layer that when the temperature is 740° C. or more and 800° C. or less, growth can be started within 1 second after introducing phosphine into the reaction chamber as described above.

Furthermore, at a substrate temperature of 740°C or higher, I
Since the re-evaporation rate of n cannot be ignored compared to the growth rate, the distribution of the growth rate within the wafer plane causes a distribution in the composition of the epitaxial layer. This effect becomes more pronounced as the growth rate decreases. Normally, the growth rate within a wafer varies by about ±10%, and the width of the composition distribution corresponding to the growth rate distribution is as shown in FIG. 7 when the substrate temperature is 740°C.

At this time, it can be seen that the growth rate must be set to 2 μm or more each time in order to suppress lattice mismatching due to fluctuations in the growth rate to within ±0.05, which is required for device fabrication over the entire wafer surface. Further, the adoption of this relatively fast growth rate is also important from the viewpoint of quickly covering the surface of the GaAs substrate with an epitaxial layer at the start of growth to suppress evaporation of As from the surface of the U plate.

As described above, according to the method of this embodiment, TM
Using A, TMG, and TMI, and using phosphine and arsine as group V raw materials, the pressure in the reaction chamber was set to 15 to 35.
Torrs substrate temperature 740℃ or higher, growth rate 2μm
/h, and by quickly replacing the raw material gas in the reaction chamber and starting growth, we have a large bandgap that matches the theoretical value, high mobility, and good luminous efficiency, and an extremely low defect density. High quality InGaAl! P can be grown and is extremely effective for manufacturing semiconductor lasers and the like.

In addition, the present inventors produced a semiconductor laser in the following manner using the method described in Example 2, and obtained very good results. That is, carrier concentration 3 x LO18
On the (100) plane of a St-doped GaAs substrate with a cT of 1°3, the substrate temperature was 750'C, the reaction tube internal pressure was 25 torr,
Growth rate 3 μn/h, flow rate in reaction tube 70 cIi/sec
By the above method, the film thickness was 0.5 μm and the carrier concentration I
177 layers of Si-doped G' a A s bar of X 10I8n-3, film thickness 1 μm, carrier concentration l×1018α°
3, St-doped 1nA, gP cladding layer, film thickness 0.07
Undoped 1nGaP active layer of μm, thickness 1um, Mg-doped InAiP with carrier concentration I x 1018-3
Cladding layer, film thickness 0.5μ side, carrier concentration 7×1O1
A Mg-doped GaAs:I intact layer of 8c11-3 was prepared. At this time, after the growth of each layer, the growth is interrupted for 30 seconds until the next layer is grown, but the interruption time is 4 seconds.
When the time was 5 seconds or more, good growth could not be achieved. Using the double hetero wafer grown in this way, 5
When we prototyped a current confinement laser using i02, the wavelength at room temperature was found when the cavity length was 250 μm and the stripe width was 16 μm.

055 layer m as the oscillation threshold current and current density, respectively.
, 80a+A, 2 KA/atr 2 is obtained, and the device is at room temperature.

It operated stably for more than 1000 hours at an optical output of 3 mW. This result shows that a semiconductor laser with the shortest wavelength reported so far can be produced by the method according to the present invention, and this also proves the usefulness of the present invention.

Note that the present invention is not limited to the method of the embodiment described above. For example, the substrate surface temperature during growth may be 740°C or higher, but a more desirable range is 745-755°C.
It is. Further, the plane orientation of the substrate is not limited to the (100) plane, and may be inclined from the (100) plane. Furthermore, organic metals other than methyl may be used as the group (1) raw materials. In addition, various modifications can be made without departing from the gist of the present invention.

[Effects of the Invention] As detailed above, according to the present invention, the decomposition efficiency of phosphine used as a raw material for phosphorus is increased by selecting the reaction chamber pressure (15 to 351 orr), and the high substrate temperature (
740℃ or higher), it has the theoretically expected band gap and ideal crystallinity.
An nGaAiP crystal can be grown on a GaAs substrate with good reproducibility, and is extremely effective for producing short wavelength, long-life semiconductor lasers.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing a growth apparatus used in a method according to an embodiment of the present invention, and FIG.
l! A characteristic diagram showing the relationship between the substrate surface temperature and band gap of P.
A characteristic diagram showing the relationship between the substrate surface temperature of P and the surface defect density; FIG. Figure 5 is a characteristic diagram showing the relationship between hole mobility and substrate surface temperature for InA and i7P, which are lattice-matched to a GaAs substrate, and Figure 6 is a characteristic diagram showing the relationship between the substrate surface temperature and the substrate surface temperature for InAJP, which is lattice-matched to a GaAs substrate. FIG. 7 is a characteristic diagram showing the relationship between the upper limit and the pressure in the reaction chamber, and FIG. 7 is a characteristic diagram showing the relationship between the distribution width of lattice mismatch of InGaP from the GaAs substrate and the growth rate within the wafer plane. 11... Reaction tube, 12... Gas inlet, 13...
Gas exhaust port, 14... Susceptor, 15... Sample substrate, 16... High frequency coil, 17... Thermocouple. Figure 1 - Sakatsukuda ≦ (6) Load

Claims (5)

[Claims] (1) A GaAs substrate is placed in a reactor used for crystal growth, gases of group III raw materials and group V raw materials are introduced into the reactor, and the substrate is heated, and metal-organic chemical vapor phase growth is performed on the substrate. By law In_1_−_x_−_yGa_xAl_y
In a method for manufacturing a compound semiconductor crystal layer in which a P layer (0≦x≦1, 0≦y≦1) is grown and formed, phosphine is used as a group V raw material gas introduced into the reactor, and the pressure in the reactor is A method for manufacturing a compound semiconductor crystal layer, characterized in that the surface temperature of the substrate is set to 15 to 35 torr, and the surface temperature of the substrate is set to 740° C. or higher. (2) The compound semiconductor crystal layer according to claim 1, wherein the surface temperature of the substrate is 745 to 755°C, and the growth rate of the compound semiconductor crystal layer is faster than 2 μm/h. Production method. (3) Before the growth and formation of the compound semiconductor crystal layer, an arsenic raw material gas is introduced into the reactor containing the substrate, and the substrate is heated to the substrate temperature at the time of growth in an atmosphere containing arsenic. , the introduction of the arsenic raw material gas is stopped, and then, within 1 second after the introduction of the arsenic raw material gas is stopped, a group III raw material gas is introduced into the reactor to start growth. A method for manufacturing a compound semiconductor crystal layer according to item 1 or 2. (4) When growing the compound semiconductor crystal layer, V
Claims 1, 2, or 3 are characterized in that phosphine and arsine, which are not predecomposed, are used as Group III source gases, and trimethylaluminum, trimethylgallium, and trimethylindium are used as Group III source gases. A method for manufacturing a compound semiconductor crystal layer. (5) The method for manufacturing a compound semiconductor crystal layer according to claim 4, wherein a vertical reactor is used as the reactor.