JP2861199B2 - Vapor phase growth of compound semiconductor crystals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention relates to a method for producing a high-concentration carbon-doped compound semiconductor crystal such as GaAs, AlGaAs, or the like by metal organic chemical vapor deposition.
The present invention relates to a method for vapor-phase growing an IV group compound semiconductor crystal.

(Prior art) Metal-organic vapor phase epitaxy (OMVPE) is a method in which an organometallic compound and a metal hydride are thermally decomposed in a reaction furnace.
This is a method of growing a single crystal of a thin film on a substrate. This method is used for manufacturing a heterojunction device wafer using a compound semiconductor because it is easy to form an ultra-thin multilayer structure and has high mass productivity. In particular, among heterojunction devices, heterobipolar transistors (HB
T) works very fast, so it's being actively developed.

HBT is a collector of n-GaAs, a base of P ⁺ -GaAs, n
-Consists of an AlGaAs emitter. As shown in FIG. 3, the structure of the HBT is such that a collector layer of n ⁺ -GaAs and an n-GaAs layer is laminated on a semi-insulating or conductive GaAs substrate, and a base layer of the p ⁺ -GaAs layer is further formed. The pn junction is formed between the p ⁺ -GaAs layer and the n-AlGaAs layer by laminating an n-AlGaAs layer and an emitter layer of an n-GaAs layer thereon. The collector electrode is formed on the n ⁺ -GaAs collector layer, the base electrode is formed on the p ⁺ -GaAs base layer, and the emitter electrode is formed on the n-GaAs emitter layer. The characteristics of such a HBT, the more excellent characteristics high hole concentration in the base layer of p ⁺ -GaAs is obtained, p ⁺ -GaAs
The steeper the interface of the pn junction between the base layer and the n-AlGaAs emitter layer, the more excellent characteristics are obtained.

Conventionally, zinc (Zn) has been used as a p-type dopant in the OMVPE method. However, since zinc has a large diffusion coefficient, diffusion from the base region to the emitter region during growth cannot be avoided, and a sharp pn junction is formed. There was a problem that can not be obtained.

1 × 10 ²⁰ cm for molecular beam epitaxy (MBE)
^Although Be that can be doped to about ^{−3 and} has a small diffusion coefficient is generally used, it is difficult to use Be with the OMVPE method from the viewpoint of safety. Therefore, Mg whose diffusion coefficient is about five orders of magnitude smaller than that of zinc has been studied as a dopant. However, Mg raw material biscyclopetadienyl magnesium (Cp ₂ Mg) and bismethylcyclopentadienyl magnesium (M ₂ Cp ₂ Mg)
Since it is adsorbed on the inner wall of the pipe or the reaction tube at room temperature, even if the supply of the Mg raw material to the reaction tube is started, the doping amount to the compound semiconductor is not constant until the adsorption on the inner wall is saturated, and Even after the Mg source is switched from the reaction tube to the exhaust pipe, Mg is continuously doped because the Mg source adsorbed on the inner wall of the pipe or the reaction tube is gradually desorbed and carried to the substrate crystal surface. Therefore, when forming a p-type compound semiconductor by doping with Mg, there is a problem that a steep doping profile cannot be obtained.

Therefore, recently, carbon doping has been studied. For example, J. Appl. Phys. Vol. 64, No. 8, p. 3975-3979,
In K. Sato et al., About 10 ²⁰ cm ⁻³ of carbon doping is performed by gas source MBE using trimethylgallium (TMGa) as a group III raw material and metallic arsenic as a group V raw material.

Appl.Pyhs.Lett.Vol. 53, No. 14, p. 1317-1319,
In TF Kuech et al., Metal-organic vapor phase epitaxy
Using TMGa as the group I material and TMAs as the group V material, with a growth pressure of 76 Tor
It is reported that the maximum value of the carbon doping amount was 2 × 10 ¹⁹ cm ⁻³ when growing carbon-doped GaAs at a growth temperature of 600 ° C. at r.

(Problems to be Solved by the Invention) When growing carbon-doped GaAs using TMGa and TMAs as raw materials under the conventional growth conditions by the OMVPE method, TMGa or TMAs
The doping amount of carbon can hardly be changed even if the flow rate of the carbon is changed. Therefore, the doping amount is controlled by changing the growth temperature. For example, Appl.P above
hys. Lett. Vol. 53, No. 14, p. 1317-1319, TF Kuech et a
In l., the growth pressure is 76 Torr and the growth temperature is 600-700 ° C.
By raising the are reported the hole concentration of 10 ¹⁹ cm ^-3 and is varied to 10 cm ^-3. This growth temperature control method has no problem when growing a single-layer epitaxial layer.However, when growing multiple layers having different carbon doping amounts, the growth is interrupted between layers and the growth takes a long time. There was a problem that the temperature had to be changed.

An object of the present invention is to solve the above problems and to provide a vapor phase growth method capable of controlling the carbon doping amount in a wide range without changing the growth temperature.

(Means for Solving the Problems) The present invention provides a method for metalorganic vapor phase epitaxy of a group III-V compound semiconductor, in which carbon is doped with an organic metal compound as a group V raw material, and the growth pressure is 1 to 5. This is a vapor phase growth method characterized by controlling the doping amount of carbon by changing the total gas flow rate to 40 Torr and a growth temperature of 625 ° C. or less.

(Action) It is considered that carbon doped into GaAs using TMGa and TMAs as raw materials is incorporated into the crystal in a form in which carbon of a methyl group of TMGa and TMAs is bonded to gallium or arsenic. When using conventional TMGa and AsH ₃ as raw materials, As
Since the hydrogen atom the amount _of H ₃ can be decomposed becomes bound methane with methyl group of TMGa, but carbon was thought unlikely to be doped, in fact, the carbon fixed amount this case is incorporated into the crystal Have been. Looking at this reaction in more detail, TMGa reacts with hydrogen atoms generated from AsH ₃ in the gas phase, and the methyl groups are removed one by one and adsorbed on the GaAs substrate in the form of monomethylgallium. It is considered that gallium and carbon are incorporated into the crystal. Therefore, As
The higher the concentration of hydrogen atoms generated from H _3, the lower the uptake of carbon. This is why carbon contamination is generally reduced by increasing AsH ₃ . Further, when TMAs is used as a raw material, it is considered that the reason why a large amount of carbon is incorporated into the crystal is that there is no hydrogen atom generated from AsH ₃ . Also, it is considered that the doping amount of carbon increases as the growth temperature decreases, but at low temperatures, the decomposition of TMGa and TMAs is slow, and the probability of reaching the substrate in the form of monomethylgallium and monomethylarsenic increases.

The present inventors have found that the decomposition of the organometallic compound is 1 to 40 Torr.
Under such a low growth pressure, it is considered that the total gas flow rate used for the growth is also affected. This is because changing the total gas flow rate while keeping the growth pressure constant changes the gas flow rate,
This is because the retention time of the organometallic compound as the raw material on the substrate surface changes, and the rate of decomposition of the organometallic compound also changes. Normally, the change in the total gas flow rate does not significantly change the growth rate, but in carbon doping, the generation probability of monomethylgallium is considered to have a dominant effect on the carbon doping amount. It was thought that the carbon doping amount could be greatly changed by the above. The experiment was repeated on the dependence of carbon doping on the total gas flow rate, and it was found that the carbon doping amount could be controlled by the total gas flow rate.

(Example 1) The pressure in the reaction tube was maintained at 10 Torr, and TM was previously introduced into the reaction tube.
With As flowing, a semi-insulating GaAs substrate is grown at 575 ° C.
After that, TMGa and TMAl were introduced into the reaction tube, and Al _0.1 G
The growth of a _0.9 As epitaxial layer was started. At this time, TM
The molar ratio of As to TMGa was set to 6.8, the flow rate of TMGa was set to 6.7 ml / min, the flow rate of TMAl was set to 3.5 ml / min, and the epitaxial layer was grown until the thickness became 3 μm. Then, TMGa and TM
The growth was terminated by switching the Al to the exhaust pipe and returning the substrate temperature to room temperature. Meanwhile, the total gas flow rate was 500,350,250sccm
Was changed. The Hall effect measurement was performed at room temperature on the grown Al _0.1 Ga _0.9 As epitaxial layer, and the obtained hole concentration is shown in FIG. Hole concentration is 500s for total gas flow
1.2 × 10 ²⁰ cm ^{-3 at} ccm to 4.0 × at 250 sccm
It was possible to greatly change to 10 ¹⁸ cm ^-3 .

(Example 2) The pressure inside the reaction tube was maintained at 10 Torr, and the total gas flow rate was 500 scc.
In this state, TMAs was flowed into the reaction tube in advance, and the semi-insulating GaAs substrate was heated to a growth temperature of 575 ° C.
was introduced into the reaction tube, and the growth of the Al _0.1 Ga _0.9 As epitaxial layer was started. At this time, the molar ratio of TMAs and TMGa was 6.8, the flow rate of TMGa was 6.7 ml / min, and the flow rate of TMAl was 3.5 ml / m
in. Then, after growing the epitaxial layer to a thickness of 1 μm, the total gas flow rate was changed to 250 sccm, and a 1 μm epitaxial layer was grown. Continuous growth was performed without providing a growth interruption between the first layer and the second layer. Thereafter, TMGa and TMAl were switched to the exhaust pipe, the substrate temperature was returned to room temperature, and the growth was terminated.

The carbon concentration of the grown Al _0.1 Ga _0.9 As epitaxial layer
The measurement was performed by the SIMS measurement method, and the results are shown in FIG. As is clear from the figure, the carbon concentration of the first layer when the total gas flow rate was 500 sccm was 1.2 × 10 ²⁰ cm ⁻³ , and the total gas flow rate was 250 sccm.
The carbon concentration of the second layer was 4 × 10 ¹⁸ cm ⁻³ , and both showed a uniform profile in the depth direction. This indicates that the amount of carbon doping can be easily controlled by changing the total gas flow rate.

In this embodiment, two hydrogen lines are provided and one of them is turned on / off to control the total gas flow. However, if the flow is changed in a short time even with one hydrogen line, any hydrogen line can be used. Can be obtained. Further, if the total gas flow rate is gradually changed with time, an arbitrary hole concentration profile can be formed.

(Effect of the Invention) According to the present invention, by adopting the above configuration, in carbon doping using an organometallic compound as a group V raw material, the carbon doping can be easily performed by changing the total gas flow introduced into the reaction tube. The amount can be controlled.
According to this method, the hole concentration can be controlled without interrupting the growth due to the change of the growth temperature, so that the operation can be controlled in a short time with a simple operation. There is no fear that unnecessary impurities or defects are introduced into the interface, and a good interface can be obtained.
This greatly contributes to improving the quality of the epitaxial layer.

[Brief description of the drawings]

FIG. 1 is a diagram showing a change in hole concentration of an AlGaAs epitaxial layer when the total gas flow rate is changed in Example 1. FIG. 2 is a diagram showing a hole concentration of an AlGaAs epitaxial layer in Example 2 in a depth direction. Diagram showing profile, Fig. 3 shows HBT
FIG.

 ──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-63-143810 (JP, A) JP-A-1-259524 (JP, A) JP-A-1-320297 (JP, A) Appl. Phys. Lett. 53 (14) 1988-10-3, pp. 1317-1319

Claims (3)

(57) [Claims] In a metal organic chemical vapor deposition method of a III-V compound semiconductor, when doping carbon with an organic metal compound as a group V raw material, the growth pressure is 1 to 40 Torr and the growth temperature is 625 ° C. or less. Wherein the doping amount of carbon is controlled by changing the total gas flow rate. 2. The method according to claim 1, wherein said group III-V compound semiconductor is GaAs, said group III raw material is trimethylgallium or triethylgallium, and said group V organometallic compound is trimethylarsenic. Vapor phase growth method. 3. The group III-V compound semiconductor is AlGaAs, the group III raw material is trimethylgallium or triethylgallium and trimethylaluminum, and the group V organometallic compound is trimethylarsenic. Item (1).