JPH03208890A - Vapor growth method for compound semiconductor crystal - Google Patents

Abstract

PURPOSE:To allow the easy control of the doping rate of carbon over a wide range by doping the carbon to an org. metal compd. by simultaneously using a group V hydrogen compd. and executing the doping while controlling the flow rate of the group V hydrogen compd. at the time of the vapor growth of the above III-V compd. semiconductor. CONSTITUTION:The doping of the carbon by using the org. metal compd. as a group V raw material in the org. metal vapor growth of the III-V compd. semiconductor is executed in the following manner: Namely, the group V hydride is simultaneously supplied and the doping rate of the carbon is controlled by controlling the flow rate of the group V hydride. The concn. of holes can be controlled by changing the flow rate of the group V hydride, for example, AsH3, to be added in the case of the growth of multilayered epitaxial films of different concns. of holes in the above-mentioned method and, therefore, there is no need for interrupting the growth. Not only the saving of the time is thereby resulted but also unnecessary impurities and defects are hardly introduced into the boundary during the interruption of the growth. The good boundary is thus obtd. and the quality of the epitaxial layers is effectively improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is directed to the production of carbon-doped compound semiconductor crystals such as GaAs, AlGaAs, etc. by organometallic vapor phase epitaxy.
-Relates to a method for vapor phase growth of group II compound semiconductor crystals.

(Prior Art) Organometallic vapor phase epitaxy (OMVPE) is a method of growing a thin single crystal film on a substrate by thermally decomposing an organometallic compound and a metal hydride in a reactor. This method is used to fabricate wafers for heterojunction devices using compound semiconductors because it is easy to form an ultra-thin multilayer structure and has high mass productivity. In particular, among heterojunction devices, hetero bipolar transistors (
HBT) is being actively developed because it operates at ultra-high speed.

The HBT consists of an n-GaAs collector, a p''-GaAs base, and an n-AlGaAs emitter.

As shown in FIG. 4, the structure of the HBT consists of laminating an n''-GaAs collector layer on a semi-insulating or conductive GaAs substrate, and further laminating a base layer of an n-GaAs layer and a pGaAs layer. Further, an emitter layer of an n-AlGaAs layer and an n-GaAs layer is laminated thereon, and the p'-G
A pn junction is formed between an aAs layer and an n-AlGaAs layer. And the collector electrode is n”-GaA
The base electrode is formed on the s-flexor layer, the base electrode is formed on the p''-GaAs base layer, and the emitter electrode is formed on the n-GaAs emitter layer.
)”-GaAs base layer has a higher hole concentration, better properties can be obtained, and p”-GaAs base layer and n-AlG
The steeper the pn junction interface between the aAs emitter layer and the ivy layer, the better the characteristics.

Conventionally, zinc (Zn) was used as a p-type dopant in the OMVPE method.
) was used, but since zinc has a large diffusion coefficient,
There is a problem in that diffusion from the base region to the emitter region cannot be avoided during growth, making it impossible to obtain a steep pn junction.

In molecular beam epitaxial layer (MBE method), 1×10”
It is possible to dope to the extent of am-', and
Generally, e with a small diffusion coefficient is used, but O
From the viewpoint of safety, it is difficult to use Be in the MVPE method. Therefore, Mg, whose diffusion coefficient is about five orders of magnitude smaller than that of zinc, is being considered as a dopant. However, Mg raw materials such as biscyclopentagenylmagnesium (CptMg) and bismethylcyclopentagenylmagnesium (MtCPzMg) are adsorbed on the inner walls of pipes and reaction tubes at room temperature, so it is difficult to supply Mg raw materials to the reaction tube. Even after starting, the amount of doping to the compound semiconductor does not become constant until adsorption on the inner wall is saturated, and even after switching the Mg raw material from the reaction tube to the exhaust pipe, adsorption on the inner wall of the piping and reaction tube continues. The Mg raw material is gradually desorbed and transported to the substrate crystal surface, so that Mg is continuously doped. Therefore, when trying to form a p-type compound semiconductor by doping Mg, there is a problem that a steep doping profile cannot be obtained.

Therefore, carbon doping has recently been considered.

For example, 19 people 1) pl, Phys, Vol, 6
4°No, 8. p, 3975-3979. 5ait
o et al, by the gas source M HE method ■
Trimethyl gallium (TMGa) is used as the group raw material, and metal arsenic is used as the group (2) raw material, and carbon doping is performed at a concentration of about 10"cm-3.

Also, ^Pp1. Phys, Left, Vol.
53. No, 14. p.

1317-1319. T, F, Kuech eL
In al, T is added to the group raw material by organometallic vapor phase epitaxy.
MGa, using TklAs as the group II raw material, growth pressure cuff 6T
Carbon doping of 2XIO"CII+3 is performed at orr. However, even if the flow rate of TMGa or TMAs is changed, the amount of carbon doping hardly changes, so the growth temperature is changed to control the !-ping h process. That is, the growth pressure cuff was 6 Torr and the growth temperature was 600°C to 700°C.
By adding 1-Gero to C, the hole concentration is 1019cm3
It has been reported that the diameter was reduced from 10 cm to 10 cm.

This method may be used when growing intermediate epitaxial layers, but when growing multiple layers with different carbon doping levels, growth must be interrupted between layers and the growth temperature must be changed. , it is necessary to take a considerable amount of time to change the growth temperature.

So, in the above example, arsine (^s I+ 3 )
7: is proposed, in which the amount of carbon doping is controlled by adding . However, in this method, even if arsine is added, under the growth conditions described in Yuki, the hole concentration is 10+@c.
, -3 to 10"cm-3, which is a fairly narrow range.

(Problems to be Solved by the Invention) The present invention aims to solve the above problems and provide a vapor phase growth method that can easily control the amount of carbon doping over a wide range.

(Means for Solving the Problems) The present invention provides for the use of a group V hydride when doping carbon using an organometallic compound as a group ■ raw material in an organometallic vapor phase epitaxy method for a group ■-■ compound semiconductor. supply at the same time,
This is a vapor phase growth method characterized by controlling the amount of carbon doping by adjusting the flow rate of group V hydride. In this method, it is particularly preferable to grow under a low growth pressure of 40 Torr or less.

(Function) When GaAs is grown in a vapor phase using TMGa and A s tl 3 as raw materials, TMGa reacts with hydrogen atoms generated from ^SH3 in the vapor phase, and methyl groups are removed one by one. Ga, l! adsorbed on the GaAs substrate in the form of monomethyl gallium! : Carbon is thought to be incorporated into the crystal. Therefore, the higher the concentration of hydrogen atoms generated from ASH3, the less carbon is incorporated. AsH3ff1
This is why the amount of carbon mixed in decreases when TMAs is increased, and the reason why a large amount of carbon is incorporated into the crystal when TMAs is used as a raw material is because there are no hydrogen atoms generated from ASH3.

Therefore, if AsHs is added when doping carbon using TMGa and TMAs as raw materials, AsHs
The active hydrogen atoms generated from carbon make it possible to suppress carbon doping.

The present inventors investigated the growth pressure dependence and growth temperature dependence of carbon doping in TMAs and TMGa over a wide range of areas.
It has been found that high concentration carbon doping is possible in a region where the growth pressure is 40 Torr or less, and an epitaxial film with a good surface condition can be formed.

In such a region of growth temperature and pressure,
We have found that the lifetime of the hydrogen atom becomes longer, and that it becomes possible to control the carbon doping Ql over a wide range by adjusting the flow rate of AsHi.

(Example 1) After heating a semi-insulating GaAs substrate to a growth temperature of 575° C. with the pressure inside the reaction tube kept at 10 Torr and TMAs flowing inside the reaction tube in advance, TMGa and AsHl were introduced into the reaction tube, GaAs growth started. At this time, T
The molar ratio of MGa and TMAs was 7, and the flow rate of TMGa was 7 m.
After growing the epitaxial layer at a rate of 1/min until the thickness of the epitaxial layer reached 2 μm, the TMGa and AsH3 were switched to the exhaust pipe, the substrate temperature was returned to room temperature, and the growth was completed. The concentration of AsH3 added was 2% (hydrogen dilution), and the flow rate was 0. 10°20, 30.50. 125sec
It was changed to m.

Hall effect measurements were performed on the grown GaAs epitaxial layer at room temperature, and the obtained hole concentration and mobility were
As shown in the figure. 5.5xl for ASH3 flow rate Osccm
1, 8 for O' 11cm-3 to 125sec
The hole concentration could be controlled over a wide range up to
74c+w/V-sec in Igcm-', 1.
330cm/V-se at 8x10I6cm-'
c, which is equal to or higher than other dopants, indicating that the obtained carbon-doped GaAs has good crystallinity.

(Example 2) After heating a semi-insulating GaAs substrate to a growth temperature of 575°C while maintaining the pressure inside the reaction tube at 10 Torr and flowing TMAs into the reaction tube in advance, TMGa and TMA 1 were heated.
and ASH3 were introduced into the reaction tube, and AlxGa1-xA5
(x=0.1) started to grow. At this time, TMAs and T
The molar ratio of MGa was set to 7. TMGa flow rate to 7+rl
/ll1in.

The flow rate of TMAI was set to 3.5 ml/+in, and after growth of 3 μm, TMGa, TMAI, and ASH3 were switched to exhaust pipes, and the substrate temperature was returned to room temperature to complete the growth. The concentration of As1a added was 2% (hydrogen dilution), and the flow rate was varied from 0+10+25secg+.

The hole concentration obtained from room temperature Hall effect measurements on the grown AlGaAs epitaxial layer is 1.2X1 in the case of AsH, flow ffff105c, as shown in Figure 2.
2.2X10” for 25sec from 0”cm-’
The hole concentration could be controlled over a wide range up to am-3.

(Example 3) With the pressure inside the reaction tube set to 1 OTorr, TMAs was flowed into the reaction tube in advance and the semi-insulating GaAs substrate was heated to a growth temperature of 575°C, and then TMGa and ^SH'3 (
2% hydrogen dilution) was introduced into the reaction tube, and GaA
The growth of s has started. , after growing 1 μm, AsH
Only No. 3 was changed to an exhaust pipe and further grown by 1 μm.

There was no growth interruption between the first layer and the second layer, and continuous growth was performed. Thereafter, the TMGa was switched to the exhaust pipe, the substrate temperature was returned to room temperature, and the growth was completed.

The hole concentration of the grown GaAs epitaxial layer is determined by C-V
The results are shown in FIG. As is clear from the figure, the hole concentration in the first layer with the AsHs flow rate of 20 sec+a is lXl0"aIl-', and the hole concentration in the second layer to which AsH is not added is 5,5XIO"CQI-'. ”
, and both exhibit uniform profiles in the depth direction. From this, it becomes possible to easily control the amount of carbon doping by changing the flow rate of ASH3 added.

In this embodiment, the hole concentration is controlled by adding 0N10FF of AsHs, but it is of course possible to obtain any desired hole concentration by changing the flow rate in a short period of time. In order to instantaneously change the ASH3 flow rate, it is also possible to prepare multiple AsH3 lines and change the hole concentration by 0 to 10FF. Further, by gradually changing the flow rate of Ashs added over time, an arbitrary hole concentration profile can be formed.

(Effects of the Invention) By adopting the above configuration, the present invention can easily control the amount of carbon doping by changing the flow rate of AsH3 added in carbon doping using an organometallic compound as a group III raw material. be able to.

In the conventional method of controlling the amount of carbon doping by changing the growth temperature, when growing a multilayer epitaxial film with different hole concentrations, it is necessary to change the growth temperature between each layer, which takes a long time. There was a problem.

However, in the present invention, the hole concentration can be controlled by changing the flow rate of ASH3 added, so there is no need to interrupt the growth.

This not only saves time, but also makes it difficult for unnecessary impurities and defects to be introduced into the interface during growth interruption, making it possible to obtain a good interface and improving the quality of the epitaxial layer. be.

[Brief explanation of drawings]

Figure 1 shows GaA due to changes in the flow rate of added ASH3 in Example 1.
Figure 2 shows an example of controlling the hole concentration in the s epitaxial layer.
+Gao, a diagram showing an example of controlling the hole concentration of sAS, 3rd
The figure shows the profile of the hole concentration in the depth direction in the GaAs epitaaxial film of Example 3, and FIG. 4 is a schematic diagram of the HBT.

Claims (4)

[Claims] (1) In the organometallic vapor phase epitaxy of III-V group compound semiconductors, when carbon is doped using an organometallic compound as a group V raw material, a group V hydride is simultaneously supplied, and V
A vapor phase growth method characterized by controlling the amount of carbon doping by adjusting the flow rate of a group hydride. (2) the III-V compound semiconductor is GaAs;
2. The vapor phase growth method according to claim 1, wherein the Group III raw material is trimethyl gallium or triethyl gallium, the Group V organometallic compound is trimethyl arsenic, and the Group V hydride is arsine. (3) The Group III-V compound semiconductor is AlGaAs, the Group III raw material is trimethylgallium or triethylgallium, and trimethylaluminum, the Group V organometallic compound is trimethylarsenic, and the Group V hydride is arsine. The vapor phase growth method according to claim 1, characterized in that: (4) The vapor phase growth method according to any one of claims (1) to (3), characterized in that the growth temperature is 625°C or less and the growth pressure is 40 Torr or less. .