JPH02221192A - Vapor phase growth method for compound semiconductors - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for vapor phase growth of an Mg-doped compound semiconductor by metal organic vapor phase epitaxy or the like.

(Prior art) Organometallic vapor phase epitaxy (OMVPE) is a method of growing a thin single crystal film on a substrate crystal by thermally decomposing an organometallic compound and a metal hydride compound in a reactor. . This method is easy to form an ultra-thin multilayer structure and has high mass productivity.
It is used to fabricate wafers for integrated devices. Among heterojunction devices, hetero bipolar transistors (HBTs) are being actively developed because they operate at extremely high speeds.

FIG. 2 is a cross-sectional structural diagram showing an example of IIBT. This) IBT is made of nGaAs on a semi-insulating GaAs substrate.
layer and n-GaAs, and further p”-G
A pn junction is formed by stacking an aAs base layer and an n-AlGaAs emitter layer. Collector electrode is n-Ga
A base electrode is formed on the As layer, a base electrode is formed on the base layer, and an emitter electrode is formed on the n-GaAs layer laminated on the emitter layer. The higher the carrier density of the base layer, the better the characteristics of the IBT can be obtained.

Conventionally, Zn has been used as a p-type dopant in the OMVPE method, but since Zn has a large diffusion coefficient, it is impossible to avoid diffusion from the base region to the emitter region during growth, making it difficult to obtain a steep p-n junction. The problem was that it was not possible. In the molecular beam epitaxial method (MBE method), it is possible to perform high-density doping to the order of l From, B
It is difficult to use e.

Therefore, the diffusion coefficient of Mg is about 5 orders of magnitude lower than that of Zn.
Elements are being considered as dopants.

Raw materials for such Mg dopants include biscyclopentadienylmagnesium (Cptljg) or bismethylcyclopentadienylmagnesium (LCptk).
lg) can be used. These raw materials are liquid or solid organometallic compounds, and are introduced into a reaction tube together with organometallic compounds and metal hydrides, which are the raw materials for compound semiconductors, using hydrogen as a carrier gas, and are thermally decomposed on the substrate crystal. and incorporated into the crystal.

FIG. 3 is a conceptual diagram of an apparatus for implementing such an OMVPE method. A susceptor is provided in the reaction tube, and a substrate crystal is placed on the susceptor. An RF coil is provided around the reaction tube. Group II raw materials for compound semiconductors, such as trimethyl gallium (TklG), are introduced into the reaction tube using hydrogen gas, and Group V raw materials are introduced into the reaction tube in the form of hydrides, such as arsine gas, and are heated on a heated substrate. It is decomposed and a compound semiconductor crystal grows on the substrate.

In order to form a P-type layer in this compound semiconductor, hydrogen gas containing Mg raw material, which had been previously flowed into the exhaust pipe, is introduced into the reaction tube by closing valve B and opening valve Δ. After forming a thick P-type layer, valve 8 is closed and valve B is opened to switch the Mg source gas from the reaction tube to the exhaust tube to stop the growth.

(Problems to be Solved by the Invention) In such conventional methods, the hole density increases in proportion to the flow rate of the Mg raw material.
ctronics materials, Vol.
12. No, 3°p, 507-524. C, R, L
As shown in ewiset al, 2×IO・”am
There was a drawback that the hole density did not increase and the crystal surface also deteriorated due to saturation.

The present invention overcomes the drawbacks mentioned above and
Even for the above hole density, it is possible to easily control the hole density without changing the flow rate of the Mg raw material.
The present invention aims to provide a method for growing crystals of doped compound semiconductors.

(Means for Solving the Problems) The present invention provides a method for organic metal vapor phase growth of an Mg-doped compound semiconductor, in which a constant flow rate of a compound containing an Mg element is supplied to the north of a heated substrate at the same time as a raw material for the compound semiconductor. ,
By interrupting the supply of group (III) raw materials at regular intervals and adjusting the time of interruption and/or the time of supplying group (III) raw materials,
This is a method for vapor phase growth of compound semiconductors characterized by controlling the amount of doping of elements.

In addition, the supply time of the group (Ⅰ) raw material is 1 to 20 minutes for compound semiconductors.
It is preferable to set the time required to form a molecular layer, and it is preferable to adjust the substrate temperature during crystal growth to a range of 300 to 600°C. When the temperature is lower than 300° C., decomposition of the organic metal becomes difficult to occur, making crystal growth and doping impossible.

(Function) In the OMVPE method, as seen in the above-mentioned literature, Mg element is doped in proportion to the square of the supply amount of the raw material, but it is saturated at about 2XIO "am-".
This is thought to be because even when atoms are taken into the crystal, they are not placed on the crystal lattice but are located between the crystal lattices and function as acceptors that supply holes. Therefore, by stopping the supply of group II raw materials during growth, placing Mg atoms on the V wide atoms, that is, at the lattice positions of the ■ wide atoms, and then supplying the group II raw materials again to cause crystal growth, It becomes possible to increase the number of Mg atoms that function as acceptors to 2 Therefore, the hole density can be controlled by adjusting the co-supply stopping time of the group (III) raw material.Furthermore, when the group (III) raw material that has been stopped is supplied, compound crystals grow. , determined by the supply ratio of Group ■ raw material and Mg raw material, 2
A layer having a hole density of less than XlO"cm-' can be formed, and by changing the thickness of this layer, the hole density of the crystal as a whole can be controlled.

In this way, by repeating layers in which Mg atoms are placed in the group II lattice positions between thin crystals containing Mg atoms of 2 The surface will not deteriorate.

(Example 1) Arsine (as raw material for As) (
With As li 3 ) gas flowing, the GaAs substrate was heated to the growth temperature of 600°C, and biscyclopentadienylmagnesium (Cp!Mg
) was introduced into the reaction tube. After 10 minutes, trimethylgallium (TMG), a Ga raw material, was introduced into the reaction tube to form GaAs.
Crystals began to grow.

At that time, the flow rate of TMG was set to 7 ml per minute so that the growth rate of the GaAs crystal was 2 μm per hour. CI'tIIt
The flow rate of g was set at ]00 el per minute. After 30 minutes, TMG was switched from the reaction tube to the exhaust tube, growth was interrupted for 10 seconds, only CptMg was allowed to flow, TMG was introduced into the reaction tube again, crystal growth was performed for 2 seconds, and this cycle was repeated for 27 seconds.
Repeated 0 times. After that, TMG and C22klg for 30
TII was introduced into the reaction tube for a minute to perform crystal growth, and then
IG and Cp2Mgf! -Switched to the exhaust pipe, returned the substrate temperature to room temperature, and finished the growth.

When we measured the carrier density in the thickness direction of the grown GaAs, we obtained a hole density of 5XlO19cm-3, which is 2.5 times the saturation value of the conventional method, as shown in Figure 1(a). I was able to do that.

(Example 2) After heating the GaAs substrate to the growth temperature of 600°C with As 113 gas flowing into the reaction tube of the apparatus shown in Fig. 3, CpyMg, which had been flowing into the exhaust pipe in advance, was poured into the reaction tube. Introduced. Thereafter, 300 cycles of TMG supply time of 2 seconds and interruption time of 10 seconds were performed, and then TMG
The growth was completed by repeating 300 cycles in which MG was supplied for 2 seconds and interrupted for 5 seconds.

When the carrier density in the thickness direction of the grown Gaps was measured by C-■, as shown in Fig. 1(b), the hole density in the part where the interruption time was 10 seconds was 5 × 1 OIIIC1'', whereas In the portion where the interruption time is 5 seconds, the hole density decreases to 3×10” cm −3 . This is because the amount of Mg placed in the group III lattice positions is reduced due to the short growth interruption time. It can be seen that by changing the growth interruption time in this manner, the hole density can be controlled while keeping the Cp2Mg flow rate constant.

Furthermore, the surface of this crystal was a mirror surface, and no deterioration was observed.

Note that the same effect as in the above embodiment can be obtained when the growth temperature is 60° C. (1° C. or higher), but in that case, it is necessary to set the growth interruption time in minutes, and the growth time becomes longer.

(Example 3) After heating the GaAs substrate to the growth temperature of 600°C with ^sH gas flowing into the reaction tube of the apparatus shown in Fig. 3, CpyMg, which had been flowed into the exhaust pipe in advance, was introduced into the reaction tube. It was introduced in Thereafter, 300 cycles of TMG supply time of 2 seconds and interruption time of 10 seconds were performed, and then TMG
The growth was completed by repeating 300 cycles with a supply time of 4 seconds and an interruption time of ic+ seconds.

When the carrier density in the thickness direction of the grown GaAs was measured by C-■, as shown in Figure 1(c), the hole density in the part where the TMG supply time was 2 seconds was 5X10"as-'
On the other hand, in the part where the TMG supply time is 4 seconds, the hole density decreases to 2XIQ" am 3. This is because the average hole density decreases due to the thicker GaAs layer. This shows that by changing the TMG supply time, the hole density can be controlled while keeping the CptMg flow rate constant.However, in this case, the thickness of the GaAs layer is If it becomes thicker than the free path distance, it cannot be considered as a single layer of crystal, so the thickness of the GaAs layer needs to be about 20 molecular layers or less.In this example, when the TMG supply time is 2 seconds, This corresponds to 4 molecular layers, and 4 seconds corresponds to 8 molecular layers.

(Effects of the Invention) By adopting the above configuration, the present invention stops the supply of the group (III) raw material to interrupt the growth, and only the Mg raw material is introduced into the reaction tube, and Mg is placed at the group (III) lattice position. To do so, 2X
It was possible to obtain a hole density of I[)"am-' or higher.

Furthermore, it has become possible to control the hole density by changing the growth interruption time and the thickness of the GaAs layer while keeping the supply flow rate of the Mg raw material constant. Considering that the Mg raw material is easily adsorbed on piping and it is difficult to adjust the flow rate in a short time, this method further improves the controllability of the hole density compared to the conventional method.

[Brief explanation of the drawing]

FIGS. 1(a) to (c) are diagrams showing the distribution of hole density in the depth direction of the GaAs crystal obtained in the example, and FIG.
A cross-sectional PR drawing of BT, FIG. 3 is a conceptual diagram of the OMVPE device.

Claims (5)

[Claims] (1) In the organometallic vapor phase growth method for Mg-doped compound semiconductors, a constant flow of Mg is applied at the same time as the compound semiconductor raw material.
A compound containing an element is supplied onto a heated substrate, and III
By interrupting the supply of group raw materials at regular intervals, Mg
A method for vapor phase growth of compound semiconductors characterized by controlling the amount of element doping. (2) The method for vapor phase growth of a compound semiconductor according to claim (1), wherein the amount of doping of the Mg element is controlled by changing the time during which the supply of the group III raw material is interrupted. (3) The method for vapor phase growth of a compound semiconductor according to claim (1), characterized in that the amount of doping of the Mg element is controlled by changing the supply time of the Group III raw material. (4) The method for vapor phase growth of a compound semiconductor according to any one of claims (1) to (3), characterized in that the substrate temperature during crystal growth is 600°C or less. (5) One or more compound semiconductor crystals selected from the group consisting of GaAs, AlGaAs, InP, and GaInAs are grown in a vapor phase by the vapor phase growth method according to any one of claims (1) to (4). How to do it.