JPH11354451A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the reduction of the activation factor of a semiconductor device caused by doping in it high-concentration carbon, by adding antimony to a carbon-doped p-type GaAs layer formed on a GaAs substrate. SOLUTION: On a semi-insulating GaAs (100) substrate 1, a high-concentration carbon-doped p-type GaAs layer 2 with added antimony (Sb) is formed. The p-type GaAs layer 2 can be formed by a variety of such methods as a molecular beam epitaxy(MBE) method and a metal-organic chemical vapor deposition(MOCVD) method. Here, the p-type GaAs layer 2 is grown by a gas-source MBE method using solid Ga, arsine (AsH3 ), solid Sb, and four carbon bromide (CBr4 ) as the source materials of gallium, arsenic, antimony, and carbon. As a result, the thin film of the Sb-added carbon-doped p-type GaAs layer 2 is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a III-V semiconductor device, and more particularly to a semiconductor device using GaAs suitable for forming a highly doped p-type thin film.

[0002]

2. Description of the Related Art Ultra-high-speed devices such as heterojunction bipolar transistors (HBTs) made of III-V semiconductor materials and optical devices such as semiconductor lasers require highly doped p-type semiconductor layers. .
Conventionally, zinc or beryllium has been added to the semiconductor layer as a dopant for forming the p-type region.
However, it is very difficult to form a thin film having a high hole concentration because all the dopants have a property of being easily diffused.

[0003] In order to solve this problem, carbon has recently been used as a dopant. Carbon is effective in forming a thin film semiconductor layer having a small diffusion constant and a high hole concentration. For this reason, carbon is also used as a dopant for forming a p-type GaAs layer, and a thin p-type layer having a high hole concentration of 1 × 10 ¹⁹ cm ⁻³ or more is used.
It has become possible to form a type GaAs layer.

[0004]

SUMMARY OF THE INVENTION However, GaAs
When the concentration of carbon doped in the s layer is increased to 4 × 10 ²⁰ cm ⁻³ or more, the activation rate sharply decreases as shown in FIG. 7 as the doping amount increases. This is Ga
As the concentration of carbon doped in As increases, carbon is taken into the crystal lattice position of As, which is a V group, and acts as an acceptor that forms p-type conductivity. This is because carbon is taken into a position and acts as a donor that forms n-type conductivity, so that holes are compensated by electrons. As described above, in the prior art, it is difficult to achieve a high activation rate at a high carbon concentration, and there is a limit in reducing the resistivity of the p-type GaAs layer by increasing the doping amount of carbon.

It is an object of the present invention to suppress a decrease in the activation rate caused by doping a GaAs layer with a high concentration of carbon, and to provide a p-type Ga having a high activation rate at a high carbon concentration.
To provide an As layer.

[0006]

The present invention solves the above-mentioned problems of the prior art by adding antimony Sb to a carbon-doped p-type GaAs layer formed on a GaAs substrate to increase the carbon content. This is to suppress the decrease in the activation rate caused by doping to a concentration. Since Sb has a smaller binding energy with carbon than As,
By adding Sb to the As layer and replacing part of As with Sb, it is possible to reduce the amount of carbon taken into the crystal lattice position of Ga, which is a group III material. As a result, it is possible to suppress a decrease in the activation rate of the p-type GaAs layer caused by doping carbon with a high concentration of 4 × 10 ²⁰ cm ⁻³ or more.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS <Embodiment 1> A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view of a thin film of a carbon-doped p-type GaAs layer doped with Sb formed on a GaAs substrate according to the present invention. In FIG. 1, a semi-insulating GaAs (100) substrate 1
A heavily carbon-doped p-type GaAs layer 2 to which b is added is formed. The p-type GaAs layer is formed by, for example, molecular beam epitaxy (MBE) or metal organic chemical vapor deposition (MO).
It can be formed by various methods such as a CVD method. In this embodiment, solid Ga, arsine (AsH ₃ ), solid Sb, and carbon tetrabromide (CB) are used as source materials of gallium, arsenic, antimony, and carbon.
r ₄ ) by the gas source MBE method.
An As layer was grown.

FIG. 2 shows the relationship between the carbon concentration and the activation rate of the Sb-doped carbon-doped p-type GaAs layer manufactured according to this embodiment. Here, the addition amount of Sb is determined according to the concentration of carbon in the carbon-doped p-type GaAs to which Sb is added.
The lattice constant of the layer is determined to be the same as the lattice constant of the GaAs substrate. As shown in FIG. 2, the carbon-doped p-type GaAs layer of the present embodiment realizes a higher activation rate than the conventional one at a carbon concentration of 4 × 10 ²⁰ cm ⁻³ or more.

The added Sb is carbon-doped p-type GaAs.
The same effect can be obtained even if it is added unevenly in the layer. The effect of suppressing the decrease in the activation rate is increased by increasing the amount of Sb added. However, Sb
The lattice constant of the carbon-doped p-type GaAs layer doped with
If Sb is added until the lattice constant becomes larger than the lattice constant of the aAs substrate, strain due to compressive stress occurs in the carbon-doped p-type GaAs layer to which Sb is added, and Sb segregates on the growth surface during crystal growth. It is difficult to obtain an energy band structure. For this reason, the amount of Sb added is
The lattice size of the carbon-doped p-type GaAs layer to which b is added is equal to or smaller than the lattice size of the GaAs substrate, that is, the carbon-doped p-type Ga to which Sb is added.
It is desirable that the lattice constant of the As layer is not more than one time the lattice constant of the GaAs substrate.

In the first embodiment, solid G is used as a source material of gallium, arsenic, antimony and carbon.
Although a carbon-doped p-type GaAs layer containing a, arsine, solid Sb, and Sb grown by gas source MBE using carbon tetrabromide has been described, as a crystal growth method, triethyl gallium or Ga is used as a source material of Ga. MOCVD using a source material such as trimethylarsenic or tertiary butylarsine as a source material of trimethylgallium and arsenic, stibine or trimethylantimony as a source material of Sb, and a material such as carbon tetrachloride, trimethylgallium, or trimethylarsenic as a source material of carbon The same effect can be obtained by using the method.

Further, the p-type GaAs layer is formed of solid G
It is possible to grow by MBE method using a, As, and Sb. In addition, metal-organic MBE (MO
It may be grown by the MBE) method.

<Embodiment 2> A second embodiment of the present invention is shown in FIG.
This will be described with reference to FIG. FIG. 3 illustrates the S
FIG. 5 is a cross-sectional view of an npn heterojunction bipolar transistor using a carbon-doped p-type GaAs layer to which b is added as a base layer. In the figure, semi-insulating GaAs (10
0) On the substrate 31, a highly doped n-type GaAs collector contact layer 32 (Si concentration = 5 × 10 ¹⁸ cm ⁻³ , film thickness = 50)
0 nm), n-type GaAs collector layer 33 (Si concentration = 5
× 10 ¹⁵ cm ⁻³ , film thickness = 200 nm) and a carbon-doped p-type GaAs base layer 34 doped with Sb (carbon concentration = 2 ×
10 ²¹ cm ⁻³ , film thickness = 20 nm), n-type In _x Ga _1-x P emitter layer 35 (x = 0.5, Si concentration = 1 × 10 ¹⁸ cm ⁻³ ,
A highly doped n-type GaAs layer 36a for forming an emitter ohmic contact (Si concentration = 5 × 10 ¹⁸ cm ⁻³ ,
Film thickness = 50 nm) and a highly doped n-type InGaAs layer 36b (Si
A substrate is used in which an emitter contact layer having a concentration of 4 × 10 ¹⁹ cm ⁻³ and a film thickness of 50 nm) is sequentially crystal-grown.

The substrate on which the crystal has been grown can be formed by various methods such as a molecular beam epitaxy (MBE) method and a metal organic chemical vapor deposition (MOCVD) method. In this embodiment, gas using solid Ga, arsine (AsH ₃ ), solid Sb, solid Si, and carbon tetrabromide (CBr ₄ ) as a source material of gallium, arsenic, antimony, silicon, and carbon is used. The crystal growth substrate was manufactured by the source MBE method.

The emitter contact layers 36b and 36
The a and the mesa of the emitter layer 35 are formed using the emitter electrode layer 37 made of W as a mask. The mesas of the base layer 34 and the collector layer 33 and the mesas of the collector contact layer 32 are formed using a photolithographic resist as a mask. A collector electrode layer 39 made of AuGe / W / Ni is formed on the collector contact layer 32, and Au / P is formed on the base layer 34.
Base electrode layer 38 of t / Ti / Mo / Ti / Pt
Are formed.

FIG. 4 shows a heterojunction bipolar transistor manufactured according to the present embodiment and Sb in the present embodiment.
The same device as that of the present embodiment manufactured by using a carbon-doped p-type GaAs having the same carbon concentration without adding Sb used in the prior art instead of the carbon-doped p-type GaAs base layer 34 doped with 4 shows the collector current dependency of the maximum oscillation frequency of a heterojunction bipolar transistor having a size. As shown in FIG. 4, the maximum oscillation frequency of the transistor of this embodiment is higher than that in the case of using the conventional technique in all the collector current ranges. This is because the addition of Sb suppressed the reduction in the activation rate of carbon and increased the concentration of holes, so that the base resistance could be reduced.

<Embodiment 3> A second embodiment of the present invention is shown in FIG.
This will be described with reference to FIG. FIG. 5 shows Sb according to the present invention.
Using a carbon-doped p-type GaAs layer to which is added an emitter contact layer and a collector contact layer
FIG. 3 is a cross-sectional view of a p-heterojunction bipolar transistor.
In the figure, on a semi-insulating GaAs (100) substrate 51, a carbon-doped p-type GaAs collector contact layer 52 doped with Sb (carbon concentration = 2 × 10 ²¹ cm ⁻³ , film thickness =
500 nm), undoped GaAs collector layer 53 (film thickness = 200 nm), n-type GaAs base layer 54 (Si concentration = 1 × 10 ¹⁹ cm ⁻³ , film thickness = 50 nm), p-type In _x G
a _1-x P emitter layer 55 (x = 0.5, Mg concentration = 1 × 1
0 ¹⁸ cm ⁻³ , thickness = 50 nm), and a carbon-doped p-type GaAs layer 5 doped with Sb for forming an emitter ohmic contact
6a (carbon concentration = 2 × 10 ²¹ cm ⁻³ , film thickness = 50 nm) and highly doped p-type InGaAs layer 56b (carbon concentration = 1 × 10 ²⁰ cm 3)
^-3 , film thickness = 50 nm) is used.

The substrate on which the crystal has been grown can be formed by various methods such as a molecular beam epitaxy (MBE) method and a metal organic chemical vapor deposition (MOCVD) method. In this embodiment, solid Ga, arsine (AsH ₃ ), solid Sb, and solid S are used as source materials for gallium, arsenic, antimony, silicon, magnesium, and carbon.
The crystal growth substrate was manufactured by a gas source MBE method using i, solid Mg, and carbon tetrabromide (CBr ₄ ).

The emitter contact layers 56b and 56
a and the mesa of the emitter layer 55 are formed using the emitter electrode layer 57 made of WSi / Ti as a mask. The mesas of the base layer 54 and the collector layer 53 and the mesas of the collector contact layer 52 are formed using a photolithographic resist as a mask. Au / Pt / Ti / Mo / T is formed on the collector contact layer 52.
A collector electrode layer 59 made of i / Pt is formed, and a base electrode layer 58 made of AuGe / W / Ni is formed on the base layer 54.

FIG. 6 shows a heterojunction bipolar transistor manufactured according to this embodiment and Sb in this embodiment.
In place of the carbon-doped p-type GaAs collector contact layer 52 doped with Sb and the carbon-doped p-type GaAs layer 56a doped with Sb for forming an emitter ohmic contact, the same carbon concentration as in the present embodiment is used. 4 shows the collector current dependence of the cutoff frequency of a heterojunction bipolar transistor having the same element size manufactured by using a p-type GaAs that has not been manufactured. As shown in FIG. 6, the cut-off frequency of the transistor of the present embodiment is higher than that in the case of using the conventional technique in all the collector current ranges. This is because the addition of Sb suppressed the reduction in the activation rate of carbon and increased the hole concentration, thereby reducing the parasitic resistance of the emitter and the collector.

In Examples 2-3, gallium,
As a source material of arsenic, antimony, silicon, and carbon, solid Ga, arsine, solid Sb, solid S
The heterojunction bipolar transistor in which the crystal growth substrate is manufactured by the gas source MBE method using i and carbon tetrabromide has been described. Such as trimethyl arsenide or tertiary butyl arsine as a source material, stibine or trimethyl antimony as a source material of Sb, monosilane or disilane as a source material of Si, carbon tetrachloride, trimethyl gallium, or trimethyl arsenic as a source material of carbon Similar effects can be obtained by using the MOCVD method using raw materials.

The p-type GaAs layer is formed of a solid G layer.
It is possible to grow by MBE method by using a, As, and Sb.
It may be grown by MBE (MOMBE). The silicon used as the n-type dopant can be replaced with another n-type dopant such as tin or selenium. In addition, magnesium used as a p-type dopant of InGaP can be replaced with another p-type dopant such as zinc.

In Examples 2 and 3, the carbon concentration of the carbon-doped p-type GaAs layer to which Sb was added was 2 × 10 ²¹
cm ^-3 , but the above concentration is 4 × 1
If it is 0 ²⁰ cm ^-3 or more, the same effect can be obtained.

In the above embodiments 2 and 3, the emitter layer 3
InGaP / Ga using InGaP layers 5 and 55
Although an As heterojunction bipolar transistor has been described, an AlGaAs / GaAs heterojunction bipolar transistor using AlGaAs for the emitter layer, an InGaP / AlGaAs heterojunction bipolar transistor containing Al in the base layers 34 and 54, and an AlGaAs / AlGaAs heterojunction bipolar transistor. The same applies to transistors.

Further, in the above embodiments 2 and 3, an emitter-top type heterojunction bipolar transistor in which the structure of the epitaxial growth layer is an emitter, a base and a collector from the top is explained. Collector-top type heterojunction bipolar transistor.

[0025]

According to the present invention, it is possible to suppress the reduction activation ratio of p-type GaAs layer caused by doping carbon in high concentrations, at 4 × 10 ²⁰ cm ^-3 or more high carbon concentration It is possible to form a p-type GaAs layer having a high activation rate. Further, the carbon-doped p-type GaAs layer to which Sb is added according to the present invention is formed by using a base layer of an npn heterojunction bipolar transistor and a pn layer.
By using the -p heterojunction bipolar transistor for the emitter contact layer and the collector contact layer, the base resistance, the emitter resistance, and the collector resistance can be reduced, and a heterojunction bipolar transistor that operates at a very high speed can be realized.

[Brief description of the drawings]

FIG. 1 is a sectional view of a carbon-doped p-type GaAs layer according to one embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a carbon concentration and an activation rate in one embodiment of the present invention.

FIG. 3 is a sectional view of an npn heterojunction bipolar transistor according to one embodiment of the present invention.

FIG. 4 is a characteristic diagram of a semiconductor device according to one embodiment of the present invention.

FIG. 5 is a cross-sectional view of an npn heterojunction bipolar transistor according to another embodiment of the present invention.

FIG. 6 is a characteristic diagram of a semiconductor device according to another embodiment of the present invention.

FIG. 7 is a characteristic diagram showing a relationship between a carbon concentration and an activation rate of a conventional carbon-doped p-type GaAs layer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semi-insulating GaAs substrate, 2 ... Carbon-doped p-type GaAs layer doped with Sb, 31 ... Semi-insulating GaAs substrate,
32 ... highly doped n-type GaAs collector contact layer, 3
3 ... n-type GaAs collector layer, 34 ... carbon-doped p-type GaAs base layer doped with Sb, 35 ... n-type In _x G
a _1-x P emitter layer, 36a ... highly doped n-type GaAs
Layers, 36b: highly doped n-type InGaAs layer; 37, emitter electrode layer; 38, base electrode layer; 39, collector electrode layer; 51, semi-insulating GaAs substrate; 52, carbon-doped p-type GaAs collector doped with Sb Contact layer, 5
3: undoped GaAs collector layer, 54: highly doped n
-Type GaAs base layer, 55 ... p-type InGaP emitter layer, 56a ... carbon-doped p-type GaAs doped with Sb
Layers, 56b: highly doped p-type InGaAs layer; 57, emitter electrode layer; 58, base electrode layer; 59, collector electrode layer.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01S 3/18

Claims (3)

[Claims] 1. A semiconductor device having a structure in which a thin film is formed on a GaAs substrate, wherein at least one of the thin films is formed of a GaAs layer containing carbon and antimony. 2. The semiconductor device according to claim 1, wherein a lattice constant of the GaAs layer containing carbon and antimony is one time or less of a lattice constant of the GaAs substrate. 3. A semiconductor device, wherein the GaAs layer containing carbon and antimony according to claim 1 or 2 is used as a semiconductor layer having p-type conductivity.