JPH0729916A - Heterojunction bipolar transistor - Google Patents

Abstract

PURPOSE:To restrain the decrease of current amplification factor at the time of large current operation. CONSTITUTION:On a GaAs substrate 1 the following are formed in order; a collector contact layer 2 containing n-type impurities, a collector layer 3 containing n-type impurities, a base layer 4 containing p-type impurities, an emitter layer 5 which has a forbidden bandwidth larger than the base layer and contains n-type impurities, and an emitter contact layer 6 containing n-type impurities. A collector electrode 7, a base electrode 8 and an emitter electrode 9 which constitute ohmic contacts are formed on the collector contact layer 2, the base layer 4, and the emitter contact layer 6, respectively. The base layer 4 forms stable P-H bonds by adding phosphorus as p-type impurities together with carbon, so that the variation of activation ratio of the base layer 4 can be reduced and the reliability of a transistor can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly to a heterojunction bipolar transistor.

[0002]

2. Description of the Related Art In recent years, a heterojunction bipolar transistor (hereinafter referred to as HBT) using a compound semiconductor has been attracting attention as a high frequency device. In the HBT, a semiconductor having a forbidden band width larger than that of the base semiconductor is used for the emitter, and a heterojunction is formed between the emitter and the base. Since the injection of carriers from the base to the emitter is reduced by the above heterojunction, a sufficiently large current amplification factor can be obtained even if the resistance of the base is reduced by making the width of the base thin and increasing the carrier concentration of the base. And is suitable for high frequencies.

In order to form the above-mentioned heterojunction, a crystal growth technique such as a molecular beam epitaxy (MBE) method or a metal organic vapor phase epitaxy (MOVPE) method is used. G
In aAs-based HBT, as a p-type impurity of the base,
Beryllium is mainly used in the MBE method. However, when beryllium is used as the p-type impurity, there is a problem that the current amplification factor is lowered due to the diffusion of beryllium from the base layer side to the emitter layer side during high current operation. Therefore, carbon, which has a smaller diffusion coefficient than beryllium, is used in the MOCVD method as an impurity in place of beryllium. A cross-sectional view of a conventional carbon-doped HBT is shown in FIG.

As shown in FIG. 1, a conventional HBT has a GaAs substrate 1 on which a collector contact layer 2 containing a high concentration of n-type impurities, a collector layer 3 containing an n-type impurity, and a high concentration of p-type impurities. The base layer 10, the emitter layer 5 having a forbidden band width larger than that of the base layer and containing the n-type impurity, and the emitter contact layer 6 containing the n-type impurity at a high concentration are sequentially formed. A collector electrode 7, a base electrode 8 and an emitter electrode 9 which are in ohmic contact are formed on each of the layer 4 and the emitter contact layer 6.

In the conventional type, only TMGa and AsH ₃ are supplied in the MOVPE growth of p-type GaAs of the base layer 10. Carbon is taken in from TMGa as a p-type impurity, and if this carbon enters the arsenic site, it acts as a p-type impurity. However, since hydrogen is also taken in at the same time, a bond between arsenic and hydrogen and a bond between carbon and hydrogen are formed, and activation is suppressed.

[0006]

However, recently, even in a structure in which carbon is used as an impurity, hydrogen is simultaneously mixed with carbon from the raw material organic metal during growth, and this hydrogen is dissociated from the base layer during high current operation. It has been pointed out that the current amplification factor is reduced due to, and this is a big problem in terms of reliability.

An object of the present invention is to provide an HBT having a base layer which suppresses a decrease in current amplification factor during operation and can be stably operated.

[0008]

In order to solve the above problems, the HBT of the present invention uses a base layer grown by simultaneously adding phosphorus in addition to carbon as a p-type impurity to dissociate hydrogen. It reduces the change in activation rate due to.

[0009]

According to the present invention, because of the above-described structure, hydrogen taken into the base layer together with carbon has a stronger bond between phosphorus and hydrogen than a bond between arsenic and hydrogen, so that the phosphorus is more stable than the bond between arsenic and hydrogen. The number of bonds between hydrogen and hydrogen increases, the bonds between carbon and hydrogen and the bonds between arsenic and hydrogen decrease, the change in activation rate is reduced even during high current operation, the decrease in current amplification factor is improved, and reliability is improved. improves.

[0010]

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

FIG. 1 shows a sectional view of the HBT of the present invention. As shown in the figure, the HBT of the present invention is formed on a GaAs substrate 1 with n
Collector contact layer 2 containing a high concentration of type impurities,
A collector layer 3 containing an n-type impurity, a base layer 4 containing a high concentration of a p-type impurity, an emitter layer 5 having a forbidden band width larger than that of the base layer and containing an n-type impurity, and a high concentration of an n-type impurity. The emitter contact layer 6 contained in is sequentially formed, and the collector electrode 7, the base electrode 4, and the emitter electrode 9 which make ohmic contact are formed on each of the collector contact layer 2, the base layer 4, and the emitter contact layer 6.

MOVPE formation of p-type GaAs for the base layer 4
Trimethylgallium (TMGa) in length, arsine
(AsH₃ ), Phosphine (PH₃ ) Supply at the same time
As a result, a p-type epitaxial layer can be obtained.
In the HBT of the present invention, the growth temperature is 400 to 600 ° C.,
Phosphorus concentration of 10¹⁷-10²⁰/ Cm² PH to be ₃ 
The more stable bond between phosphorus and hydrogen
Increase, the bond between carbon and hydrogen and the bond between arsenic and hydrogen decrease.
Less. This p-type epitaxial layer was used as the base layer
HBT reduces dissociation of hydrogen from the base layer during operation.
Therefore, the activation rate hardly changes.

FIG. 2 shows changes over time in the current amplification factor of a heterojunction bipolar transistor using the p-type epitaxial layer as a base layer. As shown in FIG. 2, the reliability is improved by introducing PH ₃ into the growth of the p-type epitaxial layer. Further, since the phosphorus content is at the impurity level, changes in the lattice constant and the forbidden band width are small, and the characteristics of the semiconductor are not affected. Further, in the present invention, only one kind of raw material is added only to the growth of the base layer in the crystal growth, and the conventional process can be used without modification.

[0014]

As described above, according to the present invention, the dissociation of hydrogen is reduced by adding phosphorus in the growth of the p-type epitaxial layer, and this p-type epitaxial layer is used as a heterojunction bipolar transistor. By using the base layer, it is possible to suppress a decrease in current amplification factor during high current operation and improve reliability.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an HBT having a base layer containing phosphorus and carbon according to an embodiment of the present invention.

FIG. 2 is a diagram showing a change with time of a current amplification factor of an HBT having a base layer containing phosphorus and carbon in an example of the present invention.

FIG. 3 is a cross-sectional view of a conventional HBT having a base layer containing only carbon.

[Explanation of symbols]

 1 Semi-Insulating Substrate 2 Collector Contact Region 3 Collector Region 4 Base Region (Contains Carbon and Phosphorus) 5 Emitter Region 6 Emitter Contact Region 7 Collector Electrode 8 Base Electrode 9 Emitter Electrode 10 Base Region (Contains Carbon)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akiyoshi Tamura 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A heterojunction bipolar transistor comprising p-type GaAs containing carbon and phosphorus as a base layer. 2. A p-type G substrate comprising a GaAs substrate, an n-type GaAs collector layer, a p-type GaAs base layer and an n-type AlGaAs emitter layer formed on the GaAs substrate.
A heterojunction bipolar transistor, wherein the aAs base layer contains carbon and phosphorus. 3. A carbon concentration of 10¹⁷-10²⁰/ Cm³ ,phosphorus
The concentration of 10¹⁷-10 ²⁰/ Cm³ Is characterized by
The heterojunction bipoor according to claim 1 or 2.
Rat transistor.