JPH05102178A - Heterojunction bipolar transistor - Google Patents

Abstract

PURPOSE:To provide a heterojunction bipolar transistor wherein, when a base layer is grown at a low temperature, the quality of the base layer is not deteriorated, as a result, the rate of the recombination of minority electrons can be reduced and a high current gain can be obtained. CONSTITUTION:In a heterojunction bipolar transistor 1, an emitter layer 8 composed of a compound semiconductor layer, a base layer 7 and a collector layer 5 are formed on a semiconductor substrate 2 and carbon (C) is mixed with the base layer 7. The transistor is featured in such a way that the base layer 7 is composed of InXGa1-XAsYP1-Y (where 0<=X<1 and 0<Y<=1).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heterojunction bipolar (bipolar type) transistor which operates at high speed and high current gain.

[0002]

2. Description of the Related Art In recent years, semiconductor devices using compound semiconductors have been vigorously researched and developed for higher integration and higher speed. In particular, a heterojunction bipolar transistor using a heterojunction of a compound semiconductor (hereinafter referred to as HBT; the same applies hereinafter) is expected to have high emitter injection efficiency, high gain, and high speed, and is actively studied as a next-generation semiconductor device. Development is underway.

In particular, in a GaAs-based (which means that the substrate is made of GaAs. The same applies hereinafter), as a material (dopant) mixed (doped) for converting the base layer into p-type, Carbon (C), which has a very small diffusion coefficient as compared with conventional zinc (Zn), beryllium (Be), and magnesium (Mg), is used, and it has been difficult to manufacture HBT from the base layer. Of HBTs with good characteristics by suppressing diffusion of dopant
Has become stable.

With the advent of such a dopant, it has become possible to increase the concentration of the base layer aiming at a reduction in the resistance of the base layer for the purpose of further improving the high speed property. However, on the other hand, the higher concentration of the base layer leads to an increase in the proportion of Auger recombination of minority electrons in the base layer, resulting in a decrease in lifetime and a decrease in current gain. It was Therefore, the HBT employs a graded base structure that causes an internal electric field in the base layer. Specifically, Al _x Ga _{1 -X is used.}
By changing the Al composition ratio of the base layer made of As (0 ≦ X ≦ 0.1), the band gap in the base layer is changed stepwise. That is, the Al composition is set to 0 in the base-collector junction, and the Al composition is set in the emitter-base junction.
The band gap is changed by setting the composition to 0.1.

[0005]

Al _x which is a base layer
Carbon (C) is mixed in Ga _{1 -X} As at a high concentration (dope)
In order to do so, it is necessary to grow Al _x Ga _{1 -X} As without breaking the bonds of the carbons constituting the methyl group of trimethylgallium, which is the raw material, and Ga or As of arsine. It is inevitable to lower the temperature. That is, in order to mix (dope) carbon (C) at a high concentration, Al _x Ga _1-x As must be grown at a low temperature, but this lowering of temperature lowers the quality of the Al _x Ga _1-x As base layer. Is deteriorated, and as a result, the rate of recombination of minority electrons in the base layer is increased.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to prevent the deterioration of the quality of the base layer when the base layer is grown at a low temperature. Another object of the present invention is to provide a heterojunction bipolar transistor which can reduce the recombination rate of minority electrons and obtain a high current gain.

[0007]

The structure of the present invention for achieving the above object is to form an emitter layer, a base layer, and a collector layer, which are compound semiconductor layers, on a semiconductor substrate, and to form a carbon layer in the base layer. In the heterojunction bipolar transistor in which (C) is mixed, the base layer is In _X Ga _1-X As _Y P _1-Y (0 ≦ X <1, 0 <Y ≦
It is characterized by comprising 1).

[0008]

Embodiments of the present invention will now be described in detail with reference to the drawings.

The feature of the present invention is that In _x Ga _1-x As _y P _1-y (0 ≦ X <1, 0 <y ≦) in which the base layer of the heterojunction bipolar transistor (HBT) is lattice-matched to GaAs.
It is characterized by comprising 1).

FIG. 1 is a sectional view showing a heterojunction bipolar transistor 1 according to an embodiment of the present invention. The heterojunction bipolar transistor 1 is a semi-insulating GaAs.
A buffer layer 3 made of non-doped GaAs with a thickness of 0.5 μm, which is sequentially formed on the substrate 2 by a metal organic chemical vapor deposition method (MOCVD method), and an n-type buffer layer with a thickness of 0.3 μm. Subcollector layer 4 made of GaAs (dopant: selenium (Se), concentration: 1 × 10 ¹⁹ c)
m ⁻³ ) and n-type GaA with a thickness of 0.5 μm
collector layer 5 made of s (dopant: silicon (S
i), concentration: 1 × 10 ¹⁵ cm ⁻³ ), a first base layer 6 made of p-type GaAs with a thickness of 0.05 μm.
(Energy gap: 1.42 eV, dopant: carbon (C), concentration: 4 × 10 ¹⁹ cm ⁻³ ), and a thickness of 0.05
Micrometer p-type In _0.14 Ga _0.86 As _0.73 P
Second base layer 7 consisting of _0.27 (energy gap:
1.54 eV, dopant: carbon (C), concentration: 4 × 1
0 ¹⁹ cm ⁻³ ) and an emitter layer 8 (dopant: silicon (Si), concentration: 5 × 10 ¹⁷ cm ⁻³ ) made of n-type Al _0.26 Ga _0.74 As with a thickness of 0.3 μm,
The cap layer 9 made of n-type GaAs and having a thickness of 0.1 μm (dopant: selenium (Se), concentration: 1
× 10 ¹⁹ cm ^-3 ) and the emitter electrode 10, the base electrode 11, and the collector electrode 12 formed by the vapor deposition method or the like.
It consists of and.

The heterojunction bipolar transistor 1 of this embodiment has a first base layer 6 made of GaAs and In.
_A graded base structure is formed by utilizing the difference in bandgap from the second base layer 7 made of _0.14 Ga _0.86 As _0.73 P _0.27 , and the second base layer 7 is G
Superlattice structure in which aAs and InGaP are alternately laminated, or In and Ga and As and P are simultaneously supplied I
A mixed crystal of nGaAsP may be used.

Carbon (C) used as a dopant is 100% as a p-type dopant in GaAs.
% Activated, but does not function as a dopant in In _0.49 Ga _0.51 P. However, in the HBT having the graded base structure, the maximum band gap of the base layer is at most about 1.54 eV of Al _0.1 Ga _0.9 As,
This is the composition of GaAs and InGaP (GaAs)
_This corresponds to _0.73 (In _0.49 Ga _0.51 P) _0.27 . Therefore,
When InGaAsP of this composition is doped with carbon (C), it becomes a p-type dopant with an activation rate of about 73% in calculation.

The thickness of each semiconductor layer, the type of dopant, etc. are not limited to those in this embodiment, and can be changed as appropriate.

According to the heterojunction bipolar transistor 1 of this embodiment, since InGaAsP containing no aluminum (Al) is used for the second base layer 7, when the second base layer 7 is grown at a low temperature. However, the problem that aluminum (Al) is oxidized does not occur, and as a result, the rate of recombination of minority electrons in the base layer can be reduced and a high current gain can be obtained. Specifically, the current amplification factor β was 150 and the current gain cutoff frequency ft was 100 GHz, which confirmed that excellent characteristics were obtained. Furthermore, since carbon (C) is used as a dopant to be mixed (doped) in the second base layer 7, diffusion of the dopant from the second base layer 7 can be prevented.

[0015]

According to the heterojunction bipolar transistor of the present invention, In _x Ga containing no Al in the base layer.
_{Since 1-X} As _Y P _1-Y (0 ≦ X <1, 0 <Y ≦ 1) is used, the base layer does not deteriorate when the base layer is grown at a low temperature, and as a result, in the base layer. It is possible to reduce the rate of recombination of minority electrons of and to obtain a high current gain.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

[Explanation of symbols]

 1 heterojunction bipolar transistor 2 substrate 3 buffer layer 4 subcollector layer 5 collector layer 6 first base layer 7 second base layer 8 emitter layer 9 cap layer 10 emitter electrode 11 base electrode 12 collector electrode

Claims (1)

[Claims] 1. An emitter layer, a base layer, and a collector layer made of a compound semiconductor layer are formed on a semiconductor substrate,
In the heterojunction bipolar transistor in which carbon (C) is mixed in the base layer, the base layer is In
A heterojunction bipolar transistor comprising _X Ga _1-X As _Y P _1-Y (0 ≦ X <1, 0 <Y ≦ 1).