JP2001203217A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor device in which a current amplification factor β does not decrease even if a dopant of exceeding 3×1018 cm-3 is doped into a sub-collector layer. SOLUTION: By providing an AlAs layer 3 between a sub-collector layer 2 and an collector layer 4 of an HBT epitaxial wafer acting as a semiconductor device, the current amplification factor β does not decrease even if the dopant of exceeding 3×1018 cm-3 is doped into the sub-collector layer 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor device such as a hetero bipolar transistor.

[0002]

2. Description of the Related Art Conventionally, by focusing on an emitter layer and a base layer of a hetero bipolar transistor (HBT), the crystallinity of each layer and the interface between the layers have been improved, so that a current amplification factor β has been improved.
Attempts have been made to improve. Therefore, regarding the collector layer and the sub-collector layer below the base layer, the relationship between the crystallinity of each layer and the current amplification factor β has not been well studied.

[0003]

By the way, it has recently been found that the doping concentration of the subcollector layer has a considerable effect on the current amplification factor β. In a device having a vertical structure such as an HBT, the area of an electrode for drawing out a wiring is considerably limited. For this reason, in order to obtain a sufficiently low contact resistance, it is necessary to dope the subcollector layer with n-type at a considerably high concentration.

However, when the doping concentration is 3 × 10
^When it exceeds ¹⁸ cm ^-3 , there is a problem that the current amplification factor β is extremely reduced.

Accordingly, an object of the present invention is to solve the above problems and to provide a semiconductor device in which the current amplification factor β does not decrease even if the subcollector layer is doped with a dopant exceeding 3 × 10 ¹⁸ cm ^−3. It is in.

[0006]

In order to achieve the above object, a semiconductor device according to the present invention comprises a subcollector layer made of an n-type GaAs crystal for forming an ohmic contact with a metal electrode on a GaAs substrate; A collector layer composed of an n-type GaAs crystal for extracting electrons from the layer, a base layer composed of a p-type GaAs crystal, an InGaAs crystal, or an AlGaAs crystal for controlling the flow of electrons,
A heterojunction is formed with the base layer, electrons are injected into the base layer, and an emitter layer made of an AlGaAs crystal exhibiting n-type conduction for suppressing injection of holes from the base layer, and a metal electrode and an ohmic contact are formed. N-type InG to be formed
In a semiconductor device in which an emitter contact layer made of an aAs crystal is sequentially formed, an AlAs layer is provided between a subcollector layer and the collector layer.

A semiconductor device according to the present invention comprises a subcollector layer made of a GaAs crystal exhibiting n-type conductivity for forming an ohmic contact with a metal electrode on a GaAs substrate;
A collector layer composed of an n-type GaAs crystal for extracting electrons from the base layer, and a p-type GaAs for controlling the flow of electrons
An n-type InGaP for forming a heterojunction with a base layer made of a crystal, an InGaAs crystal, or an AlGaAs crystal, injecting electrons into the base layer, and suppressing injection of holes from the base layer. An emitter layer made of a crystal, and n forming an ohmic contact with a metal electrode.
In a semiconductor device in which an emitter contact layer made of a type InGaAs crystal is sequentially formed, an AlAs layer is provided between a subcollector layer and a collector layer.

In addition to the above configuration, the semiconductor device of the present invention
Preferably, the thickness of the lAs layer is at least 1 nm.

In addition to the above structure, in the semiconductor device of the present invention, each layer on the substrate is preferably grown by MOVPE or MBE.

According to the present invention, by providing an AlAs layer between a subcollector layer and a collector layer of a semiconductor device, even if a dopant is doped into the subcollector layer beyond 3 × 10 ¹⁸ cm ⁻³ , the current is reduced. The amplification factor β does not decrease.

[0011]

Embodiments of the present invention will be described below.

A semiconductor device according to the present invention comprises a sub-collector layer made of an n-type GaAs crystal for forming an ohmic contact with a metal electrode on a GaAs substrate, and a collector made of an n-type GaAs crystal for extracting electrons from a base layer. Layer and a p-type GaAs crystal for controlling the flow of electrons, In
A base layer made of GaAs crystal or AlGaAs crystal, and an n-type AlGaAs crystal which forms a heterojunction with the base layer, injects electrons into the base layer, and suppresses injection of holes from the base layer; Alternatively, in a semiconductor device in which an emitter layer made of an InGaP crystal and an emitter contact layer made of an n-type InGaAs crystal forming an ohmic contact with a metal electrode are sequentially formed, an AlAs layer is formed between the sub-collector layer and the collector layer. It is provided. As a result, 3 × 1
Even if a dopant is doped beyond 0 ¹⁸ cm ^-3 , the current amplification factor β does not decrease.

[0013]

FIG. 1 is a structural view showing an embodiment of an HBT epitaxial wafer as a semiconductor device of the present invention.

This HBT epitaxial wafer has an n ⁺ GaAs layer (subcollector layer, Si concentration of 5 × 10 ¹⁸ cm) having a thickness of about 500 nm on a semi-insulating (SI) GaAs substrate 1 having a thickness of about 600 μm. ^-3 ) 2, A with a thickness of about 5 nm
lAs layer 3, n ^- GaAs layer (collector layer, Si concentration: 2 × 10 ¹⁶ cm ⁻³ ) 4 having a thickness of about 500 nm, thickness about 70 n
m p ⁺ GaAs layer (base layer, C concentration 4 × 10 ¹⁹ cm)
^-3 ) 5, nAl _x Ga _1-x As layer (x = 0.3, Si concentration 5 × 10 ¹⁷ cm ^-3 ) 6, nAl _x G with a thickness of about 50 nm
a _1-x As graded layer (x = 0.3 → 0, Si concentration 5 × 10 ¹⁷ → 5 × 10 ¹⁸ cm ⁻³ ) 7, thickness about 100 nm
N ⁺ GaAs layer (Si concentration 5 × 10 ¹⁸ cm ⁻³ ) 8, n ⁺ In _y Ga _{1 -y} As graded layer (y = 0 → 0.5, Se concentration 1 × 10 ¹⁹ ) having a thickness of about 50 nm → 4 × 10 ¹⁹ c
m ^-3) 9 and a thickness of about _{^{50nm n + In y Ga 1-}} y As
The layers (y = 0.5, Se concentration 4 × 10 ¹⁹ cm ⁻³ ) 10 are sequentially formed.

The HBT epitaxial wafer has a 5 nm thick Al between the subcollector layer 2 and the collector layer 4.
It is characterized in that it has a structure in which the As layer 3 is formed. The dependency of the current amplification factor β on the doping concentration of the sub-collector layer 2 in the structure of the epitaxial wafer of the present invention and the structure of the conventional epitaxial wafer (same as the structure shown in FIG. 1 except that there is no AlAs layer). In both cases, samples were prepared in which the doping concentration of the subcollector layer was changed.

The emitter size is 100 μm depending on the process.
An HBT having an evaluation of angle was prepared, and the current density of the emitter was 10 ³ A
/ Cm ² was compared.

FIG. 2 is a diagram showing the relationship between the doping concentration of the subcollector and the current amplification factor β. The horizontal axis is the doping concentration axis of the subcollector, and the vertical axis is the current amplification factor β axis.

As shown in the figure, in the conventional product, the current amplification factor β decreases from about 3 × 10 ¹⁸ cm ⁻³ of the carrier concentration of the subcollector layer. It can be seen that the current amplification factor β does not decrease even when it exceeds 3 × 10 ¹⁸ cm ⁻³ , and is constant and maintains a high current amplification factor β.

There is a relationship between the current amplification factor β and reliability,
In the case of the same structure, it is known that the higher the current amplification factor β, the higher the reliability. Therefore, according to the present invention, it is possible to greatly improve the current amplification factor β even in a structure having a highly-doped subcollector layer,
It can be said that the reliability of the device can be considerably improved.

Although it is not clear why the current amplification factor β is improved, it is considered that some crystal defects occur in the heavily doped subcollector layer.
It is considered that growing an AlAs layer on this layer prevents crystal defects from propagating to the base layer and the emitter above it.

Next, the thickness of the AlAs layer 3 will be described.

FIG. 3 is a diagram showing the relationship between the thickness of the AlAs layer and the current amplification factor β, wherein the horizontal axis is the AlAs thickness axis,
The vertical axis is the current amplification factor β axis.

The doping concentration of the subcollector layer 2 is 5 ×
It was 10 ¹⁸ cm ^-3 . Without the AlAs layer 3, the current amplification factor β is about 110, but the thickness of the AlAs layer 3 is 1 nm.
, The current amplification factor β is improved, the current amplification factor β becomes 150 when the thickness of the AlAs is 5 nm, and thereafter, the AlAs
Even when the film thickness was increased, the current amplification factor β was unchanged at about 150. In the present embodiment, the upper limit of the thickness of the AlAs layer 3 could not be obtained. However, if the thickness is too large, the electrical resistance of the AlAs layer 3 cannot be ignored.
It is considered that the current amplification factor β decreases.

Next, the carrier type of the AlAs layer 3 will be described.

In this embodiment, the undoped AlAs layer 3 is used. However, the same effect can be obtained by doping n-type or p-type. However, if the p-type is too thick, it is considered that an electric resistance is generated by the pn junction and the current amplification factor β is reduced.

Next, the dopant of the subcollector layer 2 will be described.

In this embodiment, Si is used as the n-type dopant.
By inserting the AlAs layer 3 between the gate electrode and the collector layer 4, the current amplification factor β was improved.

The insertion position of the AlAs layer 3 will be described.

In this embodiment, the case where the AlAs layer 3 is inserted between the sub-collector layer 2 and the collector layer 4 has been described. is there. For example, when the AlAs layer 3 is inserted in the middle of the collector layer 4, the same effect is obtained.

The effect was also observed when an AlGaAs layer having a high mixed crystal ratio (mixed crystal ratio of 0.5 or more) was used in place of the AlAs layer 3, but the effect was smaller than that of the AlAs layer.

As described above, according to the present invention, it is possible to provide an HBT having a current amplification factor β and improved reliability in an HBT having a sub-collector layer which is highly doped and has a sufficiently small resistance, and an epitaxial wafer thereof. it can.

[0032]

In summary, according to the present invention, the following excellent effects are exhibited.

It is possible to provide a semiconductor device in which the current amplification factor β does not decrease even if the subcollector layer is doped with a dopant exceeding 3 × 10 ¹⁸ cm ⁻³ .

[Brief description of the drawings]

FIG. 1 is a structural diagram showing one embodiment of an HBT epitaxial wafer as a semiconductor device of the present invention.

FIG. 2 shows the doping concentration of the subcollector and the current gain β
FIG.

FIG. 3 is a diagram showing a relationship between the thickness of an AlAs layer and a current amplification factor β.

[Explanation of symbols]

1 S. IGAs substrate (substrate) 2 n ⁺ GaAs layer (sub-collector layer) 3 AlAs layer 4 n ⁻ GaAs layer (collector layer) 5 p ⁺ GaAs layer (base layer) 6 nAl _x Ga _{1 -x} As layer 7 nAl _x Ga _{1 -x} As graded layer 8 n ⁺ GaAs layer _{^{9 n + In y Ga 1-}} y As graded layer _{^{10 n + In y Ga 1-}} y As layer

Continuation of the front page (72) Inventor Junichi Igarashi 5-1-1, Hidaka-cho, Hitachi-shi, Ibaraki F-term in the Hidaka Plant of Hitachi Cable Co., Ltd. 5F003 AP00 AZ01 BB00 BB04 BC02 BC05 BE00 BE04 BF06 BG06 BM02 BM03 BP32

Claims (4)

[Claims] 1. A sub-collector layer made of an n-type GaAs crystal for forming an ohmic contact with a metal electrode on a GaAs substrate, a collector layer made of an n-type GaAs crystal for extracting electrons from a base layer, A base layer made of p-type GaAs crystal, InGaAs crystal, or AlGaAs crystal for controlling flow, and a heterojunction formed with the base layer, electrons are injected into the base layer, and electrons from the base layer are removed. In the semiconductor device, an emitter layer made of an n-type AlGaAs crystal for suppressing injection of holes and an emitter contact layer made of an n-type InGaAs crystal for forming an ohmic contact with a metal electrode are sequentially formed. A semiconductor device comprising an AlAs layer provided between the semiconductor device and the collector layer. 2. A method according to claim 1, further comprising: forming a sub-collector layer made of n-type GaAs crystal for forming an ohmic contact with the metal electrode on the GaAs substrate; a collector layer made of n-type GaAs crystal for extracting electrons from the base layer; A base layer made of GaAs crystal, InGaAs crystal, or AlGaAs crystal exhibiting p-type conduction for controlling flow,
A heterojunction is formed with respect to the base layer, electrons are injected into the base layer, an emitter layer made of n-type InGaP crystal for suppressing injection of holes from the base layer, and a metal electrode and an ohmic contact are formed. N-type InGa to be formed
A semiconductor device in which an emitter contact layer made of an As crystal is sequentially formed, wherein an AlAs layer is provided between the sub-collector layer and the collector layer. 3. The AlAs layer has a thickness of at least 1 n.
3. The semiconductor device according to claim 1, wherein m is m. 4. Each of the layers on the substrate is formed by MOVPE or M
4. The semiconductor device according to claim 1, wherein the semiconductor device is grown by a BE method.