JPH06318547A - Compound semiconductor epitaxial wafer - Google Patents

Abstract

PURPOSE:To remarkably increase mutual conductance gm of an FET. CONSTITUTION:A leak current of a substrate is suppressed and good mutual conductance gm characteristic can be obtained by forming an FET from an epitaxial wafer where i-GaAs layer 2, n-GaAs layer 3, n<+>-GaAs layer 4, for example, are grown on the surface of a semi-insulated GaAs substrate 1 including carbon of the concentratmon of 0.2 to 2X10<16>cm<-3>.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a compound semiconductor, especially Ga.
The present invention relates to an As-based epitaxial wafer.

[0002]

2. Description of the Related Art Semi-insulating GaAs which has been used conventionally
Most of the substrates had a resistivity of 1 to 6 × 10 ⁷ Ω · cm and a carbon concentration of 0.2 to 2 × 10 ¹⁵ cm ⁻³ . If the resistivity is higher and the carbon concentration is higher than that, S
It was not used because the activation rate after implanting i-ions was poor. Moreover, it is one of the reasons that the technology for uniformly attaching carbon has not been developed and has not been used. On the other hand, recently, using a wafer epitaxially grown on a semi-insulating GaAs substrate, a power FET (Field Effect Transistor) for mobile band wireless communication has been recently used.
(stor) is under development. This element is several tens mA
The current of about 10 mW is applied to obtain the output of
If there is a large amount of leak current in the undoped buffer layer or the semi-insulating substrate, the threshold voltage becomes deep, and therefore the transconductance gm, which is an important characteristic of the FET, decreases.

The above-mentioned resistivity of 1 to 6 × 10 ⁷ Ω · cm
FIG. 3 shows the state of the threshold voltage when the semi-insulating substrate of 1 is used. In addition, the evaluated epitaxial wafer,
FIG. 1 shows an FE manufactured from the epitaxial wafer of FIG.
The T structure is shown in FIG. 1 and 2, 1 is a semi-insulating GaAs substrate, 2 is an i-GaAs layer, and 3 is n-GaA.
s layer, 4 is an n ⁺ -GaAs layer, 5 is a source electrode, 6 is a gate electrode, and 7 is a drain electrode. The FET of FIG. 2
Has a gate length of 1 μm and a gate width of 10 mm. As can be seen from FIG. 3, the higher the substrate resistivity, the shallower the threshold voltage tends to be. However, the conventional one has a large leak current as shown by curves A and B, and is satisfactory for the FET. The characteristics were not obtained.

[0004]

As described above, the resistivity is 1
When a FET is produced by epitaxially growing it on a semi-insulating substrate of ˜6 × 10 ⁷ Ω · cm, the leak current is large, the threshold voltage becomes deeper than the design value, and there are problems that the required characteristics of the FET are not satisfied. there were.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a compound semiconductor epitaxial wafer using a semi-insulating GaAs substrate capable of significantly increasing the transconductance gm of FET. .

[0006]

The gist of the present invention resides in the use of a semi-insulating GaAs substrate having a carbon concentration of 0.2 to 2 × 10 ¹⁶ cm ^-3 for epitaxial growth. The reason is that the leakage current of the substrate is greatly reduced.

[0007]

[Action]

(1) As acceptors for increasing the resistivity, zinc, beryllium, etc. can be considered in addition to carbon, but since these elements are diffused by the heat treatment in the process, a sharp interface is obtained. I can't. Therefore, carbon is the easiest to handle, and the effect is high at a concentration of 0.2 to 2 × 10 ¹⁶ cm ⁻³ .

The carbon concentration is 0.2 to 2 × 10 ¹⁶ cm
^As described in detail in Japanese Patent Application No. 3-260779, the leakage current is reduced by setting ^-3 .

(2) Corresponding to a carbon concentration of 0.2 to 2 × 10 ¹⁶ cm ^-3 , the resistivity of semi-insulating GaAs is 0.6 to 10 ×.
10 ⁸ Ω · cm. Ga of 6 × 10 ⁷ Ω · cm or less
If an As substrate is used, the effect of suppressing leakage current is small.
Further, when it exceeds 1 × 10 ⁹ Ω · cm, it inverts to p-type.

[0010]

【Example】

[Example 1] A substrate having a carbon concentration of 3.0 x 10 ¹⁵ cm
^-3 , using a semi-insulating GaAs substrate with a resistivity of 1 × 10 ⁸ Ω · cm, metal organic vapor phase epitaxial growth (MOVP)
By the E) method, an epitaxial wafer having the structure shown in FIG. 1 was formed similarly to the conventional method, and using this epitaxial wafer, an FET having the structure shown in FIG. 2 was manufactured similarly to the conventional method.
At this time, the relationship between √ (Ids) and Vgs is shown in FIG. As shown by the curve C in FIG. 3, the leak current is suppressed, and a power FET satisfying the required characteristics was obtained.

Example 2 A substrate having a carbon concentration of 7.0 ×
Semi-insulating G with 10 ¹⁵ cm ^-3 and resistivity 3 × 10 ⁸ Ω · cm
An FET was produced under the same conditions as in Example 1 using the aAs substrate. As a result, as shown by the curve D in FIG. 3, a FET which satisfies the same conditions as in Example 1 was obtained.

Comparative Example 1 A substrate having a carbon concentration of 2.2
× 10 ¹⁴ cm ^-3, use the semi-insulating GaAs substrate of resistivity of 1 × 10 ⁷ Ω · cm, were fabricated FET under the same conditions as in Example 1. As a result, as shown by the curve A in FIG. 3, the leak current was considerably large, the threshold voltage was deep, and a satisfactory mutual conductance gm characteristic could not be obtained.

[Comparative Example 2] A substrate having a carbon concentration of 1.7
× 10 ¹⁵ cm ^-3, use the semi-insulating GaAs substrate resistivity 5 × 10 ⁷ Ω · cm, were fabricated FET under the same conditions as in Example 1. As a result, as shown by the curve B in FIG. 3, although the leak current was slightly smaller than that in Comparative Example 1, satisfactory results could not be obtained.

Although the above-mentioned embodiment was carried out by the metal organic chemical vapor deposition (MOVPE) method, the molecular beam epitaxy (MBE) method or the simple vapor phase epitaxy (VE) method was used.
It is considered that the same effect can be obtained even when grown by the PE method.

As another method of making an FET, a method of implanting Si ions into a semi-insulating GaAs substrate and annealing is also effective in this method as well when a high resistance substrate is used.

[0016]

According to the present invention, an FET such as a GaAs power FET that allows a large current to flow can be manufactured by suppressing the substrate leakage current. Also, when applied to a normal low noise FET, the characteristics are similarly improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing an epitaxial wafer structure for an FET.

2 is an FE produced from the epitaxial wafer of FIG.
It is explanatory drawing which shows T structure.

FIG. 3 is an explanatory diagram showing a relationship between √ (Ids) and Vgs in the FET of FIG.

[Explanation of symbols]

1 Semi-insulating GaAs substrate 2 i-GaAs substrate 3 n-GaAs layer 4 n ⁺ -GaAs layer

Claims (2)

[Claims] 1. A compound semiconductor epitaxial wafer having a plurality of compound semiconductor thin films formed on a semi-insulating GaAs substrate having a carbon concentration of 0.2 to 2 × 10 ¹⁶ cm ⁻³ . 2. A compound semiconductor epitaxial wafer according to claim 1, wherein the GaAs substrate has a resistivity of 0.6 to 10 × 10 ⁸ Ω · cm.