JPH036030A - Field-effect type semiconductor device - Google Patents

Abstract

PURPOSE:To obtain a cutoff characteristic and an electrical characteristic which are excellent in spite of a short channel length by a method wherein a two-dimensional electron gas layer is formed near an interface with an n-type AlGaAs layer of an undoped GaAs channel layer and the thickness of the undoped GaAs channel is set to a specific range. CONSTITUTION:An undoped GaAs buffer Iayer 12, a superlattice layer 13 for electron cutoff use, an undoped GaAs channel layer 14, an AlGaAs layer 15 used as an electron supply layer and an n-type GaAs cap layer 16 doped with Si are laminated on a semi-insulating GaAs substrate 1. A two-dimensional electron gas layer is formed near an interface with an n-type AlGaAs iayer 15a of the undoped GaAs channel layer 14. The thickness of the undoped GaAs channel layer 14 is set to 10 to 200nm. Thereby, even when gate length is short, it is possible to form a structure by which the characteristic as a high-frequency and low-noise device is hard to deteriorate.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a field effect semiconductor device, and particularly to the structure of a heterojunction field effect transistor.

(Prior art) Figure 2 shows a conventional heterojunction field effect transistor (
Below, a cross-sectional view of r) (referred to as EMTj) is shown. In this HEMT, undoped GaAs is used to form a two-dimensional electron gas layer on a semi-insulating substrate 1.
(i-GaAs) layer 2, an n-type impurity-doped AlGaAs layer 3 serving as a carrier supply layer, and an n-type GaAs layer 4 for providing good ohmic contact with the electrode.
is formed by epitaxial growth.
A source electrode 5 and a drain electrode 6 are provided on the aAs layer 4.
A gate electrode 7 is formed on the AlGaAs layer 3.

In such HEMTs, the gate length is short (for example, 0
．． (approximately 3 μm or less), the electric field between the source and drain becomes strong, and some of the electrons in the channel layer 1-GaAs layer2 become carriers and leak to the semi-insulating substrate 1 side. It becomes like this.

The resulting current cannot be controlled by gate bias, leading to failure. In other words, even if sufficient gate bias is applied, the source
The current between the drains is not completely cut off. Such a phenomenon is called short channel effect.

In order to suppress the short channel effect, semi-insulating substrate 1 and i
-GaAs A structure in which a GaAs layer doped with a p-type impurity or an AlGaAs layer is inserted between the stone 2 and the stone 2 has been proposed.

However, in a structure in which a p-type GaAs layer is inserted, a problem arises in that parasitic capacitance increases. On the other hand, AI GaA
In the structure in which the s-layer is inserted, a problem arises in that the crystallinity of the 1-GaAs layer 2 existing on the AIGaAS layer decreases, and the -characteristics deteriorate.

For this reason, a GaAs layer doped with p-type impurities or an A
A structure in which a GaAs-AlGaAs superlattice layer is inserted in place of the LGaAs layer has been proposed (Appl, Ph.
ys, Lett, 42(7), l April
19B3)o In this structure, the superlattice suppresses impurity diffusion and improves flatness. Therefore, the crystallinity of the channel layer does not deteriorate as seen when 1 m of simple AlGaAs is inserted. In the case of a structure using this superlattice layer, electrical characteristics, particularly high frequency noise characteristics, are good.

(Problem to be solved by the invention) However, even in a structure in which a superlattice layer is inserted as an electron blocking layer as described above, if the gate length is further shortened, the short channel effect will still be present as before. appears, and HE
There was a problem that the noise figure (NF), gain, and other characteristics of the MT deteriorated.

An object of the present invention is to provide a field-effect semiconductor device having a structure in which the characteristics of a HEMT as a high-frequency, low-noise device are unlikely to deteriorate even when the gate length is further shortened.

(Means for Solving the Problems) A field effect semiconductor device of the present invention is a GaAs-AlGa
As superlattice layer, undoped GaAs channel layer, n
A laminated structure having an AlGaAs type layer and an n type GaAS layer in this order is formed on a semiconductor substrate, and the undoped GaAs layer is formed on a semiconductor substrate.
A field effect semiconductor device in which a two-dimensional electron gas layer is formed near the interface between an As channel layer and the n-type AlGaAs layer, the undoped GaAs channel layer having a thickness of 10
~2QOnm, thereby achieving the above objective.

(Example) The present invention will be described below with reference to Examples.

FIG. 1 shows an embodiment of the present invention applied to HEMT. In the HEMT shown in FIG. 1, an undoped GaAs buffer layer 12 (500 nm thick) is placed on a semi-insulating GaAs substrate 11.
), electron blocking superlattice layer 13, undoped GaAs channel layer 14 (thickness 200 nm), AlG serving as an electron supply layer
aAs layer 15, and Si-doped (2xlO18cm-3
) n-type GaAs + '77 layer 16 (thickness 10
100n are laminated.

The superlattice layer 13 is made of undoped Al a, 2sG a e
, vsAS layer 13a (thickness lonm) and undoped Ga
It has a structure in which five A3 layers 13b (thickness 10 nm) are alternately laminated. In addition, A I which becomes an electron supply layer
The GaAs layer 15 is made of undoped A l l+, 25Ga
11.7sA 5 layers 15b (thickness 2 layers m) and Si doped (I x 10I8am-3) n
Type A l 11.2sG E11! , 75A 5 layers 15
It has a laminated structure with a (thickness: 45 nm).

Each of these layers was formed by the MBE method. The growth conditions in this MBE method were an As/Ga flux ratio of about 6 and a substrate temperature of 580°C.

A source electrode 17 and a drain electrode 18 are formed using gold germanium/nickel/gold (AuGe/Ni/Au) on the above-described semiconductor stacked structure using a known technique. Further, the gate electrode 19 is made of aluminum,
The gate length is 0.2 μm and the gate width is 200 μm.

In the HEMT of this example, a two-dimensional electron gas layer is formed near the interface with the AlGaAs layer 15 in the undoped GaAs channel layer 14.

FIG. 3 shows the drain current-voltage characteristics of this example. The scale on the left vertical axis of the graph shown in Figure 3 is 2.632 mA.
It is a unit. From FIG. 3, it can be seen that if a sufficient gate bias is applied, the drain current is completely blocked. The HE MT of this example has a high mutual conductance g
II is shown.

Further, the noise figure of this example is 0.6 dB, and the gain i
;! It was 12 dB. As described above, the HEMT of this example suppresses the short channel effect even if the gate length is short, exhibits excellent cutoff characteristics, and also exhibits good electrical characteristics.

The thickness of the undoped GaAs channel layer 14 is 10 n.
m, 15 nm, 20 nm, 50
A HEMT having the same configuration as the above-mentioned example except that the thickness was nm, lOOnm, or 150 nm was fabricated, and each characteristic was investigated. As a result, these HEMTs had almost the same excellent performance characteristics as those of the above-mentioned examples.

Further, the thickness of the undoped GaAs channel layer 14 was set to 5n.
HEMTs with a thickness of m, 250 nm, 500 nm, or 11000 nm were fabricated as comparative examples.

When the thickness of the channel layer 14 was 250 nm or more, there was a tendency for the blocking characteristics to decrease slightly. - As an example, FIG. 4 shows the drain current-voltage characteristics of a HEMT in which the channel layer 14 is 500 nm thick. The scale of the left vertical axis of the graph shown in FIG. 4 is 2. ．． The unit is 476mA. In this embodiment, the drain current may not become zero depending on the gate noise, and the cutoff characteristics are degraded.

Further, in the HEMT in which the thickness of the channel layer 14 was 5 nm, the noise figure decreased to 0.8 dB.

This is considered to be due to a decrease in electron mobility and a decrease in carrier concentration.

(Effects of the Invention) According to the configuration of the present invention, a field effect semiconductor device can be obtained that exhibits excellent blocking characteristics and electrical characteristics despite having a short channel length.

4,', na: [ Fig. 1 is a schematic cross-sectional view of an embodiment of the present invention, Fig. 2 is a schematic cross-sectional view of a conventional example, and Fig. 3 is a drain current of an embodiment of the present invention. Graph showing voltage characteristics. FIG. 4 is a graph showing drain current-voltage characteristics of a comparative example.

11... Semi-insulating GaAs, 12... Undoped Ga
As buffer layer, 13... superlattice layer, 13a... undoped A I a, 2sG a l! , 75A S layer,
13b--Undoped GaAs layer, 14--Undoped GaAs channel layer, 15a-n type A1!
1.2sGas, 7sAs layer, 151) -・
・Undoped A I +1.25G a s, ysA s
layer.

that's all

Claims (1)

[Claims] 1. GaAs-AlGaAs superlattice layer, undoped GaAs channel layer, n-type AlGaAs layer, and n-type G
aAs in this order is formed on a semiconductor substrate, the n-type Al of the undoped GaAs channel layer
A field effect semiconductor device in which a two-dimensional electron gas layer is formed near the interface with a GaAs layer, the undoped G
A field effect semiconductor device in which an aAs channel layer has a thickness of 10 to 200 nm.