JPH06349862A - Semiconductor crystal and semiconductor device using it - Google Patents

Abstract

PURPOSE:To obtain a crystal increasing an In composition ratio and having the greater degree of channel change and greater sheet carrier concentration than usual by a method wherein a film thickness and an In composition ratio of an InGaAs layer are determined so that a photoluminescence spectrum from the InGaAs layer at a specific temperature can have specific quality. CONSTITUTION:In a hetero-structure compound semiconductor crystal formed on a GaAs substrate 11 with at least an undoped InGaAs layer 13 and an n-type AlGaAs layer 15, a film thickness and the indium content of the InGaAs layer 13 are determined as described later. Namely, a peak wavelength of a photoluminescence spectrum from the InGaAs layer 13 at 77K is between 1000nm and 1120nm, and a half-width of the photoluminescence spectrum is made smaller than 47meV. For example, a non-doped GaAs buffer layer 12, a non-doped InGaAs channel layer 13, etc., are successively epitaxial-grown on the semi- insulating GaAs substrate 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor crystal used for producing a field effect transistor by epitaxial growth and a semiconductor device using the same.

[0002]

2. Description of the Related Art An example of a field effect transistor using a semiconductor crystal epitaxially grown by a molecular beam epitaxy (MBE) method, a metal organic thermal decomposition (MOCVD) method, etc. is formed on a gallium arsenide substrate and has a distorted lattice. HEMT using indium gallium arsenide layer as channel
(High Electron Mobility Transistor)
61-3464. Further, an example of evaluating the optical characteristics of an indium gallium arsenide strained channel HEMT crystal by a photoluminescence method (PL method) is given in Applied Physics Letters 61 (1992) No. 122.
Pages 5 to 1227 (Applied Physics Letters Vol.61
(1992) pp.1222-1227).

[0003]

In the above-mentioned prior art, the indium composition ratio and the film thickness of the channel of the channel which is capable of sufficiently accumulating carrier electrons in the indium gallium arsenide strained channel and has excellent mobility are , 0.25 and 8 nm, respectively. When the indium composition ratio exceeds 0.3, dislocation defects and the like occur,
Mobility that is a characteristic that can be used as a low-noise device is 6000 square centimeters per volt-second, and sheet carrier concentration is 2.2 times 10 per square centimeter.
However, there is a problem that the characteristics exceeding the surplus of 12 cannot be obtained.

An object of the present invention is to increase the indium composition ratio and obtain a crystal having a channel mobility and a sheet carrier concentration higher than those of the related art and a semiconductor device using the crystal.

[0005]

In the heterostructure compound semiconductor crystal formed on a gallium arsenide substrate and having at least an undoped indium gallium arsenide layer and an n-type aluminum gallium arsenide layer, the film of the indium gallium arsenide layer is formed. The thickness and indium composition ratio are set to 7
The peak wavelength of the photoluminescence spectrum from the indium gallium arsenide layer at 7K is set to be between 1000 nanometers and 1120 nanometers, and the half width of the photoluminescence spectrum is set to be less than 47 millielectron volts. Achieved by a semiconductor crystal.

[0006]

The photoluminescence spectrum from the indium gallium arsenide strained channel shifts significantly longer wavelengths when dislocation defects occur. Further, when the substrate temperature is high and the arsenic molecular beam pressure is low, indium is significantly segregated on the surface, and the photoluminescence spectrum shifts to a short wavelength. Further, when the channel is thin, the wavelength shifts short when the indium composition ratio is small and shifts long when the indium composition ratio is small. Adjust these elements, 77K
The peak wavelength of the photoluminescence spectrum from the indium gallium arsenide layer at is in the range of 1000 nm to 1120 nm, and the half-width of the peak is set to less than 47 millielectron volts. A semiconductor crystal using an excellent indium gallium arsenide strained channel can be manufactured, and the mobility exceeds 6000 square centimeters per volt-second, and the sheet carrier concentration exceeds 2.2 times 10 12 squares per square centimeter.

[0007]

EXAMPLE 1 FIG. 2 is a schematic sectional view of a semiconductor crystal having a HEMT structure using the present invention. On the semi-insulating gallium arsenide substrate 11, the undoped gallium arsenide layer 12 is used as a buffer layer for 450 nm, and the undoped indium gallium arsenide layer 13 (indium composition ratio y) is used as a channel layer for x nm and undoped aluminum by the MBE device. The n-type aluminum gallium arsenide layer 15 (aluminum composition ratio 0.2
5, doping concentration 3 × 10 18 cubes per cubic centimeter) 20 nm, undoped aluminum gallium arsenide layer 16 (aluminum composition ratio 0.1.
25) and the undoped gallium arsenide cap layer 17 were sequentially epitaxially grown at 5 nm and 5 nm, respectively. Where x is 4 to 8 nanometers and y is 0.2
It was set to 5 to 0.4.

The electrical and optical properties of the HEMT crystal thus formed are evaluated by Hall measurement and photoluminescence method, respectively, and the peak wavelength of the photoluminescence spectrum is plotted on the horizontal axis, and the movement of the two-dimensional electron gas 18 is determined. When the degree is plotted on the vertical axis, it becomes as shown in FIG.

Regardless of the thickness of the channel or the composition ratio of indium, the peak wavelength of the photoluminescence spectrum falls between 1000 nm and 1120 nm, and the half width of the photoluminescence spectrum is 47 mm electron volts. The mobilities of the smaller samples at room temperature were all well above conventional mobilities, exceeding 6200 square centimeters per volt-second, up to 6750 square centimeters per volt-second. Further, the sheet carrier concentration stably exceeded 2.2 times 10 12 per square centimeter, and was obtained at a maximum of 2.7 times 10 12 per square centimeter.

Here, the peak wavelength of the photoluminescence spectrum falls between 1000 nanometers and 1120 nanometers regardless of the channel thickness and the composition ratio of indium, and the half width of the photoluminescence spectrum is 47 millimeters. Samples smaller than the electron volt were grown at a substrate temperature of 400 ° C to 420 ° C during channel growth when the crystal growth condition was such that the arsenic molecular beam pressure at the substrate position was about 1 times 10 -5 torr. If the arsenic molecular beam pressure at the position is about 1.5 times 10 −5 torr, the substrate temperature during channel growth is 400 ° C.
To 450 ° C only.

According to the present embodiment, it is clear that the present invention has an effect of improving the mobility and the sheet carrier concentration.

Example 2 FIG. 3 is a schematic sectional view of a HEMT device using the present invention. The undoped gallium arsenide layer 12 is used as a buffer layer on the semi-insulating gallium arsenide substrate 11 by the MBE device for 450 nm, and the undoped indium gallium arsenide layer 13 (indium composition ratio y) is used as a channel layer x.
Nanometer, undoped aluminum gallium arsenide layer 1
4 as a spacer layer, 2 nm, n-type aluminum gallium arsenide layer 15 (aluminum composition ratio 0.25,
Doping concentration 3 times 1 per cubic centimeter 1
0 18) 20 nm, undoped aluminum gallium arsenide layer 16 (aluminum composition ratio 0.25)
12 nm, n-type gallium arsenide cap layer 21
(Doping concentration of 4 times 10 18 powers per cubic centimeter) was sequentially epitaxially grown for 160 nanometers. Where x is 4 to 8 nanometers,
y was set to 0.25 to 0.4.

The optical characteristics of the semiconductor crystal thus formed were measured by photoluminescence at 77K.
A HEMT having a gate length of 0.15 μm and a gate width of 200 μm is obtained through a well-known mesa etching process, a source electrode 22, a gate electrode 23, and a drain electrode 24 forming process.
A device was made.

Regardless of the thickness of the channel or the composition ratio of indium, the peak wavelength of the photoluminescence spectrum falls between 1000 nm and 1120 nm, and the half width of the photoluminescence spectrum is 47 mm electron volts. The mobility of the smaller sample at room temperature after the device fabrication process was much higher than the mobility after the conventional device fabrication process as in Example 1, and exceeded 6000 square centimeters per 1 volt / second, and the maximum per 1 volt / second. 663
0 square centimeters were obtained. In addition, the density of the sheet carrier stably exceeds 2.0 multiplied by 10 12 per square centimeter, and the maximum is 2.6 multiplied by 10 1.
I got 2 squares.

The transconductance, which is a basic performance index of the device, is
A gate width of 200 micron was 36 millisiemens, an improvement of about 15% compared to the conventional one. Also, the maximum transconductance is 12 per 200 micron gate width.
It was 4 millisiemens, an improvement of about 20% compared to the past.

According to the present embodiment, it is clear that the present invention has an effect on improving the transconductance of HEMT devices.

Judging from the transconductance obtained in this embodiment, it is obvious that excellent performance can be obtained by using the HEMT device as a low power consumption and low noise amplifier.

[0018]

According to the present invention, a crystal having a large indium composition ratio and a higher channel mobility and a higher sheet carrier concentration than in the prior art can be obtained, which is very effective in improving the performance of the field effect transistor.

[Brief description of drawings]

FIG. 1 is a measurement diagram showing the relationship between the peak wavelength of a photoluminescence spectrum and the mobility of a two-dimensional electron gas in a channel according to an embodiment of the present invention.

FIG. 2 is a sectional view of a crystal according to an example of the present invention.

FIG. 3 is a cross-sectional view of the device structure of one embodiment of the present invention.

[Explanation of symbols]

1 ... Plot showing the relationship between the peak wavelength of the photoluminescence spectrum at a channel thickness of 8 nm and the mobility of the two-dimensional electron gas, 2 ... The peak wavelength of the photoluminescence spectrum at a channel thickness of 6 nm, and Plot showing the relationship with the mobility of the two-dimensional electron gas, 3 ... Plot showing the relationship between the peak wavelength of the photoluminescence spectrum and the mobility of the two-dimensional electron gas at a channel thickness of 5 nm, 4.
Plot showing the relationship between the peak wavelength of the photoluminescence spectrum and the mobility of the two-dimensional electron gas at a channel thickness of 4 nm, 5 ... Representing a sample in which the half width of the photoluminescence spectrum exceeds 47 millielectron volts Plot, 6 ... Plot showing a conventional structure for reference, 11 ... Semi-insulating gallium arsenide substrate, 1
2 ... Undoped gallium arsenide buffer layer, 13 ... Undoped indium gallium arsenide channel layer, 14 ... Undoped aluminum gallium arsenide spacer layer, 15 ... N-type aluminum gallium arsenide layer, 16 ... Undoped aluminum gallium arsenide layer, 17 ... Non Doped gallium arsenide layer, 18 ...
Two-dimensional electron gas, 21 ... n-type gallium arsenide cap layer,
22 ... Source electrode, 23 ... Gate electrode, 24 ... Drain electrode.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Mineo Wajima 3550 Kidayomachi, Tsuchiura City, Ibaraki Prefecture Hitachi Cable Ltd. Advanced Research Center

Claims (3)

[Claims] 1. In a heterostructure compound semiconductor crystal formed on a gallium arsenide substrate and having at least an undoped indium gallium arsenide layer and an n-type aluminum gallium arsenide layer, the film thickness and indium composition ratio of the indium gallium arsenide layer are The peak wavelength of the photoluminescence spectrum from the indium gallium arsenide layer at 77K is set to be between 1000 nanometers and 1120 nanometers, and the half width of the photoluminescence spectrum is set to be less than 47 millielectron volts. A semiconductor crystal characterized in that 2. A heterostructure compound semiconductor crystal formed on a gallium arsenide substrate and having at least an undoped indium gallium arsenide layer and an n-type aluminum gallium arsenide layer, the growth conditions, film thickness and indium composition of the indium gallium arsenide layer. The ratio of the photoluminescence from the indium gallium arsenide layer at 77K
Peak wavelength of the spectrum is from 1000 nm to 1
A semiconductor crystal, which is set to have a width of 120 nm and a half width of the photoluminescence spectrum smaller than 47 millielectron volts. 3. A field-effect transistor obtained by processing a heterostructure compound semiconductor crystal formed on a gallium arsenide substrate and having at least an undoped indium gallium arsenide layer and an n-type aluminum gallium arsenide layer. Photoluminescence from the indium gallium arsenide layer when the growth conditions, film thickness and indium composition ratio of the arsenic layer are 77K.
Peak wavelength of the spectrum is from 1000 nm to 1
A semiconductor device, wherein the semiconductor device is set so as to fall within a range of 120 nanometers and the full width at half maximum of the photoluminescence spectrum is smaller than 47 millielectron volts.