JPH07118540B2 - Semiconductor device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device using a two-dimensional electron gas generated at a heterojunction interface of a compound semiconductor, and more particularly to a high electron mobility transistor.

[0002]

2. Description of the Related Art For application to high speed computers and high speed signal processing systems, GaAs and I having high electron mobility are used.
Development of ICs and LSIs using nP is in progress. In particular, GaAs and GaAlAs or InP and InGa
A high electron mobility transistor (high electron mobility transistor (high electron mobility transistor) utilizing the high speed property of a two-dimensional electron gas generated at the heterojunction interface of As, etc.
(Transition transistor: HEMT) has been obtained until the switching time per gate at room temperature is 12 psec (see Japanese Patent Laid-Open No. 56-94780).

FIG. 2A shows a cross-sectional view of a typical HEMT. In the figure, 1 is a semi-insulating GaAs substrate, 2 is a highly pure undoped GaAs layer having a thickness of about 1 μm and a carrier concentration of 10 ¹⁴ cm ^-3 or less, and 3 is a Ga having a thickness of about 100 Å.
_1-x Al _x As layer ( _{x to} 0.3), 4 has a thickness of about 500Å,
N-Ga _1-x Al _{x with a} carrier concentration of 10 ¹⁷ to 10 ¹⁸ cm to ³
As layers (x to 0.3) and 5 are the undoped GaAs layer and the undoped Ga _1-x Al _x A in the undoped GaAs layer 2.
A two-dimensional electron gas layer induced at the heterojunction interface with the s layer 3, 6 is a source electrode in the case of a field effect transistor (hereinafter referred to as FET), 7 is a gate electrode, and 8 is a drain electrode. In addition, such a semiconductor crystal for HEMT is produced by a molecular beam epitaxy method (MBE method) or a metal organic thermal decomposition method (OM-VPE method).

FIG. 2B shows the HEM shown in FIG.
It is an energy band figure of T. In the figure, E _C is the conduction band, E _F is the Fermi level, E _V is the valence band, E _S is the electron storage layer, and w is the potential well. Other numbers are the same as those in FIG. 2 (a).

Such a HEMT has a large mobility of 8000 cm ² / V · sec or more at room temperature because the two-dimensional electron gas travels in the high-purity undoped GaAs layer 2, and thus has a high speed of the device. Shows excellent characteristics of.

[0006]

However, when the FET is used, the sheet concentration of the two-dimensional electron gas is 10 ¹¹ cm −1.
^{With two} units, the two-dimensional electron gas is only 100 Å from the interface.
Since it is confined within, it is not possible to increase the flowing current, and when the number of fanouts is large,
There is a common problem with FETs that the speed of the device is reduced. When the gate electrode width L is as small as submicron, the threshold voltage _Vth tends to decrease due to the short channel effect. That is, HEMT is a normal Ga
Compared with the AsFET (MESFET), electrons are confined in the triangular well w of the interface potential (electron storage layer E _S ), which is somewhat advantageous in terms of the speed of the device, but L is about 0.5 μm. Becomes V _th
Becomes larger, which is an important issue.

In order to improve these points, FIG.
Double hetero structure HEM as shown in (a) and (b)
T has been proposed (see JP-A-57-76879). FIG. 3 (a) is a cross-sectional view of this HEMT, FIG. 3 (b).
Is the energy band diagram. In the figure, 21,
23 is an undoped GaAs layer, 22 is undoped Ga
_1-x Al _x As layer is shown. In this HEMT, the two-dimensional electron gas layer 5 is sandwiched by the undoped Ga _1-x Al _x As layer 3 and the undoped Ga _1-x Al _x As layer 22 provided on the substrate side, and the potential well created by these is formed. It is intended to be confined in w. In this case, assuming that the molar ratio X of AlAs in the undoped Ga _1-x Al _x As layer 22 is 0.1 to 0.3 necessary for confining electrons, the potential well of the undoped GaAs layer 23 sandwiched between them is set. By increasing the width of w to, for example, about 200Å, it is expected that the sheet density of the carrier can be increased to nearly double that of the conventional one, and the short channel effect will be reduced.

However, in reality, undoped Ga _1-x Al _x
Undoped GaAs layer 23 grown on As layer 22
The electron mobility of the HEMT shown in FIGS. 3 (a) and 3 (b) is higher than that shown in FIGS. 2 (a) and 2 (b) because of the process reason that the crystallinity of the is deteriorated. It was getting low.

It is an object of the present invention to provide a high electron mobility semiconductor device having a new structure which solves the above problems.

[0010]

In order to achieve the above object, a semiconductor device of the present invention comprises a first semiconductor layer and a material for the first semiconductor layer formed on the first semiconductor layer.
Is formed of a material with a lattice mismatch and the film thickness is misfit
Multiple well layers below the critical thickness for the occurrence of
The thickness of the well layer alternated with that of the misfit dislocation
It has a superlattice structure consisting of layers below the critical thickness for generation.
A second semiconductor layer, characterized by comprising a third semiconductor layer formed on the second semiconductor layer, and means for supplying control a two-dimensional electron gas in the well layer .

The superlattice structure is characterized by being composed of an InGaAs layer and a GaAs layer, and a GaAsSb layer and a GaAs layer.

[0012]

The present invention can provide a semiconductor device having a high electron mobility using a two-dimensional electron gas with the above structure.

[0013]

FIG. 1 shows a HEMT structure according to an embodiment of the present invention.
Shown in (a) and (b). FIG. 1A is a sectional view of a HEMT according to an embodiment of the present invention, and FIG. 1B is an energy band diagram thereof.

As shown in these figures, in this embodiment,
The two-dimensional electron gas layer 5 includes an undoped GaAs layer 21 on the substrate side and an undoped Ga _1-x Al _x As layer (x>
0) 3 and undoped In _y Ga _1-y As layer (y
> 0) It is confined in a potential well w of approximately 200 Å with a width of 24. This undoped I
undoped GaAs instead of n _y Ga _1-y As layer 24
_{A 1-z} Sb _z layer (z> 0) may be used, or at least one undoped In _y Ga _1-y As layer and an undoped GaAs _1-z Sb _z layer may be stacked. In addition, an undoped GaAs layer and an undoped In _y Ga _1-y As
2 layers or undoped GaAs layer and undoped G
It may be used a superlattice structure consisting of two layers of a aAs _1-z Sb _z layer. Further, each of the above two layers may be provided in multiple stages. Undoped GaAs layer 2 when y, z-0.1
1 and these ternary mixed crystals (undoped In in FIG.
The band gap difference with the _y Ga _1-y As layer 24) is about 0.1.
At eV, y, z-0.2 is about 0.2 eV, which is sufficient to form a well.

The structure shown in FIG. 1 (a) can be easily manufactured by, for example, a molecular beam epitaxy method by adding a new In or Sb evaporation crucible to the apparatus under almost the same growth conditions as the conventional HEMT. can do. Hereinafter, a method for manufacturing the HEMT of this embodiment will be described.

1. First, a semi-insulating GaAs substrate <100> 1 is inserted into an MBE apparatus equipped with an evaporation crucible which is a molecular beam source of Ga, As, In, Al and Si.

2. Next, the substrate is heated to about 630 ° C. to clean the surface of the substrate.

3. Next, the substrate temperature was kept at about 600 ° C., the shutter of the molecular beam source of Ga and As was opened, and the thickness was about 1 μm.
The undoped GaAs layer 21 is grown. The intensity ratio of Ga and As molecular beams at that time was 1: 2.

4. Next, the shutter of the molecular beam source of In was opened, and the undoped In _y Ga _1-y As layer 2 having a thickness of about 200 Å was formed.
Grow 4

5. Next, the shutter of the In molecular beam source is closed and the shutter of Al is opened to grow an undoped Ga _1-x Al _x As layer 3 having a thickness of about 100 Å.

6. Next, the shutter of the Si molecular beam source is opened to grow the n-Ga _{1- x} Al _x As layer 4 having a thickness of about 1000Å.

7. Finally, the shutters of all molecular beam sources are closed to lower the substrate temperature to complete the product.

This undoped In _y Ga _1-y As layer 24
Was not deteriorated in quality when grown on the undoped GaAs layer 21, and was undoped Ga.
The mobility, which is slightly lower than that of the As layer due to alloy scattering, is effectively canceled by increasing the sheet electron concentration, and a higher speed can be achieved as an IC. The undoped In _y Ga _1-y As layer 24 is
The underlying undoped GaAs layer 21 and the upper undoped Ga
_{Since the} lattice constant is smaller than that of the _1-x Al _x As layer 3,
If it is too thick, misfit dislocations will occur at the interface, but dislocations were not seen up to the so-called critical film thickness of 200Å. The above is undoped I
Instead of the n _y Ga _1-y As layer 24, undoped GaAs
_The same was true when the _1-z Sb _z layer was used.

Further, instead of the undoped In _y Ga _1-y As layer 24, an undoped In _y Ga _1-y As layer and an undoped GaAs _1-z Sb _z layer are alternately attached to the undoped GaAs layer by about 50 Å. If you do, a total of 1000Å
The misfit dislocations did not occur up to the thickness of, and the effective sheet concentration could be further increased.

High-purity GaAs and InA at room temperature
The electron mobilities of s and GaSb are about 8500 and 33, respectively.
5,000 and 5000 cm ² / V · sec, the (GaIn) As mixed crystal is more preferable as the material of the layer (24 in FIG. 1A) for confining the two-dimensional electron gas layer 5.
It goes without saying that it is more advantageous than Sb). In _y
When Ga _1-y As is used, a HEMT having a higher speed than that of GaAs can be realized, but 0 ≦ x
When ≤0.25, there is no great difference in mobility between InGaAs and GaAs. When x <0.3, the mobility increases almost linearly with the mobility of InAs, but the lattice mismatch also increases. Therefore, it is preferable to alternately provide InGaAs and GaAsSb with undoped GaAs.

The above Ga _1-x Al _x As, In _y Ga _1-y A
The composition range of each mixed crystal material of s and GaAs _1-z Sb _z is preferably x to 0.1 to 0.5 and y, z to 0.05 to 0.5.

Although the above description has been applied to the FET, the CC utilizing the characteristics of the two-dimensional electron gas is also used.
D (Charge Coupled D
The present invention is also effective for devices such as evice)).

[0028]

As described above, according to the present invention,
There is an effect that a semiconductor device having a high electron mobility using a two-dimensional electron gas can be provided.

[Brief description of drawings]

1A is a cross-sectional view of a HEMT according to an embodiment of the present invention, and FIG. 1B is an energy band diagram of the HEMT shown in FIG.

2A is a cross-sectional view of a conventional typical HEMT, FIG.
(B) is an energy band diagram of the HEMT shown in (a).

3A is a cross-sectional view of a conventional improved HEMT, FIG.
(B) is an energy band diagram of the HEMT shown in (a).

[Explanation of symbols]

1 ... Semi-insulating GaAs substrate, 2, 21, 23 ... Undoped GaAs layer, 3, 22 ... Undoped Ga _1-x Al _x As
Layers, 4 ... n-Ga _1-x Al _x As layer, 5 ... Two-dimensional electron gas layer, 6 ... Source electrode, 7 ... Gate electrode, 8 ... Drain electrode, 24 ... Undoped In _y Ga _1-y As layer ( Or Ga
As _1-z Sb _z layer).

Claims (3)

[Claims] 1. A lattice mismatch between a first semiconductor layer and a material of the first semiconductor layer formed on the first semiconductor layer.
Formed of the same material, the film thickness is against the occurrence of misfit dislocations
Alternating with multiple well layers below the critical thickness
The thickness of the film arranged in the
Controlling supply of a two-dimensional electron gas to the second semiconductor layer having a superlattice structure composed of layers having a boundary thickness or less, the third semiconductor layer formed on the second semiconductor layer, and the well layer. And a means for producing the semiconductor device. 2. The superlattice structure has an InGaAs layer and GaA.
The semiconductor device according to claim 1, wherein the semiconductor device comprises an s layer. 3. The superlattice structure has a GaAsSb layer and GaA.
The semiconductor device according to claim 1, wherein the semiconductor device comprises an s layer.