JPH0695534B2 - Heterostructure semiconductor device and manufacturing method thereof - Google Patents

Description

The present invention relates to a heterostructure semiconductor device and a method for manufacturing the same.

2. Description of the Related Art A two-dimensional electron gas with high mobility is formed at a heterojunction interface of a heterostructure in which an N-type AlGaAs layer is formed on a non-doped GaAs layer. The electron mobility transistor (HEMT), which controls the concentration of the two-dimensional electron gas by a gate electrode to operate as a transistor, is promising as a high-speed switching device and a microwave / millimeter wave device. To further improve its characteristics, Much research has been done actively from the material and structural aspects. From the material side, InP instead of GaAs
In _0.53 Ga _0.47 As lattice-matched to InP using
And n-type In _0.52 Al _0.48 As heterostructure is GaAs / A
AlGaAs / G has a higher electron mobility, higher electron saturation rate and higher two-dimensional electron gas concentration than HEMTs of lGaAs system.
It is attracting attention as a material that can realize high-performance HEMTs that replace aAs HEMTs. However, InP used as a substrate
Is currently more expensive than GaAs, the substrate quality is inferior to GaAs, unnecessary impurities are incorporated into the crystal layer formed on the InP substrate, and it is more easily cracked than GaAs. Has disadvantages. From this, it is possible to use InGaAs or In
There is a demand for a new technique capable of growing AlAs with good crystal quality. Such technology is also important in manufacturing integrated circuits of light receiving / light emitting devices and high-speed electronic devices. The problem when forming on InGaAs or InAlAs substrates is the difference in lattice constant between InGaAs and InAlAs and GaAs, which is very large at 3.8% when the InAs composition ratio is 0.53.
Therefore, when InGaAs is formed on GaAs by the usual means, many dislocations occur in the InGaAs layer,
Its crystallinity is significantly reduced. The present inventors use the InxGa _1-x As buffer layer in which the InAs composition ratio X is gradually increased from the GaAs substrate side to the active layer side containing InGaAs.
It was found that it is possible to significantly improve the crystallinity of the active layer. When crystal growth of this InxGa _1-x As buffer layer is performed by a normal molecular beam epitaxy method, it is necessary to adopt a temperature of 450 ° C. or lower as the growth temperature of the InxGa _1-x As buffer layer. To 1.5x10 ^-3
It was found that the crystallinity of the active layer is further improved by controlling the ratio to be / nm or less. FIG. 2 shows a cross section of a HEMT structure formed using such a method. In FIG. 2, 1 is a semi-insulating GaAs substrate, 2 is a non-doped GaA having a film thickness of about 200 mm.
An InxGa _1-x As buffer layer 13 which is an s layer and on which an InAs composition ratio changes from 0 to 0.5, for example, is formed. 0.5
InAs composition is InAs in the InGaAs channel layer 5 of the active layer formed on the InxGa _1-x As buffer layer 13.
It is determined so as to be equal to the composition ratio, and is not particularly limited to this value. A non-doped InAlAs barrier layer 4 is formed on the InxGa _1-x As buffer layer 13.
InAs composition of InAlAs barrier layer 4 InxGa _1-x As buffer layer 13
Is determined by the InAs composition (0.5 in this case) on the outermost surface side of. It is determined so as to almost match the lattice constant of In _0.5 Ga _0.5 As. The layers 5, 6 on the surface side of the InAlAs barrier layer 4,
7,8,9 are formed under the condition of lattice matching. Reference numeral 5 is a non-doped InGaAs channel layer having a thickness of 20 nm to 100 nm. 6 is a non-doped InGaAs layer having a thickness of about 3 nm, 7
Is an N-type InAlAs layer with a thickness of about 25 nm, 8 is an undoped InAlAs layer with a thickness of about 10 nm, and 9 is an N-type InGa with a thickness of about 10 nm to 50 nm.
It is the As layer.

In this structure, N is added to the undoped InGaAs channel layer 5.
Electrons are supplied from the type InAlAs layer 7 and a two-dimensional electron gas with high mobility is formed in the InGaAs channel layer 5. The mobility of the two-dimensional electron gas actually measured is 9000 to 10000 cm ² / v at room temperature when the InAs composition of the InGaAs channel layer 5 is 0.5.
・ S shows a good value.

Problems to be Solved by the Invention Although the mobility of the two-dimensional electron gas in the structure shown in the conventional example is high and the crystallinity of the active layer is very good, actually, this structure is used to actually produce a field effect transistor (FET). It has been revealed that the following problems occur when (1) is produced.
That is, when the FET is manufactured, the island regions for element formation are selectively left, and the other regions are left undoped In
Although it is removed by etching up to the vicinity of the AlAs barrier layer 4, it is clear that the pinch-off characteristic of the FET is not good due to the leak current flowing between the island regions, making it difficult to isolate the device and the leak current flowing through this substrate. Became.

Means for Solving the Problems The possible cause of such substrate leakage current is that the energy band gap of the InxGa _1-x As buffer layer 13 is smaller than that of GaAs, and becomes smaller as the InAs composition X increases. Is. Actually, in the conventional example of FIG. 2, the N-type InAlAs layer 7 and the N-type InGaAs layer 9 were not doped with N-type and were undoped. Is 1x10 ¹² /
It was found that carriers (electrons) exist at an areal density of cm ² . The cause of this residual carrier is that the doping of about 10 ¹⁵ / cm ³ is actually natural even in the non-doped layer, and a large number is generated in the InxGa _1-x As buffer layer 13 for relaxing the lattice mismatch. Occurrence of carriers related to the lattice defects that occur is considered.
It is estimated that the main cause is that the energy band cap of the _1-x As buffer layer 13 is originally small, and InxGa _1-x
Instead of As buffer layer 13, Inx (GayAl _1-y ) _1-x As, which is a material with a larger energy band gap
We devised to use a quaternary mixed crystal. The present invention is applicable to GaAs and In when forming an InGaAs layer with good crystallinity on a GaAs substrate.
To reduce the lattice mismatch of GaAs, the composition of In, Ga, Al gradually changes from the substrate side to the target InGaAs layer.
Al _1-y ) _1-x As Quaternary mixed crystal buffer layer is used.

Action The residual carrier concentration can be significantly reduced by using the Inx (GayAl _1-y ) _1-x As quaternary mixed crystal buffer layer with a larger energy band gap than the conventional InxGa _1-x As buffer layer. This not only makes it possible to suppress substrate leakage current and facilitate element isolation, but also improves the FET pinch-off characteristics. According to the present invention, an InGaAs active layer formed on a GaAs substrate can be used to realize an FET having excellent characteristics and an integrated circuit using the FET.

Embodiment An embodiment of the present invention will be described in detail with reference to FIG. FIG. 1 is a cross-sectional view of the heterostructure of the present invention, where 1 is semi-insulating.
The GaAs substrate 2 and the non-doped GaAs layer 2 may be omitted. 3 is the non-doped Inx (GayAl
_1-y ) _1-x As buffer layer, 4 is a non-doped InGaAs barrier layer having a layer thickness of about 200 nm, 5 is a non-doped InAlAs channel layer (or active layer) having a layer thickness of about 200 nm to 100 nm, 6
Is a non-doped InAlAs spacer layer having a layer thickness of about 0 to 10 nm, 7 is an N-type InAlAs layer having a thickness of about 10 to 30 nm doped with Si impurities of about 1x10 ^{18 to} 1x10 ¹⁹ / cm ³ , and 8 is a Schottky A non-doped InAlAs layer having a thickness of about 10 to 30 nm for obtaining an electrode, and 9 is an N-type InGaAs layer doped with Si impurities at about 1 × 10 ¹⁸ to 1 × 10 ¹⁹ / cm ³ . In this structure, N
Electrons are supplied from the type InAlAs layer 7 to the non-doped InGaAs channel layer 5, and a two-dimensional electron gas having high mobility is formed in the non-doped InGaAs channel layer 5. When the heterostructure molecular beam epitaxy (MBE) method shown in Fig. 1 is used, the substrate temperature during crystal growth is important.
When the Al _1-y ) _1-x As buffer layer 3 is formed, as in the conventional example, the temperature is 450 ° C. or lower, and the temperature above the undoped InAlAs barrier layer 4 is 5,
It was found that about 500 ℃ is good for forming each layer of 6,7,8,9. Especially, the growth temperature of the buffer layer 3 is important,
Experiments have shown that the surface morphology and electron mobility decrease significantly at temperatures above 450 ℃. Inx (G
a _y Al _1-y ) _1-x As The InAs composition X of the buffer layer 3 is set to 0 on the GaAs substrate 1 side and InAl on the undoped InAlAs barrier layer 4 side.
The value Z was set so as to be substantially lattice-matched with the As layer 4, and was changed substantially linearly from O to Z. The change rate of X is
The crystallinity of the InGaAs channel layer 5 is greatly affected, but the change rate of 0.15 per 100 nm of the buffer layer, that is,
It should be 1.5x10 ^-3 / nm or less. Usually a buffer layer thickness of 800 nm was used when Z = 0.5, ie ~ 6x10 ^-4 /
The rate of change was nm. On the other hand, the value of Y can be set to any value from 0 to 1 because the lattice mismatch of GaAlAs is so small that it can be ignored. The value of Y is Inx (GayAl
_1-y ) _1-x As It may be fixed in the buffer layer or may be changed, and there is no particular limitation on the value of Y. In this embodiment, the value of Y is set to 1 on the GaAs substrate side, and non-doped InAl is used.
As 1 to 0, Inx (G
ayAl _1-y ) _1-x As buffer layer 3 was changed substantially linearly. According to the present invention, the InAs composition Z of the undoped InGaAs channel layer 5 can be arbitrarily changed from 0 to 1, but in practice, a range of 0.2 ≦ Z ≦ 0.7 is important for application. As an experimental data showing the effect of the Inx (GayAl _1-y ) _1-x As buffer layer 3 of the present invention, the case of Z = 0.53 is shown as an example. In order to show the suppression of the substrate leakage current or the reduction of the residual carrier concentration, which is the object of the present invention, the Si of the N-type InAlAs layer 7 and the N-type InGaAs layer 9 in FIGS.
A structure in which each layer of the heterostructure was undoped with the impurity doping amount of 0 / cm ³ was prepared, and the residual carrier concentration was investigated. The results are shown in the table below.

As is clear from the table below, the residual carrier concentration is
Compared to the case of using the xGa _1-x As buffer layer, the Inx (G
It can be seen that when the ayAl _1-y ) _1-x As buffer layer is used, it is reduced to about 1/10. Although the measured mobility value is higher in the conventional case, this is not because the crystallinity of the present invention is inferior to the conventional one, but the mobility and the location depend on the residual carrier and the concentration. This is because the value depends on it. Actually, in the structure of FIG. 1, when the N-type InAlAs layer 7 and the N-type InAlAs layer 9 were doped with Si at 2 × 10 ¹⁸ / cm ³ to form a two-dimensional electron gas in the non-doped InGaAs channel layer 5, the carrier concentration was increased. as, ~2x10 ¹² / cm ^2, at room temperature as a mobility satisfactory value of 10000cm ² / v · s was obtained. In addition, when a FET (HEMT) is manufactured using the heterostructure of the present invention, the leakage current between island regions for device formation formed by mesa etching is higher than that of the conventional structure.
It was also confirmed that it decreased to about 1/20 to 1/100.

EFFECTS OF THE INVENTION As described above, the use of the Inx (GayAl _1-y ) _1-x As buffer layer in which the InAs composition is gradually increased from the GaAs substrate side of the present invention makes InGaAs having good crystallinity on the GaAs substrate. In addition to being able to form a heterostructure with the active layer as the active layer, it is possible to significantly reduce the residual carrier concentration and suppress the substrate leakage current, and to improve the characteristics of the InGaAs / InAlAs-based electric devices formed on GaAs and their integration ratio. There is an effect that it becomes possible. Further, although the HEMT is mainly described in the embodiments of the present invention, the applicable range of the present invention is not limited to this, and it is possible to correspond to an optical device such as an electric device such as MESFET or HBT and a light receiving element. Needless to say.

[Brief description of drawings]

FIG. 1 is a sectional view of a hetero structure for explaining an embodiment of the present invention, and FIG. 2 is a sectional view of a hetero structure for explaining a conventional example. 1 ... Semi-insulating GaAs substrate, 2 ... Non-doped GaAs layer, 3
…… Inx (GayAl _1-y ) _1-x As buffer layer, 4 …… non-doped InAlAs barrier layer, 5 …… non-doped InGaAs channel layer, 6 …… non-doped InAlAs spacer layer, 7 …… N
Type InAlAs layer, 8 ... Non-doped InAlAs layer, 9 ... N type In
GaAs layer.

Claims (2)

[Claims] 1. A semiconductor heterostructure in which an active layer containing In _z Ga _1-z As is formed on a GaAs substrate via an Inx (AlyGa _1-y ) _1-x As buffer layer. _1-y ) _1-x
The InAs composition ratio X of the As buffer layer changes substantially linearly in the thickness direction from O to Z between the GaAs substrate side and the active layer, and the change rate of X is 1.5x10 ^-3 / nm or less. A heterostructure semiconductor device characterized by being present. 2. Inx (AlyGa _1-y ) _1-x As on a GaAs substrate in which the InAs composition ratio X is changed substantially linearly with thickness from O to Z at a rate of change of 1.5 × 10 ^-3 / nm or less. At least a step of forming a buffer layer and a step of forming an active layer containing InzGa _1-z As on the Inx (AlyGa _1-y ) _1-x As buffer layer, and the Inx (AlyGa _{1- y} ) The _1-x As buffer layer and the active layer were processed by molecular beam epitaxy at 450 ° C.
A method for manufacturing a heterostructure semiconductor device, which is formed at the following growth temperature.