JPH0156541B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an improvement in a field-effect semiconductor device that generates a two-dimensional electron gas layer and enables high-speed electron travel.

[Conventional technology]

FIG. 3 is a cross-sectional side view of a main part showing the structure of an epitaxially grown semiconductor layer in a conventional example of the field effect semiconductor device (see Japanese Unexamined Patent Application Publication No. 59-1992).
(See Publication No. 968).

In the figure, 1 is a semi-insulating GaAs substrate, 2 is a high-purity i-type GaAs active layer, 3 is a two-dimensional electron gas layer,
4 is a high purity i-type Al _x Ga _1-X As spacer layer, 5 is an n
A type Al _x Ga _1-x As electron supply layer and 6 indicate an n-type GaAs ohmic electrode contact layer, respectively.

FIG. 4 is a diagram representing the composition profile of the epitaxially grown semiconductor layer seen in FIG.

As can be seen from the figure, the x value in the high purity i-type Al _x Ga _1-x As spacer layer 4 is 0.3 or more, and
The x value in the n-type Al _x Ga _1-x As electron supply layer 5 is 0.2
and x=0 for the other semiconductor layers.

A field effect semiconductor device equipped with such a semiconductor layer is provided with a source electrode and a drain electrode that are in ohmic contact with the two-dimensional electron gas layer 3,
The two-dimensional electron gas layer 3 between them is used as a channel, and the channel is controlled by a gate electrode.

In the illustrated example, _{the i} -type Al
This is provided to ensure _{thorough spatial} separation from the ionized donor impurities from the Al becomes significantly smaller, resulting in very high electron mobility along the heterointerface. Although this effect can be obtained even at room temperature, it becomes particularly noticeable at low temperatures where scattering due to ionized impurities becomes dominant.

Furthermore, the reason why the x value in the _{n -} type Al This is to avoid this problem or to reduce the ohmic contact resistance of the source and drain electrodes.

However, if the overall x value is lowered, the electron mobility will decrease, so i-type _Al
The x value of the Ga _1-X As spacer layer 4 is set to 0.3 and is interposed as shown in the figure.

[Problem that the invention seeks to solve]

Currently, the biggest technical challenge in this type of field effect semiconductor device is the two-dimensional electron gas layer 3.
This is an improvement in the electron concentration in the .

Generally, as a means to improve the electron concentration,
Countermeasures have been taken ^, such as making _the i- _type ^Al I can't.

Although it is disadvantageous for improving the electron concentration in the two-dimensional electron gas layer 3, in the field effect semiconductor device having the structure shown in FIGS. 3 and 4, the i-type Al Since the presence of _{the X} Ga _1-X As spacer layer 4 is essential, it is unavoidable that the electron concentration in the two-dimensional electron gas layer 3 is reduced due to it.

Therefore, other methods are needed to increase this electron concentration.

The electron concentration in this two-dimensional electron gas layer 3 is n
Since it depends on the electrons leaking from the type Al _x Ga _1-x As electron supply layer 5 to the i-type GaAs active layer 4, n
It would be better to increase the doping to _the type _Al
0.2, normal molecular beam epitaxy:
MBE) method, the doping limit for the n-type Al _x Ga _1-x As electron supply layer 5 is 2×10 ¹⁸ [cm
^-3 ], and therefore, with the conventional technology, there is a limit to increasing the electron concentration in the two-dimensional electron gas layer 3.

To grow semiconductor layers such as those illustrated in FIGS. 3 and 4, the MBE method is usually applied, which is a process in which one or more source atoms or molecules are grown on a substrate. It is an ultra-high vacuum growth process in which a semiconductor layer is grown by colliding with a surface and absorbing it and moving it to an appropriate lattice point using thermal energy provided from a heated substrate.
When growing a GaAs layer, a molecular beam cell with a shutter in an ultra-high vacuum chamber is used for Ga, As, and
Three shutters for Si (n-type impurity) are provided, and when the molecular beam cell is heated and the vapor pressure rises to a predetermined value, each shutter is opened and the growth of n-type GaAs begins.

Various explanations and arguments are being developed as to why the impurity concentration in the n-type Al _x Ga _1-x As electron supply layer 5 cannot be increased, but the reality is that it is still not clear. be.

The inability to increase the electron concentration in the two-dimensional electron gas layer 3 leads to the inability to extract current, and therefore the transfer conductance g.
Since m is small, for example, when used for memory access, it takes time to charge and discharge the load capacitor, so the speed of the entire system is kept low.

[Means for solving problems]

To explain with reference to FIGS. 1 and 2, which are diagrams for explaining one embodiment of the present invention, the field effect semiconductor device of the present invention includes a semi-insulating GaAs substrate 1.
a high-purity i-type GaAs active layer 2 formed on the high-purity i-type GaAs active layer 2; a high-purity i-type Al _x Ga _1-x As spacer layer 4 formed on the high-purity i-type GaAs active layer 2;
n-type formed on Al _X Ga _1-X As spacer layer 4
Al _x Ga _1-x As electron supply layer 5 and the high purity i-type
Al _X Ga _1-X As spacer layer 4 and the n-type Al _X Ga _1-X
A high impurity concentration thin film 5A formed by an atomic plane doping method is provided near the interface of the _As electron supply layer ₅ , and the x value of the high purity i-type Al The relationship is that the x value is larger than the x value in the _X Ga _1-X As electron supply layer.

In the present invention, when forming the high impurity concentration thin film 5A, as described above, the atomic plane
Doping (APD) laws are applied to:
This is because it is possible to obtain a highly impurity-concentrated thin film 5A with a higher impurity concentration than by doping by a normal technique while growing each semiconductor layer by the MBE method.

Next, as an example, a case will be described in which an n-type GaAs layer is grown by applying the APD method.

Three molecular beam cells with shutters for Ga, As, and Si are installed in an ultra-high vacuum chamber, and a semi-insulating cell for growing an n-type GaAs layer is installed.
A GaAs substrate is placed and heated.

When each molecular beam cell is heated and the vapor pressure rises to a predetermined value, for example, the shutters of the molecular beam cells for As and Si are opened. As can only be deposited as GaAs on a GaAs substrate in the presence of Ga, and as mentioned above, even if the shutter of the molecular beam cell for As is opened, the GaAs substrate will not be sufficiently heated. As long as As is present, it is impossible for As to adhere to it alone. Therefore, in this case,
Only Si is deposited on the GaAs substrate, and the Si collides with and is absorbed by the heated GaAs substrate, and moves over the surface over a sufficient period of time, allowing it to search for appropriate lattice points. The reason why the shutter of the molecular beam cell for As is kept open even though As does not adhere to the GaAs substrate is because the temperature of the GaAs substrate is rising, so the atmosphere is such that As maintains a vapor pressure above a certain level. If it is not generated, As will be released from the GaAs substrate.

Now, after depositing Si on the lattice points where Si can occupy on the entire surface of the GaAs substrate, we close the shutter of the molecular beam cell for Si and open the shutter of the molecular beam cell for Ga. The GaAs layer is grown by several atomic layers, and the shutter of the molecular beam cell for Ga is closed again, and the shutter of the molecular beam cell for Si is opened to deposit Si. Thereafter, this process is repeated as necessary to grow a highly concentrated n-type GaAs layer.

The technique described above is the APD method, and according to this technique, the impurity concentration can be increased approximately twice as much as doping in the conventional MBE method.

[Effect]

In the field-effect semiconductor device according to the present invention, since the electron supply layer includes a thin film with high impurity concentration formed by the APD method, the two-dimensional electron gas layer generated in the high-resistance semiconductor active layer The electron concentration increases by about 20% to 30%, and as a result, the transfer conductance gm increases, making it possible to extract a large current.

[Example] FIG. 1 is a cross-sectional side view of the main part showing the structure of an epitaxially grown semiconductor layer in an example of the present invention, and the same symbols as those used in FIGS. 3 and 4 are shall represent the same part or have the same meaning.

The difference between this embodiment and the conventional example shown in FIGS. 3 and 4 is that the n-type Al _x Ga _1-x As electron supply layer 5
High impurity concentration thin film 5A formed by APD method inside
The substance of this high impurity concentration thin film 5A is that by applying the APD method,
For example, n-type which is heavily doped with Si.
It is an Al _x Ga _1-x As (x≦0.2) thin film.

FIG. 2 is a diagram representing the composition profile of the epitaxially grown semiconductor layer seen in FIG.

As can be seen from the figure, even if the high impurity concentration thin film 5A formed by the APD method exists in the n-type Al _x Ga _1-X As electron supply layer 5, the x value shown in Fig. 4 There is no difference from the conventional example.

Here, the case of manufacturing an epitaxially grown semiconductor layer as shown in FIGS. 1 and 2 will be described in comparison with the conventional technique described in connection with FIGS. 3 and 4.

3 and 4 until the high purity i-type Al _x Ga _1-x As spacer layer 4 is grown or a part of the n-type Al _x Ga _1-x As electron supply layer 5 is grown. This is exactly the same as the conventional example described above.

Next, close the shutter of the molecular beam cell for Al and the shutter of the molecular beam cell for Ga, and open only the shutter of the molecular beam cell for Si and the shutter of the molecular beam cell for As to perform high concentration Si doping. . A specific example of the doping concentration in this case is 1.1×10 ¹⁹ [cm ⁻² ].

Next, while leaving the shutters of the molecular beam cell for Si and the shutters of the molecular beam cell for As open, the shutters of the molecular beam cell for Al and the shutters of the molecular beam cell for Ga are opened again to obtain n-type Al _X Ga _1-X. The As electron supply layer 5 is grown to a predetermined thickness.

After this, the n-type GaAs ohmic contact layer 6 can be grown in the same manner as in the conventional technique explained with reference to FIGS. A gate electrode, a source electrode, a drain electrode, etc. are formed by the following steps. Incidentally, in the above embodiment, the high concentration i
Formed by APD method at the interface between the type Al _x Ga _1-x As spacer layer 4 and the n-type Al _{x Ga} 1 _{- x} As electron supply layer 5 or within the n-type Al A high impurity concentration thin film 5A was formed, which was a high purity i-type _Al
It may also be formed within the Ga _1-X As spacer layer 4.

〔Effect of the invention〕

In the field effect semiconductor device according to the present invention,
An i-type Al _x Ga _1-X As spacer layer is formed on the GaAs active layer, and an n-type Al _x Ga _1-X
An As electron supply layer is formed, and has a high impurity concentration thin film formed by an APD method near the interface between the spacer layer and the electron supply layer, and the x value in the spacer layer is equal to that in the electron supply layer. It is larger than the x value.

Therefore, in order to eliminate the photoresponse effect caused by the deep donor level, which is a drawback of this type of field effect semiconductor device, or to reduce the ohmic contact resistance of the source and drain electrodes, it is necessary to In order to set a low x value in the _{Al X Ga 1-X As} electron supply layer and to avoid the resulting decrease in electron mobility, i-type Al _x Ga _1-x with it being greater than the value
Even when an As spacer layer is formed, the electron concentration in the two-dimensional electron gas layer generated in the active layer is lower than that of the electron supply layer formed by the APD method that does not use a high impurity concentration thin film. Compared to conventional field effect semiconductor devices of this kind, which have 20 to 30
[%], and as a result, the transfer conductance gm becomes higher and it is possible to extract a large current. Therefore, even when used for memory access, etc., the load capacitance can be charged and discharged at high speed. It can be carried out.

In addition, it is possible to maintain the temperature of each molecular beam source high not only when epitaxially growing each semiconductor layer but also when epitaxially growing a thin film with high impurity concentration.・Problems such as a decrease in output will not occur.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional side view of essential parts showing the structure of an epitaxially grown semiconductor layer in an embodiment of the present invention, and FIG. 2 is a diagram showing the composition profile of the epitaxially grown semiconductor layer shown in FIG. 1. , FIG. 3 is a cross-sectional side view of essential parts showing the structure of the epitaxially grown semiconductor layer in the conventional example, and FIG. 4 is a diagram showing the composition profile of the epitaxially grown semiconductor layer shown in FIG. 3. represents. In the figure, 1 is a semi-insulating GaAs substrate, 2 is
High-purity i-type GaAs active layer, 3 is a two-dimensional electron gas layer, 4 is high-purity i-type Al _x Ga _1-x As spacer layer, 5
5A shows an n-type Al _x Ga _1-x As electron supply layer, 5A shows a high impurity concentration thin film formed by the APD method, and 6 shows an n-type GaAs ohmic electrode contact layer.

Claims (1)

[Claims] 1. An active layer formed on a semi-insulating semiconductor substrate and made of a high-resistance semiconductor with high electron affinity;
a spacer layer formed on the high-resistance semiconductor active layer and made of a high-resistance semiconductor having a smaller electron affinity and a larger energy band gap than the high-resistance semiconductor active layer, and the high-resistance semiconductor; An electron supply layer formed on the spacer layer and made of a highly impurity-concentrated semiconductor having a smaller electron affinity than the high-resistance semiconductor active layer and a smaller energy band gap than the high-resistance semiconductor spacer layer. and a high impurity concentration thin film formed by an atomic plane doping method near the interface between the high resistance semiconductor spacer layer and the electron supply layer.