JPH0156542B2 - - 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.

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 i-type Al _X Ga _{1-X As} spacer layer 4 and the n-type Al It is.

A field effect semiconductor device including such a semiconductor layer is provided with a source electrode and a drain electrode 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.

Note that _{the i - type} Al
This is provided to eliminate spatial separation from the ionized donor impurities from the electron supply layer 5.
In this way, the degree to which electrons undergo Crohn scattering due to ionized donor impurities is significantly reduced, and extremely high electron mobility can be obtained 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.

[Problem that the invention seeks to solve]

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

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
0.3, the doping limit for the n-type Al _x Ga _1-x As electron supply layer 5 is 2×10 ¹⁸ [cm
^-3 ], therefore, the electron concentration in the two-dimensional electron gas layer 3 cannot be increased.

To grow semiconductor layers such as those illustrated in FIGS. 3 and 4, molecular beam epitaxy (MBE) is typically used.
This MBE method involves colliding and absorbing one or more raw material atoms or molecules onto the growth surface of the substrate, and moving them to appropriate lattice points using thermal energy provided by the heated substrate. It is an ultra-high vacuum growth process for growing semiconductor layers, for example,
When growing an n-type GaAs layer, a molecular beam cell with a shutter in an ultra-high vacuum chamber is used for Ga and As.
The molecular beam cell is heated, and when the vapor pressure rises to a predetermined value, each shutter is opened and the growth of n-type GaAs is started.

n-type Al _x Ga _1-x As electron supply layer 5 as described above
Although various explanations or arguments are being developed as to why it is not possible to increase the impurity concentration in the material, the reality is that it is still not clear.

In addition, as a means to eliminate the above-mentioned drawbacks, for example,
Countermeasures have ^been taken, such as making _the i _- type Al Only about [cm ^-2 ] can be obtained.

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 is a semi-insulating semiconductor substrate, which is a type of semi-insulating semiconductor substrate. A high-purity i-type GaAs active layer 2, which is a type of active layer formed on a GaAs substrate 1 and made of a high-resistance semiconductor with high electron affinity;
High-purity i-type _Al Ga _1-X As spacer layer 4
and an electron supply layer formed on the high-purity i-type Al _x Ga _1-x As spacer layer 4 and made of a highly impurity-concentrated semiconductor having a lower electron affinity than the high-purity i-type GaAs active layer 2. n-type Al _x Ga _1-X
The As electron supply layer 5 is formed near the interface between the high-purity i-type Al _x Ga _{1-X As} spacer layer 4 and the n-type _Al The structure includes a high impurity concentration thin film 5A.

Here, a case will be described in which an n-type GaAs layer is grown by applying the above-mentioned atomic plane doping (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, As alone cannot adhere to GaAs.
It is impossible for it to adhere to the substrate.

Therefore, in this case, only Si is deposited on the GaAs substrate, and the Si collides with the heated GaAs substrate, is absorbed, and moves over the surface for a sufficient amount of time to form appropriate lattice points. You can search. still,
The reason why the shutter of the molecular beam cell for As is kept open even though As is not deposited on the GaAs substrate is because the temperature of the GaAs substrate is rising, which creates an atmosphere in which As maintains a certain level of vapor pressure. Otherwise, GaAs
This is due to As being released from the substrate.

Now, after depositing Si on the entire surface of the GaAs substrate at lattice points where Si can occupy, we close the shutter of the molecular beam cell for Si and open the shutter of the molecular beam cell for Ga. After growing the GaAs layer by several atomic layers, the shutter of the molecular beam cell for Ga was closed and the shutter of the molecular beam cell for Si was opened again.
Deposit Si. Thereafter, this step 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 a high impurity concentration thin film formed by the APD method exists near the interface between the spacer layer and the electron supply layer, 2 The electron concentration in the dimensional electron gas layer increases by about 20% to 30%, and as a result, the transfer conductance gm
becomes high, and it is possible to extract a large current.

〔Example〕

FIG. 1 is a cross-sectional side view of essential parts showing the structure of an epitaxially grown semiconductor layer in one embodiment of the present invention, and the same symbols as those used in FIGS. 3 and 4 represent the same parts. 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 produced by APD method inside
The substance of this high impurity concentration thin film 5A is, for example, an n-type Al _x Ga _1-x As thin film doped with a high concentration of Si.

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 is There is no difference from the conventional example. The case of obtaining an epitaxially grown semiconductor layer as shown in FIGS. 1 and 2 will be described in comparison with the prior art described with reference to FIGS. 3 and 4.

The process up to the growth of the high-purity i-type Al _x Ga _1-x As spacer layer 4 is exactly the same as the conventional example explained with reference to FIGS. 3 and 4.

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 at this time is approximately 1.1×
10 ¹⁹ [cm ^-2 ].

Next, the shutter of the molecular beam cell for Si is closed, and the shutter of the molecular beam cell for Al and the shutter of the molecular beam cell for Ga are opened again to form n-type Al _X Ga _1-X As.
The electron supply layer 5 is grown. Here, the high impurity concentration thin film may be formed during the growth of the n-type Al _x Ga _1-x As electron supply layer 5.

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. In addition, in the above embodiment, APD
Although the high impurity concentration thin film produced by the method is formed within the electron supply layer, it may also be formed within the spacer layer.

Moreover, if high-concentration Si doping is performed multiple times, a two-dimensional electron gas layer with a higher electron concentration can be generated.

〔Effect of the invention〕

In the field effect semiconductor device according to the present invention, near the interface between the spacer layer and the electron supply layer on the active layer,
It has a structure in which a thin film with high impurity concentration is formed using the APD method.

According to this configuration, 2 generated in the active layer
The electron concentration in the dimensional electron gas layer is about 20 to 30% higher than that of this type of field effect semiconductor device manufactured using conventional technology, and as a result,
As the transfer conductance gm increases, it is possible to extract a large current, and therefore, even when used for accessing a memory, the load capacitance can be charged and discharged at high speed.

In addition, since it is possible to maintain a high temperature not only when epitaxially growing each semiconductor layer but also when epitaxially growing a thin film with high impurity concentration, it is possible to reduce throughput. No problem arises.

[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 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, 5A is a
High impurity concentration thin film formed by APD method, 5 is n-type
6 represents an Al _x Ga _1-x As electron supply layer and 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 whose electron affinity is smaller than that of the high-resistance semiconductor active layer; An electron supply layer made of a high impurity concentration semiconductor whose electron affinity is lower than that of the semiconductor active layer, and a high resistance spacer layer formed by an atomic plane doping method near the interface between the high resistance spacer layer and the electron supply layer. 1. A field effect semiconductor device comprising: a thin impurity concentration film.