JPS63250863A - Field-effect semiconductor device - Google Patents

Abstract

PURPOSE:To eliminate P.P.C. (Persistent Photoconductivity) and to improve mutual conductance gm of a field effect semiconductor device by laminating a spacer layer made of non-doped AlGaAs between an electron supply layer made of Si-doped GaAs and an electron transit layer. CONSTITUTION:An electron supply layer 9 made of Si-doped GaAs, an electron transit layer 7 made of InGaAs, and a spacer 3 made of non-doped AlGaAs interposed between the layers 9 and 7 are laminated between a gate electrode 6 and a compound semiconductor substrate 1. Since the layer 9 uses Si-doped GaAs having no D-X sensor as the layer 9, the temperature change of a threshold value voltage Vth is less, P.P.C is eliminated, and since the non-doped AlGaAs layer is used as the layer 3, a discontinuity to a conduction band to the InGaAs of the layer 7 can be increased to be able to increase the sheet carrier concentration of secondary electron gas, thereby improving gm.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to field effect semiconductor devices, particularly InGaA semiconductor devices.
The present invention relates to an element structure in an s-based modulation doped PET (MODFET).

(b) Conventional technology In general, compound semiconductors have advantages such as high carrier mobility and the fact that most of them are direct transition type semiconductors, so they are used in ultrahigh-speed semiconductor devices, light-emitting devices, etc. Its uses are expanding. In addition to the original advantages of molecular beam epitaxial growth, such as the ability to grow steep hetero-interfaces that cannot be produced with other crystal growth methods, in recent years, direct heating of the substrate, larger diameters of each source crucible, and growth Due to improvements such as improved uniformity of the grown layer due to faster substrate rotation, it is rapidly progressing as a basic technology for manufacturing compound semiconductor devices. In addition, in the above-mentioned ultra-high-speed semiconductor device, in order to reduce noise and increase gain, the mutual conductance g1 is improved, the source resistance Rs and the gate force capacity @Cg
Progress is being made to reduce s, and this has resulted in, for example, shortening the gate length, adopting a Verirad channel profile that increases the carrier concentration at the bottom of the active layer, and introducing an n layer on the surface and the accompanying deep recess structure. In order to obtain electrons with high drift speed, AlGaAs/GaAs,
GaAs/InGaAs, AlGaAs/InGaAs
MOD FETs using heterojunctions such as these have been adopted.

Conventionally, the most common type of MOD FET is an AlGaAs/GaAs MMODFET as shown in FIG.
A GaAs layer 4 is grown, and non-doped AlGaA is grown between the Si-doped n''-AIGaAs layer 4 which is an electron supply layer and the non-doped GaAs buffer layer 2 which is an electron transport layer.
By providing the s-spacer layer 3, improvements such as increasing the mobility of electrons by moving the two-dimensional electron gas away from the clone field caused by the ionized donors in the electron book layer 4 have been made.

In addition, in recent years, as shown in FIG.
s-based MODFET, and as shown in Figure 5, InGaA
GtIA 5 in which a Si-doped n''-GaAs layer 9 is grown on the s-layer 7 with a non-doped GaAs spacer layer 8 interposed therebetween.
/InGaAs-based MODFETs and the like have been proposed, and improvements have been made to increase the electron drift speed.

In addition, in FIGS. 3 to 5, 5.6 is an ohmic electrode and a gate electrode, respectively.

(c) Problems to be solved by the invention However, the above-mentioned MODFET, for example, the AlGaAs/GaAs-based MODFET as shown in FIG.

AlGaAs/InGaAs-based MOD as shown in Figure 4
In the FET, AlxGa+- is used as the electron supply layer 4.
Since a mixed crystal consisting of xAs is used, M OD F
At a mixed crystal ratio of about
The threshold voltage vth of
Persistent Photoconductiv
ity (P, P.

There is a drawback that phenomena such as C, ) occur. Also, the fifth
GaAs/InGaAs system MOD F E as shown in the figure
In T, since there is no DX center in the electron supply layer 9, the above-mentioned defects do not occur, but regarding the discontinuity of the conduction band between the spacer layer and the electron transit layer, Ga
The conduction band discontinuity between As and InGaAs causes Alx
Gal-xA s (X = 0.3) and GaAs
Since the conduction band discontinuity (0.3eV) is smaller than that of the conduction band, the two-dimensional electron sheet carrier concentration at the heterojunction interface is lower than that of AlGaAs/GaAs-based MODFBT, which does not lead to an improvement in gl. There is.

The present invention provides a field-effect semiconductor device that can simultaneously achieve improvements in electron drift velocity, increase in sheet carrier concentration, and improvement in characteristic stability that are impossible with MODFETs having the above-described structure. It is.

(d) Means for Solving the Problems The present invention provides an S
An electron supply layer made of i-doped GaAs and InGaAs
This is a field-effect semiconductor device formed by laminating an electron transport layer consisting of the above-mentioned electron transit layer and a spacer layer interposed between the two layers and made of non-doped AlGaAs.

That is, by using non-doped AlGaAs as a spacer layer between the Si-doped n''GaAs of the electron supply layer and the InGaAs of the electron transport layer as shown in FIGS. 4 and 5, changes in the threshold voltage vth due to temperature can be suppressed. In addition to ensuring the prevention of the P, P, and C phenomena, the discontinuity of the conduction band between the electron transit layer and the spacer layer is improved, thereby improving the mutual inductance g. Can be done.

(e) Function The field-effect semiconductor device of the present invention uses Si-doped GaAs without a DX center as the electron supply layer, and is therefore compared to a conventional device using a Si-doped AlGaAs layer as the electron supply layer. , P, P, C with little temperature change in threshold voltage vth.

disappears. In addition, since a non-doped AlGaAs layer with a larger band gap and lower electron affinity than GaAs is used as the spacer layer, the discontinuity of the conduction band with InGaAs, which is the electron transport layer, is reduced compared to that of conventional GaAs.
It can be made larger than the s/1nGaAs-based MOD FET, the sheet carrier concentration of the two-dimensional electron gas can be increased, and an improvement in g can be realized.

(F) Example Hereinafter, an example of the present invention will be described in detail in the order of steps with reference to FIGS. 1 and 2.

First, a GaAs substrate was coated with molecular beam epitaxy (Molec).
ular beam epitaxy, hereinafter MBE
Before using it in a sulfuric acid-based etchant (sulfuric acid: hydrogen peroxide: water = 3:1:l), it is immersed for 30 seconds for pretreatment. Next, the GaAs substrate is carried into a growth chamber of an MBE apparatus, and baked at 600° C. for 1 hour under As pressure to remove the oxide film adhering to the surface of the GaAs substrate. After that, the substrate temperature was lowered to 580°C, and Ga(8
84 DEG C.) The cell shutter was opened, and a buffer layer 2 made of undoped GaAs was grown to a thickness of 1 .mu.m on the GaAs substrate 1, as shown in FIG. 2(a). Then I n (
950℃) Open the cell shutter and remove the non-doped InGa.
Grow 300 electron transport layers consisting of As7. Thereafter, the I n (950° C.) cell shutter is closed and the A I (1020° C.) cell shutter is simultaneously opened to grow 30 single layer spacers made of non-doped AlGaAs3. Furthermore, the temperature of the A I (1020°C) cell was lowered at a rate of 1°C per second, and when the A1 cell reached 950°C, the
Close the I cell shutter and at the same time S i (1040℃
) Open the cell shutter and remove Si-doped n'''-GaAs.
Grow the electron supply layer consisting of 9 people by 6000 people. Thereafter, the Si cell shutter and the Ga cell shutter are closed simultaneously to lower the substrate temperature to 400° C., and after the As cell shutter is closed, the substrate temperature is returned to room temperature. After that, Ga
The As substrate 1 is taken out from the MBE growth chamber.

Thereafter, a mesa pattern IO is formed on the GaAs growth layer using a photoresist (see FIG. 2(a)). Thereafter, using this mesa pattern 10 as a mask material, the growth layer is etched (see FIG. 2(b)) to avoid separation between elements, and then the photoresist IO for mesa etching is etched.
is removed using an organic solvent. Thereafter, ordinary photolithography, electrode deposition, and alloying processing are performed to form the ohmic electrode 5 (see FIG. 2(c)). after that,
A gate pattern II is formed using a photoresist (see FIG. 2(d)), and using this gate pattern 11 as a mask, a part of the n''-GaAs layer 9 is etched with a phosphoric acid-based etchant (phosphoric acid: hydrogen peroxide). :water=3+l:50) to obtain a grooved shape as shown in FIG. is removed using an organic solvent to obtain a field effect semiconductor device having a structure as shown in FIG.

By the method described above, a semiconductor device having an electron supply layer without a D-X center and a large conduction band discontinuity at the heterointerface can be obtained, and the sheet carrier concentration of the two-dimensional electron gas can be reduced to IX 10"/ As a result, it became possible to improve g by about 50 m5/mm. Also, vth was -1, 10 V and -1,08 V for 300 and 77, respectively. Temperature dependence has almost disappeared, and it has become possible to completely eliminate P, P, and C.

Note that the present invention is applicable not only to InGaAs-based MODFETs using GaAs substrates, but also to MODFETs using InAs, rnP, etc. as materials for compound semiconductor substrates.
It can also be applied to ET.

(g) Effects of the invention As described above, according to the present invention, D-X
Since Si-doped GaAs without a center is used, the temperature change in threshold voltage vth is smaller than that in a conventional Si-doped AlGaAs layer used as an electron supply layer, and P, P, and C are eliminated. In addition, since a non-doped AlGaAs layer with a larger band gap and lower electron affinity than GaAs is used as the spacer layer, the discontinuity of the conduction band with InGaAs as the electron transport layer is reduced compared to the conventional GaAs/InGaAs-based MODF.
'ET, it becomes possible to increase the sheet carrier concentration of the two-dimensional electron gas, and there is an effect that an improvement in ga can be realized.

[Brief explanation of drawings]

FIG. 1 is in accordance with one embodiment of the present invention. GaAs/UnGaA using AlGaAs only in one layer of non-doped spacer
A sectional view of an s-based MODFET, FIGS. 2(a) to 2(e) are process explanatory diagrams of the field-effect semiconductor device, and FIG. 3 is a sectional view of an AlGaAs/GaAs-based MODFET with a conventional structure.
Figure 4 shows the conventional structure of AlGaAs/InGaAs system M.
A cross-sectional view of OD FET, Figure 5 shows the conventional structure of GaA.
FIG. 2 is a cross-sectional view of an s/InGaAs-based MODFET. l...GaAs substrate, 2...non-doped GaAs buffer layer, 3...
...Non-doped AlGaAs spacer layer, 5.
...Ohmic electrode, 6...Gate electrode, 7-=InGaAs layer, 9...Si-doped n''GaAs layer. Fig. 2 (a) (b) Fig. 2 (C) Figure 3 Figure 4

Claims (1)

[Claims] 1. An electron supply layer made of Si-doped GaAs and an electron transport layer made of InGaAs are interposed between the gate electrode and the compound semiconductor substrate, and non-doped Al
A field effect semiconductor device formed by laminating a spacer layer made of GaAs.