JPH10229185A - Semiconductor device and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small leakage and highly controllable semiconductor device, having a back gate structure capable of forming a high quality hetero- structure on a back gate. SOLUTION: Region-selective ion-implantation is applied to a non-doped GaAs epitaxial layer 1', formed on a GaAs semi-insulative substrate 1 to form a Be-implanted region 3 to be a back gate and an AlGaAs/GaAs modulation doped structure 2 (composed of a non-doped GaAs layer 2-a, non-doped AlGaAs layer 2-b and Si-doped AlGaAs layer 2-c) is re-grown thereon, the form a front gate at a predetermined position on the modulation doped structure 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to controlling a two-dimensional electron gas (hereinafter abbreviated as 2DEG) or a two-dimensional hole gas (hereinafter abbreviated as 2DHG) formed at a semiconductor heterojunction interface from a substrate side. The present invention relates to a semiconductor device having a back gate control structure, and particularly to a back gate and a 2DEG (or 2D
HG) are close to each other, have excellent controllability, and are suitable for combination with a front gate.

[0002]

2. Description of the Related Art In order to improve the controllability of 2DEG (or 2DHG) formed at a hetero interface, a back gate on the substrate side has been used in addition to a front gate. However, many of these are, for example, 2DEG
Is controlled by an n-type GaAs disposed thereunder, and the carrier at the gate and the hetero interface is the same type. In such a structure, the gate leakage is increased. To suppress this, it is necessary to sandwich an AlGaAs barrier between the heterostructure and the back gate, and further increase the distance between the back gate and the hetero interface. However, in the structure sandwiching the AlGaAs barrier, the AlG
Since GaAs is grown on aAs, there is a problem that high-quality crystal growth becomes difficult.
In the configuration in which the distance is set as described above, there is a problem that the gate voltage required for control is increased, and the controllability of the gate is deteriorated.

[0003] On the other hand, a method of growing a heterostructure on an n-type or p-type substrate (or an epitaxial layer) as a pn junction type back gate and using the substrate as a back gate has also been performed. However, in this case, the substrate (or epitaxial layer) covers the entire surface, and a back gate cannot be provided locally.
In such a structure, 2DEG is formed by mesa etching or the like.
(Or 2DHG), the back gate layer always exists underneath.
G (or 2DHG) ohmic contacts reach the back gate layer by sintering, which causes gate leakage.
There is a problem that the interval of G (or 2DHG) cannot be reduced.

In addition, the conventional structure as described above has a problem that the condition of the back gate cannot be locally changed.

[0005]

SUMMARY OF THE INVENTION The present invention has the problems of the conventional back gate structure as described above, in that the distance between the back gate and the hetero interface is large and the controllability is poor, and the leakage of the back gate is increased. It is an object of the present invention to provide a semiconductor device having a back gate structure which has a small leakage, is excellent in controllability, and can form a high-quality heterostructure on the back gate, and a method for manufacturing the same. .

[0006]

Means for Solving the Problems In order to achieve the above object, the present invention is configured as described in the claims. That is, according to the first aspect of the present invention, there is provided a semiconductor device having a back gate structure in which a concentration of a two-dimensional electron gas or a two-dimensional hole gas in a modulation doping structure formed on a substrate is controlled by a voltage from the substrate side. , A back gate structure composed of a pn junction formed region-selectively using the same semiconductor material as the substrate.

In the semiconductor device according to the first aspect of the present invention, the back gate and the hetero interface are close to each other, and the ohmic contact can be formed without touching the back gate. Is realized in which a back gate structure can be controlled in a wide range. Further, since the back gate is a pn junction type, there is no need to sandwich a barrier between the hetero structure and the back gate.

Further, in the invention according to claim 2,
The structure according to claim 1, wherein the front gate structure and the back gate structure formed on the surface side of the modulation dope structure are formed in a so-called self-aligned manner so as to be in the same region. . According to the second aspect of the present invention, the controllability of carriers at the hetero interface in the first aspect of the present invention is improved by a combination with a front gate.

According to a third aspect of the present invention, there is provided a semiconductor having a back gate structure in which the concentration of a two-dimensional electron gas or a two-dimensional hole gas in a modulation-doped structure formed on a substrate is controlled by a voltage from the substrate side. In the method of manufacturing the device,
A step of selectively ion-implanting a substrate or a non-doped semiconductor layer grown on the substrate, a step of re-growing a modulation-doped structure on the substrate or the non-doped semiconductor layer, and etching for element isolation. And a step of forming a mesa structure. Incidentally, the modulation doping structure,
For example, as shown in the embodiment of FIG. 1 described later, a second non-doped semiconductor layer (for example, a non-doped III-V semiconductor such as non-doped GaAs) and a third non-doped semiconductor layer (for example, non-doped III such as non-doped AlGaAs).
-V mixed crystal semiconductor) and a doped semiconductor layer (for example, a doped III-V mixed crystal semiconductor such as Si-doped AlGaAs).

In the above manufacturing method, a back gate region is formed by selectively forming a back gate region and combining it with regrowth. Since the back gate and the carrier at the interface are pn junctions, the same material is used. Gate leakage can be suppressed, and a hetero barrier is not required. Regrowth after back gate fabrication is easy, and high quality regrowth can be realized. Furthermore, since the ion implantation conditions can be locally changed, there is a feature that a back gate structure having various characteristics can be formed at a desired place.

[0011]

FIG. 1 is a schematic view showing an embodiment of a semiconductor device according to the present invention, wherein FIG.
(B) shows a sectional view. In this structure, the back gate and the front gate are formed in a self-aligned manner. In FIG. 1, details of ohmic contacts and the like are omitted.

In this embodiment, an example in which the invention described in claims 1 and 2 is applied to an AlGaAs / GaAs system will be described. In this embodiment, a front gate arranged in the self-alignment described in claim 2 is also provided.

The manufacturing process is as follows. First, a non-doped GaAs layer 1 'is formed on a semi-insulating GaAs substrate 1 by molecular beam epitaxy (hereinafter, referred to as "Molecular Beam Epitaxy").
MBE). Here, the growth is interrupted and the sample is transported to a focused ion beam (FIB). Using a FIB, Be ions are implanted into appropriate locations at appropriate doses to form Be implanted regions 3. In this case, since the FIB is used, the implantation location, shape, dose amount, etc. can be arbitrarily set.

After the Be implantation, the sample is returned to the MBE chamber, and the AlGaAs / GaAs modulation doped structure 2 is grown again. By this regrowth, the non-doped GaAs layer 2
-A and a non-doped AlGaAs layer 2-b (Al _x Ga
_1-x As) and the Si-doped AlGaAs layer 2-c (Al _x
A modulation doping structure 2 made of Ga _1-x As) is formed. In this embodiment, the non-doped GaAs layer 2-a
Has a thickness of 250 nm. In addition, since Be is sufficiently activated at the temperature at the time of regrowth by MBE, no special heat treatment is performed.

After the growth of the modulation-doped structure by MBE, first, a large hole bar is formed by chemical etching (element separation). Subsequently, in FIG. 1A, a 2DEG 5 is provided at a portion (for example, point A) on the mesa structure below the front gate 4 and not in contact with the front gate 4.
An ohmic contact (n-type ohmic region: not shown) is formed at the portion (for example, point B) where the Be implantation region 3 is drawn out to the outer peripheral portion (for example, point B). (Omitted).

An important point in this embodiment is that since the Be implantation region 3 is locally limited, a Be implantation layer is formed below an n-type ohmic region (not shown) which is an ohmic contact to the 2DEG 5. Is not present. This has the effect of reducing unnecessary gate leakage.

Thereafter, Au /
A Ti Schottky gate 4 is deposited, and finally, the central portion is chemically etched by self-alignment using the Au / Ti Schottky gate 4 as a mask (etching region 6).
By doing so, the structure is completed. At this time, the depth of the etching region 6 is selected to be sufficiently deeper than the Be implantation region 3.

In this structure, the front gate 4 does not directly touch the Be implantation region 3 serving as the back gate, and is always (front gate 4) -2DEG5- (p-type back gate 3). The voltage range that can be applied without power is increased.

As a feature of this embodiment, 2DEG5
And the back gate 3 form a pn junction. When the non-doped GaAs layer 2-a after the regrowth is thin and the 2DEG 5 is close to the back gate 3, 2
DEG5 is depleted, but if the pn junction is brought closer to the forward direction, a forward current flows to the gate unless Be diffuses to the hetero interface when fabricating the structure of the embodiment. 2DEG can be formed before. p
As a feature of the n-junction, the leak current is small until a forward current flows around 1.5 V, so that the non-doped GaAs layer 2-a after regrowth is thin, and the 2DEG 5 is
2, a large change in carrier density can be obtained with a sufficiently small gate voltage as shown in FIG. 2 (described later in detail). In the structure of FIG. 1, the carrier density is also controlled by the front gate 4.

Further, in the structure of FIG. 1, a hetero junction is not required between the back gate 3 and the 2DEG 5, and the 2DEG 5
Are all formed of GaAs up to the hetero interface where the is formed. And G compared to GaAs on AlGaAs
GaAs on aAs has the characteristic that high quality can be easily maintained during crystal growth, and is particularly advantageous for structure fabrication including regrowth.

FIG. 2 is a characteristic diagram showing the result of controlling the carrier density of the two-dimensional electron gas by the back gate and the front gate. In FIG. 2, the parameter is the front gate voltage, and the Be dose of the back gate is 5 ×
It is 10 ¹³ cm ~ ² . The measurement temperature was 1.6 K, and the gate leakage was 10 nA or less for both the back gate and the front gate in all the measurement ranges in FIG.

As shown in FIG. 2, in the voltage range where the back gate voltage is 1.5 V or less, the carrier density is 0 to 0.
It can be seen that they are firmly controlled within the range of 5.5 × 10 ¹¹ cm ~ ^2. In addition, since the resistance becomes large in a region close to the pinch-off and correct measurement cannot be performed, the plot in FIG. 2 is 5 × 10 ¹⁰ cm to ² or more, but it is confirmed that 2DEG is completely depleted by the back gate. did.
Further, the change in carrier density with respect to the back gate is linear, and the distance between the back gate and 2DEG is calculated to be about 130 nm from this slope. This is an appropriate value in consideration of the diffusion of Be toward the regrown layer.

FIG. 3 is a characteristic diagram showing the relationship between the mobility of the two-dimensional electron gas and the carrier density when the carrier density is controlled by the back gate structure. The characteristics obtained in the region without the back gate are also shown for comparison. As shown in FIG. 3, the mobility is increased rather than the normal 2DEG formed where no Be implantation is performed. The slight increase in mobility due to the decrease in front gate voltage is due to the fact that the distribution of 2DEG in the crystal growth direction is modulated by the gate voltage. This data shows Be for the regrown AlGaAs / GaAs heterointerface.
This indicates that the characteristic deterioration due to the influence of diffusion is sufficiently small to be negligible, indicating the usefulness of this structure.

The measurement example described here is a characteristic at a low temperature in consideration of evaluation by mobility, etc. As is clear from the fact that the characteristic of the pn junction can be obtained even at room temperature,
It can operate up to higher temperatures.

Although an example in which control is performed by a p-type buried gate in which 2DEG is buried below has been described, 2DHG can be achieved by combining a Be modulation doped structure and a Si-implanted n-type layer.
Can be controlled by an n-type buried gate embedded below.

Further, the present invention can be applied to a high index surface. For example, in GaAs on the (311) A plane, Si doping becomes p-type, but Si ion implantation becomes n-type.
(311) 2D by Si doping and Si implantation if A surface is used
A structure in which HG is controlled by an n-type buried gate embedded below can be realized.

Needless to say, the structure of the present invention
The present invention can be widely applied to compound semiconductors utilizing a modulation doping structure other than the aAs type.

[0028]

As described above, according to the present invention,
A back gate structure with a small gate leak current, excellent controllability, and a high-quality heterostructure can be formed on the back gate, and a combined structure with the front gate can be realized. Further, since the ion implantation conditions can be locally changed, back gate structures having various characteristics can be easily formed at desired locations. Therefore, the effects of reducing the leakage current, making the back gate structure thinner, arbitrarily setting the back gate conditions, and improving the quality of the modulation doping structure can be obtained.

[Brief description of the drawings]

1A and 1B are schematic views showing one embodiment of a semiconductor device according to the present invention, wherein FIG. 1A is a perspective view and FIG. 1B is a cross-sectional view.

FIG. 2 is a characteristic diagram showing a result of controlling a carrier density of a two-dimensional electron gas by a back gate and a front gate.

FIG. 3 is a characteristic diagram showing a relationship between mobility of two-dimensional electron gas and carrier density when carrier density is controlled by a back gate structure.

[Explanation of symbols]

1: GaAs semi-insulating substrate 1 ′: non-doped GaAs epitaxial layer 2: regrown AlGaAs / GaAs modulation doped structure 2-a: non-doped GaAs layer 2-a: non-doped AlGaAs layer 2-b: Si-doped AlGaAs layer 3: Be injection region acting as back gate 4: Au / Ti Schottky gate (front gate) 5: two-dimensional electron gas (2DEG) 6: etching region

Claims (3)

[Claims] 1. A semiconductor device having a back gate structure for controlling the concentration of a two-dimensional electron gas or two-dimensional hole gas having a modulation doping structure formed on a substrate from a substrate side by a voltage, wherein the same semiconductor material as the substrate is used. A semiconductor device having a back gate structure composed of a pn junction formed region-selectively by using a semiconductor device. 2. The semiconductor according to claim 1, wherein the front gate structure and the back gate structure formed on the surface side of the modulation dope structure are formed in a so-called self-aligned manner so as to be in the same region. apparatus. 3. A method of manufacturing a semiconductor device having a back gate structure in which the concentration of a two-dimensional electron gas or two-dimensional hole gas having a modulation doping structure formed on a substrate is controlled by voltage from the substrate side. A step of region-selectively implanting ions into the non-doped semiconductor layer grown on the substrate; a step of re-growing the modulation-doped structure on the substrate or the non-doped semiconductor layer; and forming a mesa structure by etching for element isolation. Forming a semiconductor device.