JPH01166569A - Semiconductor device - Google Patents

Abstract

PURPOSE:To reduce a surface space charge density by forming a delta-doped monoatomic layer on a boundary between the surface of a semiconductor or an insulating film and the semiconductor, the surface or at a position within several atom layers from the boundary. CONSTITUTION:When the number of doner impurities to be ionized by a delta- doped monoatomic layer 105 is equalized to that of the surface level of an active layer 103 to be activated as acceptors, a depletion layer of an intermediate region 107 is completely eliminated, and operated as a preferable FET. Since space charge is not provided on the layer 103, an electric field concentration is not provided between a gate electrode 106 and source, drain electrodes 104. Thus, even if the region 107 has a considerable conductivity, the breakdown strength of the electrode 106 is held high.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a compound semiconductor device, and particularly to a GaAs MESFET suitable for high-speed operation.

[Conventional technology]

On the surface of compound semiconductors or at the interface with insulators.

A large number of surface levels or interface levels exist, and space charges caused by these levels form a depletion layer, which greatly affects the characteristics of semiconductor devices. For example, I.E.E., Transactions on International Electron Devices Meeting (198
6) pages 763 to 766 (IEEEtE, Tr.
ans, IEDM (1986) pp763-766
), GaAs MESFET is discussed, in order to reduce the effect of this depletion layer, a region with an intermediate carrier concentration is placed between the gate electrode and the source/drain region with a sufficiently high carrier concentration. Made by ion implantation. If this intermediate region is missing, especially in enhancement type FETs (EFETs),
This region is completely depleted, and no current flows between the source and drain even if a positive gate voltage is applied. Furthermore, in a depletion type FET as well, the resistance between the source and drain increases and the effective mutual conductance decreases. Furthermore, the so-called recessed gate structure, in which the gate is formed in a recess on the semiconductor surface, attempts to reduce the influence of the one-surface depletion layer by increasing the thickness of the semiconductor on both sides of the gate. On the other hand, semiconductors
In particular, the application of delta-doped monoatomic layers to GaAs MESFF/T has already been done;
The delta-doped monoatomic layer can either form an active layer, be embedded in the source/drain region, or be formed near the interface with the source/drain electrode.

[Problem that the invention seeks to solve]

The above-mentioned conventional technology does not give consideration to essentially eliminating or reducing the space charge due to the level of the semiconductor surface or the interface with the insulating film. Therefore, for example, in a GaAqM [ESFET], the gate and source
It is necessary to perform complicated processing between the drain regions (intermediate region) to prevent the influence of the depletion layer from reaching the channel, which causes various problems.

For example, in a gate recessed structure, the thickness and carrier concentration of the semiconductor layer in the intermediate region must be highly controlled, and in IC devices that require uniformity within the substrate surface, This intermediate region, which is difficult to apply, is provided with an intermediate carrier concentration. LDD41
The Y structure had a drawback in that it was difficult to control the carrier concentration.

Also, the surface depletion layer does not essentially disappear.

When the gate length is shortened, the effective gate length becomes longer, causing a so-called long gate effect in which mutual conductance decreases.

An object of the present invention is to essentially eliminate or reduce the surface space charge that causes the surface depletion layer in a semiconductor device. In IMIESFIET, the objective is to reduce the adverse effects of surface space charges.

[Means for solving problems]

The above object is achieved by forming a delta-doped monoatomic layer at the surface of the semiconductor or the interface of the insulating film with the semiconductor, or within a few atomic layers from the surface or interface.

[Effect]

If the impurity atoms in the delta-doped monoatomic layer are donors, the charges are completely neutralized if the numbers of the two atoms compensating for the acceptor type surface level or interface level are equal. Moreover, if a delta-doped monoatomic layer exists on the surface or interface, the charges are neutralized at the same position globally, so there is no internal electric field, just like in a neutral region with no space charge. Therefore, no depletion layer is formed due to this, and since it is substantially the same as a neutral region, no special electric field concentration occurs even if there is an external electric field.A delta-doped monoatomic layer is formed from one surface or interface. If it is within a few atomic layers, it will have a similar effect.

Furthermore, if the impurity atoms in the delta-doped monoatomic layer are acceptors, they compensate for the donor type level and have the same effect as described above.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1st
The figure is a cross-sectional structural diagram of a GaA+MESFET.

101 is a semi-insulating GaΔS substrate, 102 is a source/drain region, 103 is an active layer, 104 is a source and drain electrode, 105 is a delta-doped monoatomic layer, 106 is a gate electrode, 107 is a gate 106 and a source/drain This is an intermediate area between areas 102. delta·
Without the doped monoatomic layer 105, the intermediate region 1
07, a surface depletion layer is formed, which is G a A
The effect is the same as biasing the surface of the s-active layer 103 to -0.4 to 0.9V, and this FET has an EFR.
If T, no current will flow in this part. Also.

Even if the FET is a DFET, the current is reduced. If the number of donor impurities ionized in the delta-doped monoatomic layer 105 is made equal to the number of surface states of GaAs 103 activated as acceptors, then
The depletion layer is completely eliminated, and the intermediate layer 107 is in an ideal state. For example, the sheet carrier concentration of the active layer 103 is 1
In the case of an EFET with a threshold value of ~2X10"■""2 and Ov, the intermediate layer 107 has a low resistance value of 1 to 3 Ω/unit. Therefore, no special processing is required for this part. also works as a good FET.Also, GaAs10
Since there is no space charge on the surface of 3, there is no electric field concentration caused by this structure between the gate and the source or drain electrode, and therefore, even though the intermediate region 107 has equivalent conductivity, the breakdown voltage of the gate is low. is held high. This is also due to the absence of a surface depletion layer. There is no electric field concentration nearer to the drain than the gate end, and this serves to prevent the long gate effect that becomes noticeable when the gate length becomes short. Similar space charges exist at the interface between Ga As and an insulating film such as 5ift, so the intermediate region 107
The delta-doped monoatomic layer had similar effects even when the surface was covered with these insulating films.

Note that if the carrier concentration of the delta-doped monoatomic layer becomes higher than the space charge density caused by the surface wall, a conductive layer will be formed on the surface and the gate leakage current will increase. . Therefore, in consideration of safety, it is preferable to form a delta-doped monoatomic layer with a doping amount that does not reverse the charge of the space charge layer on the surface. For example, even if this delta-doped monoatomic layer 105 exists on the surface of the source/drain region 102, it will not have a negative effect on the device characteristics. Although this delta-doped monoatomic layer 105 is formed by epitaxial growth, If an insulating film is subsequently deposited in the same device, it will not be affected by the natural oxide film. If this is not the case, it is sufficient to take into account the thickness of the natural oxide film and form it below in advance. Moreover, in order not to form the layer under the gate, after the gate is formed, it may be formed by selective epitaxial growth using the gate as a mask.

FIG. 2 shows another embodiment according to the invention. active layer 20
No. 1 has a high carrier concentration of about 2×10 “cm−” and a thin film thickness of about 10 cm. On top of this, undoped A
QxGal-xAs 202 separates the gate and active layer. In such an FET, the delta-doped monoatomic layer 105 functions similarly, resulting in a good FET. The delta-doped monoatomic layer has a similar improvement effect on FETs having an undoped GaAs barrier layer or p-type GaAs under the active layer.

〔Effect of the invention〕

According to the present invention, the surface space charge density of a compound semiconductor can be essentially reduced, so that the characteristics of surface-sensitive semiconductor devices can be improved.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 show the GaAs S FI according to the present invention.
It is a cross-sectional structure diagram of ET.

Claims (1)

[Claims] 1. In a semiconductor in which a space charge due to a surface state or an interface state exists on the surface or the interface with an insulating film, at least a part of the surface or the interface, or from the surface or the interface At least a portion of one atomic layer within a few atomic layers is a delta-doped monoatomic layer consisting of doped atoms, and the space charge is
A semiconductor device characterized in that the amount of the monoatomic layer is reduced compared to a case without a monoatomic layer. 2. A patent claim characterized in that the space charge density composed of ionized impurity atoms in the delta-doped monoatomic layer is approximately equal to and opposite in sign to the space charge density in the above item 1. A semiconductor device according to scope 1. 3. When the delta-doped monoatomic layer is on the surface or interface of the semiconductor, the delta-doped monoatomic layer
The space charge density formed by the surface level or interface level caused by the monoatomic layer and the space charge density caused by the ionized dope atoms in the delta-doped monoatomic layer are approximately equal, and their signs are opposite to each other. A semiconductor device according to claim 1. 4. The above-mentioned semiconductor device is a MESFET, and the above-mentioned delta
4. A semiconductor device according to claim 1, 2 or 3, characterized in that a doped monoatomic layer is present. 5. The semiconductor device according to claim 1, 2, 3, or 4, wherein the insulating film is a natural oxide film of the semiconductor.