JPH04280622A - Semiconductor device - Google Patents

Abstract

PURPOSE:To manufacture a semiconductor having less temperature dependent carrier density and specific resistance for a diamond semiconductor having a deep doping level of impurities. CONSTITUTION:A high density impurity doped two-dimensional layer or a one- dimensional linear film is encircled by a non-impurity doped layer or a low- impurity-doped layer. The high density impurity-doped layer has less temperature dependency of carrier density similar to the conductivity of metal. However, as there is a non-doped layer, the average carrier density can be brought to the desired value. As a result, carrier density and the temperature dependency of electric resistance is low.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to devices such as diodes and transistors using diamond semiconductors. In particular, it relates to diamond semiconductors whose carrier concentration changes little with temperature.

0002

2. Description of the Related Art Diamond semiconductors are attracting attention for their applications as devices that operate stably under environments such as high temperatures and radiation, or as devices that can withstand operation at high outputs. The reason why diamond semiconductors can operate even at high temperatures is that they have a large band gap of 5.5 eV. This shows that there is no temperature range (intrinsic region) below 1400° C. in which semiconductor carriers are no longer controlled. Diamond without impurities is an insulator, but when appropriate impurities are added, it becomes n
type or p-type semiconductor. For example, impurities such as Al and B are added to make the material p-type, and N, P, and S are added to make it n-type.

However, even when diamond is doped with Al, B, N, P, S, etc., the doping level of these impurities is deep, making it difficult to use carriers in the saturated region. A comparison with silicon will reveal where the problem lies. In the case of silicon, the p-type impurity is boron, and this impurity level is 0.045 eV from the valence band.
It is in. The n-type impurities are P, As, and Sb, and their levels are 0.045 eV, 0.049 eV, and 0.049 eV from the conduction band edge.
It is 0.039 eV and creates a shallow impurity level extremely close to the band edge. This is equivalent to the energy at room temperature -0.025eV, so the holes and electrons brought by these impurities are excited to the valence band and conduction band, respectively, and their numbers do not change much at temperatures around room temperature. . This temperature range is called the saturated region. However, if the level of the doped impurity is deep, more energy is required to excite it, so the density of excited carriers varies greatly depending on the temperature. The carrier density is exp(-
ΔE/kT), but since ΔE almost corresponds to the impurity level, when the impurity level is deep, the carrier density changes significantly depending on the temperature T. The resistance of a semiconductor depends on the carrier density and mobility, and the mobility also changes depending on the temperature, but here we will focus on changes in the carrier concentration.

[0004] If the semiconductor is not used in the saturated region, the characteristics of the device will change significantly depending on the temperature. This is because carrier density, resistivity, etc. change greatly due to temperature changes. Problems arise, such as a narrowing of the temperature range in which the device functions as an element with desired characteristics. For example, when diamond is doped with boron, the activation energy of the carriers is 0.2 to 0.4 eV, and the activation energy is 0.2 to 0.4 eV.
The carrier concentration changes by two to three orders of magnitude in the 0°C range. Here, the activation energy is the distribution function exp(-Δ
It is the energy of ΔE in E/kT). This is half the energy from the band edge to the impurity level when there is no compensation effect, and is the same value as the energy from the band edge to the impurity level when there is a compensation effect.

[0005]

Problems to be Solved by the Invention In order to increase the utility value of diamond as a semiconductor, it is necessary to prevent the carrier density from changing in the operating temperature range. In order to do this, a method of doping a large amount of impurities to degenerate the impurity level can be considered. However, if this is done, the carrier density becomes too high and becomes similar to that of metals. Then, the properties necessary for semiconductors, such as the ability to create a carrier depletion layer by an electric field and control the current,
Properties such as bondability and rectification properties are lost. It is an object of the present invention to avoid this and provide a diamond semiconductor in which the carrier density is within a desired range and the change in carrier density due to temperature is reduced.

[0006]

[Means for Solving the Problems] A semiconductor device of the present invention includes:
A diamond semiconductor having a deep doping level and a dopant that is not in the saturation region at room temperature;
Highly doped semiconductor layers doped with a large amount of punt and having a two-dimensional spread are alternately laminated with non-doped or lightly doped layers to achieve a desired carrier concentration as a whole. Features. Alternatively, a diamond semiconductor having a dopant with a deep doping level and not in the saturation region at room temperature, and a large number of parallel highly doped semiconductor lines heavily doped with the dopant. membrane and this high dose
It is characterized in that it consists of a non-doped layer or a lightly doped layer that one-dimensionally confines the doped semiconductor line film, and has a desired carrier concentration as a whole. In other words, it has a structure in which a highly doped two-dimensional layer or a highly doped one-dimensional line is surrounded by a lightly doped layer or a non-doped layer. The former is called a two-dimensional structure, and the latter is called a one-dimensional structure. For example, in the case of a two-dimensional structure, a p+ -i-p+ -i-p+ -i . Use a multilayer structure. Regarding the one-dimensional structure, a large number of highly doped p+ ray films are provided in parallel and surrounded by lightly doped, non-doped layers. In other words, by confining the p+ layer and line film two-dimensionally and one-dimensionally with a non-doped layer, temperature changes in carrier density are reduced and the doping concentration is controlled within an appropriate range. Do
Since the ping concentration is approximately proportional to the carrier density, a semiconductor having a desired range of carrier density can be obtained. This also applies to n-type diamond. A large number of n+ layers doped with n-type impurities and non-doped layers are alternately laminated to form a laminated structure of n+ -i-n+-i-.... In this way, the average carrier density is the average of the carrier densities in each layer multiplied by the layer thicknesses, so any average carrier density can be achieved by changing the ratio of the layer thicknesses.

[0007] Simply doped with a large amount of p-type impurities
For a film with only + layers, the Fermi level approaches the valence band or enters the valence band. Alternatively, if the film is simply an n+ layer doped with a large amount of n-type impurities, the Fermi level approaches or enters the conduction band. There are large amounts of free holes and free electrons, respectively, and they exhibit metallic electrical conductivity. The electrical conduction of such a membrane can be made to have almost no temperature dependence. However, this is far higher than the optimum doping concentration for diodes and transistors. Therefore, in the present invention, in order to lower the doping concentration while keeping the Fermi level close to the conduction band, a structure is used in which the doped layer is sandwiched between thick non-doped layers and the doped layer is confined two-dimensionally. . When the thickness of the doped layer is d, the thickness of the non-doped layer is D, and the hole concentration of the doped layer is p+, the average hole concentration p is p=p+ d/
(d+D).

[0008]

[Operation] Since diamond has a large band gap of 5.5 eV, a temperature region corresponding to the intrinsic region does not exist below 1400° C., where diamond is thermally stable. It is also chemically very stable. Furthermore, diamond has a thermal conductivity of 20 (W/cm·K), which is more than 10 times that of Si, and has excellent heat dissipation. Furthermore, the diamond
Carrier mobility is large (electron mobility: 2000 (c
m2 /V・sec), Hall mobility: 2100 (cm2
/V・sec), 300K), low dielectric constant (K=5.5
) and a large breakdown electric field (E=5×10 6 V/cm), making it possible to fabricate high-frequency, high-power devices.

Furthermore, diamond has the characteristic that it is an insulator unless it contains impurities, so when manufacturing devices, it is possible to completely electrically separate the diamond used as the substrate and the diamond in the active layer. There are advantages. The present invention aims to form semiconductor diamond that has a saturation region between room temperature and 600°C in order to realize a diamond device with excellent environmental resistance that can operate at high temperatures, high power, and high frequency. That's true. In the present invention, p+ doped with a large amount of impurities or n+
The layer is sandwiched between non-doped layers, and while the average carrier density is within a range suitable for semiconductors, the doped layer has a high carrier density and the carrier density does not change much with temperature. Therefore, as a whole, there is little change in carrier density due to temperature. The applied semiconductor diamond has the same effect whether it is a natural or artificial (high-pressure synthesis) bulk single crystal, a thin film polycrystal formed by vapor phase synthesis, or a thin film single crystal (epitaxial film).

[0010] Methods for forming a vapor phase synthesized diamond film include (1) a method in which discharge is caused by a DC or AC electric field to activate the raw material gas, and (2) a method in which a thermionic emitter is heated to activate the raw material gas. Activation method, (3) method of bombarding the surface on which diamond will grow with ions, (
There are various methods such as 4) a method of exciting the raw material gas with light such as a laser or ultraviolet light, and (5) a method of burning the raw material gas, and any of these methods can be used in the present invention.
The effect of the invention remains the same.

[0011]

[Example] [Example 1] Microwave plasma CVD on the (100) plane of an artificial single crystal diamond substrate (Ib)
A non-doped layer and a p+ layer were alternately formed by a method under the following conditions. (1) The conditions for forming the non-doped layer are as follows. Gas flow rate H2 flow rate
100sccm
CH4 flow rate
6sccm pressure
40Torr power
200W Substrate temperature
6
00°C (2) The conditions for forming the p+ layer (boron doped layer) are as follows. Gas flow rate H2 flow rate
100sccm
CH4 flow rate
6sccm
B2 H6 flow rate
1sccm
(200ppm)

pressure
40To
rr power
200W
Substrate temperature
600℃

[0012] Non-doped layers and high-concentration layers were alternately laminated on the (100) plane of single crystal diamond, and the following two types of samples were prepared with different film thicknesses. Sample (a) Non-doped layer 5000 Å, p+ layer 50 Å
5-cycle growth sample (b) Non-doped layer 500 Å, p+ layer 50 Å
In both cases of 10-cycle growth, it was confirmed by electron beam diffraction that epitaxial growth occurred in the (100) direction. Figure 1 shows the results of measuring the Hall effect of this sample. The horizontal axis is 1000/T, which is the reciprocal of the absolute temperature multiplied by 1000. The vertical axis is the carrier density (cm-3). This result shows that the carrier density hardly changes depending on the temperature. In other words, the existence of a temperature-independent saturated region in the range of 600° C. to room temperature was confirmed. In addition, samples with different carrier concentrations could be prepared in (a) and (b). (a)
(b) has a p+ layer of 50 Å and a non-doped layer of 500 Å, so the average carrier density in (a) is 1 in (b). /10, and actual measurements show that this is the case.

[Example 2] Samples (a) and (b) were prepared under the same conditions as in Example 1 using artificial diamond (high-pressure synthesis, Ib and boron added) as a substrate. Sample (a), (
The temperature dependence of the electrical resistance in the longitudinal direction of b) was measured. Figure 2
The results are shown below. The horizontal axis is the reciprocal of the absolute temperature multiplied by 1000, and the vertical axis is the specific resistance (Ωcm). This result shows that the temperature dependence of resistivity is small. As in Example 1, the existence of a saturated region was confirmed in the range of 600° C. to room temperature. Furthermore, by comparing the results in FIGS. 1 and 2, it can be seen that carrier mobility (proportional to the reciprocal of the product of carrier density and specific resistance) hardly depends on carrier density. Normally, when a semiconductor is doped with carriers at a high density, impurity scattering increases and the mobility decreases, but these results show that the mobility does not decrease despite the high density doping.

[Example 3] Microwave plasma CV on the (100) plane of an artificial single crystal diamond substrate (Ib)
A large number of highly doped line films were formed in parallel in a lightly doped layer by alternately growing a non-doped layer, a p+ layer, and etching a p layer under the following conditions using method D. (1) The conditions for forming the non-doped layer are as follows. Gas flow rate H2 flow rate
100sccm
CH4 flow rate
6sccm pressure
40Torr power
200W Substrate temperature
6
00°C (2) The conditions for forming the p+ layer (boron doped layer) are as follows. Gas flow rate H2 flow rate
100sccm
CH4 flow rate
6sccm
B2 H6 flow rate (200ppm)
2sccm pressure
4
0Torr power
200W
Substrate temperature
600℃

A method for preparing a sample will be explained in order with reference to FIG. (a) A non-doped film of 1000 Å is formed on the (100) plane of a single crystal diamond substrate. (b) A high concentration boron film of about 50 Å is grown thereon. (c) Further evaporate aluminum, 0.5 μm width, 4.5
Aluminum was patterned at micrometer intervals. This resulted in a parallel aluminum mask. (d) The area not covered by the aluminum mask is 70
Etch approximately 300 yen. After that, the aluminum mask is dissolved and removed. (e) A non-doped layer of 1000 Å was further grown thereon. (f) After this, (b) to (e) were repeated three times. A large number of parallel high-concentration boron doped wire films can be formed in four layers.

It was confirmed by electron beam diffraction that the sample thus prepared was epitaxially grown in the (100) direction. Figure 4 shows the results of measuring the Hall effect of this sample.
Shown below. The horizontal axis is 10, which is the reciprocal of absolute temperature multiplied by 1000.
It is 00/T. The vertical axis is the carrier density (cm-3
). This result shows that the carrier density of this sample hardly changes with temperature. The existence of a temperature-independent saturated region is confirmed in the range of 600° C. to room temperature. Further, by this method, a sample having a different carrier concentration from Example 1 (a) could be prepared.

[0017]

Effects of the Invention In the semiconductor device of the present invention, the carrier density has almost no temperature dependence in the range from room temperature to 600°C. Moreover, the carrier density can be freely controlled. Further, although a single film has the problem that carrier mobility decreases due to high concentration of doping, the structure of the present invention has the advantage that no significant decrease is observed. Therefore, the semiconductor device of the present invention is effective in realizing a device that exhibits stable diode or transistor characteristics in a temperature range up to high temperatures.

[Brief explanation of the drawing]

FIG. 1: Sample (a) of the semiconductor device of the present invention (non-doped 5000 Å, p+ 50 Å, 5-cycle lamination) and sample (
b) A graph showing the results of hole measurements for (non-doped 500 Å, p+ 50 Å, 10-cycle lamination) and the temperature dependence of carrier density.

FIG. 2: Sample (a) of the semiconductor device of the present invention (non-doped 5000 Å, p+ 50 Å, 5-cycle lamination) and sample (
Graph showing the results of determining the temperature dependence of resistivity for b) (non-doped 500 Å, p+ 50 Å, 10-cycle lamination).

FIG. 3 is a diagram illustrating a process for producing a diamond semiconductor sample having a highly doped line film according to Example 3 of the present invention.

FIG. 4 is a graph showing the results of measuring the temperature dependence of the carrier concentration of a sample according to Example 3 of the present invention.

Claims (4)

[Claims] 1. A diamond semiconductor having a deep doping level and a dopant that is not in the saturation region at room temperature, which is a diamond semiconductor having a two-dimensional spread and doped with a large amount of the dopant. 1. A semiconductor device characterized in that doped semiconductor layers and non-doped or lightly doped layers are alternately laminated to provide a desired carrier concentration as a whole. 2. A diamond semiconductor having a dopant having a deep doping level and not in the saturation region at room temperature, comprising a large number of parallel highly doped semiconductors heavily doped with the dopant. 1. A semiconductor device comprising a semiconductor line film and a non-doped layer or a lightly doped layer that one-dimensionally confines the highly doped semiconductor line film, and has a desired carrier concentration as a whole. 3. The dopant concentration of the highly doped semiconductor layer or the highly doped semiconductor line film is 1019 cm-3 or more, and the dopant concentration of the no-doped layer or the lightly doped layer is 101 cm-3 or more.
Claim 1 or 2, characterized in that it is 7 cm-3 or less.
The semiconductor device described in . 4. The semiconductor device according to claim 1, wherein the doping level is 0.1 eV or more.