JPH0456140A - Compound semiconductor device and manufacture thereof - Google Patents

Abstract

PURPOSE:To reduce generation of a boundary level of high concentration by composing an insulating solid layer of a material containing one or both of aluminum selenide and aluminum sulfide. CONSTITUTION:A substrate 11 made of clean undoped GaAs is first emitted with a molecular beam obtained by heating solid aluminum and a molecular beam obtained by heating solid selenium in vacuum, and an insulating film 12 made of aluminum selenide is formed. Then, after a gate electrode 13 is formed on an insulting film 12, with the electrode as a mask the excess film 12 is removed. Further, n<+> type GaAs layers 14 are formed at both sides of the electrode 13 for holding the electrode 13. Eventually, an ohmic electrode 15 is formed on the layer to obtain a MIS type field effect transistor.

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a compound semiconductor device and a method for manufacturing the same, and more particularly to a compound semiconductor device and a method for manufacturing the same that have little deterioration in characteristics as a discrete element or an integrated circuit. [Prior Art] Conventionally, in semiconductor devices, it has been widely practiced to form an insulating solid layer on a semiconductor surface, between a semiconductor region and an electrode region, or between semiconductor regions by some method. This insulating solid layer is used as a protective film on the surface of the semiconductor, and in other cases as an intermediate insulating film for separating the semiconductor region and the electrode region or between the semiconductor regions. In particular, in field effect transistors of MIS type (or MOS type) structure, it is used as an intermediate insulating film to separate the gate electrode region and the semiconductor region, and in this case, the intermediate insulating film and the semiconductor region are The two-dimensional electron gas induced at the interface functions as a conductive layer. By the way, in the case of compound semiconductor devices that use gallium arsenide (GaAs) and other ■-■ group compounds, silicon dioxide (SiC2) has conventionally been used as a material for forming this type of insulating solid layer. (For example, Jia
-Fa Fan et al, JapaneseJ
Internal of Applied Physics
, Vol, 27. No, 7. pp+L1331～
1333 [1988)). However, since compound semiconductors have relatively high reactivity with other substances, for example, when an insulating solid layer made of 8102 is formed on the surface of a GaAs semiconductor, SiOz
Oxygen therein reacts with GaAs, and a highly concentrated interface state is often generated in the bandgap of the semiconductor region. Therefore, in a compound semiconductor device using the same solid layer as a surface protection film, recombination of electrons or holes occurs through the interface state, which causes deterioration of the characteristics as a discrete element or an integrated circuit. In addition, in MIS field effect transistors that use the same solid layer as an intermediate insulating film, the interface states cause a Fermi-level pinning phenomenon, which makes it difficult to control the two-dimensional electron gas at the interface. Or it becomes a factor that deteriorates the characteristics as an integrated circuit. Furthermore, since the dielectric constant of SiO□ is relatively small at 3.9,
For example, when 5 in 2 is used as the intermediate insulating film of a tIs field effect transistor, there is another problem that the concentration of two-dimensional electron gas that can be changed by gate bias is small. Problems to be Solved by the Invention Accordingly, one object of the present invention is to provide a compound semiconductor device and a method for manufacturing the same in which the occurrence of high concentration interface states is reduced.

[Means to solve the problem]

The present invention provides a compound semiconductor device in which an insulating solid layer is formed on a semiconductor surface, between a semiconductor region and an electrode region, between semiconductor regions, etc., in which the insulating solid layer is formed from one or both of aluminum selenide and aluminum sulfide. It is characterized by being constructed using the following materials. Since aluminum selenide and aluminum sulfide are similar compounds, each can be used alone or in the form of a mixture or a composite compound. The insulating solid layer preferably uses molecular beams obtained by heating a solid aluminum raw material in a vacuum, and molecular beams obtained by heating a raw material containing at least one or both of selenium and sulfur as a main component. It can be formed by irradiating it onto a semiconductor region and causing them to react with each other. In this case, selenium and sulfur can each be used alone, but if necessary, they can also be used in the form of a compound with another suitable material that can replace aluminum. In addition, the molecular beam of It is also possible to use a molecular beam in combination, and in that case, an insulating solid layer made of a mixture or composite compound of aluminum selenide and aluminum sulfide can be formed. Note that the insulating solid layer is formed by irradiating a predetermined semiconductor region with a molecular beam obtained by heating a solid aluminum raw material in a vacuum, and at the same time applying either hydrogen selenide (H2Se) or hydrogen sulfide (H2S). Alternatively, it is also possible to form the material by supplying gaseous raw materials containing at least both of them as main components and allowing them to react with each other.

[Effect 1] As a result of numerous trials, experiments, and considerations, the inventors of the present invention have discovered that an I! ! It has been found that the occurrence of interface states, which cause the deterioration of characteristics of a homogeneous solid-layer semiconductor device, is extremely small. Therefore, for example, if the insulating solid layer of the present invention is used as a surface protection film, it is possible to effectively prevent the generation of recombination current in the semiconductor surface region. When used with an intermediate insulating film such as a field effect transistor, it is possible to effectively suppress the Fermi level pinning phenomenon. Furthermore, since the dielectric constants of aluminum selenide and aluminum sulfide are larger than that of Sin, the concentration of two-dimensional electron gas that can be changed with the same gate bias can be increased. Note that since the dielectric constant of aluminum selenide is higher than that of aluminum sulfide, aluminum selenide is a more excellent material for the purpose of the present invention. As mentioned above, an insulating solid layer can be formed by heating a raw material and irradiating a predetermined semiconductor region with a molecular beam obtained by heating the raw material, but this method requires film formation at a relatively low temperature. This method is suitable for manufacturing compound semiconductor devices with good reproducibility without variations in characteristics because the film thickness can be controlled extremely well. The same applies to the method of using H2Se gas or H2S gas instead of molecular beams obtained by heating selenium or sulfur. The insulating solid layer made of aluminum selenide or aluminum sulfide (or a mixture or composite compound thereof) can be made into an amorphous or microcrystalline state by controlling the film forming conditions. Note that in order to optimize the thermal stability and electrical properties of the produced insulating solid layer, it is preferable to include other materials as subcomponents rather than using pure selenium and sulfur. However, in that case, it is necessary to carefully select a material that does not adversely affect the physical properties of the insulating solid layer. Embodiments The present invention will be described in more detail below with reference to embodiments shown in FIGS. 1 to 4. <Embodiment 1> FIG. 1 shows an embodiment in which the present invention is applied to a MIS type field effect transistor. First, in a vacuum,
A molecular beam obtained by heating solid aluminum and a molecular beam obtained by heating solid selenium are combined into clean undoped Ga
Irradiated onto a substrate If made of As, made of aluminum selenide! 11 film 12 was formed (see FIG. 1C). The thickness of the insulating film 12 was set to 50n+i. Next, insulating film 1
After forming a gate electrode 13 on 2, the excess insulating film 12 was removed using the gate electrode as a mask (see FIG. 1). The gate length was 1 micron. Furthermore, n-type GaAsMf4 was formed on both sides of the gate electrode 13 (see FIG. 1C). Finally, an ohmic electrode 15 was formed on the same layer to form a MIS type field effect transistor (see FIG. 1C). When a positive bias is applied to the gate electrode 13, a two-dimensional electron gas 16 is generated at the interface between the aluminum selenide intermediate insulating film 12 and the undoped GaAs substrate 11. Therefore, by adjusting the bias value of the gate electrode I3, the concentration of the two-dimensional electron gas 16 is changed, and -
By controlling the current flowing between the ohmic electrodes 15, transistor operation can be obtained.
The same applies when InP is used. As a result of measuring the interface state density between the insulating film 12 and the undoped GaAs substrate 11, 1012/c+a2
It was confirmed that it was as small as / eV or less. Therefore, it was possible to obtain a high-speed device with almost no characteristic deterioration caused by Fermi level pinning caused by interface states. The transfer conductance was 150 mS/mm. In addition, in this example, since aluminum selenide is deposited by irradiating aluminum molecular beams and selenium molecular beams in a vacuum, the thickness of the insulating film 12 can be precisely controlled by adjusting the intensity of each molecular beam. Good control was possible, and as a result, devices with less variation in characteristics could be manufactured with good reproducibility. The same is true when aluminum sulfide is used instead of aluminum selenide.
We were able to obtain a good device with a low interface state density. Transfer conductance was room S/mm. Although the case where GaAs is used as the compound semiconductor material has been described above, other compound semiconductors may also be used. <Embodiment 2> FIG. 2 shows another embodiment in which the present invention is applied to a MIS type field effect transistor. First, an n-type GaAs layer 22 and an undoped A I Ga A layer are formed on an undoped GaAs substrate 21 by single molecular beam epitaxy.
After sequentially growing the s-layer 23, an aluminum selenide insulating film 24 was formed by irradiating molecular beams obtained by heating solid aluminum and molecular beams obtained by heating solid selenium in a vacuum. (See Figure 2C). Next, aluminum selenide #! A gate electrode 25 is formed on the edge film 24, and the excess I'l! is removed using the gate electrode 25 as a mask. ! Membrane 2
4 and the AIGaAs layer 23 were removed (second
(see figure). The gate length was 1 micron. Furthermore, n-type GaAs layers 26 were formed on both sides of the gate electrode 25 (see FIG. 2C). Finally, an ohmic electrode 27 was formed on the same layer to complete a MIS type field effect transistor (see FIG. 2C). The transistor of this example has an MIS type structure as in the case of Example 1, but uses an n-type GaAs layer 22 as a conductive layer, and there is a gap between this layer and an aluminum selenide insulating film 24. Undoped A
This example differs from Example 1 in that an lGaAs layer 23 is inserted. When a bias voltage is applied to the gate electrode 25, n-type Ga
The width of the conductive carrier depletion layer in the As layer 23 changes. This changes the number of conductive carriers in the same layer, resulting in transistor operation. In this structure, the conductive layer 22
and the aluminum selenide insulating film 24 is undoped AlG.
Since it is separated by the aAs layer 23, the conductive layer 22
It has the advantage that electrons flowing through the aluminum selenide insulating film 24 are hardly affected by defects. Furthermore, compared to the case where the aluminum selenide insulating film 24 is not provided, in the transistor of this embodiment in which the insulating film is provided under the gate electrode 25, the leakage current flowing into the gate electrode 25 is small, and a large operating margin can be obtained. Ta. The thickness of the n-type GaAs layer 22 is 10 nm, and the undoped AI Ga As layer 23
When the thickness of the aluminum selenide insulating film 24 was 20 nm and the thickness of the aluminum selenide insulating film 24 was 3 on I11, the transfer conductance was 140a+S/ll1m. Note that the transfer conductance when aluminum sulfide is used instead of aluminum selenide as the intermediate insulating film 24 is as follows:
It was 90mS/mm. The n-type GaAs layer 22 can be omitted, and in that case, the undoped GaAs layer 21 and the undoped Al
Two-dimensional electron gas induced at the interface of the GaAs layer 23 functions as a conductive layer. In addition, the n-type Ga As layer 22
is omitted, and the undoped AlGaAs layer 23 is made of n-type A.
It may be replaced with an lGaAs layer. Also in this case, the n-type A I Ga A substituted for the undoped GaAs layer 21
Two-dimensional electron gas induced at the interface of the s-layer functions as a conductive layer. In either case, since the conductive layer of the semiconductor and the aluminum selenide insulating film 24 are separated, electrons flowing through the conductive layer are hardly affected by defects in the aluminum selenide layer, and the aluminum selenide insulating film 24
Similarly, since the gate electrode 25 is located under the gate electrode 25, the leakage current flowing into the gate electrode 25 is small, and a large operating margin can be obtained. As mentioned above, the material of the compound semiconductor forming the conductive layer is Ga
Although the case of As is shown, the same applies to the case of using other compound semiconductors such as InGaAs and InP. <Embodiment 3> Next, an embodiment in which the present invention is applied to surface protection of a compound semiconductor heterostructure bipolar transistor (HBT) will be described. Figure 3 is. FIG. 3 is a cross-sectional view showing a manufacturing process of an HBT having an AlGaAs/GaAs structure. First, on the surface of a semi-insulating GaAs substrate 30, a modified GaAs layer 31, an n-type GaAs layer 32, a p-type G
aAs layer 33, n-type AlGaAs layer 34 and n-type Ga
After the As layer 35 was epitaxially grown in sequence, an emitter electrode 36 was formed (FIG. 3, C). Next, using the same electrode as a mask, unnecessary n-type GaAs layer 35 and n-type AlGaAs layer 34 were removed (see FIG. 3). Further, a side wall 37 made of a solid layer of aluminum selenide was formed on the side of the emitter electrode 36, and then a base electrode 38 was formed between the side walls 26 (see FIG. 3C). Finally, an n-type GaAs layer 32 corresponding to the collector electrode region
and the collector electrode 3 by removing the p-type Ga A s33.
9 and completed the main part of the HBT (Fig. 3C)
reference). In this embodiment, aluminum selenide is used for the side wall 37 which functions as a surface preservation layer. Therefore, the generation of interface states between the sidewall and the underlying p-type GaAs 33 is suppressed, and p-type Ga
The electrons injected into the As layer 33 do not recombine and disappear through the interface state, but instead flow into the n-type Ga collector layer.
- Diffuses into the As layer 31. As a result, the gain loss of the transistor could be reduced, and when the modified layer was formed as in this example, the gain could be improved by more than five times compared to the case where it was not formed. The same thing happened when aluminum sulfide was used as the side wall 37 instead of aluminum selenide. Although the HBT having the A IG aA s/G aA s heterostructure has been described above, other compound semiconductors such as InGaAs, InP, InGaAs, etc.
The same applies when P etc. are used. <Example 4> Finally, an example in which the present invention is used to protect the surface of a compound semiconductor laser will be described. Figure 4 shows a cross section of the light emitting region of a compound semiconductor laser.
0 is an n+ type GaAs substrate, 41 is an n type AlGaAs layer,
42 is an undoped GaAs layer, 43 is a p-type AI G
It is an aAs layer, and has a so-called double heterojunction structure. 44 and 45 are ohmic electrodes. 46 is an insulating solid film made of aluminum selenide, which functions as a surface protection film for a portion corresponding to the end face of the laser cavity. A current is passed in the direction perpendicular to the semiconductor layer (arrow 47 in FIG. 4), and the active layer of undoped GaA
Laser light 48 is obtained from the end face by causing recombination of carriers in the s-layer 42 and generating photons. In a conventional compound semiconductor laser, a 5 in 2 film is used as a surface protective film on the end facet, so a high density of interface states exists at the interface between the protective film and each region of the compound semiconductor. As a result, the carrier density decreases near the edge due to the recombination of non-emissive carriers that occurs via the same interface state, increasing the reabsorption of the second light near the edge, and the associated temperature rise causes the carrier density to decrease near the edge. However, since the compound semiconductor laser according to this example uses aluminum selenide as a surface protective film, there is almost no generation of interface states, which significantly shortens the device life. I was able to improve it. The improvement in life was more than three times. Similar effects can be fully expected for compound semiconductor lasers other than the double heterojunction type.

【Effect of the invention】

According to the present invention, a good insulating solid layer/compound semiconductor structure with few interface states can be obtained, and a good compound semiconductor device with little characteristic deterioration due to the interface states can be obtained. That is, when the present invention is applied to a field effect transistor having an MIS type structure, there is little deterioration in characteristics due to interface states. It is possible to manufacture devices with high speed and a large operating margin with good reproducibility. Further, when the present invention is applied to a compound semiconductor heterojunction bipolar transistor, recombination of carriers via interface states is suppressed, and a decrease in the number increase rate of the transistor can be prevented. Furthermore, if the present invention is applied to a compound semiconductor laser, deterioration at the cavity end face can be prevented. In the description of the embodiments, four types of embodiments have been cited, but the present invention can also be applied to various other compound semiconductor devices where it is desired to reduce the interface state between the insulating solid layer and the compound semiconductor. A similar effect can be obtained by applying . For example, if the present invention is applied to the surface protective film of a solar cell, it is possible to prevent recombination of photocarriers at the interface level and improve the conversion efficiency of the solar cell. Furthermore, if the present invention is applied to a surface protective film between the source and gate electrodes and between the drain and gate electrodes of a field effect transistor,
It is possible to prevent the pinning of the Fermi level due to the interface state, and it is possible to suppress the increase in resistance of the surface layer due to carrier depletion.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the manufacturing process of an MIS type field effect transistor which is a first embodiment of the present invention, and FIG. 2 is a sectional view showing the manufacturing process of an MIS type field effect transistor which is a second embodiment of the present invention. 3 is a sectional view showing the manufacturing process of a compound semiconductor heterostructure bipolar transistor according to the third embodiment of the present invention, and FIG. 4 is a cross-sectional view showing the manufacturing process of a compound semiconductor heterostructure bipolar transistor according to the third embodiment of the present invention. It is a cross-sectional view of a compound semiconductor laser as an example. <Explanation of symbols> 11... Undoped GaAs, 12... Aluminum selenide insulating film, 13... Gate electrode, 14n...
... n-type GaAs layer, 15 ... ohmic electrode, 16 ... two-dimensional electron gas, 21 ... undoped Ga
As substrate, 22-n type Ga As ffJ, 23.
... Undoped AlGaAs layer, 24 ... Aluminum selenide insulating film, 25 ... Gate electrode, 26 ... n
Type G a As layer, 27... Ohmic electrode, 30
・・・Semi-insulating GaAs substrate, 31- n-type GaAs layer, 32- n-type GaAs layer, 33=・P-type GaA
s layer, 34n-type AlGaAs layer, 35-n-type GaAs
Layer, 36... Emitter electrode, 37 - Aluminum selenide side wall, 38... Base electric bottle, 39 Collector electrode, 4L-n" type Ga As substrate, 41-n type AlG
aAs layer, 42・Undoped GaAs layer, 43-
P-type AlGaAs layer, 44, 45... Ohmic electrode, 46... Aluminum selenide surface protective film, 47.
・Current direction, 48...the light. (a)

Claims (1)

[Claims] 1. In a compound semiconductor device in which an insulating solid layer is formed on a semiconductor surface, between a semiconductor region and an electrode region, between semiconductor regions, etc., the insulating solid layer is made of aluminum selenide or aluminum sulfide. 1. A compound semiconductor device comprising a material made of one or both of the following. 2. The compound semiconductor device according to claim 1, wherein the insulating solid layer is made of a material made of aluminum selenide. 3. The compound semiconductor device according to claim 1, wherein the insulating solid layer is made of a material made of aluminum sulfide. 4. The compound semiconductor device according to any one of claims 1 to 3, wherein the insulating solid layer is used as an intermediate insulating film in an MIS type structure. 5. Claims 1 to 3, characterized in that the insulating solid layer is used as a surface protection layer of a semiconductor.
The compound semiconductor device according to any one of paragraphs. 6. The compound semiconductor device according to any one of claims 1 to 5, wherein the semiconductor region is composed of a III-V group compound. 7. Simultaneously irradiate a desired semiconductor region with a molecular beam obtained by heating a solid aluminum raw material and a molecular beam obtained by heating a raw material containing at least one or both of selenium and sulfur as main components. A method for manufacturing a compound semiconductor device, comprising: forming an insulating solid layer made of one or both of aluminum selenide and aluminum sulfide on the region. 8. Irradiating a desired semiconductor region with a molecular beam obtained by heating a solid aluminum raw material, and simultaneously supplying a gaseous raw material containing at least one or both of hydrogen selenide and hydrogen sulfide as a main component. A method for manufacturing a compound semiconductor device, comprising: forming an insulating solid layer made of either or both of aluminum selenide and aluminum sulfide on the semiconductor region.