JPH07254560A - Method for semiconductor crystal growth - Google Patents

Abstract

PURPOSE:To provide means of forming high-quality hetero junction by preventing the segregation of an element constituting a III-V compound semiconductor into a growing semiconductor when growing a group IV semiconductor or a II-VI compound semiconductor on III-V compound semiconductor crystal. CONSTITUTION:When growing a semiconductor of group IV such as Ge, Si, SiGe and the like or a semiconductor of II-VI compound semiconductor such as ZnSe on III-V compound semiconductor crystal such as GaAs, a composition ratio between the surface crystal structure of compound semiconductor crystal and the elements constituting a compound semiconductor is so adjusted that no electric charge will occur on the growth interface and then a single element semiconductor such as Ge or a II-VI compound semiconductor such as ZnSe is grown. When growing Ge on GaAs, the surface structure is made to (2X4) structure, (6X4) structure, (5X4) structure, (5X2) structure and (3X1) structure, and V/III ratio is set to 0.5 to 3.0.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a molecular beam crystal growth method (M
BE), metalorganic vapor phase epitaxy (MOVPE) or the like, and a semiconductor crystal growth method for growing a group IV semiconductor or a compound semiconductor on a compound semiconductor by an epitaxial crystal growth method to form a heterojunction.

With the recent demand for higher performance of semiconductor devices, the demand for the quality of heterojunctions has also become higher. It is required that a plurality of semiconductor layers forming a heterojunction can be arbitrarily selected and that the composition distribution at the interface is steep.

Ge / III-V group compound semiconductor heterojunctions are expected to be applicable to ultra-high speed transistors such as heterojunction field effect transistors and heterojunction bipolar transistors. In particular, as a semiconductor device of high speed and low power consumption, an integrated circuit device of a complementary field effect transistor using a compound semiconductor heterojunction (complementary H
The EMT integrated circuit device) is drawing attention.

As an n-channel HEMT, III
It is considered promising to use a group-V compound semiconductor, Ge for the channel layer in the p-channel HEMT, and III-V group compound semiconductor for the hole supply layer. In addition, these semiconductor heterojunctions have a steep composition profile,
In addition, it is desired to form with high purity.

[0005]

2. Description of the Related Art When a compound semiconductor is grown by a molecular beam crystal growth method (MBE) or a metalorganic vapor phase epitaxy method (MOVPE), it is possible to grow the compound semiconductor by controlling in atomic layer units. Since it is possible to grow a crystal of high purity, it is widely used for manufacturing semiconductor devices utilizing a heterojunction. Now, when Ge is grown on a III-V group compound semiconductor using these crystal growth methods, the constituent atoms of the underlying III-V group compound semiconductor are segregated in Ge, and the quality of the heterojunction is impaired. there were.

[0006]

The group III atoms segregated in the growing Ge become p-type impurities in the Ge, and the group V atoms become n-type impurities. Therefore, high-purity Ge that does not segregate the elements constituting the III-V group compound semiconductor is
It could not be grown on the group V compound semiconductor. According to the present invention, when a Group IV semiconductor such as Ge or a Group II-VI compound semiconductor such as ZnSe is grown on a Group III-V compound semiconductor, the constituent atoms of the Group III-V compound semiconductor are added to the growing semiconductor. It is an object of the present invention to provide a method for growing a semiconductor crystal capable of forming a high-quality heterojunction by reducing the segregation of Al.

[0007]

In a method for growing a semiconductor crystal according to the present invention, when a group IV semiconductor or a group II-VI compound semiconductor is epitaxially grown on a group III-V compound semiconductor, the compound semiconductor The crystal structure of the surface and the surface composition ratio of the elements constituting the compound semiconductor are
After adjusting to a state where no charge is generated at the interface between the compound semiconductor and the IV semiconductor or compound semiconductor that grows,
A process of growing a group IV semiconductor or a compound semiconductor was adopted.

In this case, the compound semiconductor is GaAs or Al.
A group III-V compound semiconductor such as As, AlGaAs, or InGaP is used, and a group IV semiconductor layer grown on the surface of the group III-V compound semiconductor is G
e, Si and SiGe, and the growing compound semiconductor is Zn
It can be a II-VI compound semiconductor such as Se.

In these cases, GaAs crystal or AlA
The s crystal has a V / III ratio of the surface of Vs of a desired surface structure.
After growing to a ratio higher than the / III ratio, the GaAs crystal or AlAs crystal is heated until the desired surface structure is obtained, and then Ge can be grown at the growth temperature of Ge.

Further, in these cases, after growing a GaAs crystal or an AlAs crystal so that the V / III ratio of the surface thereof is higher than the V / III ratio of the desired surface structure, Ga or Al is changed to a desired surface structure. After irradiating the obtained amount, Ge can be grown.

Further, in these cases, after growing a GaAs crystal or an AlAs crystal in a state where the V / III ratio of the surface is lower than the V / III ratio of the desired surface structure, As is obtained in the desired surface structure. After irradiating with a large amount, Ge can be grown.

In these cases, the surface structure of the GaAs crystal or AlAs crystal is determined by the RHEED method or the RDS method.
Ge can be grown after confirming that the desired surface structure is obtained by using the method.

[0013]

As in the present invention, a III-V compound semiconductor, for example, an IV group semiconductor such as Ge or Zn on the (001) plane is used.
When growing II-VI group compound semiconductors such as Se,
The V / III ratio on the surface of the III-V compound semiconductor is set to 0.5.
When it is set to 3, the surface of the underlying III-V compound semiconductor can be stabilized and the generation of interface charge can be suppressed,
Group III atoms or V constituting III-V group compound semiconductor
It is possible to effectively reduce the segregation of group atoms into the growing semiconductor and form a good heterojunction.

When a Ge / III-V compound semiconductor heterojunction is formed by the MBE method, the III-V compound semiconductor grows in a V-group excess atmosphere in order to suppress evaporation of V-group atoms. When Ge is grown in the chamber, the group V atoms are doped in Ge, so that Ge grows in another growth chamber connected by an ultra-vacuum valve.

III-V compound semiconductor growth chamber III-V
After the group compound semiconductor was grown, when the sample was transported to the Ge growth chamber, the III-V compound semiconductor surface was exposed to the III-
Since the group V atom is attached while the temperature of the group V compound semiconductor is lowered, the structure becomes a (2 × 2) structure or a c (4 × 4) structure.
This surface is a surface on which 1.75 layers or more of group V atoms are attached to the outermost surface. When Ge is grown on the surface, not only a large amount of group V atoms are segregated in Ge but also a large amount of electrons are generated. However, it becomes a driving force for segregation of atoms constituting the III-V compound semiconductor into Ge.

FIG. 3 is a schematic cross-sectional view when Ge is grown on a III-V group compound semiconductor having a (2 × 2) structure. In this case, as shown in this figure, III-V
Group V atoms are attached to the entire outermost surface of the group compound semiconductor to form V
The / III ratio is infinite. In this case, since a negative charge is generated by the excess electrons of the group V atom, G
When e is grown, a large amount of group V atoms are segregated in Ge.

On the other hand, known as a group III stabilizing surface (4
The surface having a x2) or c (8x2) structure is a surface on which 0.75 layers of group III atoms are attached, and when Ge is grown on the surface, a large amount of holes are generated and similarly III- It becomes a driving force for segregation of atoms constituting the group V compound semiconductor into Ge.

FIG. 4 is a schematic sectional view of a case where Ge is grown on a III-V group compound semiconductor having a (4 × 2) structure. In this case, as shown in this figure, III-V
Group III atoms are attached to the outermost surface of the group compound semiconductor, and V /
The III ratio is 0.33. In this case, a deficient electron in the group III atom generates a positive charge on the surface of the group III-V compound semiconductor, so that if Ge is grown on it, a large amount of group III atom is likely to segregate in Ge.

1A and 1B are explanatory views of a method for growing a semiconductor crystal according to the present invention. FIG. 1A is an explanatory view of the relationship between the maximum substrate temperature and the hole mobility before the Ge growth, and FIG. FIG. 4 is a diagram illustrating the relationship between the maximum substrate temperature, the surface structure, and the V / III ratio of the surface of FIG.

The horizontal axis in FIG. 1 (A) and the horizontal axis in FIG. 1 (B) are the maximum elapsed substrate temperatures before Ge growth, and their scales are the same. First, as shown in FIG. 1 (A), the hole mobility of Ge exceeds 400 cm ² / Vs because the maximum substrate temperature before growth of Ge is 495 ° C. to 595 ° C.
The temperature range is shown in FIG. 1B, and the surface structure of FIG. 1B shows that the GaAs has a (2 × 4) structure and a (6 ×)
4) structure, (5x4) structure, (5x2) structure, (3x
1) Including the structure, the V / III ratio corresponds to a range of 3 to 0.5.

AlAs includes (2 × 4) structure, (6 × 4) structure, (5 × 4) structure, (5 × 2) structure or (3 × 2) structure, and has a V / III ratio of Looking at it, G
Like aAs, it corresponds to a range of 3 to 0.5.

Further examining FIG. 1 (A),
The hole mobility of Ge rapidly increases to exceed 430 cm ² / Vs when the maximum substrate temperature before the growth of Ge is from 500 ° C to 5 ° C.
The temperature is in the range of 75 ° C. When this temperature range is viewed in the surface structure of FIG. 1B, the GaAs has a (2 × 4) structure,
A (6 × 4) structure, a (5 × 4) structure, a (5 × 2) structure or a (3 × 1) structure is included, and the V / III ratio is
This corresponds to a range of 2 to 0.55.

AlAs includes (2 × 4) structure, (6 × 4) structure, (5 × 4) structure, (5 × 2) structure or (3 × 2) structure, and has a V / III ratio of Looking at it, G
Like aAs, it corresponds to the range of 2 to 0.55.

Within the V / III ratio range of the above crystal structure, segregation is suppressed and the characteristics of grown Ge are improved. As shown in FIGS. 1 (A) and 1 (B), it is possible to suppress the generation of interfacial charges by keeping the V / III ratio of the surface of the III-V compound semiconductor at a value not greatly deviating from 1. It is thought to be a tame.

Incidentally, in the range where the hole mobility becomes high first
The crystal structure of the surface of the III-V group compound semiconductor is mentioned.
In fact, there are other structures with narrow range of conditions,
The surface V / III ratio of these surface structures is 0.5.
If it is ~ 3, the same effect as the above is produced.

FIG. 2 is a schematic sectional view of the case where Ge is grown on the III-V group compound semiconductor having the structure of the present invention. In this case, as shown in this figure, III-V
A group V atom of 0.5 atomic layer is attached to the outermost surface of the group compound semiconductor, and the V / III ratio is 1. In this case, the excess electrons of the group V atoms and the deficient electrons of the group III atoms are averaged so that no charge appears, and when Ge is grown on top of it, III
Group atoms or group V atoms do not segregate in Ge and high quality heterojunctions are formed. It is known that the temperature of the substrate shows a slightly different value depending on the measuring method, but there is no problem in explaining the present invention.

[0027]

EXAMPLES Examples of the present invention will be described below. Ge was grown on AlAs by the MBE method. That is, the semi-insulating GaAs substrate is transferred to the III-V group compound semiconductor-dedicated growth chamber, the native oxide film is removed, and then the substrate temperature is set to 600 ° C.
Undoped GaAs 350 Å, undoped AlAs
Has grown to 50Å. Growth rate is 0.7 μm /
h, 0.3 μm / h.

At this time, the As / Ga beam ratio was set to 10, but the As atmosphere was equivalent to an As / Ga ratio of 1 even when the As shutter was closed. After lowering the substrate temperature to 300 ° C., it was transferred to a Ga-dedicated growth chamber. In this case, RHEE
D method (Reflection High Energy
When the surface structure was examined by Electron Diffraction, it was (2 × 2) structure.

After raising the substrate temperature, the temperature is fixed at 250 ° C. which is the Ge growth temperature, and the thickness of undoped Ge is set to 4000.
Å I grew up. Ge was heated to 1150 ° C. in a K cell and supplied, and in this case, the growth rate was 0.14 μm / h. The grown sample was taken out into the atmosphere and subjected to Hall measurement at room temperature.

(Comparative Example) First, a comparison will be made with the example of the present invention.
Therefore, the method of growing Ge by the conventional technique is explained.
Reveal Do not raise the substrate temperature before growing the Ge
It was grown at a growth temperature of 250 ° C. In this case, positive
Hole mobility is 190 cm²/ Vs, hole concentration 3.9 × 1
0¹⁷cm ^-3Met. In addition, the substrate temperature is set to 8 before the Ge growth.
When the temperature is raised to 60 ° C, the surface structure is a (4x6) structure.
And the hole mobility is 180 cm²/ Vs, hole concentration is 6.
2 x 10¹⁸cm^-3Met.

(First Embodiment) In the method of growing Ge,
Then, the substrate temperature was raised to 525 ° C. before the Ge growth. That conclusion
The surface structure of the obtained sample is (5 × 4) structure, V / II
The I ratio was 1. The hole mobility of this sample is 56.
0 cm²/ Vs, hole concentration is 2.8 × 10 ¹⁷cm^-3And
The mobility is more than double that of the conventional one, and the hole concentration is also reduced.
It was

(Second Example) After growing AlAs, the substrate temperature was lowered to 500 ° C., and the (2 × 4) structure and V / III ratio were set to 3. Since 0.75 layer of As was attached to the outermost surface of this sample, a 0.25 layer of Al, that is, a (5 × 4) structure was obtained when irradiated for 3.4 seconds. At this time, in order to prevent As from adhering to the atmosphere, the As should be transported in a short time, or
It is necessary to lower the cell temperature and then perform Al irradiation.

(Third Embodiment) When AlAs is intentionally grown under the As-deficient condition (4 × 2) structure, the V / III ratio is set to 0.
33 samples are obtained. As was 0.
25 layers, that is, 3.4 with an As / Al beam ratio of 1.
After irradiation for a second, it became a (5 × 4) structure.

(Fourth Embodiment) The inside of the growth apparatus is not a vacuum M
In the OVPE method, the surface cannot be observed by the RHEED method using an electron beam, but in this case, R using light is used.
DS method (Reflectance-Difference)
Observe the surface by e-Specocopy). According to the observation result, it is clear that the surface structure is similar to that observed by the MBE method, the correspondence between the RDS spectrum and each surface structure can be determined, and the V / III ratio of the surface can be determined. Can also be determined. Therefore, when growing Ge by the MOVPE method, the surface structure may be controlled while observing by the RDS method.

In the above embodiment, GaAs, Al
The case of growing Ge on As has been described, but in principle, these are used as AlGaAs, InGaP, etc. III.
It can be selected from the group V compound semiconductors. In addition, the semiconductors grown on the Si, SiGe,
It can be selected from Group IV semiconductors such as SiC.

Further, in the present invention, from the relationship between the charge generated at the interface and the segregation of the atoms constituting the compound semiconductor, III-V
The present invention is applicable to the case of growing a II-VI group compound semiconductor such as ZnSe on a group III compound semiconductor, and vice versa, when the group III-V compound semiconductor is grown on a group II-VI compound semiconductor. It is supposed to be possible.

[0037]

As described above, according to the present invention,
Since epitaxial crystal growth that prevents segregation can be performed, a high quality heterojunction can be formed,
It greatly contributes to the performance improvement of the semiconductor device using this heterojunction.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a semiconductor crystal growth method of the present invention, (A) is an explanatory diagram of the relationship between the maximum substrate temperature and hole mobility before Ge growth, and (B) is the maximum transition before Ge growth. It is a board | substrate temperature, surface structure, and V / III ratio of a surface, explanatory drawing of a relationship.

FIG. 2 is a schematic cross-sectional view when Ge is grown on a III-V group compound semiconductor having a structure of the present invention.

FIG. 3 is a schematic cross-sectional view when Ge is grown on a III-V group compound semiconductor having a (2 × 2) structure.

FIG. 4 is a schematic sectional view when Ge is grown on a III-V group compound semiconductor having a (4 × 2) structure.

Claims (8)

[Claims] 1. When a group IV semiconductor or a group II-VI compound semiconductor is epitaxially grown on a group III-V compound semiconductor, the crystal structure of the surface of the compound semiconductor and the surface composition ratio of the elements constituting the compound semiconductor. Is adjusted so that no charge is generated at the interface between the compound semiconductor and the group IV semiconductor or compound semiconductor that grows, and then the group IV semiconductor or compound semiconductor is grown. . 2. The compound semiconductor is GaAs, AlAs, A
It is a III-V group compound semiconductor such as 1GaAs or InGaP, and the IV group semiconductor layer grown on the surface of the III-V group semiconductor is Ge or S.
i, SiGe, and the growing compound semiconductor is ZnSe
2. The method for growing a semiconductor crystal according to claim 1, which is a II-VI compound semiconductor such as 3. When epitaxially growing Ge on a GaAs crystal, the V / III ratio of the surface of the GaAs crystal before growing Ge is (2 × 4) structure, (6 × 4) structure, (5 × 5)
X4) structure, (5x2) structure or (3x1) structure V
/ III ratio, that is, Ge is grown after adjusting to a value of 0.5 to 3. A method for growing a semiconductor crystal. 4. When epitaxially growing Ge on an AlAs crystal, the V / III ratio of the surface of the AlAs crystal before growing Ge is (2 × 4) structure, (6 × 4) structure, (5
X4) structure, (5x2) structure or (3x2) structure V
/ III ratio, that is, Ge is grown after adjusting to a value of 0.5 to 3. A method for growing a semiconductor crystal. 5. A GaAs crystal or AlAs crystal is grown so that the V / III ratio of the surface thereof is higher than the V / III ratio of a desired surface structure, and then the GaAs crystal or AlAs crystal is grown.
The temperature of the crystal is raised until the desired surface structure is obtained and then Ge
The method for growing a semiconductor crystal according to claim 3 or 4, wherein Ge is grown at the growth temperature of. 6. A GaAs crystal or AlAs crystal is grown so that the V / III ratio of its surface is higher than the V / III ratio of the desired surface structure, and then Ga or Al is irradiated in an amount sufficient to obtain the desired surface structure. The method for growing a semiconductor crystal according to claim 3 or 4, wherein Ge is grown after the step. 7. After growing a GaAs crystal or an AlAs crystal in a state where the V / III ratio of the surface thereof is lower than the V / III ratio of a desired surface structure, and then irradiating As with an amount sufficient to obtain the desired surface structure. , Ge is grown, The method for growing a semiconductor crystal according to claim 3 or 4, wherein 8. A surface structure of a GaAs crystal or an AlAs crystal is observed by an RHEED method or an RDS method,
8. The method for growing a semiconductor crystal according to claim 3, wherein Ge is grown after confirming that a desired surface structure has been obtained.