JPH10289997A - Semiconductor quantum structure and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a uniform quantum box structure which is applicable to various electron/optical devices practically. SOLUTION: At first, a distortion introducing body 102 consisting of a fine projecting part is arranged on a semiconductor board 101 by lattice arrangement. Then, a buffer layer 103 formed of a semiconductor material which is in lattice matching to the semiconductor board 101 is formed and the distortion introducing body 102 is thereby buried completely. Thereafter, following processes are carried out continuously in a crystal growth device. At first, a barrier material layer (barrier layer) 104 which is nearly in lattice matching to the semiconductor board 101 is formed on the buffer layer 103. Then, a distortion quantum well layer 105 is formed on the barrier layer 104.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a semiconductor quantum structure having a quantum box structure exhibiting a quantum effect and a method of manufacturing the same.

[0002]

2. Description of the Related Art When the thickness and width of a semiconductor fine structure are about the wavelength of electrons in a semiconductor crystal, a quantum effect due to one-dimensional or zero-dimensional confined carriers appears. Such a structure is called a quantum wire or a quantum box, and it is expected that a high-performance optical device or electronic device, which has never existed before, will be realized by utilizing the quantum effect in a low dimension. Under such circumstances, a typical method for manufacturing a semiconductor quantum box is to process a two-dimensional quantum well film into a box structure by lithography. In recent years, instead of this, a method of forming a quantum box structure in a self-organizing manner in one crystal growth process has appeared. This new method solves the problem of damage and contamination introduced secondary to the lithography process, which could not be avoided conventionally.

In the above-described quantum box manufacturing method, particularly when the quantum box structure is formed in a self-aligned manner during the crystal growth of the compound semiconductor heterostructure, the most promising and practical means is to use a lattice for the substrate. This utilizes a three-dimensional island structure generated when growing a mismatched strained film. As is well known, generally, the crystal growth of a compound semiconductor thin film on a semiconductor substrate is one of three crystal growth modes, S
It belongs to the K (Transki-Krastnov) mode.

FIG. 8 is an explanatory diagram of the SK mode. FIG.
As shown in (a), after forming a non-strained semiconductor barrier layer 802 on a semiconductor substrate 801, a growth layer 803 is grown. In the initial stage, the growth layer 803 has a flat surface and a two-dimensional structure. Layer. Here, when the growth layer has no strain as in the case of homoepitaxial growth, this state is maintained until the growth is completed. However, in the case where distortion due to lattice mismatch or the like exists in heteroepitaxial growth using a heterogeneous material, the growth layer 803 undergoes a two-dimensional and three-dimensional phase transition through an initial stage and shifts to a second stage. As a result of this phase transition from the initial stage to the second stage,
As shown in FIG. 8B, the uniform growth layer 803 is
A very thin two-dimensional layer 804 called a wetting layer is left, and aggregates into a large number of three-dimensional island structures 805. This island structure 80
In 5, the lattice constant is shifted from that of the substrate, so that the strain is relaxed.

This phase transition, as is well known,
This is based on the action of minimizing the free energy of the growth layer. Specifically, it is determined by the balance between surface energy and crystal distortion. An island structure obtained by controlling crystal strain within a range in which strain relaxation due to a crystal defect called misfit dislocation does not occur is called a coherent island. Then, as shown in FIG. 8C, when a barrier layer 806 is formed on the island structure 805 made of the coherent island obtained as described above, a quantum box made of the island structure 805 is obtained. What has been described above is a series of methods that have recently been spotlighted as the “SK mode self-assembly method” of the quantum box.

For example, when the growth is performed on a non-tilted (100) plane substrate by MBE under a low substrate temperature at a low growth rate and under group V atom stabilization conditions, an extremely fine and high density A quantum box, ie, a coherent island, is obtained.
In this case, by using a substrate having the (100) plane as the main surface, the step density on the substrate is minimized, and minute islands are easily formed. In addition, the small island grows stably due to the low substrate temperature and the group V atom stabilization condition. By lowering the growth rate at a low substrate temperature, the surface migration length of the raw material is reduced, which is useful for generating high-density and minute coherent islands.

If a crystal growth method capable of realizing a high-quality semiconductor microheterostructure such as a molecular beam epitaxy (MBE) method and a metal organic chemical vapor deposition (MOVPE) method is used, the quantum box having the above-described structure can be obtained. Can be realized. When the growth is performed at a low substrate temperature, the MBE method is less susceptible to decomposition of the raw material on the substrate surface than the MOVPE method.
This is advantageous for forming a high-quality quantum box. For example, InAs / GaAs manufactured by the method described with reference to FIG.
Interesting phenomena have been observed in the s quantum box structure, such as the detection of light emission from 0-dimensional confined excitons at extremely low temperatures. In the quantum box structure based on the “SK mode self-assembly method” described above, the energy level, the box density, the interval, and the like can be controlled to some extent by changing the material, the film thickness, the amount of strain, the growth conditions, and the like. Further, it has been reported that, depending on the plane orientation and the off-angle of the substrate, the quantum box has an alignment property in a specific direction, and the density and the uniformity also increase.

[0008]

The quantum box structure having such excellent properties and formed in a self-organizing manner during the crystal growth of the compound semiconductor strained film is used for various electronic and optical devices. Had serious problems that had to be resolved, as described below. The first problem is that the uniformity of the quantum box is still insufficient. It is expected that the size variation alone must be within 10%, but in practice only far beyond that was obtained. Furthermore, variations in the composition and the amount of strain also deteriorated the uniformity of the levels between quantum boxes.

The second problem is that the position at which the quantum box is self-formed is determined essentially at random and has no controllability. The local fluctuation of the box density and the interval has been an obstacle to the performance of an optical device using a quantum box as an active layer that exceeds the performance of existing devices.
Furthermore, in order to realize a memory element using individual quantum boxes as cells or an electronic element using a tunnel effect between quantum boxes, a technique for forming quantum boxes at predetermined positions on a substrate is required. Was. Conventionally, window opening selective growth,
Attempts have been made to limit the quantum box formation region to a specific narrow region or line by using a patterned substrate such as a V-groove, an atomic step or a dislocation line. However, those attempts have essentially failed to solve the randomness of quantum box formation locations.

Here, the reason why the formation position of the quantum box = coherent island is randomly determined in the SK mode growth will be described. Recent studies have revealed that island formation is dominated by fluctuations in the local strain field in the strained thin film, specifically, fluctuations in the thickness of the microislands. Here, the situation will be described with reference to FIG. FIG. 9 shows a microscopic model of crystal growth of a group III-V compound semiconductor such as GaAs under general group V atom stabilization conditions. II
In a state where the group I atomic planes 901 and the group V atomic planes 902 are alternately stacked, on the growth surface that is the group V atomic plane 902, the adsorbed group III atoms (III) 903 freely migrate. This is the group III atomic molecule 90
4 and nucleation to form a nucleus 905, which evolves into a microisland 906.

The micro islands 906 are in a metastable state to the last, and may disappear when the substrate temperature is high or the growth is interrupted. Although the micro island 906 has a three-dimensionally convex shape, it is very small and stays less than a few atomic layers in height due to a flattening action in crystal growth. Therefore, even if the minute island 906 exists, it is regarded as a two-dimensional state as a whole. This micro island 906 is
It is formed irrespective of the presence or absence of strain. However, since the strain has not been relaxed yet during the growth of the strained film, it is considered to be in a state before the SK mode phase transition. However, when the strained film continues to grow and the micro island 906 grows and the local strain there exceeds the critical point, the strain is finally relaxed and the island changes to the coherent island 907. In this case, since the strain locally increases at the micro island 906, the SK mode phase transition occurs in a relatively thin strained film.

As described above, the formation of the coherent island in the SK mode growth is formed at the position of the fluctuation of the local strain field. Therefore, the formation position is determined essentially at random and the controllability is controlled. do not have. For this reason, as described above, there has been a problem that a uniform quantum box structure has not been obtained conventionally and cannot be practically applied to various electronic and optical devices. The present invention has been made to solve the above-described problems, and has as its object to obtain a uniform quantum box structure that can be practically applied to various electronic and optical devices.

[0013]

A semiconductor quantum structure according to the present invention comprises a plurality of convex portions formed on a main surface of a semiconductor substrate, and locally introduces strain on the convex portions. A strain introducing layer was provided. The semiconductor device further includes a barrier layer formed on the semiconductor substrate so as to bury the strain introducing layer and made of a material lattice-matched to the semiconductor substrate. The semiconductor substrate is formed of a convex region serving as a quantum box disposed on the convex portion via the barrier layer, and a wetting layer having a smaller film thickness than the convex region. Have semiconductor layers made of different materials. With such a configuration, if the convex portions of the strain-introducing layer are regularly arranged in, for example, a square lattice, the quantum boxes are also regularly arranged in a square lattice. In the method of manufacturing a semiconductor quantum structure according to the present invention, first, a strain-introducing layer that includes a plurality of convex portions and locally introduces a strain on the convex portions is formed on the main surface of the semiconductor substrate. I do. Next, a barrier layer made of a material lattice-matched to the semiconductor substrate is formed on the semiconductor substrate so as to bury the strain-introducing layer. Then, a material having a lattice constant different from that of the semiconductor substrate is grown on the barrier layer, and a convex region serving as a quantum box disposed on the convex portion via the barrier layer, A semiconductor layer composed of a thin wet layer was formed. Therefore, if the convex portions of the strain-introducing layer are regularly arranged in, for example, a square lattice, the quantum boxes are also formed in a state of being regularly arranged in a square lattice.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory diagram illustrating a method for manufacturing a semiconductor quantum structure according to an embodiment of the present invention. In this embodiment, as shown in FIG. 1A, first, on a semiconductor substrate 101, strain introducing members 102 each composed of a minute convex portion are arranged in a lattice arrangement. Next, a buffer layer 103 made of a semiconductor material lattice-matched to the semiconductor substrate 101 is formed, and the strain introducing body 102 is completely buried with the buffer layer 103. Next, the following steps are continuously performed in the crystal growth apparatus. First, a barrier material layer (barrier layer) 104 substantially lattice-matched to the semiconductor substrate 101 is grown on the buffer layer 103. Subsequently, a strained quantum well layer 105 is grown on the barrier layer 104.

At this time, as shown in FIG. 1A, since a local strain field 102a is formed on the strain introducing body 102, formation of a coherent island by SK mode growth of the strain quantum well layer 105 is performed. Is the local strain field 102
a. As a result, FIG.
As shown in FIG. 7, a convex coherent island (convex region) 107 is formed with a very thin wetting layer 106. Then, a quantum box structure including the coherent island 107 is formed by forming the barrier layer 108 thereon.
Note that the buffer layer 103 is not always necessary, and the barrier layer 104 may be formed on the semiconductor substrate 101, and the strain introducing body 102 may be embedded in the barrier layer 104.

By the way, as described with reference to FIG.
The formation of the coherent island in the SK mode growth is formed at the position of the fluctuation of the local strain field. The occurrence of micro islands and film thickness fluctuations observed in the process of SK mode growth are caused by the growth methods such as MBE and MOVPE, the raw material supply amount and the substrate temperature during the growth, and the plane orientation of the substrate to be grown. Greatly influenced by Therefore, even when the same substrate and the same material are grown with the same film thickness, completely different SK mode growth results can be obtained under different growth conditions as shown below.

That is, by eliminating local strain fluctuations such as minute islands, the occurrence of SK mode two-dimensional and three-dimensional phase transition (island formation) is suppressed, and a relatively thick and high-quality strained quantum well can be obtained. It is a state to get. That is, a coherent island cannot be obtained under these growth conditions. That is, as shown in FIG. 2, when the atomic steps 208 are present at high density on the group V atomic plane 202 on the group III atomic plane 201, the adsorbed group III atoms 203 are removed before forming the nuclei. The probability of being taken into is increased. If the growth is performed only by the steps, the growth surface is kept flat. Therefore, in the case where the growth is caused only by the step, the strain becomes uniform throughout the film at the time of growing the strained film, so that the SK mode phase transition can be hardly caused up to a considerably large film thickness.

As a specific method for realizing the growth by only this step, there is a method using an inclined substrate having a narrow step interval. As another realizing method, there is a method in which the substrate temperature is increased in the above-described MOVPE method or the like. Then, by using the “surfactant” growth method, it is possible to cause the growth by only steps. In the method of keeping the substrate temperature high, it is possible to increase the migration of the adsorbed atoms and shorten the time until the atoms are taken into the step, so that the growth can be caused only by the step.

By raising the substrate temperature during film growth, even if micro islands are generated due to nucleation, an effect of thermally decomposing the micro islands can be expected. In some cases, if the film is grown in a state where the substrate temperature exceeds a certain temperature, it is possible to prevent the occurrence of micro islands at all. On the other hand, the “surfactant” growth method, particularly “surfactant”
factant edited epitaxy "
In the method, the growth surface is made of "surf" having high segregation property such as Te.
Actant "and emphasizes the increase in surface energy associated with the three-dimensionalization, thereby suppressing island generation.

Further, among the "surfactant" growth methods, there is a method in which simultaneous supply of Group III atoms and Group V atoms is stopped in crystal growth of a compound semiconductor layer, and nucleation is essentially eliminated. By MBE method, In is formed on a GaAs substrate.
When growing As, under normal conditions for stabilizing As, the three-dimensional structure is formed around one atomic layer. However, it has been reported that three-dimensionalization does not occur and misfit dislocations do not occur up to a 4-atomic layer when the growth is performed under the In stabilization condition by stopping supply of the As material (Reference: Tournie et al., Eu).
rophyscs Lett. 25 (1994) 66
6, 26 (1994) 315). In atoms adsorbed on the In stable lower surface not only have a large migration, but also have a very short life until evaporation and desorption.
Droplet generation due to excessive supply is unlikely to occur. Therefore, it is considered that the growth occurs only in the substrate step as shown in FIG.

As described above, in the SK mode growth, the occurrence of islands is suppressed in a state in which local fluctuation of distortion is eliminated. In the present invention, such S
In the K-mode growth, a portion where a two-dimensional and three-dimensional phase transition in the SK mode growth is likely to occur is provided at a predetermined position. That is, the strain amount (free energy) of the island is smaller at a place where the lattice constant is shifted from the substrate having the strain field than at the same lattice constant as the substrate, and the two-dimensional and three-dimensional phase transition in the SK mode growth is performed. Is more likely to occur. This strain field can be prepared at a predetermined position on the base on which the strained quantum well layer is grown, for example, by arranging the strain introducing bodies at predetermined intervals as described above.

Here, an important point in the formation of the quantum box structure from the above is that coherent islands must be formed only on the strain-introducing body. For this purpose, a plurality of things described below are required. First, it is important to optimize the arrangement of the strain introducer. That is, if the interval between the strain introducing bodies is too large, islands are formed randomly even at intermediate positions where the strain introducing bodies are not formed in the lower layer. Further, in order to make the size of the quantum box uniform, it is necessary to make the amount of the material agglomerated on the coherent island uniform, so that it is necessary to make the interval between the strain introducing bodies uniform.

Second, it is necessary to eliminate the phenomenon of nucleation at irregular places in SK mode growth → fine island → coherent island formation as described with reference to FIG. For this purpose, it is necessary to select various measures according to the combination of the substrate, the material, the growth conditions, and the like. First, there is a method of growing at a high substrate temperature so that micro islands generated at random are thermally decomposed immediately or raw material species are taken into a substrate surface step before nucleation. This method is more effective for an inclined substrate having a small step interval. However, depending on the type of the group III atom, re-evaporation from the substrate becomes too large at a high substrate temperature, and desired growth may not be obtained. In such a case, a "surfactant" growth method is used,
There is a method of growing at a low substrate temperature while suppressing nucleation.

Further, there is also a method in which normal crystal growth is performed, the growth is interrupted before island formation, and thermal decomposition of minute islands is promoted. In any case, a technique capable of suppressing nucleation or decomposing fine islands may be applied according to a combination of a substrate, a material, and growth conditions. As described above, it is possible to form a state in which minute coherent islands are lattice-aligned, as shown in FIG. On the other hand, if a coherent island is formed only by the SK mode growth as in the related art, the coherent island is formed at random as shown in FIG. In addition,
FIG. 3 is a photograph showing the result of observing a fine pattern with an atomic force microscope.

By the way, as shown below, a minute dot made of a strained compound semiconductor may be used as shown below. For example, a microdot formed by forming a strained compound semiconductor film that is not lattice-matched on a substrate and having a predetermined arrangement with a cross-sectional length of 100 nm or less by electron beam lithography becomes a strain-introduced body. As shown in FIG. 4A, in a state where no two-dimensional and three-dimensional phase transition occurs and no misfit dislocation occurs,
When a strained semiconductor film 402 not lattice-matched to the substrate is grown on 01, the in-plane lattice constant of the strained semiconductor film 402 matches the substrate. In this state, the strained semiconductor film 40
The distortion of No. 2 has not been alleviated. However, FIG.
As shown in (b), when minute dots 403 are formed by finely processing the strained semiconductor film 402, the distortion is relaxed above the minute dots 403. As a result, the minute dots 403 are placed on the minute dots 403.
Can be a strain-introducing body for a semiconductor layer grown so as to bury the semiconductor layer.

Further, as shown below, fine dots made of a dielectric material may be used as the strain introducing body. This is because the dielectric material itself has inherent strain. As shown in FIG. 5, when the minute dots 502 made of a dielectric are formed on the layer 501 lattice-matched to the substrate, the layer 50 on which the minute dots 502 are formed is formed.
2 to introduce a local strain field. This allows
In the semiconductor layer grown so as to embed the minute dots, the minute dots can be a strain introducing body.

By the way, as shown in FIG. 2C, the local strain field 102a is also present in the barrier layer 108. Therefore, if a strained quantum well layer is formed on the barrier layer 108, a coherent island is formed in accordance with the position of the local strain field 102a. Then, if a barrier layer is formed thereon and a strained quantum well layer is formed, similarly,
A coherent island is formed in accordance with the position of the local strain field. That is, as shown in FIG. 6, the coherent islands are formed to overlap.

[0028]

【Example】

Embodiment 1 Hereinafter, a first embodiment of the present invention will be described. In Example 1, a dot pattern made of InGaAs was used as a strain introducing body. InAs is used as a material for forming a quantum box (coherent island). InAs, which is a III-V compound semiconductor, has a large lattice mismatch of 3.2% with respect to an InP substrate, which is also a III-V compound semiconductor. For this reason,
Compressive strain occurs in InAs grown on InP. M
First, a barrier layer made of InAlAs lattice-matched to the InP substrate is grown on the InP substrate by the BE method.
When the As layer is grown, the InAs layer grows in a typical SK mode, so that formation of a quantum box can be expected.

The first embodiment will be described below in more detail. First, as shown in FIG. 7A, a 10 nm-thick In _0.7 Ga _0.3 As is formed on a substrate 701 made of InP and having a 0.5-degree slightly inclined (100) plane by the MBE method.
The layer 702 made of was crystal-grown. The MBE apparatus used for this crystal growth was equipped with a general Knudsen cell, and used solid In, Ga, Al, and As as raw material sources. The substrate temperature during crystal growth was set at 600 ° C. Since In _0.7 Ga _0.3 As has a lattice mismatch of 1.5% with respect to InP, the formed layer 702 has a compressive strain therein. Then, an electron beam resist film 703 (ZEP-520) was applied thereon to a thickness of 0.2 μm.

Next, as shown in FIG. 7B, a mask pattern 703a made of an electron beam resist was formed by electron beam lithography. As shown in FIG. 7F, the mask patterns 703a are arranged in a square lattice at intervals of 120 nm, and each side has a size of 70 nm. Next, as shown in FIG.
Layer 702 was selectively etched away using 03a as a mask. In this etching, wet etching using a mixed solution of sulfuric acid: hydrogen peroxide: water was used. As a result, a minute columnar strain introducing body 704 having a height of 10 nm was formed. The diameter of this strain introducing body 704 is adjusted by the mask pattern 7
03a, which was 50 nm. However, the arrangement was the same as the mask pattern 703a.

Then, these were introduced again into the above-mentioned MBE apparatus, and the following crystal growth was performed on the substrate 701 including the strain introducing body 704. First, at a substrate temperature of 550 ° C., a thin film of In _0.52 Al _0.48 As was grown to a thickness of 50 nm. As a result, as shown in FIG. 7D, the barrier layer 705 in which the strain introducing body 704 is embedded and the surface is flattened.
Was formed. This barrier layer 705 lattice-matches with the substrate 701 and serves as a barrier for quantum confinement. continue,
An InAs strained thin film was grown on the barrier layer 705. At this time, the substrate temperature was lowered to 400 ° C., and A
The supply of the raw material was stopped. As a result, as shown in FIG. 7E, the coherent island 707 with the wetting layer 706 is formed.
Was formed at the position where the strain introducing body 704 was formed.

In the growth of the strained InAs film, the supply of the As material was stopped, so that the As pressure in the crystal growth atmosphere was reduced by about two orders of magnitude as compared to when the As material was supplied. Then, the reflection high energy electron diffraction (RHEED) image of the crystal growth surface at this time changed to a 4 × 2 pattern peculiar to the In stabilized surface. Then, when InAs was grown for 9 atomic layers, the supply of the In material was stopped, and the growth was terminated. At the end of this RHEED image, spots indicating the occurrence of a coherent island structure were observed. here,
As described above, the purpose of stopping the supply of the As raw material is to suppress nucleation, that is, generation of micro islands in a region other than the upper portion where the strain introducing body 704 is formed.

When the state of the coherent island 707 on the barrier layer 705 obtained as a result of the above was observed by SEM, it was found that the I
An array of coherent islands 707 made of nAs was formed. All of the coherent islands 707 were arranged in a lattice having a period of 120 nm over a wide area of 5 μm × 5 μm observed, and no island was formed outside the lattice points of the lattice. As a result of observation, each coherent island was disc-shaped with a height of 10 nm and a bottom diameter of 40 nm, and its size variation was less than 10%. Then, if a barrier layer is formed on the coherent island, a quantum box structure including the coherent island is completed.

COMPARATIVE EXAMPLE 1 As Comparative Example 1 to Example 1 described above, an InAs strained thin film was grown on a barrier layer without forming a strain introducing body. As a result,
The surface of the formed InAs strained thin film was flat, and no island structure occurred. As described above, this In
Since the growth of the As strained thin film is performed under the In stabilization condition, the nucleation is suppressed, so that the generation of an irregular quantum box is suppressed, and the InAs having a uniform thickness of 9 atomic layers is formed.
It is considered that the strained film thickness was formed. Therefore, as is clear from the results of this comparative example, the local strain field due to the embedded strain introducing body formed in Example 1 has a uniform I field.
This shows that it is the driving force for changing the nAs strained thin film into a quantum box arrangement.

Embodiment 2 Hereinafter, a second embodiment of the present invention will be described. First, on a substrate having a vicinal (100) plane made of GaAs, strain introduction bodies made of SiN having tensile stress therein were arranged in a square lattice at intervals of 250 nm. In the formation of SiN film with tensile stress, high frequency plasma CVD
Substrate temperature 350 ° C, plasma output 100W
And Under these conditions, a SiN film having a tensile stress of 5 × 10 ⁹ dyn · cm ⁻² and a relative refractive index of 1.87 can be obtained. The internal strain is caused by the stoichiometric composition of the SiN film deviating from Si ₃ N ₄ . As the SiN film is thicker, the amount of strain to be introduced can be increased, but if it is too thick, dislocations and crystal defects are introduced into the semiconductor. In this example, an appropriate thickness is 20
nm was chosen.

Then, the SiN film was processed by electron beam lithography to form a strain-introduced body made of SiN. In this formation, the etching using the resist pattern as a mask was performed by RF plasma reactive ion etching using C ₂ F ₆ gas. In addition, these are lightly immersed in hydrofluoric acid diluted with pure water while maintaining the temperature at 20 ° C. to form a strain-introduced body having a diameter of 60 nm, and the SiN film in other areas is completely removed. did. Thereafter, the resist pattern was completely removed.

On this, the following growth was performed by the MOVPE method. First, the substrate temperature was set to 750 ° C., and a buffer layer made of GaAs was grown to a thickness of 10 nm. Subsequently, a lower barrier layer made of Al _0.5 Ga _0.5 As was grown to a thickness of 50 nm on the buffer layer. In this step, the strain introducing body made of SiN was completely embedded. Further, the surface of the formed lower barrier layer was almost flattened. Subsequently, a GaAs cap layer was grown to a thickness of 10 nm on the lower barrier layer, and the growth was terminated. In this MOVPE growth, hydrogen was used as a carrier gas under reduced pressure, and trimethylgallium, trimethylaluminum, and arsine were used as source gases.

Next, a substrate temperature of 600
The following growth was carried out at a temperature of ° C. First, a barrier layer made of Al _0.5 Ga _0.5 As was grown to 30 nm on the cap layer. Here, as described above, the lower barrier layer, the cap layer,
The reason why the barrier layer is formed is as follows. That is, after the film is formed by MOVPE, the film is once exposed to the atmosphere, and then the film is formed by MBE. For this reason,
A natural oxide film is formed on the surface of the layer containing aluminum,
A strained layer cannot be formed directly on this. Therefore, MO
It is necessary to form a lower barrier layer and a cap layer thereon by film formation by the VPE method. As described above, when the barrier layer is formed again on the cap layer in the MBE formation stage, the In _0.3 Ga
_{A 0.7} As strained layer was grown in 12 atomic layers, where growth was terminated.

In _0.3 , a group III-V compound semiconductor,
Ga _0.7 As also has a large lattice mismatch of 2.2% with respect to the GaAs substrate, and In _0.7 grown on GaAs.
Compressive strain is generated in the _0.3 Ga _{0 .7} As. First, an AlGa lattice-matched to a GaAs substrate is formed on the GaAs substrate by the MBE method.
When an As barrier layer is grown and In _0.3 Ga _0.7 As is grown thereon, In _0.3 Ga _0.7 As grows in a typical SK mode, so that formation of a quantum box can be expected. Then, in growing the strained layer, a method different from that of the first embodiment was used. That is, the growth of the InGaAs layer was performed under the As stabilization condition while the As material was supplied. In addition, a high substrate temperature and a slight inclination of the substrate were used to suppress generation of micro islands due to nucleation. Regarding the tilt of the substrate, the step interval was reduced to about 10 nm by tilting the substrate twice in the [0-11] direction. These conditions are:
As will be described later, it was effective in suppressing the formation of coherent islands other than the lattice points where the strain introducing bodies were formed.

As described above, on the barrier layer,
Coherent islands with regular lattice formation were formed with a wetting layer. When this state was observed by SEM, a coherent island made of In _0.3 Ga _0.7 As was formed according to the arrangement of the strain-introduced bodies embedded in the buffer layer. All quantum boxes were arranged in a lattice with a period of 250 nm over a wide area of 5 μm × 5 μm observed, and no quantum boxes were found outside the lattice points.
Each quantum box was a disk with a height of 20 nm and a bottom diameter of 120 nm, and the size variation was less than 10%. Then, if a barrier layer is formed on the coherent island, a quantum box structure including the coherent island is completed.

Comparative Example 2 As Comparative Example 2 with respect to Example 2 described above, Si
N is not formed on the barrier layer without forming a strain-introducing body made of N.
A GaAs strained thin film was grown. As a result, although a slight island structure was observed on the surface of the grown strained film, it was entirely flat. That is, in Comparative Example 2, the strain In _0.3 Ga _0.7 As with a uniform thickness of 12 atomic layers was obtained by the effective suppression of nucleation and micro islands.
It is considered that a layer was formed. Here, a slight coherent island was formed in Comparative Example 2, which is considered to be due to the following reason. That is,
In Comparative Example 2, it is conceivable that nucleation cannot be suppressed as completely as in Comparative Example 1, and that the distortion is larger because the distortion in the quantum box arrangement is not relaxed as in Example 2.

As described above, as is apparent from the results of Comparative Example 2, the strain field generated by the strain-introducer embedded under the barrier layer is a driving force for converting a uniform strained thin film into a coherent island. It has become. Note that the present invention is not limited to only the above-described embodiment. For example, even with the following material configuration, an arrangement of coherent islands that matches the arrangement of the strain introducing body can be obtained. That is, an AlGaAs or InG lattice-matched to a GaAs substrate provided with a
A semiconductor layer made of aP is provided, and Al is lattice-matched to the substrate.
In this case, a barrier layer made of GaAs or AlInGaAs is provided, and a coherent island (quantum box) made of InAs or InGaAs is formed thereon.

Further, on an InP substrate provided with a strain introducing body arrangement, InGaAs, InAl is lattice-matched to the substrate.
As, AlGaP, InGaAsP, or AlG
A semiconductor layer made of any one of aAsP is provided, and InGaAs, InAlAs, InGa lattice-matched to the substrate.
The same applies to the case where a barrier layer made of any one of AsP and AlGaAsP is provided to form a coherent island made of any one of InAs, InGaAs, and InGaAsP. In addition, as a strain introducing body, InGaAs, InAlAs, InG which do not lattice match with the substrate.
It may be made of any one of aAsP and AlGaAsP, and may have a fine dot shape whose cross-sectional length does not exceed a maximum of 100 nm. Further, the strain introducing body may be, for example, a minute dot made of a dielectric material having internal strain, which is formed by performing high-resolution lithography.

[0044]

As described above, according to the present invention, first, a plurality of convex portions are formed on the main surface of the semiconductor substrate.
A distortion introducing layer for locally introducing distortion is provided on the convex portion. Further, a barrier layer made of a material lattice-matched to the semiconductor substrate is provided so as to bury the strain introducing layer. And, through the barrier layer,
It is composed of a convex region serving as a quantum box arranged on the convex portion, and a wetting layer having a smaller thickness than the convex region,
A semiconductor layer made of a material having a different lattice constant from the semiconductor substrate is provided. As a result, according to the present invention, if the convex portions of the strain-introducing layer are regularly arranged in, for example, a square lattice, the quantum boxes are also regularly arranged in a square lattice. A uniform quantum box structure that can be applied practically can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating a method for manufacturing a semiconductor quantum structure according to an embodiment of the present invention.

FIG. 2 is a perspective view illustrating an example of SK mode growth.

FIG. 3 is a photograph taken by an atomic force microscope showing a state in which minute coherent islands are formed in lattice alignment.

FIG. 4 is an explanatory diagram showing a state in which materials having different lattice constants are stacked.

FIG. 5 is an explanatory diagram showing a state in which a crystal is distorted by minute dots having distortion therein.

FIG. 6 is a transmission electron micrograph showing a state where coherent islands are superimposed.

FIG. 7 is an explanatory diagram for explaining the manufacturing method according to the first embodiment of the present invention.

FIG. 8 is an explanatory diagram showing SK mode growth.

FIG. 9 is a perspective view illustrating an example of SK mode growth.

[Explanation of symbols]

101: semiconductor substrate, 102: strain introducing body, 102a ...
Local strain field, 103: buffer layer, 104: barrier material layer (barrier layer), 105: strain quantum well layer, 106: wet layer, 107: coherent island, 108: barrier layer.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Hiromitsu Asai 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo Nippon Telegraph and Telephone Corporation

Claims (5)

[Claims] 1. A distortion-introducing layer comprising a plurality of convex portions formed on a main surface of a semiconductor substrate, the distortion-introducing layer locally introducing distortion on the convex portion, and the distortion-introducing layer is embedded. A barrier layer formed on the semiconductor substrate and made of a material lattice-matched to the semiconductor substrate, and a convex box which becomes a quantum box disposed on the convex portion via the barrier layer. A semiconductor quantum structure comprising at least a region and a wet layer having a thickness smaller than that of the convex region, and a semiconductor layer made of a material having a different lattice constant from the semiconductor substrate. 2. The semiconductor quantum structure according to claim 1, wherein a main surface of said semiconductor substrate is inclined from (100). 3. The semiconductor quantum structure according to claim 1, wherein the strain-introducing layer is made of a material having a different lattice constant from the semiconductor substrate. 4. The semiconductor quantum structure according to claim 1, wherein the strain-introducing layer is made of a material having strain therein. 5. A first step of forming a strain introducing layer comprising a plurality of convex portions on a main surface of a semiconductor substrate and locally introducing strain on the convex portions; A second step of forming a barrier layer made of a material that lattice-matches with the semiconductor substrate on the semiconductor substrate so as to bury the layer, and forming the barrier layer using a material having a different lattice constant from the semiconductor substrate. Forming a semiconductor layer including a convex region which becomes a quantum box and is formed on the convex portion via the barrier layer, and a wetting layer having a smaller thickness than the convex region. A method for manufacturing a semiconductor quantum structure, comprising: a third step.