JPH10289996A - Semiconductor quantum dot and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a device such as a single electronic element wherein a plurality of quantum dots are connected (arranged), by controlling arrangement of a semiconductor quantum dot consisting of an S-K type growth mode, and enabling a semiconductor quantum dot without damage to be generated in uniform size and uniform density in a semiconductor quantum dot, and its manufacturing method. SOLUTION: An S-k (stranski-Krastanor) type growth mode 13A which is generated in an initial stage during formation of strain hetero crystal (such as InAs to GaAs of a foundation) is formed, a first over-growth layer 14 whose material (GaAs, for example) is different from a constituent mateal of the S-K type growth mode 13A and whose thickness is at most a height of the S-K type growth mode 13A is formed, and heat treatment is carried out to vaporize or extend a top part of the S-K type growth mode 13A to make it flush with the surface of the first over-growth layer 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an SK which appears at the initial stage of growing a quantum dot composed of a compound semiconductor, for example, strained heterocrystal such as InAs / GaAs.
The present invention relates to a semiconductor quantum dot using a (Transky-Krastanov) type growth island and a method of manufacturing the same.

At present, individual semiconductor quantum dots have been realized and many experiments and measurements have been made.
In order to use this as a device, it is necessary to form an array, and the shape of the growth island must be uniform.

However, it is extremely difficult to arrange uniform semiconductor quantum dots in a controlled state to form an array, and this is a major factor hindering practical use.
This problem must be solved, and the present invention can provide a means for responding thereto.

[0004] Generally, two types of methods are known for forming semiconductor quantum dots (boxes). That is, a method of realizing a structure by processing with a lithography technique or the like A method of growing a structure in a self-forming manner using a surface phenomenon (natural phenomenon) during crystal growth.

Specifically, (1) molecular beam epitaxial growth (molecular)
Beam epitaxy (MBE) and metalorganic chemical vapor deposition
al vapor deposition: MOCV
D) By applying the method or the like, a necessary semiconductor layer is formed on the substrate by lamination, and this is etched and box-shaped by applying lithography technology, in particular, electron beam lithography or ion beam lithography. Process into

(2) The substrate is processed in the same manner as in the above (1), and thereafter, a box-shaped structure is formed by utilizing the selectivity of growth in the MBE method, the MOCVD method or the like.

(3) A box is formed by controlling crystal growth in the lateral direction by using surface steps and kinks on a vicinal substrate.

(4) A box is obtained by using SK type growth islands appearing at an early stage of growth of a high strain type heterostructure such as InAs / GaAs. And the like.

By the way, when the means described in the above (1) and (2) are adopted, damage is easily caused from the surface of the semiconductor layer toward the inside, and the size of the box depends on the precision of the current working technology. Therefore, it is difficult to control the size to 100 nm or less, and the size varies greatly.

When the means described in (3) above is employed, it is difficult to control the shape of the surface steps and, in addition, mixing of the material occurs in the lateral direction, so that the size, composition, and abruptness of the lateral interface are reduced. Cannot be precisely controlled.

Furthermore, when the means described in (4) above is employed, no processing is used, and no processing damage is caused. Since the growth island formation is caused by surface energy and strain energy, the equilibrium is not obtained. By approaching the state, the sizes of the boxes can be considerably uniformed, and a standard deviation of about 10% is obtained although it is an experimental level.

As described above, although the means described in (4) has an advantage that is not provided in the means described in (1) to (3), the formation of the growth island is achieved by the surface condition of the base, that is, the step. Alternatively, various problems occur because they strongly depend on kinks, rearrangement structure of atoms on the surface, surface defects, and the like.

That is, the formed quantum dots are sparse and dense, do not have a uniform density, and due to this, there is a slight variation in the size. (PL) is 80 [meV] to 100
[MeV].

This emission half width is much larger than that of a quantum well which is currently in practical use as an active layer of a semiconductor laser. Therefore, it is assumed that a semiconductor laser having the SK type growth island is manufactured. However, such an effect cannot be obtained that the characteristics are improved as expected, for example, the threshold value is lowered.

In the case where the means (4) is adopted,
If the arrangement of the quantum dots can be controlled and quantum dots without damage can be generated with a uniform size and a uniform density, application to a device in which a plurality of quantum dots are connected (arranged), for example, a single electron element Also becomes possible.

Up to now, the above-mentioned means (4) has been adopted,
Various attempts have been made to arrange semiconductor quantum dots of a uniform shape in a controlled state,
For example,

(A) A method of processing a substrate so that a step is formed on the substrate surface and generating semiconductor quantum dots in the vicinity of the step (if necessary, see DSL Mui et al., A
ppl. Phys. Lett. 66 (1995) ").

(B) A method of forming a V-shaped groove by applying a selective growth method on a substrate on which a pattern is formed, and arranging semiconductor quantum dots at the bottom thereof (if necessary, "IPRM'9").
Oral Presentation at 5 Late News ").

(C) A multi-step with step bunching is formed, and semiconductor quantum dots are preferentially generated on the multi-step (refer to “M. Kita if necessary”).
muraet al. Proc. of IPRM '
95, (1995) p. 736 "). (Note that in the above description, “IPRM '95”
Is "The Seventh International
nal Conference on Indium
Phosphide and Related Mat
erials ").

[0020]

The problem (A) is that it is difficult to control the shape of the step for arranging the semiconductor quantum dots.

The problem of the above (B) is that a region used for forming a V-shaped groove, that is, a region where semiconductor quantum dots are not generated, needs to be large, and therefore, it is impossible to increase the density. In addition, the processing steps are complicated, and the processing does not become flat (Planer).

The problem (C) is that it is difficult to control the bunching of the surface steps, and the kink is locally concentrated on the bunching surface or the bunching surface fluctuates. Cannot be formed by

The present invention makes it possible to control the arrangement of semiconductor quantum dots composed of SK type growth islands and to produce semiconductor quantum dots having no damage at a uniform size and a uniform density. Are connected (arranged), for example, a single electron element can be realized.

[0024]

According to the present invention, InAs /
After forming semiconductor quantum dots composed of SK type growth islands appearing in the early stage of growth of a high strain type heterostructure such as GaAs, the vapor pressure is lower than that of the material forming the growth islands, and the thermal pressure is lower. The first overgrowth layer is formed to be lower than the height of the growth island using a material which is stable to
Basically, the height of the growth island is made uniform by re-evaporating or scattering the portion protruding from the first over-growth layer.

FIG. 4 is an explanatory view of a principal part of a semiconductor quantum dot for explaining the height of the SK type growth island. In the figure, 1 is a GaAs substrate, 2 is an InAs layer, and 3 is InA.
H indicates the height of the growing island, and D indicates the diameter of the bottom surface of the growing island 3.

Usually, a growth island generated by SK type growth,
For example, the In on the GaAs substrate 1 as shown in FIG.
In the As growth island 3, the height H is 3 [nm] to 5 [n
m] and the diameter D is 20 [nm] to 25 [n
m], and the cut side surface of the growth island 3 is flat.

With respect to the quantum level in the growing island 3, the height H of the growing island 3 is dominant, and the fluctuation of the quantum level caused by the fluctuation of the height H is the quantum level generated by the fluctuation of the diameter D. It is much larger than the fluctuation of the level, and it is considered that the emission half width is dominated by the fluctuation of the height.

Therefore, if the height H of the growth island 3 can be made uniform, the half-width of light emission that has been realized so far can be greatly reduced. Incidentally, the emission half width determined by the fluctuation of the diameter D is about 10 [meV], and this value is substantially equal to the half width of the quantum well.

As described above, in the semiconductor quantum dot and the method for manufacturing the same according to the present invention, (1) the strain is generated at the initial stage of growing a strained heterocrystal (for example, GaAs and InAs) and the height is entirely SK-type growth islands (for example, growth island 1) that are made uniform according to the thickness of the first over-growth layer (for example, first over-growth layer 14) to be covered.
3A), or

(2) In the above (1), the first over
The growth layer is made of a constituent material having a lower vapor pressure than that of the constituent material of the SK type growth island (for example, GaAs when the growth island is InAs), or

(3) a step of forming an SK type growth island generated at the initial stage of growing the strain-based heterocrystal;
Forming a first over-growth layer made of a material different from the constituent material of the K-type growth island and having a thickness equal to or less than the height of the SK-type growth island; Evaporating or spreading the top of the mold growth island in the lateral direction to adjust the height to the surface of the first overgrowth layer.

By employing the above means, the arrangement of semiconductor quantum dots composed of SK type growth islands can be controlled, and semiconductor quantum dots without damage can be generated with uniform size and uniform density. A device in which a plurality of dots are connected (arranged), for example, a single-electron element, or a semiconductor laser with a small threshold current and excellent temperature characteristics can be realized.

[0033]

1 to 3 are cutaway side views showing a main part of a semiconductor quantum dot in a process step for explaining an embodiment of a method invention. This will be described with reference to FIG.

1 (A) 1- (1) A GaAs substrate 11 having a plane index of (001) is formed by MBE.
(Molecular beam epitaxy) An oxide film is removed by setting the apparatus in a growth chamber and performing a heat treatment at a temperature of 680 ° C.

1- (2) A GaAs layer 12 having a thickness of, for example, 400 [nm] is formed on a GaAs substrate 11 by applying the MBE method.

The main growth conditions at this time are listed as follows: growth temperature: 620 ° C., growth rate: 0.8 μm / hour, As pressure: 6 × 10 ^-6 [Torr].

Referring to FIG. 1B, the shutter of the Ga molecular beam cell in the MBE apparatus is closed, and the InAs layer 13 having a thickness corresponding to, for example, about 1.8 molecular layers is formed on the GaAs layer 12. Grow.

The main growth conditions at this time are as follows: growth temperature: 510 [° C.] growth rate: 0.1 [molecular layer / second] As pressure: 6 × 10 ⁻⁶ [Torr].

According to this, the diameter D of the bottom surface is 20 [n
m] to about 25 [nm], and the height H is 3 [nm].
Conical growth islands 13A distributed to about 5 [nm]
^Are formed at a density of 1 × 10 ¹¹ [cm ⁻² ].

2 (A) 2- (1) In the state where only As is irradiated, the same temperature, that is, 510
It is left for 30 [seconds] while maintaining [° C].

2- (2) The thickness is, for example, 2 [n] by applying the MBE method.
m], the first overgrowth layer 1 made of GaAs
4 is formed.

Since the height H of the growth island 13A varies, the top of the growth island 13A protrudes from the first overgrowth layer 14, and the height of the protruding portion also varies. You.

2 (B) 2- (3) In the state where only As was irradiated, the same temperature, that is, 510
Leave for 3 minutes while maintaining [° C]. The temperature applied at this time must be selected so that the first overgrowth layer 14 is not damaged.

Accordingly, the first overgrowth layer 1
The top of the growth island 13A protruding from the growth island 4 is re-evaporated or spread out in the lateral direction and flattened, the height H of the growth island 13A is made uniform, and the thickness of the first overgrowth layer 14 is increased. It will be almost the same.

The movement of the growth islands 13A is caused by the effect of the strain between the first over-growth layer 14 made of GaAs and the InAs layer 13 or the growth islands 13A, so that an equal spacing, that is, an arrangement occurs. The portion indicated by the symbol 15 is a two-dimensional growth island composed of InAs supplied from the InAs layer 13.

Referring to FIG. 3, 3- (1) the second GaAs layer is formed by applying the MBE method.
An overgrowth layer 16 is formed to completely cover the growth island 13A.

Since the PL half-width of the grown island 13A manufactured as described above is reduced to about 1/2 to 1/3 as compared with the grown island depending on the conventional technique, It can be confirmed that homogenization has occurred.

In the present invention, without being limited to the above-described embodiment, many other modifications can be realized.

For example, as the main composition of the base crystal and the first overgrowth layer, in addition to GaAs, AlGaAs,
InGaP can be used. In this case, the main composition of the growth island is InP, GaSb, In, in addition to InAs.
Sb or a mixture thereof can be used.

The selection of such a material is also possible in other material systems. The main composition of the underlying crystal and the first overgrowth layer is Si, and the main composition of the growth island is SiG.
e, Ge, etc. can be used.

[0051]

According to the semiconductor quantum dot and the method for manufacturing the same according to the present invention, the height is adjusted to the thickness of the first overgrowth layer which is formed at the initial stage of growing the strained heterocrystal and has a height covering the entire surface. To form a uniform SK type growth island.

By adopting the above configuration, the arrangement of semiconductor quantum dots composed of SK type growth islands can be controlled, and semiconductor quantum dots without damage can be generated at a uniform size and a uniform density. A device in which a plurality of dots are connected (arranged), for example, a single-electron element, or a semiconductor laser with a small threshold current and excellent temperature characteristics can be realized.

[Brief description of the drawings]

FIG. 1 is a fragmentary side view showing a semiconductor quantum dot at a key point in a process for describing an embodiment of a method invention.

FIG. 2 is a fragmentary side view showing a semiconductor quantum dot at a key point in a process for describing an embodiment of a method invention;

FIG. 3 is a cutaway side view showing a main part of a semiconductor quantum dot at a main point of a process for describing an embodiment of a method invention.

FIG. 4 is an explanatory view of a main part of a semiconductor quantum dot for explaining the height of an SK type growth island.

[Explanation of symbols]

 11: GaAs substrate 12: GaAs layer 13: InAs layer 13A: growth island 14: first overgrowth layer 15: two-dimensional growth island 16: second overgrowth layer

Claims (3)

[Claims] 1. An SK type growth island formed at the initial stage of growing a strained heterocrystal and having a uniform height according to the thickness of a first overgrowth layer covering the entire surface. Semiconductor quantum dots. 2. The semiconductor quantum dot according to claim 1, wherein the first overgrowth layer is made of a constituent material having a lower vapor pressure than a constituent material of the SK type growth island. 3. A step of forming an SK-type growth island generated at the initial stage of growing a strain-based heterocrystal, and comprising a material different from a constituent material of the SK-type growth island and having a thickness of the SK-type growth island. Forming a first overgrowth layer having a height equal to or less than the height of the SK type growth island; and performing heat treatment to evaporate or spread the top of the SK type growth island in the lateral direction to increase the height. Adjusting the surface of the first overgrowth layer to the surface of the first overgrowth layer.