JP4066002B2 - Manufacturing method of semiconductor quantum dots - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a semiconductor quantum dot using a SK (Stransky-Krastanov) type growth island that appears early in growing a quantum dot made of a compound semiconductor, for example, a strained heterocrystal such as InAs / GaAs. About.
[0002]
Currently, individual semiconductor quantum dots have been realized, and many experiments and measurements have been made. However, in order to use them as devices, it is necessary to form an array, and the shape of the growth island is made uniform. There must be.
[0003]
However, it is extremely difficult to array uniform semiconductor quantum dots in a controlled state, and this is the main cause that hinders practical use. The invention can provide a means for responding thereto.
[0004]
Generally, as a method for forming a semiconductor quantum dot (box), two types of methods are known. That is,
(1) A method of realizing a structure by processing with lithography technology or the like (2) A method of growing a structure in a self-forming manner by utilizing a surface phenomenon (natural phenomenon) during crystal growth.
[0005]
Specifically,
(1)
By applying a molecular beam epitaxy (MBE) method, a metal organic chemical vapor deposition (MOCVD) method, or the like, a necessary semiconductor layer is formed on a substrate and formed by lithography. Apply technology, especially electron beam lithography, ion beam lithography, etc., and perform etching into a box shape.
[0006]
(2)
The substrate is processed in the same manner as in the above (1), and then a box-like structure is formed by utilizing the growth selectivity in the MBE method, the MOCVD method or the like.
[0007]
(3)
By using surface steps and kinks on a slightly inclined substrate, crystal growth is also controlled in the lateral direction to form a box.
[0008]
(4)
A box is obtained using an SK type growth island that appears in the early stage of growth of a highly strained heterostructure such as InAs / GaAs.
Etc.
[0009]
By the way, when the means listed in the above (1) and (2) are adopted, damage is likely to enter from the surface of the semiconductor layer to the inside, and the size of the box depends on the accuracy of the current processing technique. It is difficult to control the size below [nm], and the size variation is large.
[0010]
In addition, when the means listed in (3) above is adopted, the shape of the surface step is difficult to control, and in addition, material mixing occurs in the lateral direction, so the size, composition, and sharpness of the lateral interface are precisely controlled. Can not do it.
[0011]
Furthermore, when the means mentioned in the above (4) is adopted, since no processing process is used, there is no processing damage, and the growth island formation is caused by surface energy and strain energy, so that it approaches the equilibrium state. Therefore, the sizes of the boxes can be made quite uniform, and a standard deviation of about 10% is obtained although it is an experimental level.
[0012]
As described above, although the means listed in (4) has advantages not found in the means (1) to (3), the formation of the growth island is caused by the surface condition of the base, that is, the step or kink. Various problems arise because of the strong dependence on the rearrangement structure of atoms on the surface, surface defects, and the like.
[0013]
That is, the formed quantum dots are sparse and dense, and do not have a uniform density, and due to this, there is a slight variation in size, and the emission half-width (PL) obtained by a normal method Is 80 [meV] to 100 [meV].
[0014]
This half-width of light emission is much larger than that of a quantum well that is currently in practical use as an active layer of a semiconductor laser. Therefore, even if a semiconductor laser having the SK type growth island is manufactured, it is expected. It is not possible to obtain the effect of improving the characteristics as much as possible, for example, lowering the threshold value.
[0015]
If the above means (4) is adopted, the arrangement of quantum dots can be controlled, and if quantum dots having no damage can be generated with a uniform size and a uniform density, a plurality of quantum dots can be formed. Application to connected (arranged) devices, such as single-electron elements, is also possible.
[0016]
So far, various attempts have been made to arrange the semiconductor quantum dots in a controlled state using the means of (4), for example,
[0017]
(A)
A method of processing so that a step is generated on the surface of the substrate and generating semiconductor quantum dots in the vicinity of the step (if necessary, “DSL Mui et al., Appl. Phys. Lett. 66 (1995) ”).
[0018]
(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 on the bottom thereof (if necessary, "Oral presentation at IPRM'95 Late News", See).
[0019]
(C)
A multi-step with a step bunching is formed, and semiconductor quantum dots are preferentially generated on the multi-step (if necessary, “M. Kitamura et al., Proc. Of IPRM '95, (1995) p. 736 ").
(In the above description, “IPRM'95” is “The Seventh International Conference on Indium Phosphate and Related Materials”).
[0020]
[Problems to be solved by the invention]
The problem (A) is that it is difficult to control the step shape for arranging the semiconductor quantum dots.
[0021]
The problem of (B) is that it requires a wide area for forming a V-shaped groove, that is, an area where no semiconductor quantum dots are generated, and therefore cannot be densified. The processing steps are complicated and do not become flat.
[0022]
The problem of (C) is that bunching control of the surface step is difficult, and kinks are concentrated locally on the bunching surface or fluctuations occur on the bunching surface, so that uniform-sized quantum dots are formed at uniform intervals. I can't.
[0023]
The present invention makes it possible to control the arrangement of semiconductor quantum dots made of SK-type growth islands, and to generate semiconductor quantum dots having no damage at a uniform size and a uniform density. A connected (arranged) device such as a single-electron element can be realized.
[0024]
[Means for Solving the Problems]
In the present invention, after forming a semiconductor quantum dot composed of a SK type growth island that appears in the early stage of growth of a highly strained heterostructure such as InAs / GaAs, the vapor pressure is higher than that of the material constituting the growth island. Using a low and thermally stable material, forming the first over-growth layer below the height of the growth island and performing heat treatment to re-evaporate the portion protruding from the first over-growth layer, or Basically, the height of the growing island is made uniform by scattering it around.
[0025]
FIG. 4 is an explanatory view of the main part of the 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, 3 is an InAs growth island, H Indicates the height of the growth island, and D indicates the diameter of the bottom surface of the growth island 3.
[0026]
Usually, in a growth island generated by SK type growth, for example, an InAs growth island 3 on a GaAs substrate 1 as shown in FIG. 4, the height H is 3 [nm] to 5 [nm]. In addition, the distribution is observed in the range of 20 nm to 25 nm in diameter D, and the cut side surface of the growth island 3 is flat.
[0027]
Regarding the quantum level on the growth island 3, the height H of the growth island 3 is dominant, and the fluctuation of the quantum level that the fluctuation of the height H is generated is the fluctuation of the quantum level that the fluctuation of the diameter D is generated. It is considered that the half width of light emission is governed by fluctuations in height.
[0028]
Therefore, if the height H of the growth island 3 can be made uniform, the light emission half-value width realized so far can be greatly reduced. Incidentally, the light 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.
[0029]
As described above, in the method of manufacturing a semiconductor quantum dot according to the present invention, an SK type growth island (for example, the growth island 13A) generated in the initial stage of growing a strained heterocrystal (for example, GaAs and InAs). A first over-growth layer made of a material different from the constituent material of the SK-type growth island so that a part of the SK-type growth island protrudes. For example, by forming a first over-growth layer 14) and performing a heat treatment and maintaining it at a constant temperature for a predetermined time, the protruding portion of the SK type growth island is evaporated or spread in the lateral direction. Adjusting the height to the surface of the first overgrowth layer, and a second overgrowth layer (for example, the second overgrowth layer so as to cover the semiconductor quantum dots and the first overgrowth layer). Includes a step of forming a scan layer 16), characterized by comprising.
[0032]
By adopting the above means, it is possible to control the arrangement of the semiconductor quantum dots made of the SK type growth island, and to generate semiconductor quantum dots having no damage at a uniform size and a uniform density. Individually connected (arranged) devices such as single-electron elements can be realized, or a semiconductor laser having a small threshold current and excellent temperature characteristics can be realized.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
FIGS. 1 to 3 are side sectional views showing main parts of semiconductor quantum dots in process steps for explaining an embodiment related to the invention of the method, and will be described below with reference to these drawings.
[0034]
Refer to FIG. 1 (A) 1- (1)
The GaAs substrate 11 having a plane index of (001) is set in a growth chamber in an MBE (molecular beam epitaxy) apparatus, and the oxide film is removed by heat treatment at a temperature of 680 [° C.].
[0035]
1- (2)
By applying the MBE method, the GaAs layer 12 having a thickness of, for example, 400 nm is formed on the GaAs substrate 11.
[0036]
Enumerating the main growth conditions at this time,
Growth temperature: 620 [° C]
Growth rate: 0.8 [μm / hour]
As pressure: 6 × 10 ⁻⁶ [Torr]
It is.
[0037]
Refer to FIG. 1 (B) 1- (3)
The shutter of the Ga molecular beam cell in the MBE apparatus is closed, and an InAs layer 13 having a thickness corresponding to, for example, about 1.8 molecular layers is grown on the GaAs layer 12.
[0038]
Enumerating the main growth conditions at this time,
Growth temperature: 510 [° C]
Growth rate: 0.1 [molecular layer / second]
As pressure: 6 × 10 ⁻⁶ [Torr]
It is.
[0039]
Accordingly, the diameter D of the bottom surface is about 20 [nm] to 25 [nm], and the conical growth island 13A having a height H distributed about 3 [nm] to 5 [nm] is 1 It is formed with a density of × 10 ¹¹ [cm ⁻² ].
[0040]
Refer to FIG. 2 (A) 2- (1)
It is left for 30 [seconds] while maintaining the same temperature, that is, 510 [° C.], with As irradiated.
[0041]
2- (2)
By applying the MBE method, the first over-growth layer 14 made of GaAs having a thickness of, for example, 2 nm is formed.
[0042]
Since there is a variation in the height H of the growth island 13A, the top portion of the growth island 13A protrudes from the first over-growth layer 14, and the height of the protruding portion also varies.
[0043]
Refer to FIG. 2 (B) 2- (3)
The substrate is left for 3 minutes while maintaining the same temperature, that is, 510 [° C.], while being irradiated with As alone. The temperature applied at this time must be selected so that the first overgrowth layer 14 is not damaged.
[0044]
As a result, the top of the growth island 13A protruding from the first over-growth layer 14 is re-evaporated or flattened by spreading laterally, and the height H of the growth island 13A is made uniform. Thus, the thickness of the first over-growth layer 14 substantially matches.
[0045]
Further, the movement of the growth island 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 island 13A, so that an equal interval, that is, an arrangement occurs. The portion indicated by the symbol 15 is a two-dimensional growth island made of InAs supplied from the InAs layer 13.
[0046]
See Fig. 3 3- (1)
By applying the MBE method, the second overgrowth layer 16 made of GaAs is formed to completely cover the growth island 13A.
[0047]
The PL half-width of the growth island 13A produced as described above is about 1/2 to 1/3 smaller than that of the growth island depending on the conventional technology. You can see what is happening.
[0048]
The present invention is not limited to the embodiment described above, and many other modifications can be realized.
[0049]
For example, as the main composition of the base crystal and the first overgrowth layer, AlGaAs and InGaP can be used in addition to GaAs. In this case, the main composition of the growth island is InP, GaSb, InSb in addition to InAs. Alternatively, a mixture thereof can be used.
[0050]
In addition, such a material can be selected in other material systems. The main composition of the base crystal and the first overgrowth layer is Si, and the main composition of the growth island is SiGe, Ge, or the like. be able to.
[0051]
【The invention's effect】
In the method of manufacturing a semiconductor quantum dot according to the present invention , a step of forming a semiconductor quantum dot composed of an SK type growth island generated at an early stage of growing a strained heterocrystal, and the SK type growth described above. Forming a first over-growth layer made of a material different from the constituent material of the SK type growth island so that a part of the island protrudes, and applying heat treatment to maintain at a constant temperature for a predetermined time. A step of evaporating or laterally extending the projecting portion of the SK-type growth island to adjust the height to the surface of the first overgrowth layer; and the semiconductor quantum dot and the first overgrowth Forming a second over-growth layer over the growth layer.
[0052]
By adopting the above configuration, it is possible to control the arrangement of semiconductor quantum dots made of SK-type growth islands, and it is possible to generate semiconductor quantum dots having no damage at a uniform size and a uniform density. Individually connected (arranged) devices such as single-electron elements can be realized, or a semiconductor laser having a small threshold current and excellent temperature characteristics can be realized.
[Brief description of the drawings]
FIG. 1 is a side view of a principal part showing a semiconductor quantum dot at a process point for explaining an embodiment relating to a method invention;
FIG. 2 is a cutaway side view of a principal part showing a semiconductor quantum dot at a process point for explaining an embodiment relating to a method invention.
FIG. 3 is a cut-away side view of a main part showing a semiconductor quantum dot in a process key point for explaining an embodiment relating to a method invention;
FIG. 4 is a main part explanatory view 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 (1)

Forming a semiconductor quantum dot composed of an SK type growth island generated at an early stage of growing a strained heterocrystal;
Forming a first over-growth layer made of a material different from the constituent material of the SK-type growth island so that a part of the SK-type growth island protrudes;
By applying heat treatment and maintaining at a constant temperature for a predetermined time, the protruding portion of the SK type growth island is evaporated or spread in the lateral direction so that the height is matched with the surface of the first over-growth layer. Process,
Forming a second overgrowth layer so as to cover the semiconductor quantum dots and the first overgrowth layer;
A method for producing a semiconductor quantum dot, comprising:

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