JPH1187689A - Manufacture of quantum dot - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformly grow an InGaAs quantum dot for emitting light in a 1.3 [μm] band, at high density in the case of growing the dot by adopting a method of raw material alternate supplying. SOLUTION: This method for manufacturing a quantum dot comprises the steps of repeating a step of alternately supplying group III organic metallic material and a group V element material onto a GaAs buffer layer 31 of semiconductor substrate, having a first lattice constant to form III-V semiconductor thin film having a second lattice constant different from the first constant, i.e., an InGaAs wet layer 31, an InGaAs wet layer 34 and the like, generating a quantum dot 32A, a quantum dot 34A and the like, and repeating the generation of dot by sandwiching a GaAs spacer layer 33 of a semiconductor layer which has a thickness of D (D>=10 [nm]) or more therebetween and a first lattice constant by M (M>1) times.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a 1.3 ± 0.05 [.mu.m]
The present invention relates to a method for manufacturing a quantum dot that emits light in a wavelength band called a 1.3 [μm] band.

At present, research on semiconductor lasers using quantum dots for the active layer, which can realize three-dimensional quantum confinement, has been actively conducted, and if the quantum dots have a crystal composition emitting light in the 1.3 [μm] band, Can improve the differential gain depending on the delta-function density of states, and can expect low threshold oscillation beyond quantum well lasers and improvement in high-temperature operation characteristics.

The present invention intends to disclose a means for growing quantum dots having a crystal composition emitting light in the 1.3 [μm] band at high density and uniformly.

[0004]

2. Description of the Related Art In the early days of manufacturing quantum dots, an electron lithography technique or a technique for finely processing a semiconductor crystal using a focused ion beam was used.

[0005] However, due to problems such as limitations and damages of nano-scale fine processing, the above-mentioned methods have been abolished, and in recent years, the natural formation technique during crystal growth has been exclusively used.

[0006] There are several methods for producing quantum dots by crystal growth.
This is a method for manufacturing a quantum dot utilizing crystal growth of a lattice mismatched material.

FIG. 3 is a cutaway side view of a main part showing a quantum dot at a key point in a manufacturing process for explaining a conventional technique.

FIG. 3 (A) 3- (1) Group III having a lattice constant (> 〔2 [%]) larger than the first lattice constant on the semiconductor substrate 1 having the first lattice constant. Growing the group V semiconductor layer 2;

In this case, the group III-V semiconductor layer is grown in a lattice-matching two-dimensional layer at the beginning of the growth.

Referring to FIG. 3B, 3- (2) When the growing semiconductor layer 2 reaches a certain thickness, a nano-scale three-dimensional island 3 is formed thereon. This phenomenon is what is called SK (Transki-Krastan).
ov) growth. The three-dimensional island 3 has such a property that the larger the lattice mismatch between the base 1 and the group III-V semiconductor layer 2, the smaller it becomes.

As a material of a quantum dot having a crystal composition that emits light in the 1.3 [μm] band, InGaAs on GaAs is used.
s can be used, and as a crystal growth technique for forming the same, metalorganic vapor phase epitaxy (metalorganic) can be used.
vapor phasepitaxis: MOVP
E) method, molecular beam epitaxy (molecular beam)
A method of alternately supplying a raw material of a Group III material and a Group V material based on an am epitaxy (MBE) method, a MOVPE method or an MBE method is known.

In any of these growth methods, 1.3 is used.
InGaAs quantum dots emitting light in the [μm] band have been obtained. Among them, the alternate material supply method is an excellent technique that can control the emission wavelength of the quantum dots depending on the number of repetitions of the alternate supply. .

Quantum dots emitting light in the 1.3 [μm] band
In order to realize low threshold oscillation in a laser, it is necessary to form quantum dots having a uniform size at a high density. Theoretically, the surface coverage per layer is 30 [%]. Alternatively, it is necessary to make the dot size uniform so that the half width at half maximum is about 15 [meV] or less.

However, in the method of alternately supplying the raw materials, the surface coverage of the quantum dots is as low as about 10%, and
Since the emission half width is also broad at about 30 [meV], laser oscillation occurs, but oscillation at a low threshold has not been realized.

In order to increase the density of the quantum dots, it is considered that if one layer is impossible, it is considered that the number of layers should be increased. However, in that case, another problem occurs.

FIG. 4 is a cutaway side view of a main part showing a multilayered InGaAs quantum dot. In FIG.
As buffer layer, 12 is an InGaAs wetting layer, 12A is a quantum dot, 13 is a GaAs spacer layer, 14 is InG
aAs wetting layer, 14A is a quantum dot, 15 is a GaAs spacer layer, 16 is an InGaAs wetting layer, 16A is a quantum dot, and 17 is a GaAs cap layer.

As is apparent from the figure, the second and subsequent quantum dots 14 are interposed with the GaAs spacer layer 13 and the like interposed therebetween.
Even when A and 16A are grown under exactly the same conditions as the quantum dots 12A in the first layer, the dot size becomes larger as it is closer to the surface side.

Although the reason for this is still uncertain, it is considered to be due to the surface segregation of In. That is, GaA
In a lattice mismatched growth of s and InGaAs, In and G
Due to the difference in chemical properties from that of In, In has a stronger tendency to segregate on the surface. Therefore, even if a GaAs spacer layer is interposed, the underlayer before the second and subsequent quantum dots are completely grown. InG not containing GaAs but containing some In
It seems to be aAs.

Therefore, the dot growth conditions for the second and subsequent layers,
For example, if the group III raw material supply composition ratio is the same as the growth condition of the dots of the first layer, the degree of lattice mismatch between the dot crystals of the second and subsequent layers and the underlying crystal should be small, and as a result,
It is considered that the size of the dots in the second and subsequent layers inevitably increases.

According to the above description, in order to make the dot size uniform among the layers, the number of repetitions of the alternate supply of the raw material when growing the surface side layer dots is compared with the case where the substrate side layer dots are grown. It may seem that reducing it is effective.

As a supporting reason, a study by a group belonging to the applicant has found that in InGaAs quantum dots having a single-layer structure, the dot size can be controlled by controlling the number of repetitions of alternately supplying the raw material. (If necessary,
"Applied Physics Letters
68, 3013 (1996). 2 "or" Jpn. J. Appl. Phys. 35, L26
2 (1996) ").

More specifically, the dot size increases as the number of repetitions of the alternate material supply is increased. In the case of a multilayer structure, the alternate material supply is performed with a GaAs spacer layer having a thickness of 10 nm. When the number of repetitions was 18 times, 14 times, and 10 times in order from the substrate side, a three-layer structure of InGaAs quantum dots was produced. As a result, the dot size became larger as approaching the surface side.

FIG. 5 is a cross-sectional side view showing a main part of a multilayer InGaAs quantum dot formed by changing the number of times of alternate supply of the raw material.

In the figure, 21 is a GaAs buffer layer,
22 is an InGaAs wetting layer, 22A is a quantum dot, 23
Is a GaAs spacer layer, 24 is an InGaAs wetting layer, 2
4A is a quantum dot, 25 is a GaAs spacer layer, 26 is an InGaAs wetting layer, 26A is a quantum dot, and 27 is Ga
As cap layer, S ₂₃ the thickness of the spacer layer 23, S ₂₅ is the thickness of the spacer layer 25, S ₂₇ indicates the thickness of the cap layer 27, respectively.

The major surface index of the buffer layer 21 is (100), and the thicknesses S ₂₃ and S _{25 of the} spacer layers 23 and 25 are
Is 10 [nm], and the thickness S ₂₇ of the cap layer ₂₇ is 20 [n].
m], the number of repetitions of the alternate supply of the raw material when growing the quantum dots 22A is 18 times, 14 times for the quantum dots 24A, and 10 times for the quantum dots 26A.

The raw material and the supply time for growing each quantum dot were 2 seconds for trimethylindium dimethylethylamine adduct (TMIDMEA), 0.3 seconds for trimethylgallium (TMGa), and 0.3 seconds for arsine (AsH).
₃ ) was supplied alternately as 7 seconds.

[0027]

According to the present invention, when a quantum dot is grown by employing the alternate material supply method, 1.3 is used.
InGaAs quantum dots emitting light in the [μm] band can be grown at high density and uniformly.

[0028]

Means for Solving the Problems The present inventor has found that 1.3 [μ]
m] InG having a multilayer structure (for example, a three-layer structure) emitting light in a band
Many experiments were conducted on aAs quantum dots. As a result, the thickness of the GaAs spacer layer interposed between the InGaAs quantum dots was increased to a certain value D or more (D> 10 [n
m]), it has been found that the dot linear density in the lower layer can be increased as compared with the case of a single layer structure.

In particular, the thickness of the GaAs spacer layer is set to 20 [n].
m], the dot linear density of the lower layer is more than twice that of the single-layer structure, and this is converted to a surface coverage of four times that of the single-layer structure, that is, about 40% or more. Become.

In addition to the above conditions, another invention by the present inventor (refer to Japanese Patent Application No. 9-220263 if necessary)
In other words, the crystal growth temperature is set to 500 ° C.
To 560 [° C.], and the number of repetitions N of the alternate material supply is set to 1.3 times or more the number of repetitions N ₀ when the growth mode of the InGaAs thin film changes from two-dimensional growth to three-dimensional growth. In that emits light in the 1.3 [μm] band
By combining the methods of manufacturing GaAs quantum dots, an InGaAs quantum dot multilayer structure that emits light in the 1.3 [μm] band can be easily manufactured.

In the production of this multi-layer structure, the number of repetitions of alternate supply of the raw material may be the same for each layer. However, in order to always have the same degree of lattice mismatch with the underlying crystal, the upper layer dots are grown. By making the In supply composition ratio larger than the In supply composition ratio at the time of growing the lower layer dots, the dot size can be made uniform between the respective layers.

As described above, in the method of manufacturing a quantum dot according to the present invention, (1) a group III organometallic material and a five-membered organic metal material are formed on a semiconductor base (for example, a GaAs buffer layer 31) having a first lattice constant. A group III-V semiconductor thin film having a second lattice constant different from the first lattice constant (e.g., I
nGaAs wet layer 32, InGaAs wet layer 34, etc.)
In the process of forming quantum dots (for example, quantum dots 32A and quantum dots 34A), a semiconductor layer having a first lattice constant having a thickness of D (D ≧ 10 [nm]) or more is used. For example, the generation of quantum dots is repeated M times (M> 1) across the GaAs spacer layer 33, or

(2) In the above (1), when the semiconductor having the first lattice constant is GaAs and the Group III-V semiconductor having the second lattice constant is InGaAs, In the temperature range of 500 ° C. to 560 ° C., the number of repetitions N of the alternate material supply is set to one of the number of repetitions N ₀ of the alternate material supply when the growth mode of the InGaAs thin film changes from two-dimensional growth to three-dimensional growth. .3 times or more,
Or

(3) A step of alternately supplying a Group III organometallic material and a Group V material onto a semiconductor substrate having a first lattice constant is repeated to obtain a semiconductor having a second lattice constant different from the first lattice constant. In the process of forming the group III-V semiconductor thin film and forming the quantum dots, the composition ratio of the group III raw material supply at the time of forming the upper layer of the group III-V semiconductor thin film is adjusted to the ratio at the time of forming the lower layer. (For example, the supply time of TMIDMEA is set to 1
2 seconds for the layer, 2.5 for the second layer
[Second], 3 seconds for the third layer), or

(4) In the above (3), when the semiconductor having the first lattice constant is GaAs and the group III-V semiconductor having the second lattice constant is InGaAs, the InGaAs thin film is used. Is characterized in that the In supply composition ratio when forming the upper layer is made larger than the In supply composition ratio when forming the lower layer.

By adopting the above means, 1.3 [μ
m] It is possible to easily achieve high density and uniform size of quantum dots emitting light in the band, which can contribute to ultra-low threshold of the semiconductor laser for optical communication and improvement of temperature characteristics.

[0037]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a cutaway side view showing an essential part of a quantum dot for explaining a first embodiment of the present invention. FIG. 1 (A) is a quantum dot having a multilayer structure, and FIG. ) Are quantum dots having a single-layer structure for comparison.

In the figure, 31 is a GaAs buffer layer,
32 is an InGaAs wetting layer, 32A is a quantum dot, 33
Is a GaAs spacer layer; 34 is an InGaAs wet layer;
4A Quantum dots 35 are GaAs cap layer, S ₃₃ is the thickness of the spacer layer 33, S ₃₅ indicates the thickness of the cap layer 35, respectively.

Here, the surface index of the main surface of the buffer layer 31 is (100), and the thickness S ₃₃ of the spacer layer ₃₃ is 20.
[Nm], and the thickness S ₃₅ of the cap layer ₃₅ is 20 [nm].

According to the present invention, in order to fabricate the quantum dot multilayer structure of Embodiment 1, TMID is used as a growth material.
MEA, TMGa, triethylgallium (TEGa),
GaAs buffer layer 31 having a growth index of 15 [Torr] and a plane index of (100) using arsine (AsH ₃ ) and hydrogen (H ₂ ) as a carrier gas.
A multilayer structure of InGaAs quantum dots is formed thereon.

The growth of the GaAs buffer layer 31, the GaAs spacer layer 33, and the GaAs cap layer 35 is performed using TEGa.
Is used, and TMIDMEA and TMGa are used for the growth of the InGaAs quantum dots 32A and 34A.
The growth temperature of the As buffer layer 31 is 630 ° C., and the growth temperatures of the other layers are 520 ° C.

InGaAs quantum dots 32A and 34A
The unit sequence of the alternate supply of materials in the growth of
IDMEA supply → TMGa supply → H ₂ purge (3
[Sec]) → AsH ₃ supply (7 [sec]) → H ₂ purge (0.5 [sec]).

When forming quantum dots, TMIDME
The supply time of A is 2 seconds, and the supply time of TMGa is 0.3
[Sec], the number of repetitions of the raw material alternate supply is 18 times,
This condition is a condition in which a single-layer structure emits light in the 1.3 [μm] band.
This is a condition under which nGaAs quantum dots can be obtained with good reproducibility.

As shown in FIG. 1, quantum dots 34A are hardly formed in the second layer, but the dot linear density in the first layer is increased to about 2.5 times that of the single layer structure. This corresponds to an increase of about 6 times in terms of surface coverage.

FIG. 2 is a sectional side view showing a main part of a quantum dot for explaining a second embodiment of the present invention.

In the figure, 41 is a GaAs buffer layer,
42 is an InGaAs wetting layer, 42A is a quantum dot, 43
Is a GaAs spacer layer; 44 is an InGaAs wetting layer;
4A is a quantum dot, 45 is a GaAs spacer layer, 46 is an InGaAs wetting layer, 46A is a quantum dot, and 47 is Ga
As cap layer, S ₄₃ is the thickness of the spacer layer 43, S ₄₅ is the thickness of the spacer layer 45, S ₄₇ is the thickness of the cap layer 47,
D indicates the diameter of each dot.

Here, the thickness S of the spacer layers 43 and 45
₄₃ and S ₄₅ are 10 nm, and the thickness S _{47 of the} cap layer 47 is
Is 20 [nm].

The TMGa supply time is 0.3 [sec] for all three layers.
However, the supply time of TMIDMEA is 2 for the first layer.
[Second] The second layer is 2.5 [seconds], and the third layer is 3 [seconds]. By doing so, the In supply composition ratio becomes higher in the upper layer. In addition, the number of repetitions of the alternate material supply is 3
18 times for each layer.

As a result, the dot diameter D of all three layers was approximately 2
The uniformity is about 0 [nm], and each dot is formed in a state of being arranged in the vertical direction.

[0050]

In the method of manufacturing a quantum dot according to the present invention, the first lattice constant is obtained by alternately supplying a Group III organometallic material and a Group V material on a semiconductor substrate having a first lattice constant. In the process of forming a group III-V semiconductor thin film having a second lattice constant different from the above and forming quantum dots, the thickness becomes D (D ≧ 1
The generation of quantum dots is repeated M times (M> 1) with a semiconductor layer having a first lattice constant of 0 [nm] or more interposed therebetween.

By adopting the above configuration, 1.3 [μ
m] It is possible to easily achieve high density and uniform size of quantum dots emitting light in the band, which can contribute to ultra-low threshold of the semiconductor laser for optical communication and improvement of temperature characteristics.

[Brief description of the drawings]

FIG. 1 is a cutaway side view of a main part showing a quantum dot for explaining Embodiment 1 of the present invention.

FIG. 2 is a fragmentary side view showing a quantum dot for describing Embodiment 2 of the present invention.

FIG. 3 is a fragmentary side view showing a quantum dot at a key point in a manufacturing process for explaining a conventional technique.

FIG. 4 is a cutaway side view of a main part showing a multilayered InGaAs quantum dot.

FIG. 5 is a cross-sectional side view of a main part showing a multilayer InGaAs quantum dot formed by changing the number of repetitions of alternate material supply.

[Explanation of symbols]

Reference Signs List 31 GaAs buffer layer 32 InGaAs wetting layer 32A quantum dot 33 GaAs spacer layer 34 InGaAs wetting layer 34A quantum dot 35 GaAs cap layer S ₃₃ Thickness of spacer layer 33 S ₃₅ Thickness of cap layer 35

Claims (4)

[Claims] 1. A group III material having a second lattice constant different from the first lattice constant by repeating a step of alternately supplying a group III organic metal material and a group V material on a semiconductor substrate having a first lattice constant. In the process of forming a group V semiconductor thin film and forming a quantum dot, forming a quantum dot with a semiconductor layer having a first lattice constant having a thickness of D (D ≧ 10 [nm]) or more interposed therebetween; To M (M
> 1) A method for producing a quantum dot, which is repeated a number of times. 2. The semiconductor having a first lattice constant is GaAs.
Group III-V semiconductor having a second lattice constant
In the case of GaAs, when the crystal growth temperature is in the range of 500 ° C. to 560 ° C., the number of repetitions N of the alternate supply of the raw material is changed when the growth mode of the InGaAs thin film changes from two-dimensional growth to three-dimensional growth. method of manufacturing a quantum dot according to claim 1, characterized in that 1.3 times or more the number of iterations N ₀ of the raw material alternating supply. 3. A group III material having a second lattice constant different from the first lattice constant by repeating a step of alternately supplying a group III organic metal material and a group V material on a semiconductor substrate having a first lattice constant. -In the process of forming the group V semiconductor thin film and forming the quantum dots, the composition ratio of the group III raw material supply in forming the upper layer of the group III-V semiconductor thin film is changed to the group III in forming the lower layer. A method for producing quantum dots, wherein the composition ratio is different from the raw material supply composition ratio. 4. The semiconductor having a first lattice constant is GaAs.
Group III-V semiconductor having a second lattice constant
4. The method according to claim 3, wherein in the case of GaAs, the In supply composition ratio when forming the upper layer of the InGaAs thin film is made larger than the In supply composition ratio when forming the lower layer. Manufacturing method of quantum dots.