JP2007311463A - Quantum dot semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a size and a shape of a self-forming quantum dot uniform in a quantum dot semiconductor device. <P>SOLUTION: A short-period superlattice structure layer 4 in which an integral multiple of a plurality of two-dimensional compound semiconductor molecular layers are alternately laminated is provided on a semiconductor substrate 1, and in addition the self-forming quantum dot 5 is provided on the structure layer 4. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a quantum dot semiconductor device, and in particular, a quantum dot semiconductor characterized by a configuration for making the size and shape of self-forming quantum dots that constitute a quantum dot semiconductor laser, a quantum dot optical amplifier, and the like uniform. It relates to the device.

  In recent years, quantum dot structure devices using InP substrates have been used as semiconductor lasers and semiconductor optical amplifiers used in optical communications and the like. In this case, for example, an InGaAsP layer that is a quaternary mixed crystal from the viewpoint of optical waveguide formation. It is common to use an InGaAsP layer (see Non-Patent Document 1) or an InGaAlAs layer (see Patent Document 1) as an intermediate layer in which InAs quantum dots are formed using an AlGaInAs layer as a base layer and an InAs quantum dot is embedded therein. Is.

For example, in Patent Document 1, an InGaAlAs buffer layer including InAsP quantum dots is provided on an InP substrate, and an InAs quantum dot and an In _0.47 Ga _0.11 Al _0.42 As intermediate layer are repeatedly stacked thereon.
IEEE ELEOS 2003 abst. , P. 949 JP 2003-197900 A

  However, the above-described conventional method has a problem that the size / shape distribution of the quantum dots formed on the quaternary mixed crystal underlayer is increased.

  This is because the element distribution of the InGaAsP mixed crystal or InGaAlAs mixed crystal serving as the underlayer is not uniform in the plane, so that a local strain distribution is generated, and the quantum dots formed on the upper layer have a strain distribution distribution of the underlayer. This is thought to be affected.

  Accordingly, an object of the present invention is to make the size and shape of self-forming quantum dots uniform.

FIG. 1 is a diagram illustrating the basic configuration of the present invention. Means for solving the problems in the present invention will be described with reference to FIG.
Reference numerals 2, 3, 6, and 7 in the figure denote a buffer layer, a quantum dot structure layer, an intermediate layer, and a cladding layer, respectively.
See FIG. 1 In order to solve the above-described problem, the present invention provides a short-period superlattice structure layer in which an integer multiple of molecular layers of a plurality of binary compound semiconductors are alternately stacked on a semiconductor substrate 1 in a quantum dot semiconductor device. 4 and a self-forming quantum dot 5 is provided on the short-period superlattice structure layer 4.

  As described above, the short-period superlattice structure layer 4 in which integer multiples of the molecular layers of the binary compound semiconductor are alternately stacked is used as the base layer constituting the quantum dots, thereby forming the short-period superlattice structure layer 4. Since the surface is made of a binary compound semiconductor of a complete molecular layer, the element distribution in the underlayer becomes uniform, and the strain becomes uniform accordingly, so the size and shape of the self-forming quantum dots 5 become uniform. .

  In this case, the semiconductor substrate 1 is typically an InP substrate or a GaAs substrate. When an InP substrate is used, the short-period superlattice structure layer 4 is formed of an AlAs molecular layer, a GaAs molecular layer, and an InAs molecule. What is necessary is just to comprise by a layer, and when using a GaAs substrate, the short period superlattice structure layer 4 should just be comprised by an AlAs molecular layer and a GaAs molecular layer.

  Furthermore, in the case of using an InP substrate, the short period superlattice structure layer 4 may be composed of a GaP molecular layer, an InP molecular layer, a GaAs molecular layer, and an InAs molecular layer. Alternatively, the short-period superlattice structure layer 4 may be composed of an AlAs molecular layer, a GaAs molecular layer, and an InAs molecular layer.

  The self-forming quantum dots 5 are typically InAs quantum dots, but InSb quantum dots or GaSb quantum dots may be used.

Further, as the short period superlattice structure layer 4, the lattice constant a _ave corresponding to the average composition of the short period superlattice structure layer 4 is equal to the lattice constant a _sub of the semiconductor substrate 1.
−0.5 [%] ≦ [(a _sub −a _ave ) / a _sub ] × 100 ≦ 0.5 [%]
It is desirable to satisfy this relationship, whereby the crystallinity of the short-period superlattice structure layer 4 can be maintained.

The average composition of the short-period superlattice structure layer 4 in this case represents the ratio of the number of atoms in the repetitive unit period. For example, the repetitive unit period is (InAs) _1ML (GaAs) _1ML ( InAs) _1ML (AlAs) _1ML , the average composition is Al _0.25 Ga _0.25 In _0.50 As.
Note that 1 ML (Mono Layer) represents a single molecular layer.

  According to the present invention, the uniformity of the size and shape of the self-formed quantum dots is improved as compared with the case where the self-formed quantum dots are formed on the quaternary mixed crystal underlayer, so that this quantum dot structure is used as an active layer of a semiconductor laser. When applied, the gain at the oscillation wavelength increases, and a reduction in threshold current value and an increase in relaxation frequency can be realized.

  The present invention provides a short-period superlattice structure layer in which an integer multiple of molecular layers of a plurality of binary compound semiconductors are alternately stacked via a buffer layer on a semiconductor substrate such as an InP substrate or a GaAs substrate. A self-forming quantum dot is formed on the short-period superlattice structure layer, and the self-formation quantum dot is embedded with a quaternary mixed crystal semiconductor intermediate layer (barrier layer). The formation type quantum dots are repeatedly stacked as many times as necessary, and finally a cladding layer and, if necessary, a contact layer are provided.

In this case, when the substrate is an InP substrate, for example, a short-period superlattice structure layer having a repetition period of (InAs) _1ML (GaAs) _1ML (InAs) _1ML (AlAs) _1ML is used, and the substrate is a GaAs substrate. In this case, for example, a short-period superlattice structure layer having a repetition period of (GaAs) _2ML (AlAs) _1ML is used.

  As the stripe structure, a buried heterojunction structure is generally used when the substrate is an InP substrate, and a ridge stripe structure is generally used when the substrate is a GaAs substrate.

Here, a quantum dot semiconductor laser according to Example 1 of the present invention will be described with reference to FIGS.
See Figure 2
First, using a gas source MBE method on an n-type InP substrate 11 having a (100) plane as a main surface, for example, doping at an Si concentration of, for example, 5.0 × 10 ¹⁷ cm ⁻³ at a growth temperature of 600 ° C. Then, the n-type InP buffer layer 12 having a thickness of, for example, 300 nm is grown.

Subsequently, after the growth temperature is lowered to 500 ° C. in a PH ₃ atmosphere, one period is (InAs) _1ML 14 / (GaAs) _1ML 15 / (InAs) _1ML 16 / (AlAs) _1ML 17 for a total of 20 periods ( A short-period superlattice structure layer 13 having a thickness of about 25 nm is formed.
The short-period superlattice structure layer 13 has an average composition of Al _0.25 Ga _0.25 In _0.50 As, which corresponds to a composition wavelength of 1.13 μm and a compressive strain of 0.19%.

  Subsequently, the InAs quantum dots 18 are self-formed by supplying 2ML (molecular layer) of InAs while keeping the substrate temperature at 500 ° C.

See Figure 3
Subsequently, the AlGaInAs barrier layer 19 having a composition wavelength of 1.13 μm is formed to a thickness of 10 nm, for example, while the substrate temperature remains at 500 ° C.
By forming the 10 nm AlGaInAs barrier layer 19, the InAs quantum dots 18 are completely embedded, and the surface is in a state where sufficient flatness is obtained.

  Subsequently, the quantum dot structure layer 20 having one period until the growth of the above-described short period superlattice structure layer 13, InAs quantum dots 18, and AlGaInAs barrier layer 19 is repeated to form, for example, 10 periods.

Subsequently, the substrate temperature is again raised to 600 ° C. under an AsH ₃ atmosphere, and a p-type InP cladding layer 21 having a Zn concentration of, eg, 5.0 × 10 ¹⁷ cm ⁻³ and a thickness of, eg, 300 nm is formed. Form.

See Figure 4
Then, the width on the p-type InP cladding layer 21 is, for example, to form a SiO ₂ mask 22 of 1.5 [mu] m, by dry etching, the SiO ₂ mask 22 is a n-type InP substrate 11 and the top of the area to be etched Then, a striped mesa structure is formed in which the level difference from the n-type InP substrate in the region that is not etched is 1.5 μm, for example.

Next, a p-type InP buried layer 23 and an n-type InP current blocking layer 24 are provided by MOCVD using the SiO ₂ mask 22 as a selective growth mask.

See Figure 5
Next, after removing the SiO ₂ mask 22, the p-type InP cladding layer 25 with a Zn concentration of 1.0 × 10 ¹⁸ cm ⁻³ and a thickness of, for example, 2000 nm and a Zn concentration of 1 are again formed by MOCVD. A p-type InGaAs contact layer 26 doped with 0.0 × 10 ¹⁹ cm ⁻³ and having a thickness of, for example, 500 nm is provided, and then an n-side electrode 27 and a p-side electrode 28 are sequentially provided.
Finally, although not shown, the basic structure of the quantum dot semiconductor laser of Example 1 of the present invention is completed by providing a low reflection film on the laser front end face and a high reflection film on the rear end face.

  The half width of photoluminescence in the quantum dot semiconductor laser of Example 1 of the present invention is 20 to 30 meV, which is a significant improvement over the half width of 50 to 100 meV when InAs quantum dots are formed on bulk AlGaInAs. This is thought to be because the uniformity of InAs quantum dots was improved by adopting a short-period superlattice structure layer as the underlayer.

Next, a quantum dot semiconductor laser according to Example 2 of the present invention will be described with reference to FIGS.
See FIG.
First, an n-type GaAs substrate 31 having a (100) plane as a main surface is doped with a Si concentration of, eg, 5.0 × 10 ¹⁷ cm ⁻³ at a growth temperature of, eg, 600 ° C. by a solid source MBE method. The n-type GaAs buffer layer 32 having a thickness of, for example, 300 nm is grown.

Subsequently, after the growth temperature is lowered to 500 ° C. in an As ₄ atmosphere, a short period superlattice structure layer in which one period is (GaAs) _2ML 34 / (AlAs) _1ML 35 for a total of 36 periods (thickness of about 30 nm). 33 is formed.
The short-period superlattice structure layer 33 has an average composition of Al _0.33 Ga _0.67 As, which corresponds to a composition wavelength of 0.667 μm and a strain amount of 0%.

  Subsequently, the InAs quantum dots 36 are self-formed by supplying 2ML (molecular layer) of InAs while keeping the substrate temperature at 500 ° C.

See FIG.
Subsequently, the Al _0.33 Ga _0.67 As barrier layer 37 is formed to a thickness of 10 nm, for example, while the substrate temperature remains at 500 ° C.
By forming the 10 nm Al _0.33 Ga _0.67 As barrier layer 37, the InAs quantum dots 36 are completely embedded, and the surface is in a state where sufficient flatness is obtained.

Subsequently, the quantum dot structure layer 38 having one period until the growth of the above-described short period superlattice structure layer 33, InAs quantum dots 36, and Al _0.33 Ga _0.67 As barrier layer 37 is repeated to form, for example, 10 periods. .

Subsequently, the substrate temperature is again raised to 600 ° C. under an As ₄ atmosphere, a p-type GaAs cladding layer 39 having a Be concentration of, for example, 5.0 × 10 ¹⁷ cm ⁻³ and a thickness of, for example, 1500 nm, and A p ⁺ -type GaAs contact layer 40 having a Be concentration of, for example, 2.0 × 10 ¹⁹ cm ⁻³ and a thickness of, for example, 300 nm is formed.

See FIG.
Next, a SiO ₂ mask 41 having a width of, for example, 1.5 μm is formed on the p ⁺ -type GaAs contact layer 40, and a p-type GaAs cladding layer 39 in an area to be etched by dry etching, and an SiO ₂ mask on the upper part. A ridge structure is formed in which a step with respect to the p-type GaAs cladding layer 39 in a region where there is 41 and is not etched is 1.0 μm, for example.

Next, after removing the SiO ₂ mask 41, an n-side electrode 42 and a p-side electrode 43 are sequentially provided. Finally, although not shown, a low reflection film and a high reflection film are applied to the laser front end face and the rear end face, respectively. This completes the basic structure of the quantum dot semiconductor laser of Example 2 of the present invention.

  Also in the case of the quantum dot semiconductor laser of Example 2 of the present invention, since the short-period superlattice structure layer is employed as the underlayer for forming the InAs quantum dots, the uniformity of the InAs quantum dots is improved and photoluminescence is achieved. It becomes possible to narrow the half width of.

  The embodiments of the present invention have been described above, but the present invention is not limited to the configurations and conditions described in the embodiments, and various modifications are possible. For example, in the above embodiments It goes without saying that the current confinement structure is merely an example, and various known current confinement structures and stripe structures may be used.

In the first embodiment, the short-period superlattice structure layer is formed by repeating (InAs) _1ML (GaAs) _1ML (InAs) _1ML (AlAs) _1ML , but InAs is interposed between GaAs and AlAs. Is present, the stacking order is arbitrary.

  In Example 1 described above, the short-period superlattice structure layer is composed of the InAs molecular layer, the GaAs molecular layer, and the AlAs molecular layer as described above. However, the GaP molecular layer, the InP molecular layer, and the GaAs molecular layer are used. , And an InAs molecular layer.

In the second embodiment, the short-period superlattice structure layer is composed of (GaAs) _2ML (AlAs) _1ML , but is composed of other layer ratios such as (GaAs) _1ML (AlAs) _1ML. It is good.

  Further, in Example 1 described above, the number of periods of the short-period superlattice structure layer is 20 periods, and in Example 2, the period number of the short-period superlattice structure layer is 36 periods. Is arbitrary, and is not limited to 20 cycles or 36 cycles.

  In Example 2 described above, the short-period superlattice structure layer is composed of the GaAs molecular layer and the AlAs molecular layer as described above, but is composed of the AlAs molecular layer, the GaAs molecular layer, and the InAs molecular layer. You can do it.

In each of the above embodiments, no particular mention is made of lattice matching between the short-period superlattice structure layer and the semiconductor substrate, but the lattice constant a _ave corresponding to the average composition of the short-period superlattice structure layer is For the lattice constant a _{sub of the} semiconductor substrate,
−0.5 [%] ≦ [(a _sub −a _ave ) / a _sub ] × 100 ≦ 0.5 [%]
It is sufficient to satisfy this relationship, whereby the crystallinity of the short-period superlattice structure layer can be kept good.

  Further, in each of the above embodiments, the quantum dots are composed of InAs quantum dots, but are not limited to InAs quantum dots, and may be InSb quantum dots or GaSb quantum dots.

  In each of the above embodiments, GaAs or InP is used as a substrate, but other substrates such as a mixed crystal substrate such as an InGaAs substrate may be used.

  Further, in each of the above embodiments, the non-nitride group III-V compound semiconductor device is described. However, the present invention is also applicable to a GaN group III-V compound semiconductor device. GaN, SiC, sapphire or the like may be used as the substrate.

Here, the detailed features of the present invention will be described again with reference to FIG.
1 again. (Supplementary Note 1) A short-period superlattice structure layer 4 in which an integer multiple of molecular layers of a plurality of binary compound semiconductors are alternately stacked on a semiconductor substrate 1 is provided. 4. A quantum dot semiconductor device comprising a self-forming quantum dot 5 provided on a substrate 4.
(Supplementary note 2) The quantum according to Supplementary note 1, wherein the semiconductor substrate 1 is an InP substrate, and the short-period superlattice structure layer 4 is composed of an AlAs molecular layer, a GaAs molecular layer, and an InAs molecular layer. Dot semiconductor device.
(Supplementary note 3) The semiconductor substrate 1 is an InP substrate, and the short-period superlattice structure layer 4 is composed of a GaP molecular layer, an InP molecular layer, a GaAs molecular layer, and an InAs molecular layer. 1. The quantum dot semiconductor device according to 1.
(Additional remark 4) The said semiconductor substrate 1 is a GaAs substrate, The said short period superlattice structure layer 4 is comprised by the AlAs molecular layer and the GaAs molecular layer, The quantum dot semiconductor device of Additional remark 1 characterized by the above-mentioned.
(Supplementary note 5) The quantum according to Supplementary note 1, wherein the semiconductor substrate 1 is a GaAs substrate, and the short-period superlattice structure layer 4 is composed of an AlAs molecular layer, a GaAs molecular layer, and an InAs molecular layer. Dot semiconductor device.
(Appendix 6) The quantum dot according to any one of appendices 1 to 5, wherein the self-forming quantum dot 5 is composed of any one of an InAs quantum dot, an InSb quantum dot, and a GaSb quantum dot. Semiconductor device.
(Supplementary Note 7) The lattice constant a _ave corresponding to the average composition of the short-period superlattice structure layer 4 is equal to the lattice constant a _sub of the semiconductor substrate 1.
−0.5 [%] ≦ [(a _sub −a _ave ) / a _sub ] × 100 ≦ 0.5 [%]
7. The quantum dot semiconductor device according to any one of appendices 1 to 6, wherein the relationship is satisfied.

  As a practical example of the present invention, a semiconductor laser is typical, but it is also applied to a semiconductor optical amplifier (SOA), and further, quantum dot infrared detection using transition between subbands. The present invention is also applied to an element (QDIP) or the like.

It is explanatory drawing of the fundamental structure of this invention. It is explanatory drawing of the manufacturing process to the middle of the quantum dot semiconductor laser of Example 1 of this invention. It is explanatory drawing of the manufacturing process to the middle after FIG. 2 of the quantum dot semiconductor laser of Example 1 of this invention. It is explanatory drawing of the manufacturing process to the middle after FIG. 3 of the quantum dot semiconductor laser of Example 1 of this invention. It is explanatory drawing of the manufacturing process after FIG. 4 of the quantum dot semiconductor laser of Example 1 of this invention. It is explanatory drawing of the manufacturing process to the middle of the quantum dot semiconductor laser of Example 2 of this invention. It is explanatory drawing of the manufacturing process to the middle after FIG. 6 of the quantum dot semiconductor laser of Example 2 of this invention. It is explanatory drawing of the manufacturing process after FIG. 7 of the quantum dot semiconductor laser of Example 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Buffer layer 3 Quantum dot structure layer 4 Short period superlattice structure layer 5 Self-forming quantum dot 6 Intermediate layer 7 Cladding layer 11 n-type InP substrate 12 n-type InP buffer layer 13 Short period superlattice structure layer 14 InAs) _1ML
15 (GaAs) _1ML
16 (InAs) _1ML
17 (AlAs) _1ML
18 InAs quantum dots 19 AlGaInAs barrier layer 20 Quantum dot structure layer 21 p-type InP cladding layer 22 SiO ₂ mask 23 p-type InP buried layer 24 n-type InP current blocking layer 25 p-type InP cladding layer 26 p-type InGaAs contact layer 27 n-side electrode 28 p-side electrode 31 n-type GaAs substrate 32 n-type GaAs buffer layer 33 short-period superlattice structure layer 34 (GaAs) _2ML
35 (AlAs) _1ML
36 InAs quantum dots 37 Al _0.33 Ga _0.67 As barrier layer 38 Quantum dot structure layer 39 p-type GaAs cladding layer 40 p ⁺ -type GaAs contact layer 41 SiO ₂ mask 42 n-side electrode 43 p-side electrode

Claims (5)

A short-period superlattice structure layer in which an integer multiple of a plurality of binary compound semiconductor molecular layers are alternately stacked is provided on a semiconductor substrate, and a self-forming quantum dot is provided on the short-period superlattice structure layer. Quantum dot semiconductor device. 2. The quantum dot semiconductor device according to claim 1, wherein the semiconductor substrate is an InP substrate, and the short-period superlattice structure layer includes an AlAs molecular layer, a GaAs molecular layer, and an InAs molecular layer. 2. The quantum dot semiconductor device according to claim 1, wherein the semiconductor substrate is a GaAs substrate, and the short-period superlattice structure layer is composed of an AlAs molecular layer and a GaAs molecular layer. 4. The quantum dot semiconductor device according to claim 1, wherein the self-forming quantum dots are any of InAs quantum dots, InSb quantum dots, and GaSb quantum dots. 5. The lattice constant a _ave corresponding to the average composition of the short-period superlattice structure layer is equal to the lattice constant a _{sub of the} semiconductor substrate.
−0.5 [%] ≦ [(a _sub −a _ave ) / a _sub ] × 100 ≦ 0.5 [%]
The quantum dot semiconductor device according to claim 1, wherein the relationship is satisfied.

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