JP5929115B2 - Semiconductor nanodevice - Google Patents

Description

  The present invention relates to a semiconductor nanodevice, and relates to a semiconductor nanodevice using a nanostructure in which semiconductor layers having strains are stacked thicker than in the past.

  For optical devices such as semiconductor lasers and photodetectors currently used in the industry or electronic devices such as high electron mobility transistors, a semiconductor multilayer film in which one or more thin films of different semiconductor materials are stacked on a semiconductor substrate It is formed by the structure.

  This semiconductor multilayer film is indispensable for expressing the original functions of the device and improving the characteristics. For one purpose, the carrier control in the semiconductor can be controlled by combining materials with different band gaps. is there.

  For example, in an optical device, by forming a heterostructure with a material having a large band gap energy difference, leakage of carriers from the light emitting layer can be prevented, and a device with excellent temperature characteristics can be formed. A typical combination of such heterostructures is InAs / GaAs.

  However, in the conventional thin film growth on a semiconductor substrate, the thickness of the thin film is limited. The reason is that dislocations are formed in the thin film to release the strain when the film thickness exceeds a certain thickness due to the difference in lattice constant between the substrate material and the thin film material, and the crystallinity of the semiconductor is significantly reduced. Responsible.

Here, the limitation of the film thickness that occurs in the growth of the thin film on the semiconductor thin film substrate will be described. The limit film thickness at which a thin film can be formed without causing dislocation is called the critical film thickness h _c . W. Based on the discussion by Matthews et al. (For example, see Non-Patent Document 1), it is possible to formulate as follows.
h _c = (b / 2πε) × (1 + ν) ⁻¹ × {ln (h _c / b) +1}
However,
ε: Strain b: Burgers vector (0.4 nm)
ν: Poisson's ratio (1/3)
FIG. 7 shows the result of solving this equation by numerical calculation and graphing. When the amount of strain is 1% or more, a bulk layer (over 25 nm) having no quantum effect is laminated. Is impossible. Incidentally, in the strain of 7% (ε = 0.07) generated in the InAs layer on the GaAs substrate, the stackable film thickness is only 1.6 nm.

  Thus, when the film thickness is limited, for example, in the case of a semiconductor laser using a quantum well structure, the emission wavelength is limited. In an InAs quantum well laser formed on a GaAs substrate, the optical communication band A usable long wavelength light emission of 1.3 μm or more could not be realized.

  On the other hand, as a method of growing a semiconductor layer having a large difference in lattice constant such as InP on a Si substrate or the like, it has been proposed to grow the semiconductor layer vertically as a nanostructure using a catalyst such as Au. (For example, refer to Patent Document 1 or Patent Document 2).

JP 2009-028797 A JP 2005-532181 A

Journal of Crystal Growth, Vol. 27, pp. 118-125, 1974

  However, in a device using nanostructures, a part of the growth direction of nanostructures is used as a functional region. When forming a heterojunction, the process is complicated due to the use of a catalyst. There is a problem. Further, since the diameter of the nanostructure is naturally small, the light output and the electric output are very small, and there is a problem that the application is extremely limited.

  Therefore, an object of the present invention is to form a semiconductor thin film having a strain exceeding a critical film thickness on a substrate to form a device region.

From one aspect disclosed, formed on the substrate, a semiconductor nanowire core extending in a direction perpendicular to the growth surface of the substrate on the substrate and having a major axis of less than 1 μm, and a sidewall of the semiconductor nanowire core, When the semiconductor nanowire core is made of a semiconductor material having a strain ε different by 1% or more and the film thickness t [nm] is a flat substrate as the constituent material of the semiconductor nanowire core, The film thickness exceeds the critical film thickness, and the film thickness t [nm] and strain ε [%]
−0.720 + 0.0988 (ε / 100) ^−1.2 <t ≦ −0.705 + 0.227 (ε / 100) ^−1.2
And at least one semiconductor thin film satisfying the above relationship, and the junction interface between the semiconductor nanowire core and the semiconductor thin film or the junction interface between the semiconductor thin films is either a light emitting region or a light absorbing region. A semiconductor nanodevice is provided.

  According to the disclosed semiconductor nanodevice, a strained semiconductor thin film having a thickness exceeding the critical film thickness on the substrate can be formed to form a device region.

1 is a configuration explanatory diagram of a semiconductor nanodevice according to an embodiment of the present invention. It is explanatory drawing of the critical film thickness at the time of using the semiconductor nanowire structure of this invention. It is explanatory drawing of the manufacturing process to the middle of the semiconductor laser of Example 1 of this invention. It is explanatory drawing of the manufacturing process to the middle after FIG. 3 of the semiconductor laser of Example 1 of this invention. It is explanatory drawing of the manufacturing process to the middle after FIG. 4 of the semiconductor laser of Example 1 of this invention. It is explanatory drawing of the manufacturing process after FIG. 5 of the semiconductor laser of Example 1 of this invention. It is explanatory drawing of the critical film thickness at the time of making it grow on a semiconductor substrate.

  Here, with reference to FIG.1 and FIG.2, the semiconductor nanodevice of embodiment of this invention is demonstrated. FIG. 1 is a configuration explanatory diagram of a semiconductor nanodevice according to an embodiment of the present invention. As shown in FIG. 1A, a semiconductor nanowire core 2 extending in the normal direction of the main surface of the substrate 1 is provided on the substrate 1, and a semiconductor thin film 3 is formed on the side surface of the semiconductor nanowire core 2, A bonding interface between the semiconductor nanowire core 2 and the semiconductor thin film 3 is defined as a functional region. Alternatively, as shown in FIG. 1B, the semiconductor thin film 3 is formed in a multilayer structure, and the bonding interface between the semiconductor thin films 3 is used as a functional region. At this time, the total film thickness of the semiconductor thin film 3 grows to a thickness exceeding the critical film thickness on the semiconductor substrate.

This is because the semiconductor nanowire core 2 that forms a bonding interface with the semiconductor thin film 2 is elastically deformed, so that the film thickness that can be stacked is greatly increased. The critical film thickness h _new in the present invention can be derived based on a state where the degree of elastic deformation of the semiconductor nanowire core 2 and the strained semiconductor thin film 3 is 1: 1,
h _new = (b / 2πε) × (1 + ν) ⁻¹ × {ln (h _new / b) +1}
It becomes.

  FIG. 2 is an explanatory diagram of the critical film thickness when the semiconductor nanowire structure of the present invention is used. According to the present invention, a material having a strain of 1% or more, preferably 1% to 16%, can be made to function as a thin film (25 nm or less) that can obtain a quantum effect while improving the critical film thickness from the prior art. Is possible. For example, an InAs thin film can be laminated on the side surface of a GaAs nanowire core to a film thickness of 5 nm, which is about three times that of the prior art. In addition, a thin film having a film thickness of 1.3 nm that functions as a thin film can be grown even with a strain of 16%, in which the thin film could not be grown at all by the prior art. As a combination of such large strain materials, there are AlP and InSb (strain: 16%).

The region of the film thickness t [nm] that can be stacked for the first time according to the present invention in the region where it was impossible to stack without causing dislocation in the prior art approximates the curve of FIG. 2 by fitting. When the strain ε is [%],
−0.720 + 0.0988 (ε / 100) ^−1.2 <t ≦ −0.705 + 0.227 (ε / 100) ^−1.2
It becomes.

  In this case, a catalytic metal such as Au, Cu, Ag, or Pt is provided on the substrate 1, and a semiconductor material is taken into the molten catalytic metal at the growth temperature, so that the semiconductor nanowire core 2 grows in the vertical direction. At this time, the catalytic metal always exists on the top surface of the semiconductor nanowire core 2 that continues to grow. Further, the diameter of the semiconductor nanowire core 2 depends on the diameter of the catalyst metal and is almost the same size.

  The substrate 1 is a group IV semiconductor substrate such as Si or a group III-V semiconductor substrate such as GaAs, but a crystalline insulating substrate such as sapphire may be used depending on circumstances. The substrate 1 and the semiconductor nanowire core 2 may be the same material as each other, such as a GaAs nanowire core for a GaAs substrate, or a combination of materials that form a heterojunction such as an InP nanowire core for a Si substrate. good.

  The cross-sectional shape perpendicular to the growth direction of the semiconductor nanowire core 2 is a triangle, a quadrangle, a hexagon, or a circle, and its major axis is less than 1 μm, more preferably 10 nm to 400 nm, particularly in a forming method using metal fine particles. Is preferably 50 nm to 200 nm. The length is preferably 3 times or more the major axis, and is 1 μm to 10 μm, more preferably 2 μm to 5 μm.

  The cross-sectional shape perpendicular to the growth direction of the semiconductor nanowire core 2 is likely to be a triangle or a hexagon when the plane orientation of the main surface of the substrate 1 is the (111) plane, and is quadrilateral when the plane is the (001) plane. The circle tends to appear during growth.

  When the plane orientation of the substrate 1 is the (001) plane, the crystal structure of the semiconductor nanowire core 2 and the semiconductor thin film 3 is a zinc blende type crystal structure. When the plane orientation is the (111) plane, the wurtzite type is used. It tends to have a crystal structure.

As described above, in the embodiment of the present invention, it is possible to form a structure and a device having a strained layer having a thickness that was impossible with the prior art, and by using the bonding interface as a functional region, Carrier control in the semiconductor becomes possible. As a result, it is possible to realize a long-wavelength laser that has a larger output and better temperature characteristics than the conventional nanodevice of Patent Document 1 or Patent Document 2 described above. Incidentally, when the semiconductor nanowire core 2 is made of GaAs and the semiconductor thin film 3 is made of a GaAs / InAs quantum well, a semiconductor laser that oscillates at a wavelength longer than 1.3 μm can be realized.

Next, with reference to FIGS. 3 to 6, the manufacturing process of the semiconductor laser of Example 1 of the present invention will be described. First, as shown in FIG. 3A, SiO _{2 is formed} on an n-type GaAs substrate 11 having a (111) plane as a main surface and an impurity concentration of 5 × 10 ¹⁷ cm ⁻³ to 1 × 10 ¹⁹ cm ^−3. A film 12 is formed, an opening 13 is formed, and gold fine particles 14 are provided in the opening 13. The gold fine particles 14 serving as the growth catalyst may be commercially available colloidal particles, or may be formed into particles by heating a small-area gold thin film formed by lithography.

Next, as shown in FIG. 3B, trimethylgallium (TMG), arsine (AsH ₃ ), and disilane (Si ₂ H ₆ ) as a dopant are supplied by the MOVPE method to form the n-type GaAs nanowire 15. It grows at a growth temperature of 300 ° C to 500 ° C. In this case, the n-type GaAs nanowire 15 has an impurity concentration of 5 × 10 ¹⁷ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ .

Next, as shown in FIG. 3C, after removing the gold fine particles 14, a non-doped GaAs / InAs quantum well structure 16 is formed. The InAs well layer 18 may be a single layer or multiple layers. In the case of multiple layers, the total film thickness of the InAs well layers 18 may be equal to or less than the critical thickness h _{new of the} present invention, that is, 5 nm or less. In the drawing, three GaAs barrier layers 17 and two InAs well layers 18 are shown. When the InAs well layer 18 is grown, it is grown at a growth temperature of 300 ° C. to 500 ° C. by supplying trimethylindium (TMI) and AsH ₃ by the MOVPE method.

Subsequently, as shown in FIG. 4D, as the MOVPE raw material, TMG, AsH ₃ , trimethylaluminum (TMAl) as the Al raw material, and diethylzinc (DEZ) as the dopant source are supplied, and the p-type AlGaAs layer 19 is supplied. Grow. The impurity concentration of the p-type AlGaAs layer 19 is 5 × 10 ¹⁷ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ and the film thickness is 50 nm to 300 nm. In order to obtain good conductivity, the Al composition of the p-type AlGaAs layer 19 is preferably 0.1 to 0.3.

Subsequently, TMG, AsH ₃ and DEZ are supplied to grow a p-type GaAs contact layer 20 having a thickness of 1 nm to 10 nm. In this case, since AlGaAs and GaAs are lattice-matched with the n-type GaAs substrate 11, there is no limitation on the growth film thickness. Although a semiconductor thin film grows also on the top surface of the n-type GaAs nanowire 15, there is no problem because it is much thinner than the semiconductor thin film grown on the side wall and is removed by etching or the like in the middle of the process.

Next, as shown in FIG. 4E, an opening is formed in the SiO ₂ film 12, and AuGe / Au is deposited to form the n-side electrode 21. Next, as shown in FIG. 4F, a SiO ₂ film 22 having a thickness of 100 nm is deposited on the entire surface. Next, as shown in FIG. 5G, a photoresist 23 is applied to the entire surface.

Next, as shown in FIG. 5H, the photoresist 23 is exposed and then developed to form a resist mask 24 having an opening 25 having a diameter larger than that of the nanowire structure. Next, as shown in FIG. 5I, the SiO ₂ film 22 on the side and top surfaces of the nanowire structure is removed with a hydrofluoric acid-based etchant using the resist mask 24 as a mask.

  Next, as shown in FIG. 6J, after depositing an AuZn / Au film on the entire surface, the AuGe / Au film deposited on the top surface is selectively removed to form the p-side electrode 26. Next, as shown in FIG. 6 (k), dielectric multilayer films 27 and 28 are formed on the upper and lower sides in order to reduce the threshold current. Both of the dielectric multilayer films 27 and 28 may be reflective films, and one of the dielectric multilayer films 27 may be an antireflection film. Finally, by removing a part of the p-side electrode 26 and a part of the SiO 2 film 22 to form a contact hole 29, the basic structure of the semiconductor laser of Example 1 of the present invention is completed.

As described above, in Example 1 of the present invention, since semiconductor nanowires are used, InAs having a large strain relative to GaAs can be grown thicker than before, and oscillation in a long wavelength band of 1.3 μm or more is possible. Is possible.

Here, the following supplementary notes are attached to the embodiment of the present invention including the first embodiment.
(Appendix 1)
A substrate,
A semiconductor nanowire core extending on the substrate in a direction perpendicular to a growth surface of the substrate and having a major axis of less than 1 μm;
The semiconductor nanowire core is made of a semiconductor material having a strain ε different by 1% or more from the constituent material of the semiconductor nanowire core, and the thickness t [nm] is flattened of the constituent material of the semiconductor nanowire core. In the case of a substrate, it is a film thickness exceeding the critical film thickness on the flat substrate, and the film thickness t [nm] and the strain ε [%]
−0.720 + 0.0988 (ε / 100) ^−1.2 <t ≦ −0.705 + 0.227 (ε / 100) ^−1.2
And at least one semiconductor thin film satisfying the above relationship, and the junction interface between the semiconductor nanowire core and the semiconductor thin film or the junction interface between the semiconductor thin films is either a light emitting region or a light absorbing region. Semiconductor nanodevices.
(Appendix 2)
The semiconductor nanodevice according to appendix 1, wherein the semiconductor nanowire core and the semiconductor thin film are made of semiconductor materials having different band gap energies.
(Appendix 3)
The semiconductor nanodevice according to appendix 1 or appendix 2, wherein the semiconductor nanowire core is made of a material different from that of the substrate.
(Appendix 4)
The semiconductor nanodevice according to any one of appendix 1 to appendix 3, wherein the semiconductor nanowire core and the semiconductor thin film have either a zinc blende crystal structure or a wurtzite crystal structure.
(Appendix 5 )
The substrate is a semiconductor substrate, the semiconductor substrate and the semiconductor nanowire core are of a first conductivity type, and at least the outermost layer of the semiconductor thin film is of a conductivity type opposite to the first conductivity type. The semiconductor nanodevice according to appendix 4 , characterized by:
(Appendix 6 )
The semiconductor nanowire core is made of Al _x Ga _1-x As (where x includes 0), the semiconductor thin film is made of a quantum well structure film made of GaAs / InAs, and light emission in the quantum well structure film 6. The semiconductor nanodevice according to appendix 5 , wherein the wavelength is a long wavelength of 1.3 μm or more.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Semiconductor nanowire core 3 Semiconductor thin film 11 n-type GaAs substrate 12 SiO ₂ film 13 Opening 14 Gold fine particle 15 n-type GaAs nanowire 16 GaAs / InAs quantum well structure 17 GaAs barrier layer 18 InAs well layer 19 p-type AlGaAs layer 20 p-type GaAs contact layer 21 n-side electrode 22 SiO ₂ film 23 photoresist 24 resist mask 25 opening 26 p-side electrodes 27 and 28 dielectric multilayer film 29 contact hole

Claims (3)

A substrate,
A semiconductor nanowire core extending on the substrate in a direction perpendicular to a growth surface of the substrate and having a major axis of less than 1 μm;
The semiconductor nanowire core is made of a semiconductor material having a strain ε different by 1% or more from the constituent material of the semiconductor nanowire core, and the thickness t [nm] is flattened of the constituent material of the semiconductor nanowire core. In the case of a substrate, it is a film thickness exceeding the critical film thickness on the flat substrate, and the film thickness t [nm] and the strain ε [%]
−0.720 + 0.0988 (ε / 100) ^−1.2 <t ≦ −0.705 + 0.227 (ε / 100) ^−1.2
And at least one semiconductor thin film satisfying the relationship
A semiconductor nanodevice, wherein a bonding interface between the semiconductor nanowire core and the semiconductor thin film or a bonding interface between the semiconductor thin films is set to either a light emitting region or a light absorbing region .   The semiconductor nanodevice according to claim 1, wherein the semiconductor nanowire core is made of a material different from that of the substrate.   The semiconductor nanodevice according to claim 1, wherein the semiconductor nanowire core and the semiconductor thin film have either a zinc blende crystal structure or a wurtzite crystal structure.

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