JP6390052B2 - Quantum well structure and semiconductor device - Google Patents

Description

  The present invention relates to a quantum well structure and a semiconductor device including the quantum well structure.

The development of optical / electronic devices using quantum wells (QW) is very active, and various studies have been made on quantum well structures.
Patent Document 1 describes an oxide artificial superlattice thin film obtained by epitaxially growing an oxide in atomic layer units on a substrate crystal plane.
Patent Document 2 describes a quantum well structure of a non-doped ZnO layer and a p-type doped ZnTe layer.
Patent Document 3 describes a structure using a zinc oxide or zinc oxide mixed crystal thin film as a quantum well.
Patent Document 4 describes a quantum well structure of GaN and InGaN formed on a β-Ga ₂ O ₃ substrate via an AlN buffer layer.
Patent Document 5 describes a semiconductor laser including a quantum well composed of an InGaAsP well layer and an InGaPSb barrier layer.

  However, when fabricating quantum wells, it is necessary to control the film formation at the atomic layer level, and migration of the deposited atoms is very important, so the substrate temperature has to be increased to a high temperature (> 500 ° C.). . On the other hand, in order to produce QW on general-purpose equipment such as glass, it is necessary to try film formation at a lower temperature. Thus, attempts have been made to lower the production temperature (about 400 ° C.) by using a surfactant such as bismuth (surfactant effect), but this has not been satisfactory.

By the way, a semiconductor device using gallium oxide (Ga ₂ O ₃ ) having a large band gap is attracting attention as a next-generation switching element capable of realizing high breakdown voltage, low loss, and high heat resistance, and a power semiconductor device such as an inverter. Application to is expected. According to Non-Patent Document 1, the gallium oxide can control the band gap by using mixed crystals of indium and aluminum, respectively. In particular, In _{X ′} Al _{Y ′} Ga _Z An InAlGaO-based semiconductor represented by _' O ₃ (0 ≦ X ′ ≦ 2, 0 ≦ Y ′ ≦ 2, 0 ≦ Z ′ ≦ 2, X ′ + Y ′ + Z ′ = 1.5 to 2.5) is extremely It is an attractive material.
However, an InAlGaO-based semiconductor cannot grow a crystal having a corundum structure unless indium oxide or gallium oxide is formed at a low temperature. On the other hand, however, the existence of a trade-off that high temperature growth (> 500 ° C.) is required to promote atomic migration in the fabrication of quantum wells is the reason that InAlGaO-based quantum having a high-potential corundum structure. Since the realization of the well structure was hindered, the production itself was difficult, and the establishment of the production method was awaited.

JP 2000-154100 A JP 2000-332296 A International Publication No. WO2002 / 056392 International Publication No. WO2012 / 137781 JP 2012-212748 A

Kentaro Kaneko, “Growth and Physical Properties of Corundum Structure Gallium Oxide Mixed Crystal Thin Films”, Kyoto University Doctoral Dissertation, March 2013 Sawada, H .: Mater. Res. Bull. 29 (1994) 127 – 133 W.H.Zachariasen, Skr. Nor. Vidensk.-Akad., Kl. 1: Mat.-Naturvidensk. Kl., 4 (1928) 6-166.

  An object of this invention is to provide the quantum well structure which consists of an oxide which has a corundum structure with high potential.

As a result of diligent studies to achieve the above object, the present inventors have used a mist CVD method to produce an oxide having a corundum structure with a low temperature, a wide band gap, and a high potential as a power device or an optical device. It was found that a quantum well structure composed of the above could be produced, and found that the conventional problems described above could be solved at once.
Moreover, after obtaining the said knowledge, the present inventors repeated investigation further, and came to complete this invention.

That is, the present invention relates to the following inventions.
[1] A quantum well structure in which a first layer and a second layer mainly composed of a material different from the first layer are alternately stacked at least one layer,
The main component of the first layer is an oxide having a corundum structure,
A quantum well structure characterized in that the main component of the second layer is a material having a corundum structure.
[2] The quantum well structure according to [1], wherein the oxide is a semiconductor.
[3] The quantum well structure according to [1] or [2], wherein the oxide semiconductor includes one or more metals selected from gallium, iron, indium, and aluminum.
[4] The quantum well structure according to any one of [1] to [3], wherein the material includes gallium, iron, indium, aluminum, vanadium, titanium, chromium, rhodium, nickel, or cobalt.
[5] The quantum well structure according to any one of [1] to [4], wherein each of the first layer and the second layer has a thickness of 20 nm or less.
[6] The quantum well structure according to any one of the above [1] to [5], wherein the first layer and the second layer are laminated at least two layers.
[7] The quantum well structure according to any one of [1] to [6], wherein a crystal is grown using a mist on a base substrate containing a substrate material having a corundum structure as a main component.
[8] A semiconductor device including the quantum well structure according to any one of [1] to [7].
[9] The semiconductor device according to [8], which is a semiconductor laser, a diode, or a transistor.

  ADVANTAGE OF THE INVENTION According to this invention, the quantum well structure which consists of an oxide which has a corundum structure with high potential can be provided.

It is a block diagram of the mist CVD apparatus used in the Example. It is a figure which shows the film-forming time in an Example. It is a figure which shows the measurement result of the scanning transmission electron microscope (STEM) in an Example. It is a figure which shows the measurement result of the energy dispersive X-ray spectrometer and the measurement result of a STEM image in an Example. It is a figure which shows the X-ray-diffraction image in an Example. It is a figure which shows the X-ray-diffraction pattern in an Example. It is a figure which shows the result of the reciprocal lattice mapping of the (0006) plane by the X-ray diffraction in an Example. It is a figure explaining the (0006) plane in FIG. 7 using an atomic structure model. It is a figure which shows the result of the reciprocal lattice mapping of the (10-1, 10) plane by the X-ray diffraction in an Example. It is a figure explaining the (10-1, 10) plane in FIG. 9 using an atomic structure model. It is a figure which shows the result of the reciprocal lattice mapping of (11-2,9) plane by the X-ray diffraction in an Example. It is a figure explaining the (11-2, 9) plane in FIG. 11 using an atomic structure model. A comparison of the satellite peaks of FIGS. 7, 9 and 11 is shown.

  The quantum well structure of the present invention is a quantum well structure in which a first layer and a second layer mainly composed of a material different from that of the first layer are alternately stacked one by one. The main component of the first layer is an oxide having a corundum structure, and the main component of the second layer is a material having a corundum structure.

(First layer)
The first layer may be a semiconductor or an insulator, but is preferably a layer containing a semiconductor as a main component, and preferably contains an oxide semiconductor having a corundum structure as a main component. More preferred. Note that the “main component” means that the oxide semiconductor having the corundum structure has an atomic ratio of preferably 50% or more, more preferably 70% or more, and still more preferably with respect to all components of the first layer. It means that 90% or more is included, and that it may be 100%.

The oxide semiconductor is not particularly limited as long as it has a corundum structure. In the present invention, the oxide semiconductor preferably contains one or more metals selected from gallium, iron, indium, and aluminum. More preferably, iron is included.
In the present invention, the oxide semiconductor may be α-type In _X Al _Y Ga _Z O ₃ (0 ≦ X ≦ 2, 0 ≦ Y ≦ 2, 0 ≦ Z ≦ 2, X + Y + Z = 1.5 to 2. 5 and 0 <X or 0 <Z.). A preferable composition in the case where the oxide semiconductor is α-type In _X Al _Y Ga _Z O ₃ is not particularly limited as long as the object of the present invention is not impaired, but gallium in the metal element contained in the crystalline semiconductor film The total atomic ratio of indium and aluminum is preferably 0.5 or more, and more preferably 0.8 or more. In addition, a preferable composition in the case where the oxide semiconductor includes gallium is such that the atomic ratio of gallium in the metal element included in the crystalline semiconductor film is preferably 0.5 or more, and is 0.8 or more. Is more preferable.

(Second layer)
The second layer is a layer mainly composed of a material different from that of the first layer, and is not particularly limited as long as it contains a material having a corundum structure as a main component. Here, the “material different from the first layer” means that it has a composition or composition ratio different from that of the first layer, and is composed of the same component as the first main component. However, if the composition ratio is different, it is included in a material different from that of the first layer. The “main component” means that the material having the corundum structure is preferably 50% or more, more preferably 70% or more, and still more preferably 90%, in terms of atomic ratio, with respect to all components of the second layer. This means that it is included, and it may be 100%.

The material having a corundum structure in the second layer is not particularly limited as long as it has a corundum structure, and includes, for example, gallium, iron, indium, aluminum, vanadium, titanium, chromium, rhodium, nickel, or cobalt. Examples thereof include compounds having a corundum structure. In the present invention, the material is preferably an oxide containing gallium, iron, indium, aluminum, vanadium, titanium, chromium, rhodium, nickel or cobalt, more preferably a semiconductor oxide, gallium, Most preferred is one or more semiconductor oxides selected from iron, indium and aluminum. More specifically, examples of the oxide include α-Ga ₂ O ₃ , α-Fe ₂ O ₃ , α-In ₂ O ₃ , α-Al ₂ O ₃ , α-V ₂ O ₃ , Examples include α-Ti ₂ O ₃ , α-Cr ₂ O ₃ , α-Rh ₂ O ₃ , α-Ni ₂ O ₃ , α-Co ₂ O _{3 and the} like.

The first layer or the second layer may contain a dopant. The dopant is not particularly limited as long as the object of the present invention is not impaired. Examples of the dopant include n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium or niobium, or p-type dopants. The concentration of the dopant may usually be about 1 × 10 ¹⁶ / cm ³ to 1 × 10 ²² / cm ³ , and the concentration of the dopant is set to a low concentration of about 1 × 10 ¹⁷ / cm ³ or less, for example. May be. Furthermore, according to the present invention, the dopant may be contained at a high concentration of about 1 × 10 ²⁰ / cm ³ or more.
The first layer and the second layer can be suitably used as an undoped, n-type or p-type active layer.

The quantum well structure of the present invention is not particularly limited as long as the first layer and the second layer whose main component is a material different from the first layer are alternately stacked one by one. In the present invention, the first layer and the second layer are preferably laminated at least 2 layers, more preferably 3 layers, and most preferably 5 layers. preferable.
In addition, the quantum well structure is usually provided by laminating at least one first layer and second layer on a substrate. In the present invention, a crystal is formed on the substrate using mist. It is preferably grown.

(Substrate)
The substrate is not particularly limited as long as it can support a quantum well structure. The material of the substrate is not particularly limited as long as the object of the present invention is not impaired, and may be a known substrate, an organic compound, or an inorganic compound. Examples of the shape of the substrate include plate shapes such as flat plates and disks, fiber shapes, rod shapes, columnar shapes, prismatic shapes, cylindrical shapes, spiral shapes, spherical shapes, ring shapes, and the like. A substrate is preferred. Although the thickness of a board | substrate is not specifically limited in this invention, Preferably, it is 10-2000 micrometers, More preferably, it is 50-800 micrometers.

  The substrate is not particularly limited as long as it has a plate shape and serves as a support for a quantum well structure. The substrate may be an insulator substrate, a semiconductor substrate, or a conductive substrate, but the substrate is preferably an insulator substrate, and has a metal film on the surface. A substrate is also preferred. Examples of the substrate include a base substrate containing a substrate material having a corundum structure as a main component, a base substrate containing a substrate material having a β-gallia structure as a main component, and a substrate material having a hexagonal crystal structure as a main component. Examples thereof include a base substrate. Here, the “main component” means that the substrate material having the specific crystal structure is preferably 50% or more, more preferably 70% or more, and still more preferably 90% by atomic ratio with respect to all components of the substrate material. % Or more, meaning that it may be 100%.

The substrate material is not particularly limited as long as the object of the present invention is not impaired, and may be a known material. Examples of the substrate material having the corundum structure include the same materials as those exemplified as the material having the corundum structure. In the present invention, α-Al ₂ O ₃ or α-Ga ₂ O is used. ₃ is preferred. As a base substrate mainly composed of a substrate material having a corundum structure, a sapphire substrate (preferably a c-plane sapphire substrate), an α-type gallium oxide substrate, or the like is given as a suitable example. As a base substrate mainly composed of a substrate material having a β-gallia structure, for example, a β-Ga ₂ O ₃ substrate, or a Ga ₂ O ₃ and Al ₂ O ₃ containing Al ₂ O ₃ content of more than 0 wt% Examples thereof include a mixed crystal substrate of 60 wt% or less. In addition, examples of the base substrate whose main component is a substrate material having a hexagonal crystal structure include a SiC substrate, a ZnO substrate, and a GaN substrate. Note that each layer may be stacked directly or via another layer (for example, a buffer layer) on a base substrate whose main component is a substrate material having a hexagonal crystal structure.
In the present invention, the substrate is preferably a base substrate having a corundum structure on part or all of the surface, and a sapphire substrate or α-type that may have a metal film or the like on part or all of the surface. It is more preferably a gallium oxide substrate, and most preferably a c-plane sapphire substrate which may have a metal film or the like on part or all of its surface. In the present invention, it is preferable that half or more of the surface of the base substrate has a corundum structure.

(Lamination method)
The first layer or the second layer is laminated by a mist CVD method, that is, atomizing a raw material solution (atomization step), supplying the generated mist to the substrate with a carrier gas (mist supply step), It is preferable to carry out the film formation on the substrate by a reaction (film formation process).

In the atomization step, the raw material solution is adjusted, and the raw material solution is atomized to generate mist. The raw material solution can be prepared by dissolving or dispersing the metal in the form of a complex or salt in an organic solvent or water.
The blending ratio of the metal is not particularly limited, but is preferably 0.01 to 70% by mass, and more preferably 0.1 to 50% by mass with respect to the entire raw material solution.

  In this step, the raw material solution is atomized to generate mist. The atomizing means is not particularly limited as long as it can atomize the raw material solution, and may be a known atomizing means, but in the present invention, it is preferably an atomizing means using ultrasonic waves.

  In the carrier gas supply step, a carrier gas is supplied to the mist. The type of the carrier gas is not particularly limited as long as the object of the present invention is not impaired. For example, an inert gas such as oxygen, ozone, nitrogen or argon, or a reducing gas such as hydrogen gas or forming gas is preferable. As mentioned. Further, the type of carrier gas may be one type, but may be two or more types, and a diluent gas (for example, a 10-fold diluted gas) whose carrier gas concentration is changed is used as the second carrier gas. Further, it may be used. Further, the supply location of the carrier gas is not limited to one location but may be two or more locations.

  In the mist supply step, the mist is supplied to the substrate by the carrier gas. The flow rate of the carrier gas is not particularly limited, but is preferably 0.01 to 20 L / min, and more preferably 1 to 10 L / min.

  In the film forming step, the mist is reacted by heat to form a film on part or all of the substrate surface. The thermal reaction may be performed as long as the mist reacts with heat, and the reaction conditions are not particularly limited as long as the object of the present invention is not impaired. In this step, the thermal reaction is preferably performed at a temperature of 600 ° C. or lower, more preferably 500 ° C. or lower. Further, the thermal reaction may be performed under any atmosphere of vacuum, non-oxygen atmosphere, reducing gas atmosphere and oxygen atmosphere as long as the object of the present invention is not impaired. The reaction may be performed under any of the following conditions: under pressure, under pressure, and under reduced pressure, but in the present invention, it is preferably performed under normal pressure or atmospheric pressure. The film thickness can be set by adjusting the film formation time. In the present invention, the thicknesses of the first layer and the second layer in the quantum well are each preferably 200 nm or less, more preferably 100 nm or less, and most preferably 20 nm or less.

  In the present invention, the first layer and the second layer may be laminated directly on the substrate, or may be laminated on the substrate via another layer such as a buffer layer. Other layers, such as the said buffer layer, are not specifically limited unless the objective of this invention is inhibited, You may be a well-known layer.

  Since the quantum well structure of the present invention includes an oxide semiconductor having a corundum structure, the quantum well structure is useful for a semiconductor device. When the quantum well structure is used in a semiconductor device, the quantum well structure may be used as it is in a semiconductor device, or may be used after post-processing the quantum well structure.

  In the present invention, when an insulator substrate such as a sapphire substrate is used as the substrate, for example, after bonding other layers such as a p-type semiconductor layer, the quantum well structure is peeled from the substrate to form a semiconductor device. It is preferable to use it. The peeling means is not particularly limited as long as the object of the present invention is not impaired, and may be a known means. Examples of the peeling means include a means for peeling by applying a mechanical impact, a means for peeling by applying heat and applying thermal stress, a means for peeling by applying vibration such as ultrasonic waves, a means for peeling by etching, etc. Is mentioned.

  The p-type semiconductor layer is not particularly limited as long as it does not hinder the object of the present invention, but is preferably a p-type semiconductor layer containing a metal oxide having a hexagonal crystal structure as a main component. Preferred examples of the metal oxide include Delafossite, rhodium oxide, and oxychalcogenide.

  The semiconductor device can be classified into a horizontal element (horizontal device) in which electrodes are formed on one side of a semiconductor layer and a vertical element (vertical device) having electrodes on both sides of the semiconductor layer. However, the quantum well structure of the present invention can be suitably used for both horizontal and vertical devices.

  Examples of the semiconductor device include a semiconductor laser, a diode, or a transistor, and more specifically, a distributed feedback (DFB) laser, a distributed reflection (DBR) laser, an external resonator laser, and a Schottky barrier. Diode (SBD), metal semiconductor field effect transistor (MESFET), high electron mobility transistor (HEMT), metal oxide semiconductor field effect transistor (MOSFET), electrostatic induction transistor (SIT), junction field effect transistor (JFET), Examples thereof include an insulated gate bipolar transistor (IGBT) or a light emitting diode.

  Needless to say, the semiconductor device may include other layers (for example, an insulator layer, a semi-insulator layer, a conductor layer, a semiconductor layer, a buffer layer, or other intermediate layers). Good.

  The mist CVD apparatus used in this example will be described with reference to FIG. The mist CVD apparatus of FIG. 1 includes a supply unit 10 and a reaction unit 11 having a fine channel structure. The supply unit 10 includes a carrier gas supplied from the ultrasonic vibrator 1, the container 2, and a carrier gas supply unit. 3 is provided, and a flow rate adjusting valve 4a for adjusting the flow rate of the dilution gas 4 supplied from the dilution gas supply means is provided. The reaction unit 11 includes a flow rate adjusting valve 5a for adjusting the flow rate of ozone 5 supplied from the ozone supply means, a mist mixing unit 6 for mixing mist supplied from the supply unit 10, a heater 7 and a substrate 8. It has been.

  The raw material solution 9 a is atomized by using the ultrasonic vibrator 1 to be a mist 9 b, and the mist 9 b is sent to the reaction unit 11 by the carrier gas 3. Dilution gas is supplied to the mist 9b on the way to the reaction section 11, and ozone 5 is further supplied to the mist mixing section 6. In the mist mixing unit 6, the mist 9b is mixed, and the mixed mist 9b is sent out to the reaction space having a height of 1 mm. A substrate 8 is provided in the reaction space, and the heater 7 causes the mist 9b to undergo a thermal reaction so that the Leidenfrost effect is developed and a film can be formed on the substrate 8.

Using the CVD apparatus, α-Ga ₂ O ₃ films and α-Fe ₂ O ₃ films were alternately stacked on the substrate to produce a quantum well structure. The film forming conditions are shown in Table 1 and FIG.

  The obtained quantum well structure was measured using a scanning transmission electron microscope (STEM). The measurement results are shown in FIG. FIG. 3 shows that a quantum well structure is formed on the substrate. In addition, using an energy dispersive X-ray spectrometer, the Fe source and Ga source of the produced quantum well structure were measured and compared with STEM images. The results are shown in FIG. It can be seen from FIG. 4 that the quantum well is formed by alternating layers including Fe and Ga.

About the obtained quantum well structure, each phase was identified using the X-ray-diffraction apparatus. The measurement was performed by performing 2θ / ω scan using CuKα rays. An X-ray diffraction image is shown in FIG. 5, and an X-ray diffraction pattern is shown in FIG. From the X-ray diffraction image of FIG. 5, it can be seen that a lattice image is seen and a quantum well structure is formed. Further, from FIG. 6, _α-Fe 2 _{O 3} phase and _α-Ga 2 _{O 3} phase can be confirmed, on c-plane sapphire _(α-Al 2 _{O 3)} substrate, _α-Fe 2 _{O 3} It can be seen that the quantum well structure of / α-Ga ₂ O ₃ is well formed.

FIG. 7 shows the result of reciprocal lattice mapping of the (0006) plane by X-ray diffraction. For reference, FIG. 8 shows the (0006) plane in FIG. 7 using an atomic structure model. Relates reciprocal lattice mapping of Fig. 7, derive an assumed value of (0006) plane of the axis q _Z from the non-Patent Document 2 and Non-Patent Document 3, as shown in Table 2, were compared with measured values. As a result, it can be seen that Al ₂ O ₃ and Ga ₂ O ₃ match the assumed values and the actual measurement values and are not subjected to compressive stress. On the other hand, it can be seen that Fe ₂ O ₃ has no peak and receives compressive stress from Ga ₂ O ₃ .

FIG. 9 shows the result of reciprocal lattice mapping of the (10-1, 10) plane by X-ray diffraction, and FIG. 11 shows the result of reciprocal lattice mapping of the (11-2, 9) plane. For reference, FIG. 10 shows the (10-1, 10) plane in FIG. 9 and FIG. 12 shows the (11-2, 9) plane in FIG. 11 using an atomic structure model. From these results, the normal direction of the (10-10) plane is taken as the x-axis, and measurement is performed on the x-direction plane and the y-direction plane. Since qz is horizontal in the z-direction, the interface is found to be parallel _for, it can be seen that the quantum well of _{Ga 2 O 3 / Fe 2 O} 3 is parallel to the _Al 2 _{O 3.}

FIG. 13 shows a comparison diagram of the satellite peaks of FIGS. 7, 9 and 11. From the satellite peak, it can be seen that the quantum well structure of Ga ₂ O ₃ / Fe ₂ O ₃ is well formed.
The distance between the quantum well was measured using an X-ray diffractometer _(length per unit of the repeating units of the _{Ga 2 O 3 / Fe 2 O} 3) was about 20.5 nm.

  The quantum well structure of the present invention can be used in various fields such as semiconductors (for example, compound semiconductor electronic devices), electronic parts / electric equipment parts, optical / electrophotographic related apparatuses, industrial members, etc., but particularly useful in the semiconductor field. It is.

DESCRIPTION OF SYMBOLS 1 Ultrasonic vibrator 2 Container 3 Carrier gas 3a Flow control valve 4 Dilution gas 4a Flow control valve 5 Ozone 5a Flow control valve 6 Mist mixing part 7 Heater 8 Substrate 9a Raw material solution 9b Mist 10 Supply part 11 Reaction part

Claims (7)

The quantum well structure in which the first layer and the second layer mainly composed of a material different from the first layer are alternately stacked at least one layer,
The main component of the first layer is an oxide having a corundum structure,
The main component of the second layer, and have a corundum structure, and, gallium, iron, indium, aluminum, vanadium, quantum well, which is a material comprising titanium, chromium, rhodium, nickel or cobalt Construction. The quantum well structure according to claim 1, wherein the oxide contains one or more metals selected from gallium, iron, indium, and aluminum . The quantum well structure according to claim 1 or 2 , wherein the thicknesses of the first layer and the second layer are each 20 nm or less. Quantum well structure according to the first and the layers and the second layer, any one of claims 1-3 which are laminated one by at least two layers. The quantum well structure according to any one of claims 1 to 4 , wherein a crystal is grown using a mist on a base substrate having a corundum structure on a part or all of a surface thereof. A semiconductor device comprising a quantum well structure according to any one of claims 1-5. The semiconductor device according to claim 6, which is a semiconductor laser, a diode, or a transistor.