JP2007305975A - Semiconductor device containing group iii oxide semiconductor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To find out a group III oxide semiconductor having a hexagonal structure capable of forbidden band width control; and to provide a semiconductor device, a photoelectric conversion device, an ultraviolet ray detection device, an oxide light-emitting device, and a light-emitting device that contain the group III oxide semiconductor. <P>SOLUTION: The semiconductor device contains group III oxide having a composition expressed by formula: A<SB>2</SB>O<SB>3</SB>, wherein A includes a mixed crystal semiconductor thin film made by solving at least two elements selected from In, Ga, Al, and B with thin-film technique. A solid solubility thin film is obtained having a composition beyond thermodynamic solid solubility limit area in a bulk, and a mixed crystal thin film is also obtained having a thermodynamically unstable hexagonal structure. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a group III oxide semiconductor constituent material and a semiconductor element for producing a semiconductor element including a photoelectric conversion element, an ultraviolet ray detection element, a light emitting diode, a semiconductor laser, a field effect transistor and the like.

2. Description of the Related Art Conventionally, semiconductor crystal growth and device manufacturing technology having a large forbidden band have been rapidly developed for the purpose of manufacturing semiconductor devices with high added value. Of these Group III nitride semiconductor _{(In 1-x-y-} z Ga x Al y B z N) visible with - ultraviolet region light emitting element, a power transistor, and high mobility devices already in practical use. On the other hand, as shown in Patent Document 1 and Patent Document 2, for example, blue light-emitting elements and transparent transistors using Group II oxide semiconductors (Zn _1-xy Mg _x Cd _y O) have been rapidly researched and developed in recent years. It is in the limelight.
A major feature of these semiconductors is that they have a hexagonal crystal structure unlike the cubic structure of Si, C, GaAs, and InP-based materials. Although heteroepitaxial bonding is essential for the manufacture of semiconductor elements, materials that can be epitaxially bonded to these hexagonal semiconductors are Al ₂ O as shown in Patent Documents 3 and 4 as insulators. ₃ , LiGaO ₂ , ScMgAlO ₄ , LiGaO ₂ , LiAlO ₂ , NaGaO ₂ , NaAlO ₂ , KGaO ₂ , KAlO _{2 and the} like semiconductors include In _1-xyz Ga _x Al _y B _z N, Zn _{1− x-y Mg x Cd y O} , is like 6H-SiC, is rapidly research have been made in recent years.
On the other hand, the group III oxide is considered to have an ionicity between the group III nitride and the group II oxide. Therefore, since the bond ionicity is higher than that of group III nitride, the deterioration of electron and hole transport properties due to structural disorder is small, and the bond ionicity is lower than that of group II oxide. It is expected to be a new semiconductor material that is less difficult to control and compensates for the disadvantages of Group III nitrides and Group II oxides.
Representative group III oxides in practical use to date include In ₂ O ₃ : Sn (ITO) degenerated by addition of Sn, and transparent for flat panel displays, photoelectric conversion elements, and blue light emitting diodes. Although it is widely used as an electrode or the like, there is currently no semiconductor element using a group III oxide as a wide gap semiconductor other than a transparent electrode.

JP 2004-207441 A JP 2000-150900 A JP 2003-81692 A JP 2000-277534 A Swanson et al. Natl. Bur. Stand. (US), Circ. 539, 5 (1955), 26. (JCPDS: 06-0416) Welton-Holzer, J.A. McCarthy, G .; , North Dakota State University, Fargo, North Dakota, USA. , ICDD Grant-in-Aid, (1989) (JCPDS: 41-1103) Welton-Holzer, J.A. McCarthy, G .; , North Dakota State University, Fargo, North Dakota, USA. , ICDD Grant-in-Aid, (1989) (JCPDS: 42-1468) Shannon, Prewitt. , J .; Inorg. Nucl. Chem. , 30, 1389, (1968) (JCPDS: 21-0333) D. D. Edwards, P.M. E. Folkins, T .; O. Maso, J .; Am. Ceram. Soc. 80 (1997) 253. G. Patzke and M.M. Binnewies, Sol. State Sci. 2 (2000) 689. R. J. et al. Cava, J .; M.M. Phillips, J. et al. Kwo, G .; A. Thomas, R.A. B. van Dover, S.M. A. Carter, J.A. J. et al. Krajewski, W.M. F. Peck, Jr. , J .; H. Marshall, and D.M. H. Rapkin, Appl. Phys. Lett. 64 (1994) 2071. T. T. et al. Minami, S .; Takata, and T.K. Kakumu, J. et al. Vac. Sci. Technol. A 14 (1996) 1689.

However, the use of the group III oxide described above as a semiconductor device has the following problems.
(1) In ₂ O ₃ , Ga ₂ O ₃ , and Al ₂ O ₃ as group III oxides have bixbite structures (cubic crystals) as shown in Non-Patent Document 1, Non-Patent Document 2, and Non-Patent Document 3, respectively. ), Β-Ga ₂ O ₃ structure (monoclinic crystal) and corundum structure (hexagonal crystal), respectively. Therefore, the In _2-2x-2y Ga _2x Al _2y O ₃ group III oxide is not a completely solid solution material, and the mixed crystal region is very limited. For example, FIG. 1 shows thermodynamic stability phase diagrams of In ₂ O ₃ and Ga ₂ O ₃ shown in Non-Patent Document 1 and Non-Patent Document 2. The crystal structures are cubic and monoclinic, respectively, but the respective solid solution limits are about 5% or less and about 57% or more of Ga ₂ O ₃ molar fraction at 1000 ° C., more than about 5% and about 57%. Below, it has been reported that cubic and monoclinic phase separation occurs.
(2) A group III oxide is a cubic structure of a group IV semiconductor (C, Si, Ge, SiC, etc.) and a group III-V semiconductor (GaP, GaAs, InP, etc.) currently used as semiconductor elements, III nitride semiconductor _{(in 1-x-y-} z Ga x Al y B z N) and group II oxide semiconductor _{(Zn 1-x-y Mg} x Cd y O) hexagonal structure of the crystal structure or lattice constant Are very different. Therefore, a Group III oxide epitaxial thin film and an epitaxially grown semiconductor device can be fabricated on the substrate used in the Group IV, III-V, Group III nitride, and Group II oxide semiconductor thin film devices. There wasn't. For the same reason, a semiconductor element heteroepitaxially bonded to the group IV, group III-V, group III nitride, or group II oxide semiconductor thin film could not be fabricated.
(3) The forbidden band widths of In ₂ O ₃ , Ga ₂ O ₃ , and Al ₂ O ₃ are 3.6 eV, 4.8 eV, and about 9 eV, respectively, ranging from the ultraviolet region to the extreme ultraviolet region. As described above, since the mixed crystal region is very limited, a group III oxide mixed crystal semiconductor from the viewpoint of controlling the forbidden band width and a semiconductor device having a heterojunction using the same have not been available. In addition, it is difficult to manufacture a heterojunction device having a large forbidden band width using a group III nitride or group II oxide mixed crystal having a hexagonal crystal structure. Specifically, for example, AlN (forbidden band width: 6.2 eV) has a much larger forbidden band width than GaN (forbidden band width: 3.4 eV), but the crystallinity deteriorates as the AlN molar fraction increases. It becomes. Further, in Zn _1-x Mg _x O, the solid solubility limit is about 33% MgO molar fraction (forbidden band width: 3.9 eV), and above that, the cubic structure and the hexagonal structure have different crystal structures. Phase separation occurs. Therefore, when a semiconductor element using these semiconductors is manufactured, a problem that it is difficult to manufacture a semiconductor layer having a large forbidden band becomes an obstacle to realizing the element.
Here, the semiconductor element generally includes a light receiving element, a light emitting element, and an electronic element having a semiconductor function.
In view of the above problems, the present invention provides a group III oxide semiconductor capable of forbidden band width control or a group III oxide semiconductor having a crystal structure capable of epitaxial growth with the above group III nitride semiconductor or group II oxide semiconductor. It is to provide a semiconductor element including a semiconductor element including a group III oxide semiconductor, a photoelectric conversion element, an ultraviolet ray detection element, a light emitting element, and a field effect transistor using the same.

In order to solve the above problems, the present invention
1. The semiconductor element includes a group III oxide semiconductor having a configuration of A ₂ O ₃ when A represents an arbitrary element symbol and an element of A including at least two of In, Ga, aluminum Al, and boron B. It is assumed that the effect of modulating the forbidden band width of the semiconductor thin film by changing the composition ratio of at least two elements of In, Ga, aluminum Al, and boron B is used.
2. A semiconductor element containing a group III oxide has a group III oxide thin film having a thermodynamically metastable hexagonal crystal structure or a distorted hexagonal crystal structure. Thin film production that is a non-equilibrium process such as pulsed laser deposition, sputtering, vacuum deposition, molecular beam epitaxy, metal organic chemical vapor deposition, etc. to stably form thermodynamically metastable structures in a wide composition range It is preferable to form a group III oxide thin film on a substrate or thin film having a metastable structure and a small in-plane lattice mismatch ratio using the method.
3. Using a group III oxide semiconductor thin film that can control the forbidden band width by changing the composition ratio of at least two elements of In, Ga, aluminum Al, and boron B as a window layer of a chalcopyrite solar cell, Constitute.
4). A photodetecting element is constructed using a group III oxide having photosensitivity to light in the ultraviolet region as a photodetecting material. The photodetecting element here includes a pair of electrodes and a photodetecting material layer sandwiched between the electrodes, and an element using the group III oxide thin film for the photodetecting material layer, the pair of electrodes and the electrode This is an element having a p-type and n-type semiconductor layer sandwiched between two layers and using the group III oxide thin film as at least one semiconductor layer.
5). A light-emitting element is formed using a group III oxide semiconductor thin film that can control the forbidden band width by changing the composition ratio of at least two elements of In, Ga, aluminum Al, and boron B as a cladding layer of the light-emitting element. Here, the light emitting element is an element that includes at least an n-type cladding layer, an active layer, and a p-type cladding layer on a substrate, and uses a group III oxide semiconductor thin film as a cladding layer having a larger forbidden band width than the active layer. . The active layer herein includes a group III nitride semiconductor or a group II oxide semiconductor thin film, but is not limited thereto.
6). A group III oxide semiconductor is used as the active layer of the field effect transistor.
7). Semiconductor device using a hexagonal group III oxide thin film that can control the forbidden band width and lattice constant by changing the composition ratio of at least two elements of In, Ga, aluminum Al, and boron B as an active layer or a barrier layer Configure. The semiconductor element here is characterized by controlling the flow of a two-dimensional electron gas or a two-dimensional hole gas generated at the interface between a semiconductor thin film used as an active layer and an insulator used as a barrier layer or a semiconductor thin film, or an active layer or A hexagonal group III oxide thin film is used for at least one of the barrier layers, and the forbidden band width between the active layer and the barrier layer is changed by changing the composition ratio of at least two elements of In, Ga, aluminum Al, and boron B. The amount of offset and the amount of distortion in the thin film can be strictly controlled.

Specifically, it is as follows.
(1) The semiconductor element has a configuration of A ₂ O _{3 where} A is an arbitrary element symbol, and a group III oxide in which the element of A is at least two of In, Ga, aluminum Al, and boron B A group III oxide semiconductor thin film including a semiconductor and having a forbidden band width modulated by changing a composition amount of at least two elements selected from In, Ga, aluminum Al, and boron B To do.
(2) The semiconductor element described in the above (1) is characterized by having a group III oxide semiconductor having a hexagonal crystal structure or a hexagonal crystal structure.
(3) The photoelectric conversion element includes a first electrode layer, a p-type semiconductor layer, a window layer, and a second electrode layer in order from the substrate side, and generates photovoltaic power by light incident from the second electrode layer side. A photoelectric conversion element to be generated, wherein the window layer has the group III oxide semiconductor thin film according to any one of (1) and (2).
(4) In the photoelectric conversion element according to (3), the p-type semiconductor layer can be selected from at least one element selected from Cu and Ag, at least one element selected from In and Ga, and Se and S. A photoelectric conversion element comprising a p-type compound semiconductor containing at least one element or CdTe.
(5) The ultraviolet detection element is a light detection element having a pair of electrodes and a light detection material layer sandwiched between the electrodes, and the light detection layer is either of the above (1) or (2) A group III oxide semiconductor thin film according to item 1 is used.
(6) The ultraviolet detection element is an ultraviolet detection element having at least p-type and n-type semiconductor layers on a substrate, wherein at least one semiconductor layer of the semiconductor layer is any one of the above (1) and (2). The group III oxide semiconductor thin film according to claim 1 is used.
(7) The ultraviolet detection element according to (6) above may be selected from the group III oxide semiconductor thin film according to any one of (1) or (2) above, In, Ga, aluminum Al, and boron B as the semiconductor layer. An ultraviolet detection element comprising a group III nitride semiconductor containing at least one element and N or a group II oxide semiconductor containing at least one element selected from Zn, Mg, and Cd and O.
(8) The light emitting device is a light emitting device including at least an n-type clad layer, an active layer, and a p-type clad layer on a substrate, and the clad layer having a larger forbidden band width than the active layer is the above (1) or ( A light-emitting device comprising the group III oxide semiconductor thin film according to any one of 2).
(9) In the light emitting device according to (8), the active layer may be selected from a group III nitride semiconductor containing at least one element selected from In, Ga, aluminum Al, and boron B and N, or Zn, Mg, and Cd. A light-emitting element comprising any one of Group II oxide semiconductors containing at least one element and O.
(10) A thin film field effect transistor characterized in that the active layer of the thin film field effect transistor is the group III oxide semiconductor thin film according to any one of (1) and (2).
(11) A semiconductor element is a semiconductor element that includes at least an active layer and a barrier layer on a substrate and controls the flow of a two-dimensional electron gas or two-dimensional hole gas generated at the interface between the active layer and the barrier layer. A semiconductor element comprising the group III oxide semiconductor thin film according to any one of the above (1) and (2) in at least one of the above.
(12) The semiconductor device according to (11), wherein the group III nitride semiconductor or group II oxide semiconductor thin film is used for at least one of an active layer and a barrier layer.

Group III oxide semiconductor _{(In 2-2x-2y-2z Ga} 2x Al 2y B 2z O 3) thin film of the present invention, changes In, Ga, aluminum Al, a composition of at least two elements selected from boron B In addition to being a semiconductor with a large forbidden band width that can control the lattice constant and the forbidden band width, the lattice constant is extremely small relative to the in-plane lattice constant of the zinc oxide group II oxide semiconductor and group III nitride semiconductor. A hexagonal structure oxide thin film crystal having a small matching rate can be obtained.
The group III oxide semiconductor of the present invention is used as a window layer of a chalcopyrite solar cell, and by changing the composition amount, the conduction band offset with the chalcopyrite structure compound used in the light absorption layer can be adjusted. An efficient chalcopyrite thin film solar cell can be obtained.
In addition, when heteroepitaxial growth is performed with a zinc oxide group II oxide semiconductor or group III nitride semiconductor, the change in the composition amount causes the piezoelectric polarization field or the spontaneous polarization field, which is characteristic of these wurtzite crystals, at the interface. Therefore, the light emitting element or the high mobility electronic element with high internal quantum efficiency can be obtained.
In addition, by intentionally adding impurities such as Sn, Ge, and Si to the group III oxide semiconductor of the present invention, a function as an ultraviolet transparent conductive film can be easily provided. Therefore, visible using a group III nitride semiconductor _{(In 1-x-y-} z Ga x Al y B z N) or group II oxide semiconductor of _{(Zn 1-x-y Mg} x Cd y O) as the active layer -In the ultraviolet light emitting device, a light emitting device having excellent light extraction efficiency can be obtained by using an n-side ohmic electrode or a p-side ohmic electrode as a transparent electrode.

  Embodiments of the present invention will be specifically described below with reference to the drawings.

As an example of the group III oxide semiconductor material of the present invention, an embodiment in which a thin film made of In _2-2x Ga _2x O ₃ (0 ≦ x ≦ 0.5) is manufactured by a pulse laser deposition method will be described. The laser was a KrF excimer laser (wavelength: 248 nm), and In _2-2x Ga _2x O ₃ (x = 0, 0.10, 0.23, 0.32, 0.40, 0.50) firing as a raw material target. A ligation target was used. As the substrate, (111) YSZ (yttria stabilized zirconia) was used, and the substrate temperature was 650 ° C. and the oxygen partial pressure was 30 mTorr. The Ga ₂ O ₃ molar fraction of the thin film was determined using an x-ray microanalyzer, the presence or absence of a heterogeneous phase, the determination of solid solution / non-solid solution, and the crystal structure / lattice constant were determined using an x-ray diffraction method.

FIG. 2 shows an x-ray diffraction pattern of an In _2-2x Ga _2x O ₃ thin film provided on a YSZ substrate according to an embodiment of the present invention (horizontal axis: 2θ (diffraction angle) (°: degree), vertical axis: XRD ( x-ray diffraction) natural logarithm of intensity (LOG XRD intensity), molar fraction (x) of 0, 0.10, 0.23, 0.32, 0.40, 0.50)), FIG. Φ scan measurement pattern of YSZ substrate, In ₂ O ₃ thin film, InGaO ₃ thin film {220}, {440}, {10-11} diffraction plane (horizontal axis: φ (°: degree), vertical axis: XRD intensity Natural logarithm (LOG XRD intensity), FIG. 4 and FIG. 5 show the axial length d (Å) of the thin film obtained from FIG. 2 and the full width at half maximum Δω (°: degree) of the rocking curve (crystal mosaicness) The lower the value, the less the mosaicness ).
4 (a) is a vertical axis cubic structure _In 2-2x _Ga 2x _{O 3} thin film (222) spacing (d (222) (Å)) and hexagonal structure _In 2-2x _Ga 2x _{O 3} thin film (0004) Interplanar spacing (d (0004) (Å)), the horizontal axis represents Ga ₂ O ₃ molar fraction (x). In FIG. 4B, the vertical axis indicates the rocking curve half-value width (Δω (222) (°: degree)) of the (222) plane of the cubic crystal structure In _2-2x Ga _2x O ₃ thin film and the hexagonal crystal structure In _2-2x. The rocking curve half-value width (Δω (0004) (°: degree)) of the (0004) plane of the Ga _2x O ₃ thin film, and the horizontal axis represents the Ga ₂ O ₃ molar fraction (x). 5 _{In 2-2x Ga 2x O 3 Ga 2} O 3 molar ratio of the thin film (x), cubic structure _In 2-2x _Ga 2x _{O 3} thin film (222) spacing (d (222) (Å) ), (0004) spacing of hexagonal structure In _2-2x Ga _2x O ₃ thin film (d (0004) (Å)), rocking curve of (222) plane of cubic structure In _2-2x Ga _2x O ₃ thin film The half width (Δω (222) (°: degree)), the value of the rocking curve half width (Δω (0004) (°: degree)) of the (0004) plane of the hexagonal structure In _2-2x Ga _2x O ₃ thin film It is a table | surface which shows.
The Ga ₂ O ₃ molar ratio 0% or more and less than 23%, due to a cubic structure as illustrated in FIG. 2 (lll) (l = 2,4 ) only diffraction peaks were observed, an In ₂ of FIG. 3 As can be seen in the φ-scan measurement pattern of the {440} diffraction plane of the O ₃ thin film, the in-plane symmetry is three-fold similar to the YSZ substrate, and it has a (111) -oriented cubic structure in the inter-plane direction. I understand. In the In _2-2x Ga _2x O ₃ thin film (x = 0.1), it was confirmed by the φ scan measurement that the in-plane was a cubic structure with three-fold symmetry and (111) orientation in the inter-plane direction. In addition, as shown in FIGS. 4 and 5, the axial length d (222) decreased and the mosaicness increased as the molar fraction increased. On the other hand, only a (000 l) (l = 2, 4, 6, 8, 10.12) diffraction peak due to the hexagonal crystal structure is observed from FIG. 2 when the Ga ₂ O ₃ molar fraction is greater than 23% and less than 50%. As shown in the φ scan measurement pattern of the {10-11} diffraction plane of the InGaO ₃ thin film in FIG. 3, the in-plane is 6-fold symmetric and has a (0001) -oriented hexagonal crystal structure or strain. It can be seen that this is a hexagonal crystal structure. Here, the indexing of the crystal plane of the InGaO ₃ thin film was based on Non-Patent Document 4. In the In _2-2x Ga _2x O ₃ thin film (x = 0.32, 0.40), the in-plane symmetry is 6 times by φ scan measurement, and the inter-plane direction has a (0001) -oriented hexagonal crystal structure. I confirmed that there was. Further, from FIGS. 4 and 5, a decrease in axial length d (0004) and an increase in mosaicness were observed with an increase in molar fraction. The decrease in both axial lengths (d (222) and d (0004)) and the increase in mosaicness accompanying the increase in the Ga ₂ O ₃ molar fraction indicate that the Ga ³⁺ ionic radius when Ga is substituted at the In site and solid-dissolved. Is smaller than that of In ³⁺ , which is considered to be mainly due to the smaller unit cell and the resulting increase in lattice mismatch with the substrate. On the other hand, when the Ga ₂ O ₃ molar fraction is 23%, the diffraction peaks attributed to the cubic and hexagonal crystal structures are observed at the same time, which indicates that this is a eutectic region of a cubic solid solution and a hexagonal solid solution. However, since only the diffraction peaks of (lll) (l = 2, 4) and (000l) (l = 2, 4, 6, 8, 10, 12) can be seen in any phase, the inter-plane direction is epitaxially grown. You can see that

On the other hand, the thermodynamic stable phases of In ₂ O ₃ and Ga ₂ O ₃ are described in Non-Patent Document 5 and Non-Patent Document 6, but as shown in FIG. _Ga 2 _{O 3} molar ratio of 0% to about 5% or less _in 2-2x _Ga 2x _{O 3} indicate structure) at 1000 ° C., indicate monoclinic _(β-Ga 2 _{O 3} structure) 1000 In _2-2x Ga _2x O ₃ having a Ga ₂ O ₃ molar fraction of about 57% to 100% at a _temperature .
However, in this example, the In _2-2x Ga _2x O ₃ thin film having a Ga ₂ O ₃ molar fraction of 0% or more and less than 23% exceeding the thermal solid solution limit exhibits a cubic crystal structure, and is stably dissolved. , A thermodynamically unstable hexagonal structure that cannot exist in the bulk exists stably in an In _2-2x Ga _2x O ₃ thin film having a Ga ₂ O ₃ molar fraction of more than 23% and not more than 50%. I found it to melt. This phenomenon can be explained as follows.
The pulsed laser deposition method is a film forming technique in which a solid substance is excited into a high energy plasma state in a vacuum, and condensed and deposited on a substrate. The excited raw material solid component feels the surface structure (crystal structure) of the substrate and at the same time instantly condenses on the substrate to form crystals until it settles into a thermodynamic equilibrium state at the substrate temperature. Therefore, it is possible to produce a thin film having a composition and structure that are not allowed thermodynamically. That is, a metastable thin film crystal can be manufactured.

As an example of a laminated structure of a group III oxide semiconductor material of the present invention and a thin film having a hexagonal crystal structure, an embodiment in which an InGaO ₃ thin film is formed on a (0001) ZnO thin film by a pulse laser deposition method will be described. The laser used was a KrF excimer laser (wavelength: 248 nm), and ZnO and InGaO ₃ sintered body targets were used as raw material targets. As the substrate, (0001) Al ₂ O ₃ was used. The ZnO thin film was formed at a substrate temperature of 700 ° C. and the oxygen partial pressure was 1 μm thick at 1 × 10 ⁻⁵ Torr. The InGaO ₃ thin film was formed at a substrate temperature of 730 ° C. and an oxygen partial pressure. Was formed at 1 m thick at 30 mTorr. The presence / absence of a heterogeneous phase in the thin film, determination of solid solution / non-solid solution, and crystal structure / lattice constant were determined using an x-ray diffraction method.

FIG. 6 shows an x-ray diffraction pattern (horizontal axis: 2θ (diffraction angle) (°: degree), vertical axis) of an InGaO ₃ / ZnO laminated thin film provided on a (0001) Al ₂ O ₃ substrate according to an embodiment of the present invention. : Natural logarithm of XRD (x-ray diffraction) intensity (LOG XRD intensity)).
In the ZnO thin film, only the (000 l) (l = 2, 4) diffraction peak due to the hexagonal structure is observed, and the InGaO ₃ thin film has (000 l) (l = 2, 4, 6, 6 due to the hexagonal structure). 8, 10.12) Only a diffraction peak is observed, and it can be seen that the InGaO ₃ thin film grows on the ZnO thin film in a hexagonal crystal structure having a (0001) orientation in the inter-plane direction or a strained hexagonal crystal structure. Here, the indexing of the crystal plane of the InGaO ₃ thin film was based on Non-Patent Document 4.

The thermodynamic stable phases of In ₂ O ₃ and Ga ₂ O ₃ are described in Non-Patent Document 5 and Non-Patent Document 6, but as shown in FIG. 1, each has a cubic crystal (Bixbite structure). Indicates a Ga ₂ O ₃ molar fraction of 0% or more and about 5% or less at 1000 ° C., indicating an In _2-2x Ga _2x O ₃ monoclinic crystal (β-Ga ₂ O ₃ structure) at 1000 ° C. It is In _2-2x Ga _2x O ₃ having a Ga ₂ O ₃ molar fraction of about 57% to 100%.
However, in this example, it was found that a thermodynamically unstable hexagonal crystal structure that could not exist in bulk at a Ga ₂ O ₃ molar fraction of 50% was stably present on the ZnO thin film and dissolved. . This phenomenon can be explained as follows.
The pulsed laser deposition method is a film forming technique in which a solid substance is excited into a high energy plasma state in a vacuum, and condensed and deposited on a substrate. The excited raw material solid component feels the surface structure (crystal structure) of the substrate and at the same time instantly condenses on the substrate to form crystals until it settles into a thermodynamic equilibrium state at the substrate temperature. Therefore, it is possible to produce a thin film having a composition and structure that are not allowed thermodynamically. That is, a metastable thin film crystal can be manufactured.

In Example 1 and Example 2 of the present invention, the pulse laser deposition method is used as a film forming method. For the above-described reason, this phenomenon is a non-equilibrium process, which is a general thin film growth method (sputtering method, molecular beam). (Epitaxial method, metal organic chemical vapor deposition method, etc.). Further, by increasing the non-equilibrium of the growth conditions such as the reduction of the growth temperature and the increase of the growth rate, it is possible to produce a thin film crystal having a metastable structure in a composition range that is not permitted thermodynamically.
In the present invention, a (111) YSZ substrate or (0001) ZnO / (0001) Al ₂ O ₃ is selected as the substrate, but for the same reason as above, the in-plane of the cubic structure In _2-2x Ga _2x O ₃ By growing on another substrate or thin film that is close to the lattice constant in the plane of hexagonal structure In _2-2x Ga _2x O ₃ , or on a substrate or thin film having a different plane orientation, It is possible to increase. As a base substrate or thin film material, a group IV semiconductor (C, Si, Ge, SiC, etc.), a group III-V semiconductor (GaP, GaAs, InP, etc.), a group III nitride semiconductor (In _{1-xy-) z} Ga _x Al _y B _z N etc.), group II oxide semiconductors (Zn _1-xy Mg _x Cd _y O etc.), perovskite oxides (BaTiO ₃ , SrTiO ₃ , NdGaO ₃ , LaAlO ₃ etc.), Other oxides (Al ₂ O ₃ , SrO, BaO, MgO, CaO, Y ₂ O ₃ , In ₂ O ₃ , CeO ₂ , ScMgAlO ₄ , LiGaO ₂ , LiAlO ₂ , NaGaO ₂ , NaAlO ₂ , KGaO ₂ , KAlO ₂ ).

Further, As far as the group III oxides having a hexagonal structure, the group III nitride semiconductor by x-ray diffraction measurement _{(In 1-x-y-} z Ga x Al y B z N) or group II oxide semiconductor It is approximate to the in-plane lattice constant of (Zn _1-xy Mg _x Cd _y O), and the in-plane lattice constant is controlled by the group III ion composition ratio based on the result of FIG. It has been shown that it is possible. Therefore, when manufacturing a semiconductor device in which the group III nitride semiconductor or the group II oxide semiconductor and a group III oxide having a hexagonal structure are heteroepitaxially grown, the group III oxide or the group III nitride III is prepared. By changing the composition ratio of group ions or the composition ratio of group II ions of the above group II oxides, it is possible to precisely control the lattice strain of group III oxides, group III nitrides, or group II oxide thin films. It is. Therefore, it is possible to control the piezoelectric polarization field or the spontaneous polarization field, which is a feature of these thin film crystals. Therefore, as shown in FIG. 7, a heterojunction with the semiconductor is produced, and a semiconductor electronic device characterized by the generated two-dimensional electron gas or two-dimensional hole gas induced at the interface by the electric field is obtained. I can do it.

FIG. 7 is a diagram showing a structure of a high mobility electronic device shown in the embodiment of the present invention. FIG. 7 shows a buffer layer (2), an additive-free semiconductor active layer (3), an additive-free semiconductor barrier layer (4), and an impurity-added semiconductor barrier layer (5) that promote high quality of the active layer on the substrate (1). A source electrode (6), a drain electrode (7), and a gate electrode (8) are provided. The group III oxide semiconductor of the present invention is used for at least one of the active layer (3) or the barrier layer (4), and the two-dimensional electrons are formed at the interface between the additive-free semiconductor active layer (3) and the additive-free semiconductor barrier layer (4). A gas or a two-dimensional hole gas is formed.
Group III nitride semiconductor as an active layer _{(3) (In 1-x} -y-z Ga x Al y B z N) or group II oxide semiconductor _{(Zn 1-x-y Mg} x Cd y O) or invention Group III oxide semiconductor (In _2-2x-2y-2z Ga _2x Al _2y B _2z O ₃ ), Group III nitride semiconductor or Group II oxide semiconductor having a larger forbidden band than the active layer as the barrier layer (4) Alternatively, a group III oxide semiconductor (In _2-2x-2y-2z Ga _2x Al _2y B _2z O ₃ ) of the present invention can be used.

In Example 3, the optical characteristics and electrical characteristics of the In _2-2x Ga _2x O ₃ thin film provided on the YSZ substrate prepared in Example 1 were examined. The forbidden band width at room temperature was determined by transmission spectrum measurement in the ultraviolet and visible regions, and the electrical characteristics at room temperature were determined by the Hall measurement method.
FIG. 8 shows the transmission spectrum of each thin film. In FIG. 8, the vertical axis represents transmittance (%) and the horizontal axis represents wavelength (nm), which is normalized by the transmittance of the YSZ substrate. Each symbol in FIG. 8 corresponds to a molar fraction (x) of 0, 0.10, 0.23, 0.32, 0.40, 0.50. FIG. 9 is a table showing the transmittance at room temperature of the In _2-2x Ga _2x O ₃ thin film.
All the thin films are transparent in the visible region, and the absorption edge is changed to the short wavelength side as the Ga ₂ O ₃ molar fraction is increased. FIG. 10 is a diagram showing the change in the optical band gap at room temperature of the In _2-2x Ga _2x O ₃ thin film with respect to the Ga ₂ O ₃ molar fraction. In FIG. 10, the vertical axis represents the forbidden band width (eV), and the horizontal axis represents the Ga ₂ O ₃ molar fraction (x). The forbidden band width is 3.73, 3.79, _{3 as} the Ga ₂ O ₃ molar fraction increases to x = 0, 0.10, 0.23, 0.32, 0.40, 0.50. .94, 4.11, 4.19, 4.37 eV.
These values are forbidden band widths of bulk polycrystalline and thin film samples reported in Non-Patent Document 7 and Non-Patent Document 8, InGaO ₃ : about 3.3 eV, and In _2-2x Ga _2x O ₃ (0 ≦ x .Ltoreq.0.5) Thin film: It is found that the difference is continuously different from about 3.75 (x = 0) to 3.4 eV (x = 0.5). This phenomenon is considered to be due to the fact that the original physical properties of the material appeared as a result of successful production of a high-quality thin film with few defects by optimizing the thin film production conditions while using a YSZ substrate that is easily lattice-matched as a substrate.
FIG. 11 shows the electrical characteristics at room temperature of the In _2-2x Ga _2x O ₃ thin film on the YSZ substrate, and FIG. 12 shows a table of specific resistance, carrier concentration, and mobility. All the thin films not intentionally doped are n-type semiconductors, and a decrease in carrier concentration and an increase in resistivity are observed with an increase in the Ga ₂ O ₃ molar fraction. Further, the mobility is as low as about 8.7 cm ² / Vs in the vicinity of x = 0.23 where eutectic was observed, but generally decreases with an increase in the Ga ₂ O ₃ mole fraction. This phenomenon can be explained as follows.

In general, the origin of carriers in the In _2-2x Ga _2x O ₃ thin film is considered to be donor-type point defects such as oxygen deficiency or interstitial cations (In ³⁺ or Ga ³⁺ ). Since Ga has a higher bonding property to oxygen than In, it is considered that the above-mentioned donor type point defects are reduced and the carrier concentration is reduced. As the carrier concentration decreases, scattering due to grain boundaries other than point defects becomes dominant as the carrier scattering origin. FIG. 4 shows that the In _2-2x Ga _2x O ₃ thin film having a large Ga ₂ O ₃ molar fraction has a large _mosaicness due to increased lattice mismatch with the substrate (many macro defects such as dislocations and grain boundaries). This is suggested by the results of XRD rocking curve half width. For this reason, it is considered that with the increase of the Ga ₂ O ₃ molar fraction, the mobility decreased, and the resistivity increased together with the effect of decreasing the carrier concentration.
However, although the In _2-2x Ga _2x O ₃ thin film having a large Ga ₂ O ₃ molar fraction has a large _mosaicness , its mobility is relatively large among the general oxide thin films (˜30 cm ² / Vs). ). From this result, by introducing a growth process with measures for reducing defects, it is possible to improve the quality of the thin film and realize further higher mobility.
Thin film quality improvement methods include selection of a substrate with less mismatch between the thin film material and the lattice and thermal expansion coefficient, insertion of a buffer layer suitable for the growth of the thin film material, and growth of group III nitride semiconductors. For example, a two-stage growth method or insertion of a low-temperature buffer layer may be used.

From the above results, the Group III oxide semiconductor of the present invention has a forbidden band width, that is, a valence band by changing the composition amount of at least two elements selected from In, Ga, aluminum Al, and boron B. It can also be seen that the semiconductor has a large forbidden band width capable of controlling the energy position of the conductor.
Therefore, as shown in FIG. 13-15, the group III oxide semiconductor of the present invention is used as a window layer of a chalcopyrite solar cell, and the composition ratio of In and Ga is changed to change the light absorption layer of CuIn _1-x Ga. _x High-efficiency solar cell in which the conduction band offset amount with Se ₂ is adjusted, a UV detection element having a structure in which a group III oxide semiconductor is sandwiched between two electrodes, and a light emitting element using a group III oxide semiconductor as a cladding layer Can be obtained.
FIG. 13 is a cross-sectional view of a chalcopyrite solar cell using the group III oxide semiconductor of the present invention as a window layer of the chalcopyrite solar cell. A metal thin film (22), a chalcopyrite light absorption layer (23), an n-type group III oxide semiconductor window layer (24) of the present invention, a transparent conductive film (25), a comb electrode (26) on a substrate (21). Consists of.

FIG. 14 is a cross-sectional view of a photodetecting element using the group III oxide semiconductor of the present invention as a photodetecting layer. FIG. 14A is composed of a transparent conductive film (32), an additive-free group III oxide semiconductor photodetection layer (33) of the present invention, and an ultraviolet transmissive electrode film (34) on a substrate (31). The light detection layer may be composed of a plurality of layers as shown in FIG. In FIG. 14B, a transparent conductive film (32), a p-type semiconductor (35), an n-type semiconductor (36), and an ultraviolet transmissive electrode film (34) are sequentially provided on a glass substrate (31). In FIG. 14B, the p-type semiconductor (35) and the n-type semiconductor (36) are provided in this order, but the order of the p-type semiconductor (35) and the n-type semiconductor (46) is reversed. It may be provided.
15 (a) and 15 (b) are cross-sectional views of a light emitting diode element using the group III oxide semiconductor of the present invention as a cladding layer. FIG. 15A includes a multiple quantum well structure in which a plurality of cladding layers (42) and light emitting layers (43) are joined on a substrate (41). FIG. 15B shows a current injection type light emitting diode element. On the substrate (41), an n-side ohmic electrode (44), an n-type contact layer (45), an n-type cladding layer (46), and a light-emitting layer (47). ), A p-type cladding layer (48), a p-type contact layer (49), and a p-type ohmic electrode (50). The group III oxide semiconductor of the present invention is used for at least one of the contact layer and the cladding layer, and the conduction band and valence band offset are controlled by changing the composition of the light emitting layer and the cladding layer, thereby confining electrons and holes. Probability and emission wavelength can be controlled. Note that the multiple quantum well structure shown in FIG. 15A may be used as the light emitting layer in FIG.

Although the embodiment of the present invention has been described with reference to an example, it is not limited to the In _2-2x Ga _2x O ₃ of the above example, but is a group III oxide semiconductor (In _2-2x-2y-2z Ga _2x Al _2y application in B _2z O ₃₎ are possible, it is not excluded from the scope of the present invention.
Further, the present invention is not limited to the above embodiment, and can be applied to other embodiments based on the technical idea of the present invention.

It is thermodynamically stable phase diagram of Ga ₂ O ₃ -In ₂ O ₃ system. It is a diagram showing the _In 2-2x _Ga 2x _{O 3} thin film of x-ray diffraction pattern which is provided on the YSZ substrate shown in the embodiment of the present invention. YSZ substrate shown in the embodiment of the present invention, _{an In} 2 _{O 3} thin film, InGaO ₃ {220} of the thin film, {440} is a diagram showing the φ scan measurement pattern of {10-11} diffraction plane. The axial length in the (a) inter-plane direction of the In _2-2x Ga _2x O ₃ thin film on the YSZ substrate shown in the examples of the present invention (for the cubic structure, the (222) plane (white circle), for the hexagonal structure (B) rocking curve half-width ((222) plane (white circle) for cubic structure, (0004) plane (black rhombus) for hexagonal structure) ). Ga ₂ O ₃ molar fraction (x) of In _2-2x Ga _2x O ₃ thin film shown in the examples of the present invention, (222) spacing (d (222) of cubic structure In _2-2x Ga _2x O ₃ thin film ) (Å)), (0004) spacing of hexagonal structure In _2-2x Ga _2x O ₃ thin film (d (0004) (Å)), (222) of cubic structure In _2-2x Ga _2x O ₃ thin film Rocking curve half-value width (Δω (222) (°: degree)) of surface, rocking curve half-value width (Δω (0004) (°: degree) of (0004) surface of hexagonal structure In _2-2x Ga _2x O ₃ thin film ). Is a diagram showing an x-ray diffraction pattern of the _Al 2 _{O 3} substrate on InGaO ₃ / ZnO film in Examples of the present invention. It is a figure which shows the high mobility electronic device structure shown in the Example of this invention. It is a diagram showing the transmission spectrum at room temperature of _In 2-2x _Ga 2x _{O 3} thin film in Examples of the present invention. The _In 2-2x _Ga 2x _{O 3} transmittance at room temperature of the thin film shown in the embodiment of the present invention is a table showing. Is a diagram showing an optical band gap of _In 2-2x _Ga 2x _{O 3} thin films at room temperature shown in the embodiment of the present invention. It is a diagram showing the electric characteristics in _In 2-2x _Ga 2x _{O 3} thin films at room temperature shown in the embodiment of the present invention. _In 2-2x _Ga 2x _{O 3} resistivity of the thin film at room temperature, the carrier concentration shown in the examples of the present invention, a table showing mobility. FIG. 13 is a diagram showing a photoelectric conversion element structure shown in an example of the present invention. FIG. 14 is a diagram showing a photodetecting element structure according to an embodiment of the present invention. FIG. 15 is a diagram showing a light-emitting element structure shown in an example of the present invention.

Explanation of symbols

1, 2, 31, 41 Substrate 2 Buffer layer 3 Additive-free semiconductor active layer 4 Additive-free semiconductor barrier layer 5 Impurity-added semiconductor barrier layer 6 Source electrode 7 Drain electrode 8 Gate electrode 22 Metal thin film 23 Chalcopyrite light absorption layer 24 n Type III oxide semiconductor window layers 25, 32 Transparent conductive film 26 Comb electrode 33 Additive group III oxide semiconductor photodetection layer 34 UV transmitting electrode film 35 P type semiconductor 36 N type semiconductor 42 Clad layer 43, 47 Light emitting layer 44 n-side ohmic electrode 45 n-type contact layer 46 n-type cladding layer 48 p-type cladding layer 49 p-type contact layer 50 p-type ohmic electrode

Claims (12)

When A is an arbitrary element symbol, it has a structure of A ₂ O _{3 and} the element of A includes a group III oxide semiconductor composed of at least two of In, Ga, aluminum Al, and boron B, and has a forbidden band width. A semiconductor element, wherein the composition amount of at least two elements selected from In, Ga, aluminum Al, and boron B is changed so as to modulate. 2. A semiconductor device comprising a group III oxide semiconductor according to claim 1, comprising a group III oxide semiconductor characterized by having a hexagonal crystal structure or a hexagonal crystal structure having a strain. A photoelectric conversion element that includes a first electrode layer, a p-type semiconductor layer, a layer A, and a second electrode layer in order from the substrate side, and generates a photovoltaic force by light incident from the second electrode layer side. A photoelectric conversion element, wherein the A is the group III oxide semiconductor according to claim 1. 4. The photoelectric conversion device according to claim 3, wherein the p-type semiconductor layer is at least one element selected from Cu and Ag, at least one element selected from In and Ga, and at least one element selected from Se and S. And a p-type compound semiconductor or CdTe. An ultraviolet detection element, wherein the group III oxide semiconductor according to claim 1 is sandwiched between a pair of electrodes. An ultraviolet detection element having at least a p-type and an n-type semiconductor layer on a substrate, wherein the group III oxide semiconductor according to claim 1 or 2 is included in at least one semiconductor layer. UV detection element. 7. The ultraviolet detection element according to claim 6, wherein the semiconductor layer is a group III oxide semiconductor thin film according to claim 1 or at least one element selected from In, Ga, aluminum Al and boron B, and N. A UV-detecting element comprising a group III nitride semiconductor containing at least one element selected from Zn, Mg, and Cd and a group II oxide semiconductor containing O. 3. The group III oxidation according to claim 1, wherein the semiconductor light emitting device includes at least an n-type clad layer, an active layer, and a p-type clad layer on a substrate, and the clad layer has a larger forbidden band than the active layer. A light-emitting element using a semiconductor thin film. 9. The light emitting device according to claim 8, wherein the active layer is a group III nitride semiconductor containing at least one element selected from In, Ga, aluminum Al, and boron B and N, or at least one selected from Zn, Mg, and Cd. A light-emitting element comprising any one of a group II oxide semiconductor containing an element and O. A thin film field effect transistor comprising the group III oxide semiconductor thin film according to claim 1 as an active layer of the field effect transistor. A semiconductor device comprising at least an active layer and a barrier layer on a substrate and controlling a flow of a two-dimensional electron gas or a two-dimensional hole gas generated at an interface between the active layer and the barrier layer. A semiconductor element comprising the group III oxide semiconductor thin film according to claim 1. 12. The semiconductor element according to claim 11, wherein at least one of the active layer and the barrier layer is a group III nitride semiconductor containing at least one element selected from In, Ga, aluminum Al, and boron B and N, or Zn, Mg, Cd. A semiconductor element comprising a group II oxide semiconductor thin film containing at least one element selected from the group consisting of O and O.

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