Patent Application
20140217471
The invention relates to a Ga2O3-based semiconductor element.
A β-Ga2O3-based semiconductor element using a β-Ga2O3 crystal film formed on an α-Al2O3 (sapphire) substrate is known (see, e.g., NPL 1).
[NPL 1]
K. Matsuzaki et al. Appl. Phys. Lett. 88, 092106, 2006.
[Technical Problem]
However, it is difficult to grow a monoclinic β-Ga2O3 crystal film on an α-Al2O3 substrate having a corundum structure and it is not possible to obtain a high-quality β-Ga2O3 crystal film. Thus, it is difficult to form a high-quality Ga2O3-based semiconductor element by using a β-Ga2O3 crystal film grown on an α-Al2O3 substrate.
It is an object of the invention to provide a high-quality Ga2O3-based semiconductor element.
[Solution to Problem]
According to one embodiment of the invention, a Ga2O3-based semiconductor element as defined [1] to [3] below is provided so as to the above object.
[1] A Ga2O3-based semiconductor element, comprising:
[2] The Ga2O3-based semiconductor element according to [1], further comprising a first contact region and a second contact region that comprise a same conductive type as the α-(AlxGa1-x)2O3 single crystal film, are formed in the α-(AlxGa1-x)2O3 single crystal film and are connected to the source electrode and the drain electrode, respectively.
[3] The Ga2O3-based semiconductor element according to [2], wherein the α-(AlxGa1-x)2O3 single crystal film, the first contact region and the second contact region are of an n-type.
[Advantageous Effects of Invention]
According to an embodiment of the invention, a high-quality Ga2O3-based semiconductor element can be provided.
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According to the present embodiment, it is possible to form a high-quality α-(AlxGa1-x)2O3 single crystal film on an α-Al2O3 substrate by homoepitaxial growth and use of such a high-quality α-(AlxGa1-x)2O3 single crystal film allows a high-quality Ga2O3-based semiconductor element to be formed. Examples of embodiments thereof will be described in detail below.
A Ga2O3-based MESFET (Metal Semiconductor Field Effect Transistor) will be described as the Ga2O3-based semiconductor element in the embodiment.
(Structure of Ga2O3-based semiconductor Element)
The source electrode 12 is electrically connected to the drain electrode 13 via the n-type β-Ga2O3 single crystal film 3. Meanwhile, a Schottky junction is formed at an interface between the gate electrode 11 and the n-type β-Ga2O3 single crystal film 3 and a depletion layer is thus formed in the n-type β-Ga2O3 single crystal film 3 under the gate electrode 11. The Ga2O3-based MESFET 10 functions as either a normally-off transistor or a normally-on transistor depending on the thickness of the depletion region.
The n-type α-(AlxGa1-x)2O3 single crystal film 3 is an α-(AlxGa1-x)2O3 (0≦x≦1) single crystal film formed on the α-Al2O3 substrate 2. The n-type α-(AlxGa1-x)2O3 single crystal film 3 includes an n-type dopant such as Sn, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Ru, Rh, Ir, C, Si, Ge, Pb, Mn, As, Sb, Bi, F, Cl, Br and I. The n-type α-(AlxGa1-x)2O3 single crystal film 3 includes an n-type dopant at a concentration of, e.g, not less than 1×1015/cm3 and not more than 1×1019 cm3. In addition, the thickness of the n-type α-(AlxGa1-x)2O3 single crystal film 3 is, e.g., 0.1 to 10 μm.
Here, another film such as an undoped β-Ga2O3 single crystal film may be formed between the α-Al2O3 substrate 2 and the n-type α-(AlxGa1-x)2O3 single crystal film 3. In this case, the undoped β-Ga2O3 single crystal film is formed on the α-Al2O3 substrate 2 by epitaxial growth and the n-type (AlxGa1-x)2O3 single crystal film 3 is formed on the undoped β-Ga2O3 single crystal film by epitaxial growth.
The gate electrode 11, the source electrode 12 and the drain electrode 13 are formed of, e.g., a metal such as Au, Al, Ti, Sn, Ge, In, Ni, Co, Pt, W, Mo, Cr, Cu and Pb, an alloy containing two or more of such metals, a conductive compound such as ITO, or a conductive polymer. Polythiophene derivatives (PEDOT: poly(3,4-ethylenedioxythiophene)) doped with polystyrene sulfonate (PSS) or polypyrrole derivatives doped with TCNA are used as the conductive polymer. In addition, the structure thereof may be a two-layer structure composed of two different metals, e.g., Al/Ti, Au/Ni or Au/Co.
The contact regions 14 and 15 are regions having a high n-type dopant concentration formed in the n-type α-(AlxGa1-x)2O3 single crystal film 3 and are respectively connected to the source electrode 12 and the drain electrode 13. The n-type dopant included in the contact regions 14 and 15 and that included in the n-type α-(AlxGa1-x)2O3 single crystal film 3 may be either the same or different. The contact regions 14 and 15 include the n-type dopant at a concentration of, e.g., not less than 1×1018/cm3 and not more than 5×1019 cm3. It should be noted that the contact regions 14 and 15 do not need to be provided in the Ga2O3-based MESFET 10.
(Method of Manufacturing Ga2O3-based MESFET)
A process using the Molecular Beam Epitaxy (MBE) will be described below as an example of the method of manufacturing the α-(AlxGa1-x)2O3 single crystal film. The MBE is a crystal growth method in which a single or compound solid is heated in an evaporation source called cell and vapor generated by heat is supplied as a molecular beam onto the surface of the substrate.
A Ga raw material of the α-(AlxGa1-x)2O3 single crystal film, such as Ga powder, is loaded in the first cell 103a. The Ga powder desirably has a purity of not less than 6N. Powder of an n-type dopant raw material to be doped as a donor is loaded in the second cell 103b. An Al raw material of the α-(AlxGa1-x)2O3 single crystal film, such as Al powder, is loaded in the third cell 103c. A shutter is provided at an opening of each of the first cell 103a, the second cell 103b and the third cell 103c.
Firstly, the α-Al2O3 substrate 2 is attached to the substrate holder 101 of the MBE system 100. Next, the vacuum pump 106 is activated to reduce atmospheric pressure in the vacuum chamber 107 to about 1018 Torr. Then, the α-Al2O3 substrate 2 is heated by the heating devices 102. Here, radiation heat of heat source such as graphite heater of the heating device 102 is thermally transferred to the α-Al2O3 substrate 2 via the substrate holder 101 and the α-Al2O3 substrate 2 is thereby heated.
After the α-Al2O3 substrate 2 is heated to a predetermined temperature, oxygen-based gas is supplied into the vacuum chamber 107 through the gas supply pipe 105.
After a period of time required for stabilization of gas pressure in the vacuum chamber 107 (e.g., after 5 minutes) since the oxygen-based gas was supplied into the vacuum chamber 107, the first cell 103a, the second cell 103b and the second cell 103c are respectively heated by the first heater 104a, the second heater 104b and the third heater 104c while rotating the substrate holder 101 so that Ga, Al and n-type dopant are evaporated and are radiated as molecular beam onto the surface of the α-Al2O3 substrate 2.
As such, the α-(AlxGa1-x)2O3 single crystal is epitaxially grown on the main surface of the α-Al2O3 substrate 2 while being doped with the n-type dopant such as Sn and the n-type α-(AlxGa1-x)2O3 single crystal film 3 is thereby formed. It should be noted that as the n-type dopant other than Sn, it is possible to use Ti, Zr, Hf, V, Nb, Ta, Mo, W, Ru, Rh, Ir, C, Si, Ge, Pb, Mn, As, Sb and Bi, etc., for substituting Ga or Al site and it is possible to use F, Cl, Br and I, etc., for substituting oxygen site. The addition concentration of the n-type dopant can be controlled by temperature of the second cell 103b.
Alternatively, the n-type α-(AlxGa1-x)2O3 single crystal film 3 may be formed by the PLD (Pulsed Laser Deposition) or the CVD (Chemical Vapor Deposition) etc.
Next, the contact regions 14 and 15 are formed by ion-planting the n-type dopant such as Sn into the n-type α-(AlxGa1-x)2O3 single crystal film 3. It should be noted that the ion to be implanted is not limited to Sn and, when substituting, e.g., Ga or Al site, it is possible to use Ti, Zr, Hf, V, Nb, Ta, Mo, W, Ru, Rh, Ir, C, Si, Ge, Pb, Mn, As, Sb or Bi. In addition, it is possible to use F, Cl, Br or I when substituting oxygen site.
The implantation concentration is, e.g., not less than 1×1018/cm3 and not more than 5×1019 cm3. The implantation depth is not less than 30 nm. After implantation, the surface of the implanted region is etched about 10 nm by hydrofluoric acid. Sulfuric acid, nitric acid or hydrochloric acid may be used for the etching. After that, implantation damage is repaired by performing annealing treatment in a nitrogen atmosphere at not less than 800° C. for not less than 30 minutes. In case of performing the annealing treatment in an oxygen atmosphere, treatment temperature is not less than 800° C. and not more than 950° C. and treatment time is not less than 30 minutes.
It should be noted that the method of forming the contact regions 14 and 15 is not limited to ion implantation and thermal diffusion process may be used. In this case, after metal such as Sn is brought into contact with the n-type α-(AlxGa1-x)2O3 single crystal film 3 in a region for the contact regions 14 and 15 to be formed, heat treatment is performed to diffuse a dopant such as Sn into the n-type α-(AlxGa1-x)2O3 single crystal film 3.
After that, the gate electrode 11, the source electrode 12 and the drain electrode 13 are formed.
(Effects of the Embodiment)
According to the present embodiment, it is possible to form high-quality α-(AlxGa1-x)2O3 single crystal films by homoepitaxial growth and use of such α-(AlxGa1-x)2O3 single crystal films allows high-quality Ga2O3-based semiconductor elements to be formed. In addition, these Ga2O3-based semiconductor elements have excellent performance since a high-quality α-(AlxGa1-x)2O3 single crystal film is used as a channel layer.
It should be noted that the invention is not intended to be limited to the above-mentioned embodiment, and the various kinds of modifications can be implemented without departing from the gist of the invention. For example, the Ga2O3-based semiconductor element has been described as the n-type semiconductor element in the embodiment but may be a p-type semiconductor element. In this case, the conductivity type (n-type or p-type) of each member is all inverted.
Although the embodiment of the invention has been described above, the invention according to claims is not to be limited to the above-mentioned embodiment. Further, it should be noted that all combinations of the features described in the embodiment are not necessary to solve the problem of the invention.
A high-quality Ga2O3-based semiconductor element is provided.
2: α-Al2O3 substrate
3: n-type α-(AlxGa1-x)2O3 single crystal film
10: Ga2O3-based MESFET
11: gate electrode
12: source electrode
13: drain electrode
14, 15: contact region
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-196439 | Sep 2011 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2012/072900 | 9/7/2012 | WO | 00 | 3/7/2014 |
