Conference Programme

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X-03: Oxide Semiconductors
Tuesday, 20/Jun/2017:
10:30am - 12:00pm

Session Chair: Rajendra Singh, Indian Institute of Technology Delhi
Session Chair: Izabella Grzegory, Institute of High Pressure Physics PAS Unipress
Location: Rm 324

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10:30am - 11:00am

Application of Gallium Oxide for High-Power Electronics

Masataka HIGASHIWAKI1, Man Hoi WONG1, Keita KONISHI1, Kohei SASAKI2, Ken GOTO2,3, Hisashi MURAKAMI3, Yoshinao KUMAGAI3, Akito KURAMATA2, Shigenobu YAMAKOSHI2

1National Institute of Information and Communications Technology, Japan; 2Tamura Corporation, Japan; 3Department of Applied Chemistry, Tokyo University of Agriculture and Technology, Japan

Wide bandgap oxide semiconductor material - gallium oxide (Ga2O3) - has emerged as a new candidate for next-generation power devices by virtue of the excellent material properties and the relative ease of mass wafer production. In this talk, following a short introduction of material properties and features of Ga2O3, an overview of our recent development progress in device processing and characterization of Ga2O3 field-effect transistors (FETs) and Schottky barrier diodes (FP-SBDs) will be reported.

Depletion-mode Ga2O3 metal-oxide-semiconductor FETs (MOSFETs) were fabricated with Si-ion-implanted Ga2O3 layers on semi-insulating Fe-doped Ga2O3 (010) substrates. SiO2-passivated MOSFETs with a gate-connected field plate (FP) demonstrated a high off-state breakdown voltage (Vbr) of 755 V, a large drain current on/off ratio of over nine orders of magnitude at room temperature, DC-RF dispersion-free output characteristics, and stable high temperature operation up to 300°C.

We also fabricated Pt/Ga2O3 FP-SBDs on n--Ga2O3 drift layers grown by halide vapor phase epitaxy on n+-Ga2O3 (001) substrates. The illustrative device with a net donor concentration of 1.8×1016 cm-3 exhibited a specific on-resistance of 5.1 mΩ·cm2 and an ideality factor of 1.05 at room temperature. Successful FP engineering resulted in a high Vbr of 1076 V. Note that this was the first demonstration of Vbr of over 1 kV in any Ga2O3 power devices.

In summary, we succeeded in fabricating Ga2O3 FP-MOSFETs and FP-SBDs on single-crystal β-Ga2O3 substrates. Despite the simple structures, both devices revealed excellent characteristics and demonstrated great potential of Ga2O3 electron devices for power electronics applications.

This work was partially supported by Council for Science, Technology and Innovation (CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), “Next-generation power electronics” (funding agency: NEDO).

11:00am - 11:30am

Single Crystal Gallium Oxide Substrates and LED Application

Akito KURAMATA1,2, Kimiyoshi KOSHI1,2, Shinya WATANABE2, Yu YAMAOKA2, Takekazu MASUI1,2, Kazuyuki IIZUKA2, Yoshihiro YAMASHITA2, Yoshikatsu MORISHIMA2, Shigenobu YAMAKOSHI1,2

1Novel Crystal Technology, Inc., Sayama, Japan; 2Tamura Corporation, Sayama, Japan

Gallium oxide (Ga2O3) is a semiconductor material that has both a large band gap energy and electrical conductivity. It has been attracting attention because it has high potential for power device applications and high-brightness LED applications. Ga2O3 can be grown from a melt source; therefore, its growth rate is high. This means it has a lower production cost compared with other wide band gap semiconductor materials such as silicon carbide, gallium nitride, aluminum nitride, and diamond, whose growth rates are relatively low because they can be grown from only diluted vapor sources.

In this presentation, we’ll report on single crystal Ga2O3 substrates made from large and high-quality bulk crystals grown with an edge-defined film-fed growth (EFG) process. Residual impurities, doping controllability, and crystal defects were investigated, and the results show that Ga2O3 single crystals can be fabricated with sufficient quality for semiconductor device applications. We’ll also report on LED application of the Ga2O3 substrates. Generally, vertical LEDs have superior characteristics, in terms of efficiency and light-output power per unit area, and thus are suitable light sources in projectors, car headlights, and spot lighting. Ga2O3 substrates have a high potential for these purposes because they can be electrically conductive and optically transparent. We’ll talk about the epitaxial growth of GaN and AlGaN on single-crystal Ga2O3 substrates and the characteristics of blue LEDs and ultraviolet (UV) LEDs fabricated on Ga2O3 substrates.

11:30am - 11:45am

Inductively-Coupled Plasma Reactive-Ion Etching of beta-Ga2O3 in Chlorine-based Plasma

Amit Pushkarrai SHAH, Arnab BHATTACHARYA

Tata Institute of Fundamental Research, India

Recently β-Ga2O3 has emerged as a wide-bandgap semiconductor for device applications and substrates for GaN-based LEDs. Inductively-coupled plasma reactive-ion etching (ICP-RIE) is the standard technique for etching III-nitrides. However, there is little reported on the ICP-RIE etching of β-Ga2O3. We present our results of etching Sn-doped (-201) oriented β-Ga2O3 using BCl3/Cl2/Ar plasma chemistry. We have varied the BCl3-Cl2 gas ratio, with Ar and total gas flow constant at 10 and 60 sccm respectively. The basic plasma parameters used are: 1 Pa chamber pressure, 500 W ICP power, 30 W RF power and 2 min. etching time. The etch depths were measured using a profilometer and by atomic force microscopy (AFM).

We observe an etch rate of 135 nm/min for BCl3/Ar plasma. As the content of Cl2 is increased, the etch rate reduces, eventually reaching 15 nm/min for a Cl2/Ar plasma. This etching behavior is similar to sapphire etching in Cl2/BCl3 plasma, and will be discussed.

We carried out two sets of etching as a function of temperature; one set etched in BCl3/Ar and other set etched in Cl2/Ar plasma at 22, 75, 130, 185 and 205oC temperatures. The etch rates are almost constant for both BCl3/Ar and Cl2/Ar plasma. The maximum etch rate of Ga2O3 in BCl3/Ar plasma obtained was ~145 nm/min. There is slight increase of etch rate at 205oC which is above the sublimation temperature of GaCl3. This may indicate more effective removal of GaCl3 by sublimation and exposure of fresh Ga2O3 surface for further reaction with chlorine.

AFM measurements of RMS roughness values for Ga2O3 etching are 1.9, 2.3, 2.1, 2.2, and 2.7nm for virgin surface, BCl3/Ar plasma at 22oC, BCl3/Ar plasma at 205oC, Cl2/Ar plasma at 22oC, and Cl2/Ar plasma at 205oC, respectively.

11:45am - 12:00pm

Engineering Multifunctional Single ZnO Nanorods p-n Junction for Optoelectronic Applications

Avanendra SINGH1, Debi Prasad DATTA1, Kartik SENAPATI1, D. KANJILAL2, Pratap Kumar SAHOO1

1National Institute of Science Education and Research (NISER) Bhubaneswar, India; 2Inter-University Accelerator Centre, India

The as grown ZnO nanostructures show n-type conductivity. Deep acceptor levels, intrinsic defects and low dopant solubility are the bottle-neck to achieve p-type conductivity in ZnO. Several attempts have been taken to achieve p-type conductivity of ZnO nanostructures and is still under debate. In literature several reports claim that the p-type conductivity in ZnO can be achieved by creating O rich environment in ZnO matrix.In this work, ZnO nanorods oriented along c-axis were reproducibly grown on Si substrates by single step aqueous growth technique. We engineer p and n type zones in a vertically grown ZnO nanorods by depth selective Oxygen ion implantation in the energy range of 50 - 250 keV. Photo and electroluminescence study of implanted nanorods reveals typical near band edge emission followed by strong deep level emissions in the visible range. The deconvolution of luminescence spectra depicts that oxygen interstials and zinc vacancies are responsible for specific band emissions. The Kelvin prove force microscopy measurements demonstrates the effect of Oxygen ion implantation on the carrier concentrations of implanted ZnO nanorods and confirm the p-n junction characteristics. The obtained results support our understanding that O rich environment in ZnO matrix may alter its conductivity from n-type conductivity to p-type. Here we demonstrates that this is a very effective way of fabricating p-n junctions in a single nanorod for optoelectronic applications.

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