成果報告書詳細
管理番号20150000000594
タイトル*平成26年度中間年報 SIP(戦略的イノベーション創造プログラム) 次世代パワーエレクトロニクス 将来のパワーエレクトロニクスを支える基盤研究開発 酸化ガリウムパワーデバイス基盤技術の研究開発
公開日2015/8/4
報告書年度2014 - 2014
委託先名独立行政法人情報通信研究機構 株式会社タムラ製作所 国立大学法人東京農工大学 新日本無線株式会社 株式会社シルバコ・ジャパン
プロジェクト番号P14029
部署名電子・材料・ナノテクノロジー部
和文要約
英文要約1. The structural properties of Ga2O3 substrate surfaces that were damaged during the wafer manufacturing process were characterized by X-ray reflection topography. It turned out that a 10-um-deep dry etching process after chemical mechanical polishing is effective for removing the damaged region.

2-1. First, we succeeded in developing a homoepitaxial growth technology for undoped Ga2O3 thin films by HVPE. High-purity Ga2O3 films with a thickness of 10 um and a residual electron density of less than 1e13 cm-3 were obtained at a growth temperature of 1000degC. These results indicate that we have met the milestone of FY 2014 for this topic. Since the milestone for FY 2014 has been achieved earlier than initially planned, we embarked on an effort to develop n-type doping technology, which had been planned as the research topic for FY 2015. A supply line of Si dopant gas was added to the HVPE apparatus. We optimized the HVPE growth conditions of Si-doped Ga2O3 films and succeeded in obtaining precise control of Si and carrier concentrations. This enabled us to grow n-type Ga2O3 films with an electron concentration of less than 1e17 cm-3.

2-2. We installed a new molecular-beam epitaxy machine at NICT for epitaxial growth of Ga2O3 thin films. The machine is equipped with both oxygen plasma and ozone cells.

2-3. We surveyed past reports on the electrical properties of p-type amorphous oxide semiconductors and chose NiO and SnO as candidates from the viewpoint of their low resistivity.

3-1. It turned out that Fe atom diffusion from the Fe-doped Ga2O3 substrate to the epitaxial channel layer during the annealing process for activation of ion-implanted Si atoms was a big issue for the development of lateral Ga2O3 MOSFETs with a field plate. The insertion of an undoped Ga2O3 layer with a thickness of more than 0.7 um between the substrate and the channel turned out to be effective for suppressing the diffusion. Design and optimization of vertical normally-on Ga2O3 MOSFET device structures were also performed by using TCAD simulation in this annual year.

3-2. Ga2O3 SBDs were fabricated on epitaxial wafers with 7-um-thick Si-doped n--Ga2O3 thin films on n+-Ga2O3 (001) substrates. The specific on-resistances were estimated to be 3.0 mohmcm2 for a device with an effective carrier concentration (Nd-Na) of 1.4e16 cm-3 in the drift layer and 2.4 mohmcm2 for another with Nd-Na=2.0e16 cm-3. Excellent ideality factors of 1.02±0.01 were also obtained for the SBDs. The reverse current density-voltage characteristics revealed a high breakdown voltage of around -500 V for both SBDs.

3-3. We developed a process for depositing dielectric films on Ga2O3 substrates and studied the structural properties of dielectric/Ga2O3 interfaces. SiO2 was deposited on Ga2O3 by TEOS-CVD, and the conduction band offset between the materials was determined to be about 3 eV by x-ray photoelectron spectroscopy. This value is sufficiently large for high-temperature device operation.
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