成果報告書詳細
管理番号20130000000248
タイトル*平成24年度分中間年報 省エネルギー革新技術開発事業 超高耐圧酸化ガリウムパワーデバイスの研究開発(H23-H25)
公開日2013/5/31
報告書年度2012 - 2012
委託先名国立大学法人京都大学 国立大学法人東京工業大学 独立行政法人情報通信研究機構 株式会社タムラ製作所 株式会社光波
プロジェクト番号P09015
部署名省エネルギー部
和文要約
英文要約Title:Research and Development Program for Innovative Energy and Efficiency Technology. Research and Development of Ultra-High-Voltage Gallium Oxide Power Devices (FY2011-FY2013) FY2012 Annual Report
2-1-2) Insulating Al2O3 and (Al,Ga)2O3 thin films, aiming at gate insulators or passivation of MOSFETs, has been fabricated using a safe and cost-effective mist CVD method. We showed successive formation of amorphous Al2O3 of high resitivity (>10^13 ohm-cm) and alpha-(Al,Ga)2O3, as well as good alpha-(Al,Ga)2O3/Ga2O3 heterointerface without noticeable interface defects.
2-1-3) High-quality (x-ray omega-scan rocking curve FWHMs < 100 arcsec) alpha-Ga2O3 films were successfully grown on sapphire at higher growth rate of >2 micron/h.
2-2-1) Novel technologies for controlling carrier concentrations have been evolved. Doping of Si by PLD allowed tuning of carrier concentration from the order of 10^17 to 10^19 cm-3. Thermal anneling of conductive Ga2O3 substrates in air formed highly-resistive layers at the surface due to thermal diffusion of oxygen from the surface.
2-2-2) PLD of (Al,Ga)2O3 on (-201) beta-Ga2O3 substrates, toward the heterostructured-gate of FETs, revealed the systematic variation of Al composition from 0.51 to 0.83, though the surface roughness remained.
2-3-2) (1) Ion implantation of Sn, followed by thermal annealing in N2 at 1150 deg.C for 30 min, was effective for conductivity control of beta-Ga2O3, allowing the tuning of donor concentration. Low-resistive ohmic contacts (1.1x10^-4 ohm-cm2) were formed by the ion implantation, evaporation of Ti/Au, and thermal anneling at 500 deg.C. (2) Au/Al2O3/n-Ga2O3 MOS diodes were fabricated, where the Al2O3 layer was formed either by thermal-mode (oxygen source: H2O) or plasma-mode (oxygen source: oxygen plasma) of ALD at 250 deg.C. Small hysterisis was seen when Al2O3 was formed by the thermal-mode, while no marked hysteresis appeared by the plasma-mode. The result encourages the fabrication of high-quality Al2O3 layers and MOS interface.
2-4) Optimum condistions for Sn-doped beta-Ga2O3 have been investigated. At the growth temperatures of 550-650 deg.C, the surface was extremely smooth (surface roughness RMS of <1 nm). The minimum doping concentration was 8x10^15 cm-3, suggesting fabrication of Ga2O3 films with low donor concentration and high-quality required for ultra-high-voltage SBDs.
2-5) (1) To establish a quick evaluation method of dislocation density, we investigated a correlation between etch pits and dislocations in Ga2O3 using cross-sectional TEM. It was found that one etch pit corresponds to on dislocation. The dislocation density of the sample was estimated to be the order of 104^cm-2. (2) Highly-resistive substartes (1.8x10^12 ohm-cm) were made by Fe-doping. (3) 4-inch-wide Ga2O3 substrates were obtained by the EFG method, though several cracks were seen. Improvements of growth systems are under progress for higher quality.
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