[1] Univ Tsukuba, Inst Appl Phys, Tsukuba, Ibaraki 3058573, Japan
[2] Univ Tsukuba, Ctr Tsukuba Adv Res Alliance, Tsukuba, Ibaraki 3058573, Japan
[3] Image Related Device Dev Ctr, Electron Tube & Devices Div, Kokubunji, Tokyo 1858601, Japan
[4] AIST, Electrotech Lab, Tsukuba, Ibaraki 3050045, Japan