Materials World Network

Fumio S. Ohuchi, University of Washington, DMR 0710641

• Using NIMS’s Hard X-ray Photoemission facility at the SPring-8 synchrotron (Hyogo, Japan), surface band bending of Ga2O3 was measured.

• Large surface band bending (~ 500 mV) observed on air-exposed, cleaved crystals.

• Implications include:• Difficult to make ohmic contacts

• Ionized VO++ more likely

near surface

Phase Change Materials for Nanoelectronics

• Highlights from 2010: Unconventional electrical conductivity in β-Ga2O3

• Overall Project: US-Japan Partnership focused on nanoscale understanding of phase transformation for semiconductor applications. US: University of Washington Japan: National Institute for Materials Science

• Oxygen vacancies are predicted to be neutral for Fermi levels within 0.32 eV of conduction band minimum. Creating V++ from V0 under typical n-type conditions is unlikely (Eactivation>>kBT).

• Lowest activation energy for 3-fold coordinated O3(3)

O-vacancies do not contribute to the bulk electrical conductivity, contrary to popular belief.

Calculations show VO++ unlikely source of

observed n-type conductivityExperiments show surface band bending may impact

conduction5.6

5.2

4.8

4.4

Ener

gy A

bove

Bul

k VB

M (e

V)

CBM

VO

EF

ΦBB≅0.5 eV

Since its inception 2.0 years ago, NIMS has invested >$450K to operate this overseas office. This office also fostered visits of the UW-faculty to NIMS through the MWN program.

This project is a multi-national collaboration involving three departments (Materials Sci. & Eng., Physics, and Elec. Eng.) at the University of Washington in Seattle, WA and two groups from National Institute for Materials Science (Crystal Growth group, and SPring-8 group) in Japan. By doing experiments in foreign research facilities, students gain excellent diversity training by experiencing being in the minority first hand. Also, students are trained in establishing collaborations abroad and at home.

Left: Tracy Lovejoy (left), a UW graduate student, experiences being a minority first hand during a long collaboration at SPring-8 synchrotron facility. Professor Fumio Ohuchi (right) offers advice with SPring-8 in the background.Right: Patrick Shamberger, a UW graduate student, enjoyed working with Dr. Yoshiyuki Yamashita, a beam line scientist.

Broader Impact of the Project

MWN program helped to grow NIMS’s Overseas Operation Office (O3)

Forum reception at the House of Japanese Consul General

1. Further development of UW-NIMS joint research projects2. Student exchange through coordinated UW-NIMS graduate program3. Development of UW-NIMS

administrative infrastructure4. Establishment of joint venture company5. Held joint UW-NIMS research forum

Fumio S. Ohuchi, University of Washington, DMR 0710641