|AVS 57th International Symposium & Exhibition|
|Electronic Materials and Processing||Tuesday Sessions|
|Session:||Electronic Materials and Processing Poster Session|
|Presenter:||S.X. Zheng, University of Washington|
|Authors:||S.X. Zheng, University of Washington
T.C. Lovejoy, University of Washington
V. Garcia, NIMS, Japan
S. Ueda, NIMS, Japan
A. Pakhomov, University of Washington
M.A. Olmstead, University of Washington
F.S. Ohuchi, University of Washington
|Correspondent:||Click to Email|
Gallium oxide has a unique combination of properties that hold significant promise for variety applications. Pure beta-Ga2O3 has band gap of 4.8 eV which has potentials as UV-transparant optics material. Recent findings suggest its n-type semiconducting behavior after treating it in reducing atmospheres, which place it in the group of new generation transparent conductive oxides. On the other hand, its conductivity change after gases like CO and NO2 makes it a potential gas sensing material. Despite its unique optic/optoelectronic properties, incomplete mechanistic understanding of the origins of conductivity becomes a barrier to device development. According to recent findings, oxygen vacancy contribution to the conductivity is widely accepted due to inverse correlation of conductivity and oxygen partial pressure during material growth. However, other models were also proposed, e.g, experimental results show trace amount of impurities can enhance the conductivity of Ga2O3 without changing its crystal structure. On the other hand, formation energy calculation suggests possible vacancy alignment along conducting direction can also improve the electron hopping, thus enhance the conductivity. Unfortunately, most of the conclusions were either lack of experimental support, or based on samples prepared from different synthesizing techniques, whose properties can be substantially changed.
In this report, Single crystal beta-Ga2O3 prepared by float zone technique was used to investigate the electrical property change after heating under different atmospheres. It is discovered that by passing direct current through the material in the ultra high vacuum, resistivity of beta-Ga2O3 along  direction can have significant increase, which contradicts to the oxygen vacancies model. A detailed investigation using X-ray Photoemission Spectroscopy (XPS), Scanning Tunneling Microscopy (STM), Physical Property Measurement System(PPMS) reveals the change in stoichiometry, work function, surface morphology and polaron hopping dimensions, which bring insight to the origins of conductivity in Ga2O3 along different crystal orientations. Based on the understanding on the single crystal conductivity, epitaxial Ga2O3 thin film with designated resistive switching properties using Pulse laser deposition can also be prepared.