Delta-doped β-(AlxGa1−x)2O3/Ga2O3 heterostructure field-effect transistors by ozone molecular beam epitaxy
Marko J. Tadjer, Kohei Sasaki, Daiki Wakimoto, Travis J. Anderson, Michael A. Mastro, James C. Gallagher, Alan G. Jacobs, A. Mock, Andrew D. Koehler, Mona A. Ebrish, Karl D. Hobart, Akito Kuramata
Abstract
Heterojunction field-effect transistors based on the β-(AlxGa1−x)2O3/Ga2O3 heterostructure grown by ozone-assisted molecular beam epitaxy were demonstrated for the first time. Al composition ratios in the 14%–23% range were validated using x-ray diffraction on the three samples grown for this study. Electrochemical capacitance-voltage (ECV) measurements showed the presence of a charge sheet in the delta-doped (AlxGa1−x)2O3 barrier layer. Secondary ion mass spectroscopy and ECV measurements also revealed an unintentional Si peak at the (AlxGa1−x)2O3/Ga2O3 interface. Direct current (IDS-VGS) and transconductance (Gm-VGS) measurements demonstrated depletion-mode transistor operation as well as the presence of a parallel conduction channel. A one-dimensional Poisson model suggested that dopant redistribution in the delta-doped region could cause a secondary channel to form in the barrier in addition to the primary channel near the (AlxGa1−x)2O3/Ga2O3 interface under certain conditions met in these samples. Fabricated devices on sample A did not exhibit breakdown up to the measurement limit of 1100 V, with stability after ten cycles. A maximum output drain current density of 22 mA/mm was measured on sample B. Room temperature Hall measurements yielded a sheet carrier density of 1.12 × 1013 cm−2 with corresponding Hall mobility of 95 cm2/V s in sample C.