Normally-off HfO_2-gated diamond field effect transistors

摘要

A normally-off hydrogenated-diamond (H-diamond) field effect transistor (FET) using a HfO_2 gate oxide is demonstrated. The HfO_2 gate oxide has a bilayer structure which is fabricated by a sputter-deposition (SD) technique on a thin buffer layer prepared by an atomic layer deposition (ALD) technique. The role of the ALD-HfO_2 is found to prevent deterioration of the H-diamond surface by the SD process. The leakage current density of the SD-HfO_2/ALD-HfO2/H-diamond structure is smaller than 1.1 × 10~(-4) A cm~(-2) at gate voltages from -9.0 to 2.0 V. The capacitance-voltage characteristic shows that fixed and trapped charge densities are low enough to operate the FET. The HfO_2-gated FET has p-type channel and complete normally-off characteristics. The drain-source current maximum, threshold voltage, extrinsic transconductance maximum, and effective mobility of the FET with gate length of 4μm are -37.6mAmm~(-1), -1.3±0.1V, 11.2 ± 0.1 mSmm~(-1), and 38.7 ± 0.5 cm~2 V~(-1) s~(-1), respectively.