Design and Fabrication of GaN-based Permeable-Base Transistors

摘要

In this work, we present the first successful fabrication of an etched grooved GaN-based permeable-base transistor structure. Growth of the device structures was done by Molecular Beam Epitaxy (MBE) on thick HVPE GaN quasi-substrates. The fabrication process took advantage of isolations pads via He implantation and SiN deposition, as well as submicron ICP etching of collector fingers patterned via e-beam lithography. SEM of the finished devices shows smooth etched finger structures and base layer surface with finger sidewall angles of ～85° for 1:1 and 1:3 finger spacing. Specific contact resistivities of ～ 3 X 10~(-6) Ω·cm~2 for the ohmic contacts were achieved with Ti/Al/Ni/Au metallization scheme. Preliminary DC testing of the devices show a collector current I_C = 140 mAnm at V_(CE) of 5V and V_(BE) of +0.5V. The maximum transconductance g_m is ～111 mS/mm in the measured collector-emitter bias range. These values are comparable, within the measurement tolerance, to physics-based modeling results.