Novel fabrication of C-doped base InGaAs/InP DHBT structures for high speed circuit applications

We have fabricated InGaAs/InP based DHBTs for high speed circuit applicatio ns. A process involving both wet chemical and ECR plasma etching was develo ped. Carbon was employed as the p-type dopant of the base layer for excelle nt device stability. Both the emitter-base and base-collector regions were graded using quaternary InGaAsP alloys. The extrinsic emitter-base junction is buried for junction passivation to improve device reliability. The use of an InP collector structure with the graded region results in high breakd own voltages of 8-10 V; with no current blocking. The entire structure is e ncapsulated with spin-on-glass. These devices show no degradation in d.c. c haracteristics after operation at an emitter current density of 90 kA cm(-2 ) and a collector bias, V-CE, Of 2 V at room temperature for over 500 h. Ty pical common emitter current gain was 50. An f(t) of 80 and f(max) of 155 G Hz were achieved for 2 x 4 mu m(2) emitter size devices. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.