Investigation of Breakdown and DC Behavior in HBTs With (Al,Ga)As Collector Layer

Published in:
IEEE Electron Device Letters, vol. 25, no. 10, pp. 672-674, October 2004.
© 2004 The IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.

Abstract:
We report on the realization of an InGaP-GaAs-based double heterojunction bipolar transistor with high breakdown voltages of up to 85 V using an Al_0.2Ga_0.8As collector. These results were achieved with devices with a 2.8 µm collector doped to 6 x 10¹⁵ cm^-3 (with an emitter area of 60 x 60 µm²). They agree well with calculated data from a semi-analytical breakdown model. A β/R_SBI (intrinsic base sheet resistance) ratio of more than 0.5 by introducing a 150-nm-thick graded Al-content region at the base-collector heterojunction was achieved. This layer is needed to effciently suppress current blocking, which is otherwise caused by the conduction band offset from GaAs to Al_0.2Ga_0.8As. The thickness of this region was determined by two-dimensional numerical device simulations that are in good agreement with the measured device properties.

Index Terms:
AlGaAs, breakdown voltage, composition graded layer, double heterojunction bipolar transistor (DHBT).

Full version in pdf-format.