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Enhancement of base conductivity via the piezoelectric eect in AlGaN/GaN HBTs
 

Summary: Enhancement of base conductivity via the piezoelectric
eect in AlGaN/GaN HBTs
P.M. Asbeck*, E.T. Yu, S.S. Lau, W. Sun, X. Dang, C. Shi
University of California at San Diego, La Jolla, CA 92093-0407, USA
Received 23 May 1999; received in revised form 29 June 1999; accepted 18 August 1999
Abstract
Large polarization eects in nitride-based heterostructures provide opportunities for controllably introducing
negative charge, equivalent to acceptor-doping, in AlGaN/GaN HBT structures. This paper reviews evidence for
polarization-based doping eects in nitride-based materials, and discusses potential applications of these eects for
the improvement of p-contacts and p-type base conductivity. It is shown that in conventional HBTs grown with Ga-
terminated faces in the emitter-up con®guration, the polarization-induced charges detract from the acceptor doping
of the base. In contrast, the polarization eects add to eective doping in the base in structures that are grown and
processed as collector-up devices, or in devices that are grown emitter-up and utilize the transferred substrate
approach. # 2000 Published by Elsevier Science Ltd. All rights reserved.
1. Introduction
The development of heterojunction bipolar transis-
tors in GaN and related materials is an important
research objective. Potential advantages of HBTs with
respect to HFET structures in microwave power ampli-
®er applications, for example, include high power den-

  

Source: Asbeck, Peter M. - Department of Electrical and Computer Engineering, University of California at San Diego
Yu, Edward T. - Department of Electrical and Computer Engineering, University of Texas at Austin

 

Collections: Engineering; Materials Science; Physics