HETEROJUNCTION BIOLAR TRANSISTORS USING STRIAN-FREE GaAsN ALLOYS

Heterojunction bipolar transistor (HBT) performance would be improved by use of a new material which is closely lattice matched to GaAs, and has a low enough bandgap so that a GaAs emitter can be used; this eliminates the need for AlGaAs or GaInP, whose interface with GaAs is often hard to control. The alloy proposed is gallium arsenide nitirde, GaAs(1-x) N(x), with a few percent nitrogen, which is closely matched to the GaAs lattice and has a bandgap which can be adjusted from 1.45 eV to less than 1.0 eV. This material will be grown by metalorganic chemical vapor deposition (MOCVD) to be highly p-type (by carbon incorporation) without the use of external dopants; this makes it ideal for the base layer in a GaAs-GaAs(1-x)N(x) HBT. Use of this GaN-related alloy should lead to improved operation at high temperature, and improved reliability.In Phase I, we will design a GaAsN HBT structure, develop growth of GAAsN, characterize material properties, and calibrate growth parameters to obtain high P+ doping. The Phase I optional task will be for growth of GaAs-GaAs(1-x)N(X) heterojunctions, and fabrication and testing of n/P+ diodes. Phase II efforts will include optimizing HBT design (using measured GaAsN data), optimizing GaAsN growth and doping control, studying strain relief by addition of indium or antimony, developing graded collector-based heterointerfaces, and finally growing, fabricating, and testing HBT devices.