No abstract

Micro-Raman spectroscopy was used to study piezoelectric strain in AlGaN∕GaN heterostructure field-effect transistors under bias. The measurements were made through the transparent SiC substrate. Strain in the GaN layer varied over the device area and was dependent on bias voltage, and affected, in particular, the gate-drain gap and area underneath the drain contact. The observed strain in GaN was shown to be related to the electric field component normal to the surface. Finite element simulations of electric field distribution show good qualitative agreement with the experimental data. Effects of strain on Raman temperature measurements in transistors are also discussed.

We present a study of the effect of the growth of a thin AlN exclusion layer between the AlGaN barrier layer and GaN buffer layer in microwave heterojunction field-effect transistor structures. A dramatic improvement in carrier drift mobility is observed and we present evidence from electronic structure calculations and capacitance-voltage experiments that this improvement is associated with reduced alloy scattering. However, no significant benefit is seen at low carrier concentrations. Reduced electron trapping in the AlGaN is an additional benefit.

A study of the effect of the insertion of a thin AlN exclusion layer between the AlGaN and GaN buffer layer in microwave hetero-junction field effect transistor structures grown by MOVPE on sapphire and SI-SiC substrates is presented. A dramatic improvement in carrier drift mobility is observed and we present evidence from CV analysis that this improvement is associated with reduced penetration of the 2D electron gas into the AlGaN.

We have used a novel, simple technique based on bevel etching, to fabricate samples containing lateral n-i-p junctions in an InSb/InAlSb quantum well. The structure was designed by self-consistent solution of Schrödinger's and Poisson's equations, and grown by molecular beam epitaxy on a SI GaAs substrate. Current/voltage characteristics were measured as a function of temperature between 10 and 80 K, and rectifying characteristics were obtained over the whole temperature range.