A theory for high-efficiency oscillations in gallium arsenide avalanche diodes

Abstract

An analytic theory is presented for high-efficiency microwave oscillations in gallium arsenide avalanche diodes by extending an approach similar to that of DeLoach and Scharfetter for silicon, and incorporating realistic approximations for the velocity field profiles and the ionization coefficients of the carriers. In gallium arsenide the electrons have a negative differential mobility over a certain range of electric field values, and this is found to be an important effect necessitating the inclusion of a diffusion mechanism in some cases. The two structures n+-p-p+ and p+-n-n+ differ considerably and are treated separately.The theory enables design and performance criteria to be deduced. Results are obtained for an upper bound to the frequency, the optimum frequency and the peak diode current for a range of different depletion layer widths and doping densities. Also it is found that for a particular doping density there is an upper limit to the width for high-efficiency oscillations to occur. A comparison is made with preliminary experimental results.