New techniques for the study of Gunn diode contacts

Measurements are reported which provide direct evidence of the relationship between the frequency-temperature behaviour of GaAs and InP Gunn diodes and the quality of their cathode contacts. The technique used consists of damaging the cathode contact in a controlled manner while monitoring the current-voltage characteristic and df/dT. These results are compared with computer simulations of I-V characteristics and RF performance using a model diode with a region of either reduced carrier concentration or reduced mobility immediately beneath the contact. Qualitative agreement is obtained between theory and experiment. Magnetoresistance measurements on diodes both before and after damage are analysed to show that the damaged contact region contains both reduced carrier concentration and reduced mobility. Computer simulation using an appropriate model predicts I-V characteristics in general agreement with experimental observations

The single-mode rate equations for semiconductor lasers with thermal effects

A mathematical model describing the coupling of electrical, optical and thermal effects in semiconductor lasers is introduced. Numerical and asymptotic solutions are derived, including expressions for key physical quantities such as the initial time delay, the frequency of spike oscillation and the temperature rise, together with its influence on the photon density, the electron concentration and the threshold current. The consequences of thermal effects in reducing efficiency are thus quantified