IMPACT IONIZATION IN GAAS - DISTRIBUTION OF FINAL ELECTRON-STATES DETERMINED FROM HYDROSTATIC-PRESSURE MEASUREMENTS

We have measured the avalanche breakdown voltage (V-b) in GaAs p-i-n d iodes as a function of hydrostatic pressure up to 14 kbar. The pressur e coefficient of V-b was Small and opposite in sign compared to that o f the band gap. A lucky-drift calculation of V-b including the effects of pressure on both the phonon scattering and ionization rates showed that the ionization threshold energy does not scale with the band gap . Instead, the effective threshold scales with an average of the energ ies of the Gamma, X, and L conduction-band minima. This is direct evid ence that pair production yields final electron states distributed bet ween conduction-band valleys. (C) 1995 American Institute of Physics.