Impact ionization in GaAs: Distribution of final electron states determined from hydrostatic pressure measurements

We have measured the avalanche breakdown voltage (Vb) in GaAs p-i-n diodes as a function of hydrostatic pressure up to 14 kbar. The pressure coefficient of Vb was small and opposite in sign compared to that of the band gap. A lucky-drift calculation of Vb 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 energies of the Γ, X, and L conduction-band minima. This is direct evidence that pair production yields final electron states distributed between conduction-band valleys.