Theory of the channeling avalanche photodiode

Calculations of the electron and hole impact ionization rates in doped and undoped channeling avalanche photodiode structures are presented using the ensemble many-particle Monte Carlo technique. Surprisingly, it is found that optimal device behavior is obtained not when the electrons are highly confined to the GaAs layers and the holes are swept out into the AlGaAs but rather when the carriers can drift freely from one layer to another. The presence of the AlGaAs layer acts to heat the carrier distribution functions within the GaAs layer such that the number of "lucky-drift" electrons (i.e., those that reach threshold starting within the high-energy tail of the distribution by drifting under the action of the applied electric field without scattering) is increased. Due to the difference in the energy relaxation rates between the holes and the electrons, as well as to the difference in the band-edge discontinuities, the electron ionization rate is greatly enhanced over both the hole and bulk GaAs ionization rates.