In Part I, a new theory for impact ionization that utilizes history-dependent ionization coefficients to account for the nonlocal nature of the ionization process has been described. In this paper, we will review this theory and extend it with the assumptions that are implicitly used in both the local-field theory in which the ionization coefficients are functions only of the local electric field and the new one. A systematic study of the noise characteristics of GaAs homojunction avalanche photodiodes with different multiplication layer thicknesses is also presented. It is demonstrated that there is a definite "size effect" for thin multiplication regions that is not well characterized by the local-field model. The new theory, on the other hand, provides very good fits to the measured gain and noise. The new ionization coefficient model has also been validated by Monte Carlo simulations.

It is well known that the gain-bandwidth product of an avalanche photodiode can be increased by utilizing a thin multiplication region. Previously, measurements of the excess noise factor of InP/InGaAsP/InGaAs avalanche photodiodes with separate absorption and multiplication regions indicated that this approach could also be employed to reduce the multiplication noise. This letter presents a systematic study of the noise characteristics of GaAs homojunction avalanche photodiodes with different multiplication layer thicknesses. It is demonstrated that there is a definite ‘‘size effect’’ for multiplication regions less than approximately 0.5 μm. A good fit to the experimental data has been achieved using a discrete, nonlocalized model for the impact ionization process.

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Heteroepitaxy of single-crystal Gd2O3 on GaN (with a wurtzite hexagonal close-packed (hcp) structure) and single-crystal GaN on Gd2O3 was achieved. In situ reflection high-energy electron diffraction reveals a sixfold symmetry in the in-plane epitaxy of the rare earth oxide on GaN and also in the overgrowth of GaN on the oxide. Single-crystal x-ray diffraction measurements find that these single-crystal oxide films are indeed the high temperature hexagonal phases of the sesquioxides, stabilized by the GaN substrate epitaxy. Despite a large mismatch in the lattice constant, the fully relaxed oxide films are of excellent structural quality. The x-ray diffraction results revealed that the GaN grown on the rare earth oxide is a single-crystal and has the same crystallographic hcp structure as the underlying GaN. The structures of both layers of GaN were also studied by cross section transmission electron microscopy.

Ga 2 O 3 ( Gd 2 O 3 ), electron beam evaporated from a single crystal Ga5Gd3O12 garnet, was ex situ deposited on molecular beam epitaxy grown GaN of Ga-polar surface. Using capacitance–voltage measurement, accumulation and depletion behavior was observed in the Ga2O3(Gd2O3)/GaN metal–oxide–semiconductor diodes, with an interfacial density of states less than 1011 cm−2 eV−1. The Ga2O3(Gd2O3)/GaN interface remains intact with the samples subject to rapid-thermal annealing up to 950 °C, as studied from x-ray reflectivity measurements.