Current Injection in Semi-Insulating Indium Phosphide.

Steady-state current injection in planar n-SI -n Fe:InP is modeled both numerically and with the simplified theory of Lampert and Mark. The predicted I-V characteristics for various layer thicknesses are compared with experimental results from material grown by non-hydride metalorganic chemical vapor deposition (MOCVD). The simplified theory, which is based on electron drift only, fails to explain several of the observed phenomena --most notably a destructive breakdown at voltages below the trap-filled limit. The two-carrier numerical model can predict these phenomena, by allowing the inclusion of such processes as carrier diffusion, impact ionization, recombination through traps, field emission from traps, and nonlinear velocity-field relations. The mechanisms are added to the model one at a time, so as to clarify the effect of each on the progress of trap filling and on the I-V characteristics. For comparison of theories with experiment, we define a critical voltage as that at which the current reaches 1 A/cm^2, which would be an appropriate performance criterion for current blocking in many lasers. Critical voltages predicted by the numerical model are significantly lower than those of the simplified theory at both ends of the thickness range, and are in good agreement with the experimental results. Performance is dominated by carrier diffusion at the interfaces in the case of thin layers and low trap densities, and by avalanche injection in the case of thick layers and high trap densities. In the latter case, a positive feedback mechanism accounts for the experimentally observed destructive breakdown.