Harmonic generation in nondegenerate semiconductors at low lattice temperature

The characteristics of second harmonic generation (SHG) in covalent semiconductors at low lattice temperatures are studied here over a wide range of the bias field, beginning from a weakly heated carrier ensemble up to the onset of impurity breakdown giving due consideration to the effect of recombination of the nonequilibrium carriers in the presence of shallow attractive traps. The calculations are carried out for a parabolic law of dispersion and a scalar effective mass. The results confirm that the recombination effects bring in both qualitative and quantitative changes in the SHG characteristics throughout the entire range of the bias field. Like the situation around room temperatures, the curves for the efficiency of SHG versus the bias field at low lattice temperatures also exhibit maximum, thus illustrating the optimum bias field for which the generation can be most efficient. Depending upon the lattice temperature and the material, the recombination effects may bring in a second maximum in the characteristics of SHG. The results are found to be useful for the determination of some capture parameters. The inadequacies of the theory are pointed out and the scope for further refinement is discussed.