DEPENDENCE OF IMPACT IONIZATION COEFFICIENTS ON ELECTRIC-FIELD PROFILE AND INJECTION MODE-APPROXIMATIONS

The validity of the determination of the ionization coefficients deduc ed from the experimental measurement of photocurrent multiplication M( ph) in GaAlSb diodes, in which the electric-field profile is nonlinear and successive pure hole and pure electron injections cannot be made, are compared and discussed. Three methods for determining ionization coefficients k(p) and k(n) are discussed: (i) adjusting k(p) and k(n) in order to fit the experimentally observed M(ph) values using an appr oximated linear electric field; (ii) the same method applied to a more realistic electric-field profile; (iii) the Grant method in which k(p ) and k(n) are calculated from the results of multiplication measureme nts in the case of pure injections and using this last electric-field profile. It is concluded that when the condition of pure injection is not fulfilled the Grant method may lead to erroneous k values and the adjustment method is more valid.