A Monte Carlo study of the gunn effect behaviour of a ferromagnetic semiconductor

Abstract

A Monte Carlo method which avoids the usual approximate Boltzmann equation approach is used to calculate the electronic properties of ferromagnetic, non‐degenerate, n‐type CdCr2Se4 as a function of applied electric field strength. Full account is taken of the dispersion of the magnon system and results for the velocity–field characteristic, the mean energy, and the subband population fraction are given in graphical form. The character of the interband electron–magnon scattering rates are examined in some detail and the nature of the negative differential conductivity n.d.c. is discussed. It is shown that n.d.c. sets in (for m* = 0.1m0) at 4 kV/cm and that a peak velocity of 2.3 × 107 cm/s is achieved. These values are much more compatible with what is expected for a Gunn effect material than the previously published results which were derived from a displaced Maxwellian approximation coupled with the unrealistic assumption of a non‐dispersive magnon system.

Negative differential resistances in ferromagnetic semiconductor CdCr2Se4 single crystals

“…Following the Haas model, however, Roth and Haubenreisser [5] solved the Boltzmann equation with displaced Maxwellian approach and obtained that the peak field of N-shaped NDR for CdCr,Se4 a t 80 K was of the value of 5 x lo3 to 5 x lo4 V/cm. Aers et al [6] also obtained 4 x lo3 V/cm for the peak field for CdCr2Se4 a t 80 K with a Monte Carlo method. Thus, there is a considerable disagreement between the experimental and theoretical values of the peak field by which N-shaped NDR might be attributed to the Gunn effect.…”