Theoretical and numerical investigations of carriers transport in N-semi-insulating-N and P-semi-insulating-P diodes – A new approach

A new and simple theoretical model is developed for ambipolar transport in compensated N-semi-insulating (SI)-N or P-SI-P diodes and is validated with exact J–Va characteristics obtained through numerical modelisation. The electrical parameters used correspond to SI GaAs layers, but these results are valid for other compounds such as SI InP and InGaP. A relation between the bulk non-equilibrium excess carrier concentrations, valid for low and intermediate applied voltage, is first established. For a deep donor (Nt) compensating a residual shallow acceptor (NA): (n-ne)≈τntτptNt-NANA(p-pe), where ne and pe are the thermal equilibrium free carrier densities in the SI layer, τnt, τpt and n1t, p1t are the familiar Shockley–Read–Hall (SRH) parameters of the deep trap. This relation represents an extension of the well known quasi space charge neutrality condition: (n−ne)≈(p−pe) valid for extrinsic semiconductors. We show then that a linear J–Va relationship is observed in N-SI-N diodes when Mt(=NA(Nt-NA)τntτptp1tn1t)<1 and in P-SI-P diodes when: Mt>1. The quasi totality of the applied voltage Va is lost across the SI layer and the electric field is constant (E≈Va/LSI). Mt<1 characterizes a SI(N−) layer where a strong hole depletion (p≈0) across the SI bulk is associated to an “ohmic” electron current where n is constant but such that n1 characterizes a SI(P−) layer where forn≈0, p更多