THE TRANSPORT OF EXCESS CURRENT CARRIERS IN AN INHOMOGENEOUS SEMICONDUCTOR WITH POSITION-DEPENDENT BAND-GAP

The theory of excess carrier transport with zero magnetic field in a n ondegenerate semiconductor with position-dependent energy gap is prese nted. It is assumed that the change of energy gap is moderate at the d istance of the Debye length and in consequence the quasi-neutrality pr inciple is fulfilled. As the basis the transport equations of the ther modynamics of irreversible processes are chosen. Formulae for the tota l current density J and for the effective field J/sigma are derived. I t is shown that in addition to the ohmic component the expression for J/sigma contains the Dember effect, bulk photovoltage (Tauc's effect) and f(mu) component, the last of these being connected with the positi on dependence of mobility which is rather unavoidable in the case of a variable energy gap. The continuity equation is formulated as an exte nsion of Roosbroeck's continuity equation for a homogeneous semiconduc tor. Most typical applications of one-dimensional equations in an appr oximate form are examined, which is important from the practical point of view.