ON ELECTRON-TRANSPORT ACROSS INTERFACES CONNECTING MATERIALS WITH DIFFERENT EFFECTIVE MASSES

We reconsider the problem of electronic transport across a heterojunct ion interface connecting two materials with different effective masses . Thermionic current does not remain invariant when the position X-int of the interface is shifted relative to that of the potential energy maximum, X-max, even if the shift is smaller than the carrier mean fre e path. We analyze every situation that arises when X-max = X-int, as well as the limiting case X-max --> X-int. Besides the effective mass discontinuity at the interface, we allow for a band-edge discontinuity within a potential barrier of arbitrary shape. In most practical situ ations, the effective Richardson constant governing thermionic emissio n over a heterointerface barrier is determined by the effective mass i n the material that contains X-max. This statement is rigorously true when the effective mass at X-max is lower than that in the other mater ial, otherwise it is an approximation dependent on the value of the in terface potential. The issue clarified in this work has relevance to t heoretical constructs involving model boundary conditions at heterojun ction interfaces.