ABSTRACT
Local inhomogeneities at solid-state surfaces and interfaces are the most common reason for poor device characteristics, degradation effects and dam age in semiconductor devices. They are essentially important in the case of microwave applications due to extremely small dimensions of the active parts of high frequency devices [1]. Particular attention is attracted by factors caus ing the changes of interface potential barrier height. Fluctuations of impurity concentration near the interface or at the interface itself are usually considered as the sources of such inhomogeneities. In the latter case the surface concen-
tration of impurity atoms Ns can reach significant values (of the order of a monolayer) in the separate small regions of interface, so called "patches", due to segregation effects, surface phase generation processes or other phenomena [2]. The changes of interface or surface barrier height in such regions can be quite considerable (~ 0.1-1 eV) and such emission-active patches can exist at the emitter surfaces and in multi-layer systems [3]. Inhomogeneity sizes are usually predicted by technological factors in the range from nanometres to micrometres.
