ANALYSIS OF TRANSIENTS IN SEMICONDUCTOR SEMI-INSULATOR JUNCTIONS

A junction between an epitaxial semiconductor and a semi-insulating su bstrate serves as a tool for analyzing transient behavior in semi-insu lators (SI). At equilibrium a narrow region which is fully depleted fr om electrons exists in the SI. The application of a reverse bias resul ts in an additional partially depleted region. initially depleted just from free carriers, adjacent to the fully depleted one. As the transi ent progresses electrons are released from the deep traps in the SI. T he partially depleted region collapses into a wider fully depleted reg ion. This process is manifested by a substantial current transient thr ough the SI. The charges emitted recombine in the epitaxial layer lead ing to a decrease in its conductance due to a narrowing conducting pat h. Thus it is possible to characterize this process by measuring the ( large) current through the epilayer rather than the (small) current th rough the SI. These transients are a function of the emission coeffici ent. Their analysis provides data also on the energy gap of the traps, their capture coefficient, and the electron lifetime. The long decays can be accelerated by illuminating with photons of energy below the b and gap but larger than the energy spacing between the deep traps and the conduction band.