SPECTROMETRY OF VERY LONG-CURRENT TRANSIENTS IN ALMOST IDEAL SILICON P-N-JUNCTIONS

Proper gettering and annealing processes allow construction of silicon p-n junctions whose current-voltage characteristic either completely obeys the Shockley equation (ideal junctions) or, for reverse bias, ha s three components (almost ideal junctions): a voltage-independent ter m, which may be much smaller than the diffusion saturation current, a generation-recombination contribution, and an ohmic component. The las t two currents are due to defect centers that have the same activation energy and which are electrically neutral. In preceding works it has been shown that such an experimental finding may be ascribed to four-s tate traps, i.e., to defect centers that may be empty of carriers, or filled by an electron or a hole, or both, and which are created by loc alized states, with different positions and energy levels, due to the oxygen. In the present work an experimental system for measuring, at 0 +/-0.05-degrees-C, the current transients produced in almost ideal jun ctions by changes of the reverse-bias voltage, and an analysis method for performing the spectrometry of such transients are described. It i s found that these last a few hours and that they are composed of four exponential terms whose relaxation times range from tens to a few tho usands of seconds. Finally, it is shown that such experimental results also can be ascribed to the preceding defect centers generated by Si( y)O(x) clusters of a few hundred atoms of oxygen put near the junction interface, which emit carriers through a tunnel-assisted thermal emis sion.