Double Injection in Long Silicon p—π—n Structures

Abstract

Current—voltage characteristics and electric field distributions have been measured in a series of long silicon p—π—n structures biased into the double injection regime. The I—V characteristics obey an I∝V2/L3 relation in which the magnitude of the current is predicted within a factor of two by the Lampert expression. As predicted by Baron (in the preceding paper) it is necessary to correct for diffusion effects. A first-order correction can be made by the use of an effective length Leff=L—Q(2La), where La is the ambipolar diffusion length. The field distribution approximates the Lampert region in the center (ε∝x1/2) bounded by exponential regions due to carrier diffusion from the n—π and p—π junctions. Detailed analysis indicates that the observed I∝V2 region was not due to pure high-level double injection, but rather exhibits the transition region due to both diffusion and thermal generation. Further, the measured lifetime is greater by about a factor of two than the lifetime required for an exact fit to the theoretical current—voltage characteristics and field distribution. The reason for this discrepancy might be due to the fact that high-level conditions were not reached.