ROLE OF CRYSTAL DEFECTS IN TRANSISTOR OPERATION AT HIGH POWER LEVELS.

It is demonstrated that crystal faults which originate either during crystal growth or during the transistor processing steps create weak spots in the collector structure. When the transistor is subjected to high power levels such a spot, whose position may vary depending on the base biasing, will start to pass a larger part of the current than its area warrants. The increased current may start a regenerative process which leads to a hot spot and microplasma formation. The microplasma can be detected visually by its radiation though only the IR radiation penetrates to the surface if the collector junction is deep. If the microplasma forms in the collector base junction sidewalls and is nearer the surface, higher energy photons will also penetrate to the surface. The formation of a hot spot is indicated in the characteristics by secondary breakdown failure. The ability of the transistor to operate at high power levels is therefore limited by the number, location and relative magnitude of crystal defects inside its structure.