The spatial distribution of light from silicon LEDs

Well-defined light patterns emitted from circular guard ring avalanche silicon photodiodes made on CZ substrates provide an experimental proof that the reverse current does not flow all over the junction area. This fact should be taken into account in calculations of current densities in future device design considerations. The light patterns originate from zones of crystal striations. These striations, which are usually considered to be a negative factor, are utilized here to control the overall light-emission intensity. It is shown that the light-pattern dimensions and intensity are current controlled. The percentage of light area coverage, the overall emitted light intensity and the average reverse-current density are interrelated and determined as a function of the operating current. Four distinct regions of operation are identified. It is shown that the emitted light intensity is directly proportional to the area of light emission in three of the regions (low, medium and high currents) even at high junction temperatures. The results are application oriented with regard to the design of future silicon light-emitting diodes (LEDs).