Resistive gate MOS modulation of light emission from a silicon LED array

Abstract

Multi-terminal silicon CMOS light emitting diode structures are described where the light emission intensity from the reverse biased pn junctions is modulated by gate voltages applied to overlapping polysilicon gates. Linear arrays, as well as two-dimensional arrays of Si LED's were realized in combination with a grid of overlapping resistive polysilicon gates. The gate voltages applied to the resistive gate grid at different points modulated the pn junction breakdown, and thus the reverse avalanche current through the diodes. A novel structure where the light pattern can be changed from two point sources to a single line source using one MOS control gate has also been realized. A linear relationship exists between reverse current and light intensity, but due to the nonlinear variation of breakdown voltage with applied MOS gate voltage, the light intensity varies approximately with the square root of the applied voltage. This nonlinear behavior may facilitate electro-optical signal processing. The resistive gate grid voltages can be used to generate different breakdown voltages at different positions in the LED array. The result is that the array emission pattern is a function of the applied gate voltages. Spatial modulation of the light emission pattern is demonstrated for several device structures.