Multijunction AC or DC integrated GaP light emitting diode array

An ac or dc GaP LED array has been designed and fabricated which has potential as a direct replacement for several tungsten filament lamps and as an illuminator for new design considerations. In designing such an LED for high-voltage application, series light emitting junctions rather than series resistors are used as a voltage divider to maximize the light output/power input ratio. A figure of merit is modeled and calculated which provides a measure of total light output for a given applied current and voltage as a function of the number of series diodes. The optimum number of series diode for a given ac voltage is Vrms/1.94. Thermal calculations based upon chip size, power dissipation, and thermal contact resistance predict a peak temperature rise of 30°C for the bonded die approach. n- and p-type liquid phase epitaxial layers were grown on semi-insulating substrates, p-n junctions on the same chip were electrically isolated utilizing either proton bombardment or chemically etched trenches. An Au metallization scheme provides the series-parallel interconnection required for ac or dc operation while maintaining junction isolation. The light emitting junction areas are mesas, with edges shaped to redirect internally generated light out to the viewer. The near field radiation pattern demonstrates the optical effectiveness of the shaped-mesa emitters.