Gallium phosphide beam lead electroluminescent devices

Beam lead GaP electroluminescent diodes have been developed using a quasi-planar configuration. This new structure couples the advantages of beam lead technology to the high-efficiency GaP p-n junctions prepared by liquid phase epitaxial (LPE) growth. The devices consist of a p-type (Zn, O-doped) LPE mesa formed on an n-type (Te-doped) LPE layer grown on an n-type Czochralski-grown substrate. A deposited insulator film covers the entire mesa surface and passivates the exposed junction perimeter. Ohmic contacts are made to both the p- and n-regions through holes in the insulating layer and beam leads are applied by conventional technology. The finished devices are shaped into domed structures during the final separation of the wafer into individual devices. Complete devices bonded to substrates were operated at 10 mA with typical forward voltages of 1.95 ± 0.05 V with external quantum efficiencies of 2-2.25 per cent (unencapsulated). This beam lead quasi-planar structure takes advantage of the inherently large size of the individual devices dictated by optical considerations and allows a number of improvements in device design. The areas where advantages over existing GaP diodes can be realized are as follows, 1) Optimization of external efficiency by contact design and diode configuration is possible. 2) Planar beam lead processing and junction passivation methods can be used, 3) Array fabrication in discrete or monolithic forms is feasible.