Properties of optimally designed green light emitting GaP:N electroluminescent diodes

Several intrinsic characteristics complicate the design of nitrogen doped green-emitting electroluminescent diodes. These include an efficiency-current density characteristic which peaks at high current density (several hundred amps/cm²), and appreciable self-absorption of the emitted light by both intrinsic and nitrogen related processes. Experimental results are presented on diodes with optimized geometries chosen to provide a clear understanding of these effects. Two geometries are emphasized: (1) A slurry cut 0.4 × 0.4 mm²diode with various junction areas, and (2) A hemispherical domed antireflection coated device. It has been found possible to achieve reduced junction areas in these devices using electrochemically controlled preferential etching techniques and these will be described. Careful comparison of diode spectra with the true internal emission spectra show that the 0.4 × 0.4 mm²diodes with reduced junction areas achieve higher external quantum efficiencies both because of higher operating current densities and because of a more favorable optical coupling geometry. The experiments show that at least a factor of two is lost by self-absorption in typical devices. The hemispherically domed, reduced active area, antireflection coated diodes recover much of this loss. This structure is shown to produce optimum optical coupling at optimum current densities for green diodes within a materials technology using only GaP.