High-efficiency GaP green LED´s by Zinc diffusion into an n-LPE layer

High-efficiency GaP green LED\´s have been developed by zinc diffusion into nitrogen doped n-type liquid phase epitaxial (LPE) layers. The average efficiency for an encapsulated diode is 0.15 percent at 8 A . cm^-2and 0.23 percent at 50 A . cm^-2. In order to obtain high-efficiency diodes, an optimum nitrogen doping and a long minority carrier lifetime τhin the n-LPE layer are essential. While increasing nitrogen concentration NT, τhhas a constant value up to a certain NTvalue; at higher NTvalues τhdegrades proportionally to . The minority carrier lifetime in the low NTregion also depends strongly on the dislocation density of the n-LPE layer. For crystals with a dislocation density less than 2 × 10⁵cm^-2, a nitrogen concentration of about 6 × 10¹⁷cm^-3gives an optimum diode efficiency. A diffusion process, minimizing the deterioration of the n-LPE crystal quality, is also important. A low temperature (600-700°C) diffusion at an optimum phosphorus pressure has been developed.