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
^-2
and 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 τ
h
in the n-LPE layer are essential. While increasing nitrogen concentration N
T
, τ
h
has a constant value up to a certain N
T
value; at higher N
T
values τ
h
degrades proportionally to
N_{T}^{-2}
. The minority carrier lifetime in the low N
T
region also depends strongly on the dislocation density of the n-LPE layer. For crystals with a dislocation density less than 2 × 10
⁵
cm
^-2
, a nitrogen concentration of about 6 × 10
¹⁷
cm
^-3
gives 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.