Analysis of the temperature dependence of the forward voltage characteristics of GaInN light-emitting diodes

The forward voltage characteristics of GaInN light-emitting diodes are studied in the temperature range of 80 K to 450 K. The forward-voltage-vs.- temperature curve has a "two-slope" characteristic with a slope of dV_f/dT = -1.7 mV/K and -8.0 mV/K at room temperature and cryogenic temperatures, respectively. To investigate the two-slope characteristic, we perform transmission-line-model measurements on p-type GaN and show that both p-type contact and sheet resistance decrease drastically with increasing temperature. We conclude that dV_f/dT in the high-slope region is limited by p-type sheet and contact resistance, and in the low-slope region by the GaN pn junction properties.