The effect of the donor concentration on the optical efficiency of solution-grown GaP diodes

Abstract

The exterior quantum efficiency of GaP diodes with a p-region doped with (Zn, O) is a function of the Te concentration in the n-type side of the junction. The highest efficiency is observed when the Te concentration in the melt is ∼4.5 × 10 −3 at. % ( n ∼ 2 × 10 17 cm −3). This corresponds to a ratio ρ n / ρ p ∼ 2.9 at 300°K. A similar effect on the radiative efficiency of the Te-doped material is also observed in photoluminescence. The initial increase in diode efficiency with increasing Te concentration is explained by enhanced electron injection into the p-region and consequent efficient recombination via the Zn-0 centers. At large Te concentration, competing loss mechanisms become important. It is suggested that the primary factor which lowers the efficiency at high Te concentrations is the decrease in the radiative efficiency as a result of the formation of non-radiative centers with increasing Te concentration beyond about 6 × 10 17 cm −3. Beyond this value, the electron concentration increases sub-linearly with increasing Te concentration in the melt, possibly because of the formation of precipitates such as Ga 2Te 3. Non-radiative tunneling is believed to be an important factor only in very heavily doped diodes.