Anomalous current–voltage characteristics of InGaN/GaN light-emitting diodes depending on Mg flow rate during p-GaN growth

The dependence of the forward operating voltage of In1−xGaxN/GaN light-emitting diodes (LEDs) on Mg flow rate during the growth of the p-GaN layer has been investigated. The hole concentration in the p-GaN layer increases with Mg flow rate up to a critical value and gradually decreases for higher flow rates. We find that the forward threshold voltage of the LEDs mainly depends on the Mg concentration in the p-GaN layer and is rather independent of hole concentration. A current flow mechanism involving the impurity acceptor band, instead of the usual valence band, is proposed to elucidate this anomalous behaviour of the I–V characteristics.