The effects of interface states on the capacitance and electroluminescence efficiency of InGaN/GaN light-emitting diodes

Abstract

The capacitance-voltage characteristics and external quantum efficiency of electroluminescence in blue GaN light-emitting diodes (LEDs) with an InGaN quantum well have been investigated in the temperature range 77–300 K. The results obtained are interpreted taking into account the effect of the InGaN/GaN interface states of structural defects and impurities on the capacitance of the GaN LEDs. The nonlinearity of the C ⁻²(U) characteristics observed at low forward bias is attributed to an increase in the interface charge resulting from tunneling of free electrons and their trapping at the interface states. According to estimates, states with a density of about 3 × 10¹² cm⁻² are present at the interface. A recombination current in the interface region suppresses the injection of charge carriers into the quantum well and decreases the electroluminescence efficiency at high forward bias. Degradation of the optical power of the LEDs, accompanied by an increase in the measured capacitance, is attributed to an increase in the density of charged interface states and changes in their distribution in the band gap.