Effects of electric field on photoluminescence spectra in InGaN ultraviolet light-emitting diodes

The effect of an external electric field on photoluminescence (PL) spectra at 77 K has been investigated in a reverse-biased InGaN/AlGaN double heterojunction ultraviolet light-emitting diode. There appear two emission components separated by about 20 meV in the vicinity of about 3.4 eV when reverse-bias voltages exceed about 8 V. The lower-energy component is dramatically decreased in PL intensity and its PL peak energies shift slightly towards lower-energy side with reverse-bias voltage. On the other hand, the PL peak energies of the higher-energy component are independent of reverse-bias voltage. These luminescence properties cannot be interpreted by the usual localized excitons and by a cancellation of the piezoelectric field. The obtained results support the free-carrier recombination model of the 3.4 eV band, which has previously been identified by magnetoluminescence studies.