Electroluminescent and Electrical Characteristics of Polar and Nonpolar InGaN/GaN Light-Emitting Diodes at Low Temperature

Three types of InGaN multiple quantum-well light-emitting diodes (LEDs) were subjected to electroluminescent and electrical characterization at low temperatures and results were compared. Characterized samples included (0001) c-plane InGaN LEDs, (1120) a-plane InGaN LEDs, and AlInGaP LEDs. While electroluminescence from the (1120) InGaN LEDs and AlInGaP LEDs extinguished and became highly electrically resistive at low temperature, the (0001) InGaN LEDs emitted light down to 7 K. This result suggested the continued presence of electrical carriers in the (0001) InGaN LEDs at low temperatures. A carrier-generation mechanism is proposed by examining the energy band diagram with polarization-induced internal electric fields taken into account. Polarization fields in the (0001) InGaN LEDs give rise to local field emission, hole-trapping potential, and interface states, which assist hole injection. It is believed that (0001) InGaN LED operation was possible at low temperatures because of these effects.