GaInN/GaN multiple quantum well light-emitting diode structures in polar c-axis and non-polar m-axis growth have been compared in terms of luminescence properties. Grown under identical conditions, under low excitation density the c-axis structure has a luminescence maximum at 558 nm while the m-axis structure shows a maximum at 488 nm and shows superluminescence at 485 nm under high photoexcitation density. Under the same conditions, on increasing the excitation power, the peak intensity increases 40 fold in the in-axis structure without any variation of the emission wavelength. In similar but separately grown c-axis structures without a p-side, luminescence shifts from 555 nm at low excitation density to superluminescence at 485 nm under high excitation. The coincidence, of the superluminescence wavelength in the polar structure with the stable peak wavelength in the non-polar one, suggests that the wavelength shift in the polar structure is due to its piezoelectric polarization. The absence of such effects in the m-axis-grown structure therefore suggests a stronger dipole matrix element, potentially enabling higher quantum efficiencies and suitability for high efficiency light-emitting diode and laser diode designs in the green spectral region. (c) 2008 Elsevier B.V. All rights reserved.
Light-emitting diode development on polar and non-polar GaN substrates