Efficiency and non-thermal roll-over of violet emitting GaInN light-emitting diodes grown on substrates with different dislocation densities

Three series of 400 nm light-emitting diodes (LED) with GaInN well widths ranging from 3 nm to 18 nm were grown on freestanding GaN- substrates, on ultra low dislocation GaN templates on sapphire, and directly on sapphire substrates using conventional low temperature nucleation. The resulting defect densities in the active layers range from 4 × 10(sup 7) to 1 × 10(sup 9) cm(sup -2). Employing pulsed electroluminescence (EL) measurements to assess the EL efficiency over a wide range of current densities up to 650 A/cm(sup 2), the LEDs grown on defect reduced substrates showed the highest EL efficiency among all devices, which was achieved for GaInN well widths greater-than 10 nm and at comparatively high current densities (greater-than 100 A/cm(sup 2)). In contrast, conventional 3 nm wide quantum well LEDs showed the peak EL efficiency at low current densities (less than 100 A/cm(sup 2)), irrespective of the type of substrate used. While LEDs grown directly on sapphire showed a pronounced short-wavelength shift of the EL spectrum by as much as 35 nm upon increasing current densities for intermediate GaInN well widths around 10 nm, the EL spectra of LEDs grown on low defect density templates or substrates occur at an almost constant wavelength which shifts by less than 5 nm upon variation of the current density from 0.5 A/cm(sup 2) to 300 A/cm(sup 2)