We have studied the electrical characteristics and optical properties of GaN/InGaN multiple quantum well (MQW) light-emitting diodes (LEDs) grown by metalorganic chemical vapor deposition. It appears that there is an essential link between material quality and the mechanism of current transport through the wide-bandgap p-n junction. Tunneling behavior dominates throughout all injection regimes in a device with a high density of defects in the space-charge region, which act as deep-level carrier traps. However, in a high-quality LED diode, temperature-dependent diffusion-recombination current has been identified with an ideality factor of 1.6 at moderate biases. Light output has been found to follow a power law, i.e., in both devices. In the high-quality LED, nonradiative recombination centers are saturated at current densities as low as 1.4 10 2 A/cm 2 . This low saturation level indicates that the defects in GaN, especially the high density of edge dislocations, are generally optically inactive.Index Terms-Carrier injection, GaN, light-emitting diode (LED), multiple quantum well.

Blue and near-ultraviolet (UV) InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) with peak emission at 465 nm and 405 nm, respectively, were grown on GaN and sapphire substrates. The densities of surface and bulk defects in the homoepitaxially grown LEDs were substantially reduced, leading to a decrease in reverse currents by more than six orders of magnitude. At a typical operating current of 20 mA, the internal quantum efficiency of the UV LED on GaN was twice as high compared to the UV LED on sapphire, whereas the performance of the blue LEDs was found to be comparable. This suggests that the high-density dislocations are of greater influence on the light emission of the UV LEDs due to less In-related localization effects. At high injection currents, both the blue and UV LEDs on GaN exhibited much higher output power than the LEDs on sapphire as a result of improved heat dissipation and current spreading.

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Comparison of the annealing behavior of high-dose nitrogen-, aluminum-, and boron-implanted 4H-SiC Appl.Phosphorus and boron ion implantations were performed at various energies in the 50 keV-4 MeV range. Range statistics of P ϩ and B ϩ were established by analyzing the as-implanted secondary ion mass spectrometry depth profiles. Anneals were conducted in the temperature range of 1400-1700°C using either a conventional resistive heating ceramic processing furnace or a microwave annealing station. The P implant was found to be stable at any annealing temperature investigated, but the B redistributed during the annealing process. The implant damage is effectively annealed as indicated by Rutherford backscattering measurements. For the 250 keV/1.2ϫ10 15 cm Ϫ2 P implant, annealed at 1600°C for 15 min, the measured donor activation at room temperature is 34% with a sheet resistance of 4.8ϫ10 2 ⍀/ᮀ. The p-type conduction could not be measured for the B implants.