UV, blue and green light emitting diodes based on GaN-InGaN multiple quantum wells over sapphire and (111) spinel substrates

Recently Nakamura et al. have reported on high brightness visible LEDs based on AlGaN-InGaN multiple quantum wells (MQWs) using atmospheric pressure metal-organic chemical vapor deposition (MOCVD) and AlGaN barrier layers around an InxGa1-xN-InyGa1-yN multiple quantum well region. We now report the fabrication of high brightness vertical cavity UV, blue and green light emitting diodes using low pressure MOCVD with GaN-InxGa1-xN multiple quantum wells surrounded by GaN barrier layers. Our device structures over sapphire and cubic (111) spinel substrates consisted of a 10 period GaN-InGaN MQW (25 Angstrom well-50 Angstrom barrier) surrounded by n- and p-GaN layers. Structures with both Mg-doped and undoped quantum wells (active regions) were deposited. Mesa type LED structures were then fabricated using Ti-Al and Ni-Au for the n- and p-ohmic contacts. Light emission was observed in a vertical cavity geometry from the sapphire or the spinel substrate side. For 250 mm diameter mesa devices the series resistances ranged from 10 to 25 Omega. These are some of the lowest reported values. Spectral emission linewidths (FWHM) of 12, 25 and 40 nm were obtained respectively for the UV, blue, and green MQW LEDs. These linewidths are similar to those of Nakamura et al. We also report on optically pumped MQW InGaN-GaN lasers with different quantum well thicknesses. In these devices, we observed the quantum shift related to the subband energy dependence on the well thickness and estimated the effective conduction band discontinuity at the GaN-InGaN heterointerface from these data.