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 bar rier 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 Ga N-InxGa1-xN multiple quantum wells surrounded by GaN barrier layers. O ur device structures over sapphire and cubic (111) spinel substrates c onsisted of a 10 period GaN-InGaN MQW (25 Angstrom well-50 Angstrom ba rrier) surrounded by n- and p-GaN layers. Structures with both Mg-dope d 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 d iameter mesa devices the series resistances ranged from 10 to 25 Omega . These are some of the lowest reported values. Spectral emission line widths (FWHM) of 12, 25 and 40 nm were obtained respectively for the U V, blue, and green MQW LEDs. These linewidths are similar to those of Nakamura et al. We also report on optically pumped MQW InGaN-GaN laser s with different quantum well thicknesses. In these devices, we observ ed the quantum shift related to the subband energy dependence on the w ell thickness and estimated the effective conduction band discontinuit y at the GaN-InGaN heterointerface from these data.