No abstract

We demonstrate room temperature pulsed operation of nitride based multi-quantum-well (MQW) laser diodes with cleaved mirror facets grown on a conventional C-face sapphire substrate. Cleavage was performed along the <11*BAR*2*BAR*0> direction of the sapphire substrate, and the resultant facet was analyzed using an atomic force microscope (AFM) and theoretical calculation. A single peak emisson, at a wavelength of 417.5 nm, with a full width at half-maximum of 0.15 nm, was obtained. The threshold current density of the laser was 50 kA/cm2 and a voltage for the threshold current was 20 V.

Improvement in temperature characteristics of GaN laser diodes is important for realizing reliable devices operating at high temperatures. Thermal characteristics of GaN lasers have been analyzed by using a three-dimensional thermal conduction model. Maximum operation temperature has also been calculated. It was shown that the reduction in the stripe width as well as the reduction in threshold current density and operation voltage is very important for improving the temperature characteristics of GaN laser diodes.

Carrier overflow and perpendicular transverse mode in InGaN multi-quantum-well lasers have been analyzed by numerical calculation. A high acceptor concentration for the p-type cladding layer and the reduction of the active layer volume have a large effect on the reduction of carrier overflow. Anti-guide-like behavior of the waveguide mode is formed in InGaN laser structures where the cladding layers have insufficient thickness. The layer structure should be designed so as to reduce the carrier overflow and suppress the anti-guide-like mode.

SUMMARYDevice characteristics of GaN-based semiconductor lasers have been analysed by numerical calculation. Anti-guide-like behaviour of the waveguide mode appears in InGaN laser structures where the cladding layers have insu$cient thickness. Such phenomena are peculiar to laser structures with GaN material systems. The layer structure should be designed so as to suppress the anti-guide mode. Carrier over#ow is also a signi"cant problem for GaN lasers. A high acceptor concentration for the p-type cladding layer and the reduction of the active layer volume have a large e!ect on the reduction of such carrier over#ow. In regard to the temperature characteristics, one of the restricting factors is the use of sapphire substrates which have relatively high thermal resistivity. The maximum operation temperature has been calculated based on the analysis for the thermal resistance of the device. It was shown that reduction in the stripe width as well as reduction in threshold current density and operation voltage is very important for improving the temperature characteristics of GaN semiconductor lasers.