GaN-Based Laser Diodes

Abstract

Laser diodes have been fabricated from group-III nitride layer structures grown by metalorganic vapor phase epitaxy on c-plane sapphire substrates. The gain-guided devices emitted at a wavelength of around 400 nm. The threshold current density decreased with increasing the width of the injection stripe, which was attributed to lateral current spreading below the p-metal contact. Device operation was limited to pulsed current injection due to the heating of the material. By measuring the light emission in dependence of the device temperature, the drop in intensity during a single pulse could be converted to a rise in temperature of the active region. This experimental data was in good agreement with simulations of the heat dissipation based on solving the two-dimensional heat-conduction equation. In view of reducing the threshold current density of the device, the confinement of the optical modes guided in the structure was simulated. Coupling of modes mainly guided either in the laser waveguide or in the GaN buffer layer is predicted. The use of an Al_xGa_1-xN buffer layer or an In_xGa_1-xN waveguide is suggested for complete suppression of mode coupling.