GaN based laser diodes - epitaxial growth and device fabrication

Four selected material issues of group-III nitride layer structures grown by metalorganic vapor phase epitaxy and molecular beam epitaxy on basal plane sapphire are reviewed. 1) The decomposition of GaN under the impact of hydrogen gas was measured and described thermodynamically. 2) The nucleation and coalescence of GaN islands on a low-temperature nucleation layer was identified to be the key process for the formation of edge-type threading dislocations and heterogeneous stress. 3) The doping with magnesium was associated with pyramidal defects which formed upon a critical layer thickness and led to self-compensation of the acceptors. 4) The relaxation of plain tensile stress via cracks in bulk layers and superlattices based on AlGaN was investigated. The described studies allowed for a material optimization which finally led to the successful demonstration of a GaN based laser diode under pulsed current injection. The operation of the device is discussed in terms of the perfection of the crystallographically wet etched mirror facets and the lateral current spreading in p-type AlGaN cladding layers. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)