III-V OMVPE growth and characterisation of graded AlₓGaₓ₋₁As-GaAs layers and heterointerfaces for the development of GRIN-SCH lasers and Gunn diodes

Master Thesis


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University of Cape Town

AlGaAs-GaAs graded index single confinement heterostructure single quantum well (GRIN-SCH SQW) lasers and both 35 GHz and 94 GHz Gunn diodes have been satisfactorily grown by organometallic vapour phase epitaxy (OMVPE). This work is based on the material development of such device structures and systematically shows the steps taken to achieve the final goal of repeatedly producing high quality devices geared towards small-scale production. The key elements of the process are the realisation of high quality AlGaAs compositionally graded layers, abrupt GaAs-AlGaAs as well as dopant heterointerfaces and silicon-dopant spikes. A consistently high quality of epitaxial GaAs and AlGaAs is achievable with controllable silicon, tellurium and zinc doping on both material systems. The OMVPE system is sufficiently calibrated to grow sharp transitions in GaAs doping interfaces and quantum wells in the order of 2.5 nm. SIMS measurements showed almost square doping profiles in the 35 GHz Gunn diode structure and was able to resolve a 5 nm Si-spike doping layer in GaAs. The SIMS results of the 94 GHz Gunn diode material clearly indicates the presence of all layers with certain measured values evolving exactly as designed. These achievements are attributed to the fine pressure and flow control implemented on the reactor system by using automated steps to control the growth process.

Bibliography: pages 125-131.