The roles of surface reactions on the MOVPE growth of wide-bandgap semiconductors

Fabrication of III-V and II-VI semiconductor optoelectronic devices depends strongly on the success in growing thin film structures using techniques such as Metalorganic Vapor Phase Epitaxy (MOVPE). Although numerous applications in opto- and micro-electronics have prompted much research motivation, most of the devices are initially constructed by trial-and-error approaches due to the lack of a detailed understanding of the growth processes. In particular, the surface reactions which occur during thin film growth are largely unknown. This thesis has provided a fundamental description of the surface reactions occurring during MOVPE of II-VI and III-V materials using surface sensitive spectroscopic probes. Specific research focuses include (1) the influence of GaAs(100) surface reconstruction on the growth of ZnSe using dimethylzinc (DMZn) and diethylzinc (DEZn), and (2) the reactions of ammonia and trimethylgallium. (TMGa) on GaN/sapphire. In the ZnSe/GaAs system, the effect of surface structures on the reactivities of DMZn and DEZn were monitored. These studies demonstrate that the surface As/Ga ratio of GaAs affects the thermal stability of adsorbed metal atoms and the reaction pathways of surface alkyl groups. In the GaN/A1 2O3 system, the reaction pathways of the constituent precursors and the routes of impurity (H and C) incorporation were elucidated. The above studies also revealed the distinct reaction pathways displayed by surface methyl and ethyl groups. Surface methyl groups undergo sequential dehydrogenation resulting in carbon deposition while surface ethyl groups desorb via β-hydride elimination and deposit negligible carbon level. This result demonstrates the choice of ethylated precursors could reduce carbon levels in MOVPE and MOMBE of ZnSe and GaN thin films. The influence of surface hydrogen on semiconductor surfaces and the link between surface reactions and actual growth processes are also discussed