| In this thesis, the metal-organic chemical vapor deposition (MOCVD) method is used to study the growth of gallium nitride (GaN) semiconductor. A MOCVD system has been designed with the aim of growing high quality GaN. It is necessary that a well-designed MOCVD system has controls over background impurity level, film uniformity, surface morphology, and abrupt junction formation. Design strategies that satisfy these requirements are examined. The optimization of GaN growth by MOCVD systems is then discussed. Key factors influencing the GaN growths are the quality of the low-temperature buffer layer deposition, the control over adduct formation, and the need for abundant flow of ammonia. The dependence of buffer layer on the quality of GaN layer is shown experimentally. By examining the surface morphology, electrical property, and structural property, the GaN layer is shown to depend on the thickness, growth temperature, ramp/anneal time, and carrier gas used for the buffer layer growth. The experimental results are consistent with the model of the buffer layer deposition that has been proposed. The effect of adduct formation on GaN is examined experimentally. The results indicate that the adduct formation can severely reduce the growth rate and the thickness uniformity.; Ammonia is also shown to play a significant role in determining the quality of GaN growth. Higher growth temperature produced better quality GaN growth and is also consistent with ammonia decomposition by a catalyst. The influence of reactor configuration on growth is examined. Of the three different reactor configurations, quasi-hotwall configuration produced the best GaN growth. By using this configuration, high quality GaN growth is obtained with low ammonia flow rate. The issue of GaN doping is explored with carbon doping, using carbon tetrachloride (CCl4), as a possible p-type dopant. The carbon doping level is examined by low temperature photoluminescence and by secondary ion mass spectroscopy. The carbon doping experiments were inconclusive in determining whether carbon can be a p-type dopant for GaN. For large flows, carbon tetrachloride is shown to be an in-situ etchant of GaN. A UV metal-semiconductor-metal (M-S-M) photoconductive detector has been fabricated. The detector is characterized and possible methods to improve the response time of the detector are discussed. |
