Title
Growth kinetics and doping of gallium nitride grown by rf-plasma assisted molecular beam epitaxy
Semester
Spring
Date of Graduation
2001
Document Type
Dissertation
Degree Type
PhD
College
Eberly College of Arts and Sciences
Department
Physics and Astronomy
Committee Chair
Thomas H. Myers.
Abstract
A reduced rate for growth of GaN by plasma-assisted molecular beam epitaxy often limits growth to temperatures less than 750°C, with the reduction significantly larger than thermal decomposition rates. Conditions producing a flux consisting predominantly of either atomic nitrogen or nitrogen metastables have been established using various rf-sources. Atomic nitrogen, possibly coupled with the presence of low energy ions, is associated with the premature decrease in growth rate. An active nitrogen flux consisting primarily of nitrogen metastables produces a temperature dependence more consistent with decomposition rates. Growth with molecular nitrogen metastables results in significantly improved electrical properties.;Magnesium incorporation was studied for both (0001), or Ga-polarity and (0001), or N-polarity, orientations for various growth conditions. A significant dependence on surface polarity of Mg incorporation was observed, with up to a factor of twenty-five times more Mg incorporated on the Ga-polarity. Measurements supported surface accumulation of Mg during growth, with stable accumulations of close to a monolayer of Mg. Mg coverage of a monolayer on the Ga-polarity induced a surface polarity inversion. Atomic hydrogen was found to increase the incorporation of Mg without also incorporating potentially compensating hydrogen.;Beryllium incorporation was also studied for both polarities of GaN. Unlike Mg, surface polarity-related incorporation differences were less pronounced for Be. Measurements also support surface accumulation of Be during growth, with stable accumulations approaching a monolayer for heavier doping levels. Transmission electron microscopy studies indicate the surface layer of Be has a significant effect on structure, with severe degradation occurring when accumulation nears monolayer coverage.;High-quality GaN films were grown to study the dependence of controlled oxygen incorporation on polarity and oxygen partial pressure. Oxygen concentrations up to 2.5 x 1022 cm-3 were obtained. About 10 times more oxygen incorporates on N-polar GaN than on the Ga-polarity in high quality epilayers. Oxygen doping is controllable, reproducible, and uncompensated up to concentrations of at least 1018 cm-3 with higher levels showing significant compensation. Layers with oxygen levels above 1022 cm-3 exhibit severe cracking. Oxygen incorporation has a weak dependence on Ga overpressure during Ga-stable growth but dramatically increases for conditions approaching N-stable growth.
Recommended Citation
Ptak, Aaron Joseph, "Growth kinetics and doping of gallium nitride grown by rf-plasma assisted molecular beam epitaxy" (2001). Graduate Theses, Dissertations, and Problem Reports. 1351.
https://researchrepository.wvu.edu/etd/1351