GaN has the potential to revolutionize the high power electronics industry, enabling high voltage applications and better power conversion efficiency due to its intrinsic material properties and newly available high purity bulk substrates. However, unintentional impurity incorporation needs to be reduced. This reduction can be accomplished by reducing the source of contamination and exploration of extreme growth conditions which reduce the incorporation of these contaminants. Newly available bulk substrates with low threading dislocations allow for better study of material properties, as opposed to material whose properties are dominated by structural and chemical defects. In addition, very thick films can be grown without cracking due to exact lattice and thermal expansion coefficient match. Through chemical and electrical measurements, this work aims to find growth conditions which reduces contamination without a severe impact on growth rate, which is an important factor from an industry standpoint. The proposed thicknesses of these devices are on the order of one hundred microns and requires tight control of the intentional dopants. / Doctor of Philosophy / GaN is a compound semiconductor which has the potential to revolutionize the high power electronics industry, enabling new applications and energy savings due to its inherent material properties. However, material quality and purity requires improvement. This improvement can be accomplished by reducing contamination and growing under extreme conditions. Newly available bulk substrates with low defects allow for better study of material properties. In addition, very thick films can be grown without cracking on these substrates due to exact lattice and thermal expansion coefficient match. Through chemical and electrical measurements, this work aims to find optimal growth conditions for high purity GaN without a severe impact on growth rate, which is an important factor from an industry standpoint. The proposed thicknesses of these devices are on the order of one hundred microns and requires tight control of impurities.