| Although commercially available high-electron mobility transistors (HEMTs) based on the III-Nitride material system are available, there still remains areas for further optimization. These transistor devices are currently limited because of current leakage when the devices are operated at increased operating voltages. To reach the full potential of these devices, these leakage mechanisms need to be addressed. The objective of this work is to utilize the highly resistive properties of carbon-doped gallium nitride (GaN) as a low-leakage buffer layer for HEMTs. By increasing the resistivity of the underlying GaN layer, the source-drain current flow will be limited to electrons in the two-dimensional electron gas (2DEG) confined to the interface, reducing leakage paths through the GaN buffer layer, ultimately increasing the power density of the device.;These films are deposited via a novel ammonia-based metal-organic molecular beam epitaxy (NH3-MOMBE) system capable of producing unintentionally carbon-doped GaN films with carbon concentrations ([C]) in excess of 10 21 atoms/cm3. These high levels of carbon incorporation lead to highly-resistive GaN buffer layers with a resistivity estimated at ∼10 12 O-cm. In addition, the deposition of aluminum gallium nitride (AlGaN) has been accomplished for the first time in an NH3-MOMBE environment. The AlGaN alloy is necessary for the production of a 2DEG, which is the source of electrons for the operation of the transistor. While providing the ability to produce highly-resistive buffer layers, the carbon which is unintentionally incorporated during the deposition of the films may also become a source of channel depletion if the incorporation levels cannot be controlled. The results of this work demonstrate that carbon-doped NH3-MOMBE thin films are extremely resistive, yet further optimization is necessary for the realization of transistor devices because of the trap states that are produced from the excessive carbon incorporation levels. |
