The simulation, processing, and characterization of aluminum gallium nitride/gallium nitride heterojunction transistors grown by metalorganic chemical vapor deposition

Though silicon has traditionally been the material of choice for power devices, the use of other semiconductor materials has become increasingly important due to the need for devices with equal or greater power requirements at higher frequencies. Many communication and power systems that operate at high frequency currently rely on III-V (GaAs and InP-based) or Si technology, respectively. The recent advances in crystal growth by metalorganic chemical vapor deposition (MOCVD) and fabrication technology of III-nitride-based semiconductors in the last decade extended these same characteristics to higher temperatures and frequencies. The large saturation electron velocity, high breakdown field, and excellent thermal stability are all ideally suited for high power applications in harsh environments.; The two types of transistors that have been studied are the field-effect transistor (FET), which can operate at high power density levels at high frequency for use as high-power microwave amplifiers, and the bipolar junction transistor (BJT), which can yield performance advantages because their performance limitations are set by epitaxy and not processing, and because they have higher linearity, higher current density, and more uniform threshold voltages.; A distinct advantage of the wide-bandgap nitrides to fabricate transistors is the ability to use the properties of the AlGaN/GaN heterojunction. The large bandgap difference between AlN and GaN allows relatively low compositions of AlGaN to induce large piezoelectric, polarization, and two-dimensional effects for heterojunction FETs (HFETs) and the AlGaN emitter in heterojunction bipolar transistors (HBTs) can relax doping restrictions to optimize device performance. This study investigates the results of simulated HFET and HBT device structures and compares the results to physical and electrical characterizations.; The chemical inertness of the nitride material system introduces many processing challenges that have hampered direct application of optimized device layers. An experimental understanding of the etching and metallization in these devices and the impact of device performance have been formed and a process flow for high-quality devices has been proposed. Results will be presented to complete the cycle from design to simulation to growth, complete through full device fabrication.