Wide bandgap gallium nitride (GaN) based semiconductor devices, especially in the form of high electron mobility transistors (HEMT’s) and related heterojunction devices, are promising candidates for high-efficiency power electronics systems owing to their superior electrical characteristics, including high breakdown voltage (BV), low ON-resistance, fast switching speed and high operation temperature. Meanwhile, AlGaN/GaN heterostructures grown on silicon substrate have emerged as the dominant platform for developing GaN power devices because of silicon’s low cost and excellent scalability in wafer size, with 8-inch wafers already demonstrated in industry laboratories. Recently, a highly integrated process that is capable of delivering normally-off power HEMT’s and power rectifie...[ Read more ]

Wide bandgap gallium nitride (GaN) based semiconductor devices, especially in the form of high electron mobility transistors (HEMT’s) and related heterojunction devices, are promising candidates for high-efficiency power electronics systems owing to their superior electrical characteristics, including high breakdown voltage (BV), low ON-resistance, fast switching speed and high operation temperature. Meanwhile, AlGaN/GaN heterostructures grown on silicon substrate have emerged as the dominant platform for developing GaN power devices because of silicon’s low cost and excellent scalability in wafer size, with 8-inch wafers already demonstrated in industry laboratories. Recently, a highly integrated process that is capable of delivering normally-off power HEMT’s and power rectifiers on the same GaN-on-Si chip has been demonstrated. This thesis focuses on developing new techniques for performance enhancement and characterization of underlying device physics for the high-voltage GaN-on-Si power devices.

Three performance enhancement techniques are proposed by inserting Schottky-controlled normally-on and normally-off channel sections in various parts of power transistors and rectifiers. Based on these new techniques, performance enhancement has been achieved in: 1) an AlGaN/GaN dual-channel lateral field-effect rectifier (L-FER) with punch-through breakdown immunity and low ON-resistance; 2) a hybrid Schottky-Ohmic drain AlGaN/GaN normally-off HEMT with reverse drain blocking capability; and 3) an AlGaN/GaN L-FER with intrinsic ON-state current limiting capability.

In AlGaN/GaN HEMT’s on silicon substrate, it has been found that their breakdown voltages (BV’s) are ultimately limited by the vertical top-to-substrate leakage current. However, the physical mechanisms of the vertical breakdown process are seldom analyzed and discussed. In this thesis, vertical leakage/breakdown characteristics in an AlGaN/GaN-on-Si sample are studied based on the time- and temperature-dependent I-V characteristics between top Ohmic contacts and the Si substrate. The vertical leakage current is analyzed and explained with a space-charge-limited current (SCLC) conduction model that takes into account both the experimentally identified acceptor and donor traps in the GaN buffer/transition layer. Such a physical model developed in this thesis could provide essential framework for further optimization of the GaN buffer layer design.