Ultrawide Bandgap Semiconductor Devices and Monolithic Circuits
This thesis investigates the potential of ultrawide bandgap (UWBG) semiconductors like gallium oxide (Ga2O3) and aluminium nitride (AlN) for high-power applications, focusing on the development of monolithic devices and circuits, including pseudo-CMOS inverters, bidirectional switches, and MOSFETs, demonstrating their potential for next-generation electronics operating in extreme environments.
Overview
As the world transitions to sustainable energy with increased adoptions of green technologies like solar cells, electric vehicles, etc. Traditional narrow bandgap semiconductors like silicon (Si) are being outpaced by wide bandgap (WBG) semiconducting materials such as silicon carbide (SiC) and gallium nitride (GaN) in high-power applications. Ultrawide bandgap (UWBG) semiconductors like gallium oxide (Ga2O3), diamond, aluminium nitride (AlN), and cubic boron nitride (c-BN), with superior power density, switching capabilities, thermal stability, and radiation resistance are promising candidates for next-generation electronics.
This thesis investigates the potential of UWBG semiconductors for high-power applications with the capability of operating in extreme environments and reduced system size. The study begins with a comprehensive market analysis, highlighting the growing demand for robust power electronics and renewable energy solutions. Through a detailed assessment, UWBG semiconductors such as Ga2O3 and AlN are identified as promising candidates due to their superior electrical properties and the availability of large substrates. However, the UWBG semiconductors have their challenges such as the unavailability of complementary dopants, poor ohmic contacts, low carrier mobility, etc.
Addressing this, the thesis delves into the development of β-Ga2O3 pseudo-CMOS monolithic inverters with dual-stage configuration and is compared with conventional single-stage inverter design. The fabricated pseudo-CMOS inverters demonstrate a gain of 8 V/V for a supply voltage of 3 V along with power consumption as low as 0.2 nW. The thesis further showcases the first heteroepitaxial β-Ga2O3 monolithic bidirectional switch and the device characteristics are further improved by homoepitaxial growth with improved mobility. The optimized homoepitaxial monolithic bidirectional switch works on enhancement mode operation with a threshold voltage of ~4 V. The device shows a high ON/OFF current ratio of 107 in a bidirectional mode having an ON current density of 1.9 mA/mm at 5 V drain voltage. Furthermore, in diode mode, the device shows an ON/OFF current ratio of 108 in unidirectional mode. The fabricated monolithic bidirectional switch is then used to chop a 60 Hz input AC waveform at a chopping frequency of 1 kHz implying its promising application in various converters.
The thesis further explores AlN which has a larger bandgap and better thermal conductivity compared to Ga2O3. The challenge in the development of AlN ohmic contact is investigated and contact resistance as low as 0.148 Ω·cm2 is achieved. Using the optimized contact, the AlN metal oxide semiconductor field effect transistor (MOSFET) is demonstrated for the first time to the best of my knowledge. The fabricated AlN MOSFET exhibits a threshold voltage of −10.91 V, with an effective mobility of 2.95 V2 V-1 s-1 and an ON/OFF current ratio of two order magnitudes and a corresponding breakdown field of ~0.5 MV cm-1. This thesis lays the foundational groundwork for the development of UWBG monolithic devices and circuits, with a specific emphasis on β-Ga2O3 and AlN.
Presenters
Brief Biography
Dhanu Chettri is a Ph.D. candidate at the Advanced Semiconductor Laboratory (ASL) at King Abdullah University of Science and Technology (KAUST), under the mentorship of Prof. Xiaohang Li. His research focuses on ultra-wide bandgap semiconductors, particularly Gallium Oxide (Ga2O3) and Aluminum Nitride (AlN). Before joining KAUST, he served as a Senior Project Fellow at the Council of Scientific and Industrial Research–Central Electronics Engineering Research Institute (CSIR–CEERI).
Chettri’s research primarily involves material growth, device design, fabrication, and circuit implementation of advanced semiconductor devices such as MOSFETs and bidirectional switches. He has made significant contributions to the field, as evidenced by his publications. Notably, he achieved the first demonstration of a normally OFF β-Ga2O3 bidirectional switch, featured in Applied Physics Letters, AIP along with the first demonstration of an AlN MOSFET, published in the Journal of Physics D, IOP.
His research is particularly relevant for developing technologies suited to high-temperature and extreme environment applications, demonstrating the critical role and potential of ultra-wide bandgap semiconductors in modern electronics.
