| Description |
Power devices are intimately involved in generation, transmission, and consumption of electricity. Current silicon-based power devices are limited by the low breakdown field and low switching frequencies of silicon. Due to its large bandgap and critical breakdown field strength, β-Ga2O3 has emerged as a promising ultra-wide bandgap material for power electronic devices. DFT based transport modelling shows that by forming a two-dimensional electron gas (2DEG) at the β-(AlxGa1-x)2O3/β-Ga2O3, mobility values much higher than the β-Ga2O3 limit (~200 cm2/V. s) could be achieved. This dissertation explores doping schemes for Ga2O3 thin films and heterostructures for potential high-performance device applications. Various doping studies are undertaken to understand uniform doping, delta doping, modulation doping and polarization doping in Ga2O3. The primary focus of this work is to realize a modulation-doped 2DEG channel at β-(AlxGa1-x)2O3/β-Ga2O3 heterointerface. β-(AlxGa1-x)2O3 growth and delta doping of β-Ga2O3 are explored to understand 2DEG formation in β-(AlxGa1-x)2O3/β-Ga2O3 heterostructures. Degenerate doping up to ~8 x 1019 cm-3 is achieved in β-(Al0.26Ga0.74)2O3 by changing the silane flow. By a using a uniformly-doped β-(AlxGa1-x)2O3 barrier a sheet charge density of 2.3 x 1012 cm-2 is realized. Delta doping of β-Ga2O3 is explored to further improve the 2DEG density. The silicon incorporation and activation are studied using secondary-ion mass spectroscopy and capacitance-voltage measurements. By reducing the growth temperature to minimize surface riding of silicon dopants, sharp doping profile with a CV measured FWHM of ~3 nm is achieved. Using MOVPE based n+ regrowth process for the ohmic contacts, a completely MOVPE-based MODFET has been realized. Furthermore, a 2DEG channel with a record low sheet resistance of 5.3 kΩ/square is achieved. Further reduction in the barrier doping resulted in the formation of a pure 2DEG channel of 1 x 1012 cm-2 with a mobility of 149 cm2/V.s. This dissertation also explores 2DEG formation at ε-(AlxGa1-x)2O3/ε-Ga2O3 heterojunction with the aid of DFT calculated material properties. Finally, a new growth process was developed for achieving n-type doping in LPCVD-grown β-Ga2O3 films. The final chapter outlines ideas for future studies on improving 2DEG density in (AlxGa1- x)2O3/Ga2O3 heterojunctions and device designs for high performance devices based on (AlxGa1-x)2O3/Ga2O3 2DEG channels. |
