24. Electrical Properties 3

Traps in ultra-wide bandgap semiconductors (UWBG) are problematic for devices due to the very wide range of performance degradation phenomena they can cause, from high leakage currents, dynamic resistance and voltage dispersion in transistors, to high dark currents, low quantum efficiencies and low responsivities in various optoelectronic devices. For β-Ga₂O₃, the early stage of development for this promising UWBG semiconductor and associated lack of knowledge of many basic materials properties add more challenges as many of the trap states are unknown and their physical sources are poorly understood at present. This chapter summarizes the state of knowledge concerning deep level defects in β-Ga₂O₃ materials and early stage transistors. Deep level transient and optical spectroscopies (DLTS/DLOS) are the primary characterization methods being focused on here. DLTS/DLOS measurements made on β-Ga₂O₃ materials prepared by several growth methods and irradiated by high energy particles are discussed. Defect spectroscopy measurements made directly on β-Ga₂O₃ transistors are also described. Several traps that are in common across the range of materials and devices are revealed, several unique traps are identified, and by comparing with theory and other physical characterization results, the potential physical sources for several traps are considered. Finally, this chapter attempts to correlate defect levels found in β-Ga₂O₃ transistors with the fundamental materials studies, leading toward possible identification of specific defects as primary sources for transistor instabilities such as threshold voltage shifts.