Experimental Study Of Damage Accumulation In GaN Induced By Low-heavy Ion Irradiation

As the third generation semiconductor, GaN has attracted huge research interest due to its unique properties. It has great application and development prospects in the field of microelectronics and optoelectronics. Ion implantation has its great advantage in circuit fabrication for the integration of such devices. However, irradiation process inevitably produces lattice disorder that is detrimental to the device performance.In this dissertation, the damage accumulation in GaN crystal induced by low-heavy ion irradiation was studied. X-ray diffraction (XRD), Rutherford Backscattering/ Channeling (RBS/C), Atomic force microscopy (AFM) and Scanning electron microscopy (SEM) were utilized to study the damage and surface morphology in irradiated GaN. It is found that swelling occurred at an ion dose of 5×10¹⁴/cm² on the surface of the GaN after irradiated by 500keV Au⁺ ions. The higher the ion dose is the higher the swelling step height would be. Volatilization appeared on the surface of irradiated GaN after annealing at different temperatures. When annealed at 1000℃, it is found the step height between irradiated and unirradiated GaN is near the range of Au at energy of 500keV. In the study it is also found that GaN can be etched in AZ-400K photoresist developer and aqueous KOH at 80℃after irradiated by 100 or 500keV Au ions at ion doses from 1×10⁹/cm² to 5×10¹⁵/cm². With this method, defects in GaN films, after being irradiated by heavy ions, can be revealed with an etch pit density of 10⁶-10⁸/cm², far less than the irradiation ion dose but the similar magnitude with that in as-grown GaN films. Additionally, the etched pits present different features at different ion dose. Two different types of etch pits with different sizes can be observed when etched in aqueous KOH. Ion irradiation induced the appearance of new defects. The original defects in GaN could act as sinks to capture the produced defects by ion irradiation, which reduced the activation energy required for the etching of original defects in GaN. It indicates that single ion irradiation cannot be etched in GaN film and low-heavy ion irradiation can enhance the wet etching of GaN film at the sites having original defects.