Defect clustering in GaN irradiated with O + ions
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Transmission electron microscopy (TEM) was used to study microstructures formed in GaN irradiated with 600-keV O+ ions at room temperature. Three types of defect clusters were identified in the irradiated GaN: (i) basal-plane stacking faults with dimensions ranging from 5 to 30 nm, (ii) pyramidal dislocation loops, and (iii) local regions of highly disordered material. High-resolution TEM imaging clearly revealed that one type of the basal-plane stacking faults corresponded to insertion of one extra Ga–N basal plane in the otherwise perfect GaN lattice. The interpretation of these results indicated that interstitials of both Ga and N preferentially condensed on the basal plane to form a new layer of Ga–N under these irradiation conditions. The formation of these extended defects and their interactions with the point defects produced during irradiation contributed to a dramatic increase in the dynamic recovery of point defects in GaN at room temperature.
I. INTRODUCTION
Considerable research and development efforts have been made over the last decade to explore the potential of GaN for optoelectronic applications. These efforts include the development of appropriate methods for growing high-quality, single-crystal GaN thin films,1,2 the correlation of its electrical and optical properties with its microstructure,1,3 and ion-implantation-related phenomena.4–12 Ion implantation is a critical technique to spatially dope selective donor and acceptor ions into GaN for fabrication of advanced optoelectronic devices. However, ion implantation introduces structural damage that can significantly degrade the properties, performance, and lifetimes of the devices. Advancements in GaN technology require fundamental understanding of the defects and damage states produced during ion implantation, as well as detailed knowledge of the dynamics of recovery processes for these defects and damage states. Studies of ion-implantation-induced damage in GaN have been performed with respect to the following: (i) damage accumulation, amorphization, dynamic annealing, preferential surface disordering, and possible types of defects; (ii) effects of irradiation conditions, such as ion fluence, ion mass, ion energy, irradiation temperature, and ion flux; and (iii) recovery behavior of the damage during thermal annealing. Results of these studies have been collectively reported in a recent review by Kucheyev a)
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et al.7 One of the most prominent features of damage accumulation in ion-irradiated GaN is the efficiency of dynamic annealing, particularly above a threshold damage level (e.g., defect concentration). Consequently, GaN requires high doses to amorphize, even at low temperatures. Furthermore, GaN has been found to exhibit intermediate saturation of the relative disorder over the temperature range from liquid nitrogen to room temperature. Cross-sectional transmission electron microscopy (TEM) analysis has revealed that planar defects are a typical feature found in G
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