III-nitrür ince filmlerin plazma-destekli atomik katman biriktirme yöntemi ile büyütülmesi

III-nitride compound semiconductors and their alloys have emerged as versatile and high-performance materials for a wide range of electronic and optoelectronic device applications. Besides possessing very unique material properties individually, members of the III-nitride family with wurtzite (hexagonal) crystal structure also exhibit direct band gaps, which cover a wide range with values of 6.2, 3.4 and 0.64 eV for AlN, GaN and InN, respectively. In this respect, ternary and quaternary alloys of this family are particularly important since their bandgaps can easily be tuned by adjusting the alloy composition. Although high quality III-nitride thin films can be grown at high temperatures (>1000 oC) with significant rates, deposition of these films on temperature-sensitive device layers and substrates necessitates the adaptation of low-temperature methods such as atomic layer deposition (ALD). ALD is a special type of chemical vapor deposition, in which the substrate surface is exposed to sequential pulses of two or more precursors separated by purging periods. When compared to other low-temperature thin film deposition techniques, ALD stands out with its self-limiting growth mechanism, which enables the deposition of highly uniform and conformal thin films with sub-angstrom thickness control. Moreover, alloy thin films can be easily deposited by ALD, where film composition is digitally controlled by the relative number of subcycles. In this thesis, we report on the development of plasma-assisted ALD (PA-ALD) processes for III-nitrides, and present detailed characterization results for the deposited thin films and fabricated nanostructures. PA-ALD of polycrystalline wurtzite AlN thin films was realized at temperatures ranging from 100-500 oC using trimethylaluminum (AlMe3) as the Al precursor. Films deposited at temperatures within the ALD window (100-200 oC for both ammonia (NH3) and N2/H2 plasma processes) were C-free and had relatively low O concentrations (<3 at.%). We also demonstrated the conformality of AlMe3-NH3 plasma process by fabricating high surface area AlN hollow nanofibers using electrospun nylon nanofiber mats as sacrificial templates. Our initial efforts for depositing GaN and InN resulted in thin films with high O concentrations. Although - at first - the most probable source of this contamination was presumed as the O-containing impurities in the unpurified 5N-grade NH3 gas, subsequent experiments revealed the true source as the quartz tube of inductively coupled RF-plasma (ICP) source itself. In view of these circumstances, the choice of N-containing plasma gas (NH3, N2/H2 or N2) determined the severity of O incorporation into AlN and GaN films deposited by PA-ALD. As an effort to completely avoid this plasma-related oxygen contamination problem, we replaced the original quartz-based ICP source of the ALD system with a stainless steel hollow cathode plasma (HCP) source. Thereby we demonstrated the low-temperature hollow cathode PA-ALD (HCPA-ALD) of crystalline AlN, GaN and AlxGa1−xN thin films with low impurity concentrations (O, C <1 at.%) using AlMe3 and trimethylgallium (GaMe3) as the Al and Ga precursors, respectively. Optical band edge values of the AlxGa1−xN films shifted to lower wavelengths with the increasing Al content, indicating the tunability of band edge values with alloy composition. HCPA-ALD of InN was also investigated within the scope of this study. Initial results revealed the possibility to obtain single-phase wurtzite InN thin films using cyclopentadienyl indium (CpIn) as the In precursor. Keywords: atomic layer deposition, aluminum nitride, gallium nitride, in- dium nitride, thin lm, digital alloying, plasma-related oxygen contamina- tion, inductively coupled plasma, hollow cathode plasma, hollow nano ber, template-based synthesis, trimethylaluminum, triethylgallium, trimethylgallium, trimethylindium, cyclopentadienyl indium, ammonia, nitrogen, hydrogen.