Yusupov M. Nanostructures on surface and nearsurface layers of wide bandgap semiconductors 6H-SiC, BN and ZnS formed by pulse laser irradiation

The dissertation is devoted to the investigation of physic process laws that take place on surface and nearsurface layers of silicon carbide under laser exposure according to the radiation regimes; the formation of nanostructures on 6H-SiC surface and ohmic contact to SiC n-type monocrystal; the obtaining of nanoscale structures of BN by laser technology methods; the studying of laser radiation influence on morphology and luminescent properties of ZnS-Cu,Cl thin films. It was the first time shown the possibility of nanostructures formation by the direct laser exposure on 6H-SiC:N at microablation regimes of ultraviolet nanosecond nitrogen pulse laser in open air and room temperature. It was also shown that the liquid phase in SiC is formed under powerful nanosecond pulse laser exposure from the area of fundamental absorption. It was clarified that the main reason of nearsurface 6H-SiC:N transformation was caused by the increasing of doped nitrogen concentration that serves as substitution atoms of carbon due to thermogradient effect movement. It was expressed the explanation of nanostructures formation mechanism. The damage threshold of nearsurface layers of 6H-SiC:N under laser exposure and the threshold of nanostructure formation were determined, and derived 5.6 J/cm2 and 5.0 J/cm2. For the treated surface the effect of field emission was observed at 1000 V in the range of currents 0.7 µA 0.7 mA. The technological method of refractory ohm contact formation to 6H-SiC:N on the base of 6H-SiC:N/W/Si3N4/W/Ni structure was developed. Typical values of specific resistance of contacts с after laser annealing were 5e-4 Ohm.cm2. Also, was determined an optimal regimes for laser stimulated modification of ZnS-Cu,Cl thin films aiming to decrease surface roughness without any degradation in emission characteristics. The laser radiation method formation of nanostructures, utilizing the second harmonic generation of YAG:Nd3+ laser, on pressed surface of BN was proposed.