Pulsed Laser Deposition Of Tin Oxide Epitaxial Thin Films And Band-gap Engineering Of SnO₂

Two important oxides of metal Sn,tin oxide?SnO?and tin dioxide?SnO₂?,are known to be important wide band gap semiconductor materials.SnO as a native p-type material have attracted much attention recently owing to it's high mobility and stable p-type conductivity.The other oxide of Sn,tin dioxide?SnO₂?,is a well known n-type direct wide band-gap?3.6eV?semiconductor,and with the growing demands for short-wavelength optoelectronic devices,it has been paid increasing attention recently.Compared with the extensively studied wide band-gap oxide semiconductor,zinc oxide?ZnO?,SnO₂ has obvious advantages,such as wider band-gap,higher mechanical strength and better chemical stability.More importantly,with a tetragonal rutile structure,SnO₂ is a natural nonpolar semiconductor that can avoid the Quantum Stark Effect associated with polar semiconductors such as hexagonal GaN and ZnO.All these facts indicate that SnO₂ is a good candidate material for developing ultraviolet luminescent devices with high efficiencies and stability.Based on these,in this work we employed PLD method deposited highquality SnO and SnO₂ epitaxial films on r and c sapphire respectively using a SnO ceramic as target,the effects of substrata temperature on the tin oxide film properties,and the effects of grain size,strain,doping on band-gap of SnO₂were studied.The main contents and results of this paper are as follows:?1?Single phase SnO and SnO₂ epitaxial films were deposited on r and c plane sapphire respectively,and the influence of substrate temperature on the structure and property of films were studied systematacially.Study result indicate that the growth temperature window of deposited SnO films on r sapphire is from 425 to 575°C,and the epitaxial relationship of film and substrate is:SnO?001?|Al₂O₃?1-102?,SnO[110]|Al₂O₃[-12-10].The SnO₂ films deposited on c sapphire have a high lattice quality with the?200?rocking curve half width as low as 0.012?.The epitaxial relationship of SnO₂ and c-sapphire is:SnO₂?100?|Al₂O₃?0001?,SnO₂[010]|Al₂O₃[11-20].?2?A series of a-plane SnO₂ films with thickness ranging from 2.5 nm to 1436 nm were grown epitaxially on c-sapphire by pulsed laser deposition?PLD?,and the effect of film thickness on the band gap were investigated systematically.The results indicate that the crystal structures,micro-morphologies and optical properties of the films depended strongly on the film thickness.As film thickness increases,the lattice quality degrades?rocking curve half width increased from 0.01 to 0.02?,and the surface roughness increases.The initially deposited SnO₂ layers are compressive strained along the c-axis,and tensilely strained along the b-axis to match Al₂O₃?0001?,leading to compressive strain along the growth direction[100].The band gap of SnO₂ films varies markedly in V-shaped fashion with the film thickness.For the ultrathin films,the band gap increases rapidly with decreasing film thickness due to the Quantum Size Effect.In contrast,the band gap of thicker SnO₂ films rises almost linearly with increasing film thickness,which is attributable to the Strain Effects.?3?We used homemade Si_0.12Sn_0.88O₂ ceramic as target to deposite a series epitaxial Si_xSn_1-xO₂ films with various Si content through adjusting O₂ presuure.And then a series of homemade Si_xSn_1-xO₂ ceramic with various Si content were prepared to obtain a series of amorphous Si_xSn_1-xO₂ films.The effect of Si doping on the SnO₂ band gap were investigated systematically.Study results indicate that with the Si content increasing,the quality of Si_xSn_1-xO₂ films decreased,and the surface roughness increased.For epitaxial Si_xSn_1-xO₂ films,the band gap decreased with Si content increasing,However,for amorphous Si_xSn_1-xO₂ films,the band gap increased with Si content increasing.