Research On Properties Of P-type Nc-Si:H Thin Films Deposited By Hot-wire Chemical Vapor Deposition

Hydrogenated nanocrystalline silicon (nc-Si:H) thin film is a mixed phase material wherenanocrystals are embedded in an amorphous silicon matrix. Due to its excellent photoelectricproperties, it is an important material in the second and third generation solar cells. Especially insilicon single and tandem thin film solar cells, it is of great significance for the improvement of solarcell performance to prepare the p-type nc-Si:H thin film with the properties such as high crystallinityand conductivity, low activation energy and wide optical band gap.Hot-wire chemical vapor deposition (HWCVD) has several advantages such as no ionbombardment, high gas utilization and deposition rate, which is a promising deposition method toprepare the doped nc-Si:H thin film with high crystallinity and conductivity. In this study, p-typenc-Si:H thin films were prepared by HWCVD, and the film microstructural and photoelectricproperties were characterized by Raman, UV-visible Spectrometer, Four-Point Probe Sheet ResistanceMeter, Hall Effect Meter, Variable Temperature Conductivity Measurement System. The effects ofdeposition parameters including filament temperature, doping ratio, hydrogen dilution ratio, deposition pressure electrical on these properties were studied systematically, and the dopingmechanism was deeply discussed.The results are as follows: With filament temperature growing up, crystalline volume fraction,average grain size, optical band gap and carrier concentration increase, while activation energyreduces because of that the increase of boron doping concentration and crystalline volume fraction isbeneficial to electron tunneling. But too high temperature will make crystalline volume fraction,average grain size and optical band gap decrease. With B2H6doping ratio increasing, amorphizationoccurs, and optical band gap narrows due to the introduction of gap state into around absorption edge,and carrier concentration grows up while hall mobility and activation energy grow downmonotonously. When hydrogen dilution ratio rises, due to that more H atoms cover the growingsurface and amorphous silicon components are selectively etching, crystalline volume fraction andaverage grain size increase, and at this time chemisorption of BH3particle plays a leading role leadingto higher carrier concentration, while at higher hydrogen dilution ratio, the domination ofphysisorption results in that carrier concentration decreases a little. In this study, there is a thresholdof deposition pressure equal to6Pa. When deposition pressure is lower than the threshold, crystallinevolume fraction and average grain size increase with increasing deposition pressure owing to more H atom surface coverage and SiH3particles, but when deposition pressure is higher than the threshold,the reduction of H atom surface coverage leading to the reduction of crystalline volume fraction andaverage grain size. In addition, when deposition pressure increases, BH3particle increases, but itsadsorption manner changes gradually from chemisorption to physisorption, thus carrier concentrationfirst increases rapidly, then increases slowly and even decreases. Finally, the qualified thin film wassuccessfully obtained with crystalline volume fraction of67.6%, optical band gap of1.84eV,conductivity as high as40S/cm and activation energy only of13.5meV.