Electronic structure and defect states of transition films from amorphous to microcrystalline silicon studied by surface photovoltage spectroscopy

In this paper, surface photovoltage spectroscopy (SPS) is used todetermine the electronic structure of the hydrogenated transition Sifilms. All samples are prepared by using helicon wave plasma-enhancedchemical vapour deposition technique, the films exhibit a transitionfrom the amorphous phase to the microcrystalline phase withincreasing temperature. The film deposited at lower substratetemperature has the amorphous-like electronic structure with twotypes of dominant defect states corresponding to the occupied Sidangling bond states (D⁰/D^- and the empty Si danglingstates (D⁺). At higher substrate temperature, thecrystallinity of the deposited films increases, while their band gapenergy decreases. Meanwhile, two types of additional defect states isincorporate into the films as compared with the amorphouscounterpart, which is attributed to the interface defect statesbetween the microcrystalline Si grains and the amorphous matrix. Therelative SPS intensity of these two kinds of defect states in samplesdeposited above 300du increases first and decreases afterwards,which may be interpreted as a result of the competition betweenhydrogen release and crystalline grain size increment with increasingsubstrate temperature.