Characterization of dual-target co-sputtered novel Hf-doped ZnSnO semiconductors and the enhanced stability of its associated thin film transistors

Abstract

The novel hafnium added ZnSnO (ZTO) thin films were deposited by a dual-target magnetron co-sputtering system. The effect of hafnium doping content on the structure, surface morphology, chemical compositions, optical and electrical properties of HZTO thin films is studied. The HZTO thin films with high hafnium content show an amorphous structure, smooth surface, less carrier concentration and wider optical bandgap. XPS results show that oxygen vacancies as electron charge carrier are effectively suppressed by increasing Hf contents. In addition, their associated application in thin film transistors (TFTs) with Al2O3 gate insulator were fabricated. The interface trap states between the gate insulator and HZTO thin films become fewer with increasing the hafnium doping content. Moreover, hafnium doping content has an important influence on the electrical property and bias stability of TFTs. Although the mobility decreases with increasing the hafnium doping content, the stability is improved obviously. The improved bias stability is attributed to a fewer bulk traps in channel and interface traps between the gate insulator and channel layer, which are commonly originated from oxygen vacancies in oxide-based semiconductors. Therefore, the hafnium ion is a good electron suppressor, and the hafnium doping can effectively suppress gate bias instability of TFTs.