Semiconductor behavior of Li doped ZnSnO thin film grown by mist-CVD and the associated device property

Abstract

Lithium (Li) doped zinc tin oxide (ZTO) films were successfully grown by mist chemical vapor deposition (mist-CVD) under ambient atmosphere at a relatively low process temperature (-350 degrees C). The effects of Li incorporation on the chemical and physical properties of the host ZTO semiconductor were studied, along with the electrical characteristics of the associated thin film transistors (TFTs). The devices incorporating Li-ZTO active layers grown with a 1 mol % Li precursor exhibit superior electrical performance, with representative saturation mobility of 24.7 cm(2)/V and on/off ratio of similar to 10(10), compared to pure ZTO TFTs (exhibiting a mobility of 14.6 cm(2)/V and on/off ratio of similar to 10(8)). Under negative bias temperature stress (NBTS), the Li-ZTO TFTs undergo relatively small threshold voltage shifts (Delta V-th) of approximately -0.42 V, while the undoped ZTO TFTs exhibit net Delta V(th )values near -3.21 V. Here it is suspected that Li ions enhance the device performance by contributing additional free carriers, while passivating the defects that act as carrier traps. Li doping is thus an effective way to improve both the charge transport properties and stability of ZTO semiconductor devices, which may be realized by means of a cost-effective mist-CVD process.