Film Texture, Hole Transport and Field-Effect Mobility in Polycrystalline SnO Thin Films on Glass

Abstract

A p-type oxide semiconductor, tin monoxide (SnO), is expected for high-mobility p-channel oxide thin-film transistors. In this study, we fabricated polycrystalline SnO films by three methods based on pulsed laser deposition, direct deposition at high temperatures, in-situ thermal annealing without exposure to air, and ex-situ thermal annealing after exposure to air. It was found that the crystallite orientation depends largely on the fabrication methods; i.e., the direct deposition enhanced c-axis orientation in particular at higher temperatures, and the in-situ thermal annealing induced homogeneous nucleation of non-oriented crystallites at high temperatures. Further, ex-situ thermal annealing nucleated (101)-oriented crystallites due probably to surface contamination originating from air exposure. In-plane Hall mobility was related to the film texture; i.e., the c-axis oriented films exhibited higher hole mobilities in the a-b plane while the more (101)-oriented films exhibited lower mobilities. This observation was attributed to an intrinsic nature that heavier effective hole mass along the Γ-Z direction ([001] direction) than that of the Γ-M direction ([110] direction), originating from strong anisotropy of the layered crystal structure of SnO. The on-state currents of SnO TFTs fabricated by 300°C deposition or thermal annealing were explained qualitatively by the hole mobilities measured by Hall effect.

Recent Developments in p‐Type Oxide Semiconductor Materials and Devices

“…Fabrication of SnO thin films has been extensively evaluated using a series of methods, including physical vapor deposition (PVD) routes, such as PLD, EB, RFMS, and DCMS using Sn, SnO, and SnO 2 targets on both rigid and flexible substrates. The Hall mobility and carrier (hole) concentrations, along with the deposition conditions are listed in Table 3 for relatively recent studies.…”

“…Following this principle, a series of novel p‐type oxides with delafossite structure was discovered, namely CuMO 2 (M = Al, Ga, and In, etc) and SrCu 2 O 2 (non‐delafossite structure). However, due to the presence of a high VBM tail state, these Cu‐based oxides suffered from either low hole mobility or unsuitable carrier concentrations . As a consequence, the chemical design concept was extended to layered compounds with a higher covalency of the Cu–chalcogen (Ch) interactions (LaCuOCh); however, these materials still exhibited relatively high hole densities, which indicates that the p‐channel cannot be effectively depleted and that these materials are not suitable for electrical switching applications like thin‐film transistors (TFTs).…”

High Hall Mobility P‐type Cu2SnS3‐Ga2O3 with a High Work Function

“…Cupper‐oxide (Cu 2 O) is well known as a promising POS and considerable effort has been made to optimize the electrical properties of Cu 2 O . However, Cu‐based POS exhibits low hole concentration and low carrier mobility due to the presence of a high valence band (VB) tail states . The p‐type property of Cu 2 O is attributed to the presence of Cu vacancies.…”

Tin Oxide Based P and N-Type Thin Film Transistors Developed by RF Sputtering

“…Though there are reports of n-channel SnO 2 TFTs, [23][24][25] and pchannel SnO TFTs, [16][17][18][19][20][21][22] there are very few reports of fabrication of both n and p-type TFTs starting from same base material. 22,26,27 An important aspect of tin oxide material is that we can easily achieve ptype (SnO phase) and n-type (SnO 2 phase) conduction in this material.…”