Study on the defects in metal–organic chemical vapor deposited zinc tin oxide thin films using negative bias illumination stability analysis

Abstract

This study experimentally examined the physical and electrical characteristics of Zn x Sn y O z (ZTO) thin films grown by a metal-organic chemical vapor deposition (MOCVD) method with various Zn/Sn atomic compositions. The corresponding defect structures of the deposited films were investigated in detail using negative bias illumination stability (NBIS) analysis in the thin film transistor (TFT) structure. The ZTO thin films were deposited at a substrate temperature of 400 C and post-deposition annealed at 600 C, which still resulted in the amorphous structure except for the Sn-rich film where a nanocrystalline SnO 2 phase is detected. Among the films with different Zn/Sn atomic compositions, the film with a Zn/Sn atomic composition of $50/50 showed the best electrical performance. After applying NBIS stress for 1000 s, the transfer curves of the Zn-rich ZTO TFT showed a hump, but the transfer curves of the Sn-rich ZTO TFT exhibited a parallel shift to the negative bias direction. These phenomena were attributed to the difference in the oxygen vacancy energy states generated in the ZTO band gap by light illumination. The Zn-and Sn-related oxygen vacancies generated deep donor like trap states at $0.3 eV and shallow states at $0.1 eV from the conduction band (or mobility) edge, respectively, which were identified by the quantitative simulations of the transfer curves of the TFTs.

Atomic and electronic structures of a-ZnSnO3/a-SiO2interface byab initiomolecular dynamics simulations

“…Understanding the atomic origin of the defect states, which are undesirable in the device performance is a key task prior to developing the effective strategy to eliminate them. For a successful example, recognizing oxygen deficiency as an intrinsic source of carrier trap in off‐stoichiometric oxide channel, which degrades the device stability , is followed by the careful control of oxygen stoichiometry during the oxide thin film process . In contrast, all the interface structures in this study are stoichiometric, hence this study suggests that the interfacial gap states can be induced by the characteristic coordination states of oxygen polyhedra and its connectivity even in the stoichiometric interface.…”

“…Zinc tin oxide is one of the most promising candidates of the amorphous oxide semiconductors (AOSs) which can replace the conventional amorphous Si channel in thin film transistors (TFTs) due to its high electron mobility (>∼10 cm 2 V · s −1 ) . This high mobility comes from the fact that the lower edge of conduction band in zinc tin oxide is mostly contributed by the Sn 5s orbitals whose electronic structure is seldom influenced by the bond distortion related with the amorphous nature .…”

“…The interface structures annealed at 900 K were then quenched to 300 K at a cooling rate of 50 K ps −1 . Note that 900 K is comparable to the post‐deposition annealing temperature of the metal‐organic chemical vapor deposited ZTO/SiO 2 stack . Then, all the interface structures were relaxed at 0 K with the tight conditions as the bulk amorphous structures.…”

Optimisation of amorphous zinc tin oxide thin film transistors by remote-plasma reactive sputtering

“…32 Finally, ZTO TFTs produced from MOCVD achieve field effect mobility $7-17 cm 2 V À1 s À1 ZTO with Sn 27%, 49%, and 72% content. 27 The difference in the window of tin compositions in the ZTO in producing respectable TFTs is attributed to the different growth kinetics in each deposition technique. Despite various methodologies used, the extracted carrier mobility of TFTs produced by various deposition techniques are of the same order.…”

“…20 In addition, Gorrn et al have investigated the stability of a-ZTO TFTs under gate bias stress and showed a small threshold voltage shift of 30 mV after 1000 min stressing, 21 thereby demonstrating that ZTO TFTs are suitable as current drivers for transparent active matrix OLED displays. 22 Various deposition techniques, such as sol-gel, 23,24 atomic layer deposition (ALD), 25,26 metal organic chemical vapour deposition (MOCVD), 27 and pulsed laser deposition (PLD), 21,28 have been reported for ZTO, however, rf or dc magnetron sputtering is most commonly used. [6][7][8][9][10]20,[29][30][31][32] Ceramic ZTO targets with at.…”