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Cuprous (Cu2O) and cupric (CuO) oxide thin films have been deposited by radio frequency magnetron sputtering with two different oxygen partial pressures. The as-deposited copper oxide films were subjected to post-annealing at 300 °C for 30 min to improve the microstructural, morphological, and optical properties of thin films. Optical absorption studies revealed the existence of a large number of subgap states inside CuO films than Cu2O films. Cu2O and CuO thin film transistors (TFTs) were fabricated in an inverted staggered structure by using a post-annealed channel layer. The field effect mobility values of Cu2O and CuO TFTs were 5.20 × 10−4 cm2 V−1 s−1 and 2.33 × 10−4 cm2 V−1 s−1, respectively. The poor values of subthreshold swing, threshold voltage, and field effect mobility of the TFTs were due to the charge trap density at the copper oxide/dielectric interface as well as defect induced trap states originated from the oxygen vacancies inside the bulk copper oxide. In order to study the distribution of the trap states in the Cu2O and CuO active layer, the temperature dependent transfer characteristics of transistors in the temperature range between 310 K and 340 K were studied. The observed subgap states were found to be decreasing exponentially inside the bandgap, with CuO TFT showing higher subgap states than Cu2O TFT. The high-density hole trap states in the CuO channel are one of the plausible reasons for the lower mobility in CuO TFT than in Cu2O TFT. The origin of these subgap states was attributed to the impurities or oxygen vacancies present in the CuO channel layer.

N-type organic thin film transistor (OTFT) with a top-contact structure was fabricated by thermal vapour deposition using N,N'-Dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) as an n-channel layer on Si/SiO2 substrate. The density of localised states (DOS) in the gap of PTCDI-C8 is estimated by studying the temperature dependence of the electrical characteristics of OTFT. The measurements were done immediately after the devices fabrication (non-degraded devices) and also after 2 h of exposure to air (degraded devices). The extracted field effect mobility decreased from 0.02 to 0.004 cm2 V-1 s-1 and threshold voltage increased from 25.3 to 40.5¿V for the degraded OTFT. The degradation of OTFTs was due to the trapping of majority charge carriers in the localised trap states created by adsorbed oxygen in the PTCDI-C8 layer. These localised trap states were found to be situated at around 0.15¿eV above the lowest unoccupied molecular orbit level. The study of DOS in OTFTs gives a complete understanding of trap-limited transport in organic thin film semiconductors.Peer ReviewedPostprint (published version

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