Search

• HfO x films are deposited by ALD using Tetra-kis-ethylmethylaminohafnium (TEMAHf). • A booster is used for effective delivery of low vapour pressure precursor TEMAHf. • Precursor temperature and delivery system is important for saturated film growth. • The ALD window for HfO x was found to be from 300 °C–375 °C. The present work investigates the importance of incorporating a boosting mechanism in an Atomic Layer Deposition (ALD) process for the delivery of a low vapour pressure precursor in the reaction chamber. Here we show that in the absence of the boosting mechanism, saturated growth was compromised and poor-quality films were obtained characterized by film non-uniformity and variable refractive index within the sample. We demonstrate that a boosting sequence of 0.5 s + 0.9 s with precursor bottle heating temperature of 120 °C was sufficient to produce good quality films showing saturated growth in our system. Furthermore, we demonstrate that for Tetra-kis-ethylmethylaminohafnium/water ALD process, the ALD window for hafnium oxide was found to be in the temperature range 300 °C–375 °C where the average growth per cycle and refractive index of the films deposited within the ALD window were found to be 1.16 Å/cycle and 2.00 respectively. [ABSTRACT FROM AUTHOR]

Heterojunction-based gas sensors are very attractive as they substantially improve the sensing characteristics due to the effective potential barrier present at the interface. Taking the advantages of two excellent semiconducting gas sensing materials i.e., SnO 2 and ZnO, herein, we have constructed ZnO/SnO 2 heterojunction by the combination of vacuum evaporation and r.f. sputtering or atomic layer deposition techniques. The ZnO/SnO 2 heterostructure with optimized thickness of ZnO (∼10 nm) shows a 6-fold enhancement in sensing response compared to bare SnO 2 films against CO gas. The sensing responses of 81 and 85 % have been obtained for ZnO/SnO 2 heterostructures with ZnO deposited by sputtering and atomic layer deposition (ALD) methods, respectively, against 91 ppm of CO gas with an estimated limit of detection of 1.67 and 0.37 ppm. The ALD ZnO/SnO 2 sample displays an extremely fast response time of 5 s. The heterostructure sensors are also highly selective towards CO gas in the presence of other interfering toxic agents. The enhanced sensing characteristics of ZnO/SnO 2 are assigned to the formation of n-n heterojunction as depicted by X-ray photoelectron spectroscopic band alignment study and the strong CO adsorption on ZnO surface as derived from density functional theory calculations. [ABSTRACT FROM AUTHOR]