Soumyadeep Sinha

Atomic layer deposition of Zn3N2 thin films: growth mechanism and application in thin film transistor

In this paper we present atomic layer deposition (ALD) of zinc nitride thin films using diethylzinc (DEZ) and ammonia (NH3). Density Functional Theory (DFT) is used to calculate the atomistic reaction pathway. The self-limiting growth characteristic is verified at 315 °C. Saturated growth rate is found to be 0.9 A per ALD cycle. The as deposited films are found to be polycrystalline with preferential orientation in the {321} direction. The performance of the material is further investigated as channel layer in thin film transistor (TFT) applications.

Atomic layer deposition of textured zinc nitride thin films

Zinc nitride films are deposited by Atomic Layer Deposition (ALD) within a temperature range of 150–315 °C using diethylzinc (DEZ) and ammonia (NH3). Self-limiting growth characteristics are examined by an in situ Quartz crystal microbalance (QCM) that is subsequently verified and complemented by ex situ X-ray reflectivity (XRR) measurements. A saturated growth rate of ca. 1.4 A per ALD cycle is obtained within the ALD temperature window of 175–215 °C. In situ Fourier transform infrared (FTIR) spectroscopy is employed to study the reaction mechanism during each ALD half cycle. As deposited films on microscope glass substrates have strong orientation in the {321} direction. Films are found to be optically transparent with band-edge photoluminescence.

Highly Uniform Atomic Layer-Deposited MoS2@3D-Ni-Foam: A Novel Approach To Prepare an Electrode for Supercapacitors

This article takes an effort to establish the potential of atomic layer deposition (ALD) technique toward the field of supercapacitors by preparing molybdenum disulfide (MoS2) as its electrode. While molybdenum hexacarbonyl [Mo(CO)6] serves as a novel precursor toward the low-temperature synthesis of ALD-grown MoS2, H2S plasma helps to deposit its polycrystalline phase at 200 °C. Several ex situ characterizations such as X-ray diffractometry (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and so forth are performed in detail to study the as-grown MoS2 film on a Si/SiO2 substrate. While stoichiometric MoS2 with very negligible amount of C and O impurities was evident from XPS, the XRD and high-resolution transmission electron microscopy analyses confirmed the (002)-oriented polycrystalline h-MoS2 phase of the as-grown film. A comparative study of ALD-grown MoS2 as a supercapacitor electrode on 2-dimensional stainless steel and on 3-dimensional (3D) Ni-foam substrates clearly reflects the advantage and the potential of ALD for growing a uniform and conformal electrode material on a 3D-scaffold layer. Cyclic voltammetry measurements showed both double-layer capacitance and capacitance contributed by the faradic reaction at the MoS2 electrode surface. The optimum number of ALD cycles was also found out for achieving maximum capacitance for such a MoS2@3D-Ni-foam electrode. A record high areal capacitance of 3400 mF/cm2 was achieved for MoS2@3D-Ni-foam grown by 400 ALD cycles at a current density of 3 mA/cm2. Moreover, the ALD-grown MoS2@3D-Ni-foam composite also retains high areal capacitance, even up to a high current density of 50 mA/cm2. Finally, this directly grown MoS2 electrode on 3D-Ni-foam by ALD shows high cyclic stability (>80%) over 4500 charge-discharge cycles which must invoke the research community to further explore the potential of ALD for such applications.

Atomic layer deposition of aluminum sulfide thin films using trimethylaluminum and hydrogen sulfide

Sequential exposures of trimethylaluminum and hydrogen sulfide are used to deposit aluminum sulfide thin films by atomic layer deposition (ALD) in the temperature ranging from 100 to 200 °C. Growth rate of 1.3 A per ALD cycle is achieved by in-situ quartz crystal microbalance measurements. It is found that the growth rate per ALD cycle is highly dependent on the purging time between the two precursors. Increased purge time results in higher growth rate. Surface limited chemistry during each ALD half cycle is studied by in-situ Fourier transformed infrared vibration spectroscopy. Time of flight secondary ion-mass spectroscopy measurement is used to confirm elemental composition of the deposited films.

Facile Phase Control of Multivalent Vanadium Oxide Thin Films (V2O5 and VO2) by Atomic Layer Deposition and Postdeposition Annealing

Atomic layer deposition was adopted to deposit VOx thin films using vanadyl tri-isopropoxide {VO[O(C3H7)]3, VTIP} and water (H2O) at 135 °C. The self-limiting and purge-time-dependent growth behaviors were studied by ex situ ellipsometry to determine the saturated growth conditions for atomic-layer-deposited VOx. The as-deposited films were found to be amorphous. The structural, chemical, and optical properties of the crystalline thin films with controlled phase formation were investigated after postdeposition annealing at various atmospheres and temperatures. Reducing and oxidizing atmospheres enabled the formation of pure VO2 and V2O5 phases, respectively. The possible band structures of the crystalline VO2 and V2O5 thin films were established. Furthermore, an electrochemical response and a voltage-induced insulator-to-metal transition in the vertical metal-vanadium oxide-metal device structure were observed for V2O5 and VO2 films, respectively.

Development of Al doped ZnO as TCO by Atomic Layer Deposition

Aluminium doped Zinc Oxide (AZO) thin films were deposited on SiO2/Si and glass substrates by Atomic Layer Deposition (ALD) in the temperature range of 150 °C - 250 °C. X-ray diffraction revealed the formation of c- axis oriented wurtzite phase of undoped ZnO films. The crystallinity of the films decreased with increasing pulse ratio of Zn:Al which indicating the incorporation of Al3+ in the ZnO lattice. The minimum achievable resistivity (ρ) of the films was 4.8×10-3 Ω-cm with transparency > 80% in the visible range. The bandgap of the materials shows a blueshift with the increasing Al doping concentration.

Effect of Partial Pressure of Precursors on Atomic Layer Deposited Zinc Oxide Films as TCO Material in Solar Cell Application

Zinc Oxide (ZnO) films were deposited by Atomic Layer Deposition (ALD) using Diethylzinc and a combination of Water and Ozone as the precursores. Electrical conductivity of ALD grown ZnO films, under low field, were studied with varied partial pressure of the constituent reactants. Supressing the oxygen vacancy by introducing O3 during the reaction increase the resistivity of the films by couple of orders of magnitude. UV-Vis spectroscopy measurement showed the films to be transparent giving a room for its application as a TCO in solar cell.

ZnO as transparent conducting oxide by Atomic Layer Deposition

Zinc Oxide (ZnO) films were deposited on SiO2/Si and glass substrates by Atomic Layer Deposition using Diethylzinc (DEZ) as the metal precursor and Water (H2O) as the oxidant over a temperature range of 75°C to 225°C. Here we demonstrated self limiting behavior of the Atomic Layer Deposition and the linear growth of the deposited films by in-situ quartz crystal microbalance (QCM) study. The maximum growth rate was found to be ~1.8 to 2 Å per ALD cycle. The as deposited crystalline ZnO films were found to be c-axis preferentially oriented with dense microstructures, homogeneous grain sizes and low surface roughness. We developed ZnO as ~ 80% transparent conductor with carrier density ca. 1021 cm-3 and a controllable resistivity from the intrinsic level (highly insulating) to 10-3 Ω-cm without any intentional doping.