Ravindra Waykar

Highly Transparent Wafer-Scale Synthesis of Crystalline WS2 Nanoparticle Thin Film for Photodetector and Humidity-Sensing Applications.

In the present investigation, we report a one-step synthesis method of wafer-scale highly crystalline tungsten disulfide (WS2) nanoparticle thin film by using a modified hot wire chemical vapor deposition (HW-CVD) technique. The average size of WS2 nanoparticle is found to be 25-40 nm over an entire 4 in. wafer of quartz substrate. The low-angle XRD data of WS2 nanoparticle shows the highly crystalline nature of sample along with orientation (002) direction. Furthermore, Raman spectroscopy shows two prominent phonon vibration modes of E(1)2g and A1g at ∼356 and ∼420 cm(-1), respectively, indicating high purity of material. The TEM analysis shows good crystalline quality of sample. The synthesized WS2 nanoparticle thin film based device shows good response to humidity and good photosensitivity along with good long-term stability of the device. It was found that the resistance of the films decreases with increasing relative humidity (RH). The maximum humidity sensitivity of 469% along with response time of ∼12 s and recovery time of ∼13 s were observed for the WS2 thin film humidity sensor device. In the case of photodetection, the response time of ∼51 s and recovery time of ∼88 s were observed with sensitivity ∼137% under white light illumination. Our results open up several avenues to grow other transition metal dichalcogenide nanoparticle thin film for large-area nanoelectronics as well as industrial applications.

Low substrate temperature deposition of transparent and conducting ZnO:Al thin films by RF magnetron sputtering

Transparent and conducting Al-doped ZnO (ZnO:Al) films were prepared on glass substrate using the RF sputtering method at different substrate temperatures from room temperature (RT) to 200℃. The structural, morphological, electrical and optical properties of these films were investigated using a variety of characterization techniques such as low angle XRD, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM), Hall measurement and UV-visible spectroscopy. The electrical properties showed that films deposited at RT have the lowest resistivity and it increases with an increase in the substrate temperature whereas carrier mobility and concentration decrease with an increase in substrate temperature. Low angle XRD and Raman spectroscopy analysis reavealed that films are highly crystalline with a hexagonal wurtzite structure and a preferred orientation along the c-axis. The FE-SEM analysis showed that the surface morphology of films is strongly dependent on the substrate temperature. The band gap decreases from 3.36 to 3.29 eV as the substrate temperature is increased from RT to 200℃. The fundamental absorption edge in the UV region shifts towards a longer wavelength with an increase in substrate temperature and be attributed to the Burstein-Moss shift. The synthesized films showed an average transmission (>85%) in the visible region, which signifies that synthesized ZnO:Al films can be suitable for display devices and solar cells as transparent electrodes.

Synthesis of nanocrystalline silicon carbide thin films by HW-CVD using ethane carbon precursor for photo detector application

Hydrogenated nanocrystalline silicon carbide (nc-SiC:H) films were prepared by hot wire chemical vapor deposition (HW-CVD) method using ethane (C2H6) as a carbon precursor. The influence of deposition pressure on structural and optical properties was investigated. The formation of nc-SiC:H films was confirmed by low angle x-ray diffraction (XRD), Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy analysis. An inverse relation between deposition pressure and deposition rate was observed. Optical band gap values, ETauc and E04 increases with increase in deposition pressure. In fact, optical band gap values estimated from E04 method was found higher than the ETauc values calculated from Taucs plot. Finally, at optimized deposition pressure (450 mTorr), a photo detector having configuration glass/nc-SiC:H/Al have been fabricated and its photo response was studied. Further study is required to improve the quality of nc-SiC:H films to make use in photo detectors.