Ph.D. Thesis Defense
DEPARTMENT OF INSTRUMENTATION AND APPLIED PHYSICS
Ph.D. Thesis Defense
NAME OF THE CANDIDATE : Miss. Teena Jangid
DEGREE : Ph.D
TITLE OF THE THESIS : Sputter Deposited tin-nitride and zinc-tin-nitride
(ZnSnN2) thin-films: Growth, characterization,
and application in ammonia (NH3) gas sensing
SUPERVISORS : Prof. Mohan Rao. G & Dr. U. Chandni
DATE AND TIME : Wednesday, 22nd January 2020, @ 10 A.M
VENUE : Lecture Hall-1, Dept. of Instrumentation
and Applied Physics.
III-nitride semiconductors are widely known for their excellent optoelectronic properties and have recently attracted a lot of interests for gas sensing applications also. Tin-nitride and ZnSnN2 belong to the class of new nitride semiconductors, with their optoelectronic properties similar to extensively studied III-nitride semiconductors. These novel nitrides also have the added advantages of non-toxicity, earth abundance, and well-established recycling infrastructure of Zn and Sn compared to their III-group counterparts. However, surprisingly not much of experimental work has been reported on these new nitrides, owing to the difficulty associated with the growth of these nitrides. The limited literature on these nitrides also finds the scattered value of optical bandgap, which is one of the primary and essential property when it comes to the realization of any practical device based on these materials. The discrepancy in literature for these new nitrides (tin-nitride and ZnSnN2) with promising optoelectronic proeperties have motivated us to explore the space of tin-nitride and ZnSnN2 growth and their potential as a gas sensor, similar to their III-nitride counterparts.
The first step in this direction was the optimization of process parameters for the growth of tin-nitride thin-films. RF and DC magnetron sputtering was used for the growth of tin-nitride (Sn3N4) thin-films from an Sn target in a reactive nitrogen plasma. We studied the effect of process parameters like growth temperature, target-substrate distance, RF power, etc. on the properties of the deposited tin-nitride thin-films in detail. The process parameters were optimized for the growth of phase-pure polycrystalline tin-nitride thin-films. We also found that RF magnetron sputtering is more favourable for the growth of tin-nitride thin-films compared to DC magnetron sputtering.
Since the process parameters optimized earlier for the growth of tin-nitride, were corresponding to the normal position of Sn magnetron from the substrate surface and oblique angle deposition is needed for the growth of ZnSnN2 thin-films via co-sputtering, next, we studied the effect of deposition angle variation on the microstructural properties of tin-nitride thin-film. Growth of tin-nitride thin-films was performed at two different incident angle (90o and 45o) and 5 different RF power values for a complete understanding of incident angle variation on the growth of tin-nitride thin-films. We found that variation
on incident angle profoundly affects the surface properties of tin-nitride thin-film. However, the crystallinity of the grown films remains unaffected by this variation.
The study was further extended with the optimization of the process parameters for the growth of compound ZnSnN2 via co-sputtering of Zn and Sn target in a reactive nitrogen plasma. The grown films are characterized by material quality using SEM, XRD, XPS, and UV/Vis spectroscopy. Detailed investigation on optical properties of ZnSnN2 thin-films revealed the presence of indirect bandgap in the ZnSnN2 for the first time. Hall mobility measurements of ZnSnN2 thin-film deposited at different substrate temperature indicate n-type films. We also observed the highest value of mobility, 240 cm2/Vs reported so far for ZnSnN2.
To enable device applications, NH3 gas senor, which find use in chemical, pharmaceutical, and food process industries were fabricated with tin-nitride and zinc-tin-nitride (ZnSnN2) thin-films on glass substrate using gold metal as contacts. The ZnSnN2 based sensors were found to be responsive even in the 1-5 ppm ammonia concentration range. The ZnSnN2 sensor was also highly selective to NH3 amongst other gases like ethanol, H2S, NO2, and exhibited good sensing responses at room temperature conditions. High sensitivity and selectivity of ZnSnN2 based sensors at room temperatures make it a promising candidate for selective NH3 sensing at room temperature
ALL ARE WELCOME
Date(s) - 22/01/2020
Lecture Hall-1, Dept. of Instrumentation & Applied Physics.
Categories No Categories