Fabrication And Characterization Of Germanium, Zinc Oxide And Their Compounds By Thermal Evaporation Technique
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Date
2015-09
Authors
Jumidali, Mohd Muzafa
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Abstract
This work mainly aims to study the growth mechanism of germanium (Ge), zinc oxide (ZnO), and their compounds through simple and low-cost thermal evaporation. Potential structures were also fabricated and investigated for sensor applications. In the first part, germanium oxide (GeO2) was grown using a novel one-step method without catalyst. The effect of oxygen (O2) supply in structure formation and the structural and optical properties of GeO2 were investigated, and the vapor–solid growth mechanism was proposed. The particle size of GeO2 grown using ambient O2 was similar to that obtained with a fixed O2 flow from an external source. Uniform-sized Ge islands (GIs) were also grown on a Si substrate with Ni catalyst. The influence of different deposition durations on GI growth and the role of Ni in island formation were evaluated, and the growth mechanism was proposed. Fourier transform infrared spectrum showed that the optical band gap (Eg) of GIs varies with deposition time from 0.62 to 0.78 eV compared with bulk Ge (0.66 eV). In the second part, ZnO microstructures were synthesized through modified thermal evaporation by using the mixture of GeO2 and metallic Zn powders as raw material. The structural and optical properties, growth mechanism, and roles of GeO2 in the formation of the ZnO structures were discussed and proposed. The ZnO microstructure was grown using GeO2 as oxygen source in a furnace system without any catalyst and oxygen flow at temperature range of 500 – 9000C. Finally, Ge and ZnO powder were mixed at different mass ratio (1:2 and 2:1) to form the hybrid of ternary Ge-based structures. ZnO/zinc germanate (Zn2GeO4) with porous-like structure and Ge/zinc silicate (Zn2SiO4) were fabricated and characterized, and their growth mechanisms were proposed. ZnO/Zn2GeO4 structure was used to construct metal–semiconductor–metal devices, which exhibited significantly strong photoelectric effects under both UV-C (0.252 A/W) at 250 nm and UV-A (0.246 A/W) at 385 nm regions. The Ge/Zn2SiO4 structure also exhibited similar response to deep UV (0.280 A/W and 0.374 A/W) at 290 nm and 230 nm regions. Hence, the study demonstrated that both structures can be potentially used as UV-photodetectors for applications requiring short wavelengths. Subsequently, a hydrogen-sensing properties based on Ge/Zn2SiO4 structure was also performed. The sensitivity and the optimal operation at room temperature of the sensor are nearly 90% at 150 sccm flow rate of hydrogen gas which heightens potential interest in future H2 gas sensor devices.
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Physics (General)