Synthesis Of Gallium Nitride (Gan) Nanostructures By Electrochemical Techniques For Sensing Applications
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Date
2011-05
Authors
Al-Heuseen, Khalled Mhammad Kallef
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Publisher
Universiti Sains Malaysia
Abstract
The main goal of this work presented in this thesis was to fabricate nanostructures of GaN using two low-cost electrochemical techniques namely photoelectrochemical etching (PECE) and electrochemical deposition (ECD). In the first category of this work, the porous GaN was generated using photoelectrochemical etching techniques under different conditions, i.e. current density, different duration of etching and different electrolytes. The results showed that the average pore size was sensitive to the current density, and different electrolytes generated different morphology. The Raman spectra of all porous samples with E2 (high) peak suggested that stress relaxation has taken place in all samples. The mechanism of PECE etching of GaN was investigated, and a two-step etching model for PEC of GaN proposed that an oxide layer was formed on the GaN surface under UV and then dissolved in the electrolyte. In the second category, GaN thin films were synthesized by a low-cost ECD technique using an aqueous solution prepared by mixing gallium nitrate (Ga (NO3)3) with ammonium nitrate (NH4NO3) in deionized water. The positive ions of Ga+3 and NH3+1 were concentrated on the surface of the cathode. Combination of these two positive ions formed clusters of critical sizes of GaN. The effects of different parameters that may affect the quality of the deposited GaN were studied. GaN films contained mixed phases of h-GaN and c-GaN with grain sizes in the range of 18-29 nm.
In this work, two devices were fabricated, hydrogen gas sensors and MSM photodetectors. The Pd/porous GaN Schottky diode exhibited a dramatic change of current after the exposure to hydrogen gas as compared to the Pd/as grown GaN Schottky diode. It was found that the performance of the UV- photodetector on porous GaN was more sensitive than that on as-grown. The contrast ratio of photo-current and dark current (β) at 3V for porous sample and as-grown was found to be 1241 and 78, respectively. Two devices, i.e. hydrogen gas sensors and MSM were also fabricated by depositing Ni on ECD GaN/Si (111) and on ECD GaN/Si (100).
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Keywords
Fabricate nanostructures of GaN using , two low-cost electrochemical techniques