Polycrystalline GaN Layer On M-Plane Sapphire Substrate For Metal-Semiconductor-Metal Photodetector
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Date
2017-12
Authors
Kamarulzaman, Azharul Ariff
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
This thesis describes work on depositing polycrystalline gallium nitride (GaN) on m-plane sapphire substrate using cost effective physical deposition technique; electron beam (e-beam) evaporator and radio frequency (RF) sputtering, followed by annealing treatment in ammonia (NH3) ambient. The work was then extended to develop metal-semiconductor-metal (MSM) photodetector using the most possible metal/metal oxide contact, to increase the efficiency of the device. The initial part of this thesis focus on ameliorating the properties of the polycrystalline GaN layer by controlling gas ambient, time, temperature, and gas flow rate of the annealing treatment. Before the annealing, the layer consisted of gallium oxide (Ga2O3) inclusions, with low nitrogen (N) atomic percentage. During the annealing, the Ga2O3 inclusions were partially removed, while recrystallization of the GaN grains occurred and the N-deficiency in the polycrystalline layer was mitigated. The best annealing condition was found at 950 oC with the duration of 10 minutes with the NH3 flow rate of 3 slm. The GaN layer annealed with the best condition showed the formation of larger hexagonal facetted structure, accompanied by three narrow and distinct GaN diffraction peaks corresponding to (10 ̅0), (0002) and (10 ̅1) orientations. Furthermore, a significant optical improvement of the GaN related near band edge (NBE) emission was observed. Deposition of polycrystalline GaN layer by RF-sputtering was also conducted, focusing on controlling the thickness of aluminum nitride (AlN) buffer layer prior to annealing with the best condition as described before. The polycrystalline GaN layer deposited on 70 nm AlN buffer layer showed the best results from the XRD data, as compared to others. All other samples in this set did not exhibit promising results from surface and optical measurements. Therefore, the polycrystalline GaN layer deposited by e-beam evaporator is better than one by RF-sputtering, and worth to be developed as MSM photodetector. In order to increase the efficiency of the polycrystalline GaN based photodetector, the electrical contact of the device was optimized. Here, different contacts were studied; aluminum (Al), indium-tin-oxide (ITO), nickel (Ni), and platinum (Pt). The best polycrystalline GaN based MSM photodetector was found with the use of Ni contact at λ=385 nm. This device exhibited photo-generated current of ~900 nA/cm2 at 5 V, with a gain of ~100 between the bias voltage of ~1.5 V – ~4.0 V. The MSM photodetector showed contact resistivity, internal quantum efficiency, rise time, recovery time and sensitivity of .0 MΩ.cm2, 3.13%, 1.75 sec, 1.87 sec, and 5840 %, respectively. This behavior was related to the formation of NixO inclusions, which subsequently gave better efficiency to the photodetector.
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Keywords
Depositing polycrystalline gallium nitride , on m-plane sapphire substrate