Growth And Characterization Of Gallium Nitride Films On Porous Silicon Substrate
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Date
2016-03
Authors
Samsudin, Muhammad Esmed Alif
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Journal ISSN
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Publisher
Universiti Sains Malaysia
Abstract
This work focuses on the growth of GaN films on porous Si/Si substrate by radio frequency (RF) sputtering and electron beam (e-beam) evaporator. As a comparison, aluminium nitride (AlN) buffer layer, titanium nitride (TiN) buffer layer and Si substrate were used to grow the GaN layer. Porous Si/Si substrate was initially prepared by electrochemical etching using different parameters. It was found that the porosity of Si could be influenced by the type of electrolyte (solution), etching time and current density. From the observations, the dimethylformamide (DMF) solution with 30 minutes etched, under 10 mA/cm2 of current density produced the optimum porous structure. Next, the GaN layers were grown on Si substrate, nitrides buffer layers/Si substrate and porous Si/Si substrate by RF sputtering and e-beam evaporator, respectively. As witnessed from field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) measurements, the nitrides buffer layers gave smoother GaN surface while the porous Si resulted in rougher GaN surface, particularly for e-beam evaporator growth GaN layer. X-ray diffraction (XRD) measurements revealed that all non-annealed GaN samples were preferably grown in non-polar GaN of (101̅0) orientation. The XRD ω-scan revealed that the FWHM of the GaN peak was found to be narrow in the GaN layer on porous Si/Si substrate among others, implying the lowest threading dislocations density in the sample at ~108 cm-2, especially for RF sputtering growth GaN layer. However, the optical quality for all non-annealed GaN layers appeared to be poor since no peak related to GaN material can be detected in photoluminescence (PL) and Raman spectra. To address this problem, post-annealing treatment in ammonia (NH3) ambient at 950°C for 30 minutes was proposed. FESEM measurement revealed that all the annealed GaN layers turned into rough and distinguished hexagonal-facetted grains. In addition, the annealed GaN layers were found to be grown in polycrystalline structure with significant peaks at (101̅0), (0002), and (101̅1) planes, as confirmed by XRD 2θ-ω scan. The XRD ω-scan revealed that the threading dislocations density showed further reduction as compared to the non-annealed samples, especially for GaN on porous Si sample grown by e-beam evaporator. It is worth to note, despite of a rough surface, the optical properties of the annealed GaN layers greatly improved with significant near band edge (NBE) emission and GaN E2 (high) as compared to non-annealed samples.
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Keywords
Gallium nitride (GaN)