A1GaN Thin Films On Silicon Substrates For Photodetector And Transistor Devices

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Date
2011-07
Authors
Hussein, Asaad Shakir
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Publisher
Universiti Sains Malaysia
Abstract
This study examined AlxGa1-xN alloys grown on Si substrate for UV photodetectors and transistors applications. Radio-frequency (RF) nitrogen plasmaassisted molecular beam epitaxy (PA-MBE) technique was used to grow AlxGa1- xN/GaN/AlN thin films on the Si(111) substrates. Undoped and n-type Si-doped samples of AlxGa1-xN with different Al-mole fractions were successfully grown. Reflection high energy electron diffraction (RHEED), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), high-resolution X-ray diffraction (HR-XRD), photoluminescence (PL), Raman scattering and Hall effect measurements were used to investigate the reconstruction pattern, cross-section, surface morphology, surface roughness, mole fractions, crystalline quality and carrier concentration of the thin films. High Al-mole fractions of AlxGa1-xN samples with good crystal quality have successfully been grown on the Si(111) substrates. Hall effect measurements showed that n-type Si-doped Al0.25Ga0.75N has high carrier concentration of 3.93 × 1019 cm-3. The effect of strain on the grain size with different Al-mole fractions of undoped AlxGa1-xN samples has been investigated. The results of structural and surface morphology indicated that there is a relatively larger tensile strain in the sample with the smallest Al-mole fraction; while a smaller compressive strain and larger grain size appear with the Al-mole fraction of 0.30. The strain gets relaxed for the sample with the highest Al-mole fraction of 0.43. Ti/Al bi-layer ohmic contacts on undoped and n-type Si-doped AlxGa1-xN samples have been explored. The specific contact resistivities of this contact are sensitive to the change of annealing temperatures and annealing time as well as to the carrier concentration. For Au- and Pt-based Schottky contacts, the results showed that the sample with n-type Si-doping exhibit good Schottky behavior for both contacts. Good results for Schottky barrier heights (SBHs) have been obtained for sample annealed at 600 oC. For Ni-based Schottky contacts, the findings revealed that the highest SBH has been obtained for the sample with the Al-mole fraction of 0.30.
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Keywords
AlxGa1-xN alloys grown on Si substrate , UV photodetectors and transistors applications
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