Optical and Nanomechanical Properties of Ga 2 Se 3 Single Crystals and Thin Films
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https://doi.org/10.1007/s11837-020-04379-y Ó 2020 The Minerals, Metals & Materials Society
ADVANCED COATING AND THIN FILM MATERIALS FOR ENERGY, AEROSPACE AND BIOLOGICAL APPLICATIONS
Optical and Nanomechanical Properties of Ga2Se3 Single Crystals and Thin Films MEHMET ISIK ,1,3 CANSU EMIR,1 HASAN HUSEYIN GULLU,1 and NIZAMI GASANLY2 1.—Department of Electrical and Electronics Engineering, Atilim University, 06836 Ankara, Turkey. 2.—Department of Physics, Middle East Technical University, 06800 Ankara, Turkey. 3.—e-mail: [email protected]
The optical and nanomechanical properties of Ga2Se3 single crystals and thin films were investigated using reflection, transmission, and nanoindentation measurements. The reflection spectrum recorded in the 525- to 1100-nm range was analyzed to get the band gap energy of the crystal structure, and derivative analysis of the spectrum resulted in band gap energy of 1.92 eV which was attributed to indirect transition. The band gap energy of thermally evaporated Ga2Se3 thin film was determined from the analysis of the transmittance spectrum. The absorption coefficient analysis presented the direct band gap energy as 2.60 eV. The refractive index was investigated in the transparent region using the Wemple–DiDomenico single-oscillator model. Nanoindentation measurements were carried out on the crystal and thin film structures of Ga2Se3. Nanohardness and elastic modulus of the Ga2Se3 single crystals and thin films were calculated following the Oliver–Pharr analysis method.
INTRODUCTION The III2–VI3 (III = Ga, In, and Tl; VI = S, Se, and Te) type semiconducting family has drawn attention particularly because of its remarkable characteristics utilized in photovoltaic and electro-thermal device applications.1–3 Among the III2–VI3 type semiconductors, Ga2Se3 may be considered as one of the most attractive compounds due to its suitable electrical and optical characteristics for optoelectronic applications.4–7 Ga2Se3 provides an opportunity to form heterostructures with Al2Se3, and these heterostructures contribute to the design of optoelectronic devices based upon AlAs, GaAs, and AlxGa1xAs compounds.8 Moreover, Ga2Se3 thin films may be inserted at the interface of ZnX (X = Se, Te) to lower the valence band discontinuity in p-ZnTe/p-ZnSe multilayer structures.9,10 The semiconducting Ga2Se3 compound has a defect zinc blende structure and has been characterized previously by inductively coupled plasma spectroscopy,11 transmission,12 absorption,11 first principles density
(Received May 20, 2020; accepted September 9, 2020)
functional theory,13 Raman, and infrared reflection14 methods. Analysis of the absorption coefficient detected the presence of direct and indirect transitions with band gap energies of 2.65 eV and 2.06 eV, respectively.12 The photoelectric properties of Ga2Se3 single crystals grown by the Bridgman technique have been investigated and dependencies of DC and AC photoconductivity on light intensity, applied voltage, and ambient temperature have been reported.12 Moreove
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