Impact of Se and Te addition on optical characteristics of ternary GeInSb chalcogenide films as promising materials for optoelectronic applications

Abstract

Abstract The present study investigates the linear and non-linear optical characteristics of non-crystalline quaternary Ge 15 In 5 Sb 5 Se 75 (GIS-Se) and Ge 15 In 5 Sb 5 Te 75 (GIS-Te) chalcogenide thin films. The amorphous nature of the studied compositions was confirmed by x-ray diffraction (XRD). The values of transformation temperatures determined by differential thermal analysis (DTA), such as glass transition <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>g</mml:mi> </mml:mrow> </mml:msub> </mml:math> and crystallization <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>c</mml:mi> </mml:mrow> </mml:msub> </mml:math> temperatures, are 524.3 and 639.6 K for GIS-Se and 503.6 and 542.0 K for GIS-Te. The calculated values of glass forming ability ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>G</mml:mi> <mml:mi>F</mml:mi> <mml:mi>A</mml:mi> </mml:math> ) and thermal stability ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>H</mml:mi> </mml:math> ) for GIS-Se are higher than those for GIS-Te. The transmittance <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>T</mml:mi> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mi>λ</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:math> and reflectance <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>R</mml:mi> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mi>λ</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:math> spectrophotometric measurements in the UV–vis. wavelength range (400–2500 nm) are used to estimate the index of refraction <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>n</mml:mi> </mml:math> and extinction coefficient <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>k</mml:mi> <mml:mo>.</mml:mo> </mml:math> The obtained values of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>n</mml:mi> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>k</mml:mi> </mml:math> are found to be thickness independent in the investigated range. Tauc’s extrapolation model was used to determine both Urbach tail ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>E</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>U</mml:mi> </mml:mrow> </mml:msub> </mml:math> ) and optical band gap ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>E</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>g</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>o</mml:mi> <mml:mi>p</mml:mi> <mml:mi>t</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> ) energies. The values of ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>E</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>U</mml:mi> </mml:mrow> </mml:msub> </mml:math> ) are 0.416, 0.526 eV and ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>E</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>g</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>o</mml:mi> <mml:mi>p</mml:mi> <mml:mi>t</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> ) are 1.83, 1.31 eV with indirect allowed transitions for GIS-Se and GIS-Te, respectively. The optical conductivity <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"

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