Electrical Properties, Optical Properties, and Band Structure of CuGa<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">S</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>and CuIn<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">S</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Abstract

Various optical and electrical properties of the I-III-V${\mathrm{I}}_{2}$ compounds CuGa${\mathrm{S}}_{2}$ and CuIn${\mathrm{S}}_{2}$ have been studied. From the results of low-temperature luminescence and reflectivity, both crystals are determined to have a direct band gap. The band gaps at 2 \ifmmode^\circ\else\textdegree\fi{}K are 2.53 eV for CuGa${\mathrm{S}}_{2}$ and 1.55 eV for CuIn${\mathrm{S}}_{2}$. CuIn${\mathrm{S}}_{2}$ has been made conducting both $n$ and $p$ type, while CuGa${\mathrm{S}}_{2}$ has been made $p$ type only. Electroreflectance measurements have been performed in an attempt to determine the band structure. The highest valence band appears to be a doublet with a large admixture of Cu $3d$ wave functions.