CuO/CdS heterojunctions designed as effective light absorbers, high k-dielectric devices, terahertz band filters and gigahertz signal stabilizers

Abstract Herein CdS thin films deposited onto glass and CuO substrates by the thermal evaporation technique are treated as electro-optical devices. Investigations on the structural properties of the CuO/CdS (CS) heterojunctions have shown that the preferred growth of hexagonal CdS onto amorphous CuO results in strained structure that increased the defects concentration in CdS. Optically the energy band gap of CdS is narrowed and the light absorption and dielectric response increased by 1590% at 1.70 eV and 565% at 1.60 eV, respectively. CS exhibited a valence band aligned heterojunction and a conduction band offset of 0.43 eV. As terahertz band filters CS heterojunction exhibited cutoff frequency in the range of 5–77 THz and high optical conductivity exceeding 100 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mrow> <mml:mfenced close=")" open="(" separators=""> <mml:mrow> <mml:mi mathvariant="normal">Ω</mml:mi> <mml:mi mathvariant="normal">cm</mml:mi> </mml:mrow> </mml:mfenced> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> in the infrared range of light. The drift mobility and free carrier concentration varied in the range of 5.74–10.44 cm 2 V −1 s −1 and 1.7 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>18</mml:mn> </mml:mrow> </mml:msup> <mml:mo>−</mml:mo> <mml:mn>1.6</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>19</mml:mn> </mml:mrow> </mml:msup> </mml:math> cm −3 , respectively. Electrically, a planar waveguide benefiting from CS interfaces as a high <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>k</mml:mi> <mml:mo>−</mml:mo> </mml:math> dielectric media showed negative capacitance effect and negative cutoff frequency as a response to signal carriers in the frequency domain of 0.01–1.0 GHz. The waveguides with these features are promising as signal stabilizers and negative capacitance sources in addition to its ability to perform as terahertz band filters.