Semiconductor properties of polyacetylene <i>p</i>-(CH)<i>x</i> : <i>n</i>-CdS heterojunctions

Abstract

T r a n s:(CH)x:n-CdS heterojunctions have been fabricated and used to study the properties of undoped trans-polyacetylene. The I-V data show rectifying behavior characteristic of a p-n junction diode, thus confirming that as-grown polyacetylene is p type. From C-V characteristics we infer a residual acceptor concentration in as-grown films of p-(CH)x of NA?2×1018 cm−3. Depletion has been studied in the polymer by using CdS of different doping concentrations. Detailed studies of the photovoltaic response at energies below Eg for (CH)x imply the existence of a meta-stable deep trap in the polymer with energy near the center of the gap. The threshold energy for pumping into this level provides an independent measurement of the energy gap, Eg=1.45 eV.