Year: 2018
Type: article
Abstract: Large and persistent photoconductivity (LPPC) in semiconductors is due to the trapping of photogenerated minority carriers at crystal defects. Theory has suggested that anion vacancies in II-VI semiconductors are responsible for LPPC due to negative-$U$ behavior, whereby two minority carriers become kinetically trapped by lattice relaxation following photoexcitation. By performing a detailed analysis of photoconductivity in CdS, we provide experimental support for this negative-$U$ model of LPPC. We also show that LPPC is correlated with sulfur deficiency. We use this understanding to vary the photoconductivity of CdS films over nine orders of magnitude, and vary the LPPC characteristic decay time from seconds to ${10}^{4}\phantom{\rule{0.16em}{0ex}}\mathrm{s}$ by controlling the activities of $\mathrm{C}{\mathrm{d}}^{2+}$ and ${\mathrm{S}}^{2\ensuremath{-}}$ ions during chemical bath deposition. We suggest a screening method to identify other materials with long-lived, nonequilibrium, photoexcited states based on the results of ground-state calculations of atomic rearrangements following defect redox reactions, with a conceptual connection to polaron formation.
Source: Physical Review Materials
Authors: Han Yin, Austin Akey, R. Jaramillo
Institutions: Massachusetts Institute of Technology, Harvard University
Language: English
Subfield: Electrical and Electronic Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: green
Award: G2756207379
OpenAlex ID: W2805459711