Cu2ZnSnS4 (CZTS) has been extended to the
field of photodetection owing to its outstanding optoelectronic properties.
However, the existence of the ineluctable defects in CZTS semiconductors
affects and even determines the optoelectric processes including carrier
generation, relaxation, transfer, and recombination. Moreover, photoresponse
correlated to the defects in CZTS photodetectors has not well been
documented and the possible physics mechanism is still unexplored.
High-performance and self-powered PN heterojunction photodetectors
are built from Cu2ZnSnS4 and CdS films. The
devices exhibit a steady rectifying behavior and a prominent photovoltaic
effect. The peak values of responsivity and detectivity are 220 mA
W–1 and 2.69 × 1010 Jones, respectively.
A very fast response speed with rising and decay times of up to 18
and 19 μs and an ultrahigh photoswitching ratio beyond 104 are demonstrated in these photodetectors. An abnormal dependence
of the light response parameters on the incident power and temperature
is found in these devices. This anomaly is explained by the formation
of the defects and/or defect dipoles, which are evidenced by the temperature
dependence of the photocurrent, the dependence of the capacitance
on the bias voltage at different temperatures, and the derivative
of capacitance with temperature.