Substrate Effects on the Bandwidth of CdSe Quantum Dot Photodetectors

TL;DR

This study examines how different substrates affect the optical bandwidth of CdSe quantum dot photodetectors, revealing that polyimide substrates enhance bandwidth by reducing trapping effects and RC limitations.

Contribution

It demonstrates the substrate-dependent variation in bandwidth and identifies RC-time limitations and trapping dynamics as key factors influencing device performance.

Findings

Polyimide substrates yield higher bandwidth (85 kHz) than glass (67 kHz).

Trapping dynamics influence the transient photocurrent response.

All devices are limited by RC-time constants.

Abstract

We investigate the time-resolved photocurrent response of CdSe quantum dot (QD) thin films sensitized with zinc beta-tetraaminophthalocyanine (Zn4APc) on three different substrates, namely silicon with 230 nm SiO2 dielectric, glass as well as polyimide. While Si/SiO2(230 nm) is not suitable for any transient photocurrent characterization due to an interfering photocurrent response of the buried silicon, we find that polyimide substrates invoke the larger optical bandwidth with 85 kHz vs. 67 kHz for the same quantum dot thin film on glass. Upon evaluation of the transient photocurrent, we find that the photoresponse of the CdSe quantum dot films can be described as a combination of carrier recombination and fast trapping within 2.7 ns, followed by slower multiple trapping events. The latter are less pronounced on polyimide, which leads to the higher bandwidth. We show that all devices are RC-time limited and that improvements of the photoresistance are the key to further increasing the bandwidth.