Band to Band Tunneling at the Zinc Oxide (ZnO) and Lead Selenide (PbSe) Quantum Dot Contact; Interfacial Charge Transfer at a ZnO/PbSe/ZnO Probe Device.

Minkyong Kim,Heesun Yang,Byoungnam Park,Chang-Yeol Han

doi:10.3390/ma12142289

Abstract

We provide a comprehensive understanding of interfacial charge transfer at the lead selenide (PbSe) quantum dot (QD)/zinc oxide (ZnO) interface, proposing band to band tunneling process as a charge transfer mechanism in which initial hopping of carriers from ZnO to PbSe QDs is independent of temperature. Using the transmission line method (TLM) in a ZnO/PbSe/ZnO geometry device, we measured the ZnO/PbSe electrical contact resistance, a measure of charge transfer efficiency. Fabrication of a highly conductive ZnO film through Al doping allows for the formation of ZnO source and drain electrodes, replacing conventional metal electrodes. We found that band to band tunneling at the PbSe QD/ZnO interface governs charge transfer based on temperature-independent PbSe QD/ZnO contact resistance. In contrast, the PbSe QD channel sheet resistance decreased as the temperature increased, indicating thermally activated transport process in the PbSe QD film. These results demonstrate that, at the ZnO/PbSe QD interface, temperature-independent tunneling process initiates carrier injection followed by thermally activated carrier hopping, determining the electrical contact resistance.

Highlights

Efficient interfacial charge transfer is of central importance in assembling highly efficient display and energy storage/conversion devices [1,2,3,4,5]
We fabricated a bottom-contact ZnO field effect transistor (FET) structure as displayed in Figure 1b in which a highly doped Si served as a gate electrode
We found that the contact resistance depends on the quantum dot (QD) size, concluding that, as the QD size increases the contact resistance decreases due to lower carrier injection barrier as well as enhanced electrical mobility [30]

Summary

Introduction

Efficient interfacial charge transfer is of central importance in assembling highly efficient display and energy storage/conversion devices [1,2,3,4,5]. QD size-dependent optoelectronic properties including energy band gap and carrier mobility arising from quantum confinement effect have accelerated applications to light emitting diodes (LEDs) and energy harvesting research fields including photovoltaics (PVs) [10,11,12]. Among a class of QDs, IV-VI semiconductor lead salts (PbS, PbSe, and PbTe) have been used as an emitting layer in near infrared QD LEDs as well as a light sensitizer in highly efficient PVs [13,14,15,16]. PbSe QDs have, shown high carrier mobility and decent tunability of energy band gap through ligand and band gap engineering, demonstrating to be a versatile building block for nanostructured QD devices [18,19,20]

Methods

Results

Conclusion