Hot Electron Tunneling in Pt/LaAlO₃/SrTiO₃ Heterostructures for Enhanced Photodetection

Abstract

LaAlO3/SrTiO3 (LAO/STO) heterostructures, in which a highly mobile two-dimensional electron gas (2DEG) is formed, have great potential for optoelectronic applications. However, the inherently high density of the 2DEG hinders the observation of photo-excitation effects in oxide heterostructures. Herein, a strong photoresponse of the 2DEG in a Pt/LAO/STO heterostructure is achieved by adopting a vertical tunneling configuration. The tunneling of the 2DEG through an ultrathin LAO layer is significantly enhanced by UV light irradiation, showing a maximum photoresponsivity of ∼1.11 × 107%. The strong and reversible photoresponse is attributed to the thermionic emission of photoexcited hot electrons from the oxygen-deficient STO. Notably, the oxygen vacancy defects play a critical role in enhancing the tunneling photocurrent. Our systematic study on the hysteresis behavior and the light power dependency of the tunneling current consistently support the fact that the photoexcited hot electrons from the oxygen vacancies strongly contribute to the tunneling conduction under the UV light. This work offers valuable insights into a novel photodetection mechanism based on the 2DEG as well as into developing ultrathin optoelectronic devices based on the oxide heterostructures.

Optoelectronic Synapse Based on 2D Electron Gas in Stoichiometry‐Controlled Oxide Heterostructures

“…The LAO thin films with different stoichiometries were epitaxially grown on STO (001) substrates by pulsed laser deposition (PLD). [40][41][42] The detailed procedure for the film growth is described in the experimental section. Note that the cation stoichiometry (i.e., the La/Al ratio) of the LAO thin films was precisely controlled by the fluence of the excimer laser during the PLD process.…”

LaAlO3/SrTiO3 Heterointerface: 20 Years and Beyond

“…Jeon et al have achieved strong photo-response of the 2DEG in the Pt/LAO/STO heterostructure by adopting a vertical tunnel structure. [152] The 2DEG tunneling current through the ultrathin LAO layer is significantly enhanced under ultraviolet irradiation. This strong and reversible photo response is attributed to the thermionic emission of photoexcited hot electrons from V O defects of STO.…”

Plasmonic Bound States in the Continuum Metasurface–Semiconductor–Metal Architecture Enables Efficient Hot-Electron-Based Photodetector

“…Hot electrons are high-energy electrons produced during the nonradiative decay process of surface plasmons (SPs). − Unlike the “free electrons”, hot electrons possess a large amount of energy, which is much higher than the bandgap ( E g ) of targeted materials and usually 1–2 eV above the Fermi level . Therefore, extracting hot electrons is a promising approach for photon-induced carrier generation, which has been widely employed for photodetection, − photocatalysis, , surface imaging, and so on. , In the realm of photodetection, when SPs are excited, hot electrons may overcome the Schottky barrier before thermalization and then be injected into the conduction band of the semiconductor to generate photocurrent within a short time domain; − in addition, electron–phonon relaxation can also be used to heat the nanostructures, achieving photoelectric conversion within a long time domain based on thermal effects. , These photodetectors are collectively known as plasmonic hot-electron-based photodetectors (HEB-PDs). Although the mechanism has been intensively comprehended, the reported HEB-PDs are still limited by the low incident photon-to-electron conversion efficiency (IPCE).…”