Visible-blind ZnMgO Colloidal Quantum Dot Downconverters expand Silicon CMOS Sensors Spectral Coverage into Ultraviolet and enable UV Band Discrimination

TL;DR

This paper introduces a non-toxic ZnMgO quantum dot-based scheme that significantly enhances UV detection and discrimination in Silicon CMOS sensors, expanding their spectral coverage into the ultraviolet range.

Contribution

It presents a novel, visible-blind, quantum dot downconverter that improves UV sensitivity and enables UV band discrimination using standard CMOS sensors without complex optics.

Findings

Nine-fold increase in UV photoresponsivity of Si photodetectors.

Successful spectral tuning of ZnMgO QDs for UV and visible emission.

Effective UV band discrimination with simple stacked QD architecture.

Abstract

Selective spectral detection of ultraviolet (UV) radiation is highly important across numerous fields from health and safety to industrial and environmental monitoring applications. Herein, we report a non-toxic, visible-blind, inorganic quantum dot (QD)-based sensing scheme that expands the spectral coverage of Silicon CMOS sensors into the UV, enabling efficient UV detection without affecting the sensor performance in the visible and UV-band discrimination. The reported scheme employs zinc magnesium oxide (ZnMgO) QDs with compositionally tunable absorption across UV and high photoluminescence quantum yield (PLQY) in the visible. The efficient luminescence and large stokes shift of these QDs have been exploited herein to act as an efficient downconverting material that enhances the UV sensitivity of Si-photodetector (Si-PD). A Si-PD integrated with the QDs results in a nine-fold improvement in photoresponsivity from 0.83 mA/W to 7.5 mA/W at 260 nm. Leveraging the tunability of these QDs we further report on a simple UV band identification scheme, using two distinct band gap ZnMgO QDs stacked in a tandem architecture whose spectral emission color depends on the UV-band excitation light. The downconverting stack enables facile discrimination of UV light using a standard CMOS image sensor (camera) or by the naked eye and avoids the use of complex optics.