Field-Effect Transistor and Photo-Transistor of Narrow-Band-Gap Nanocrystal Arrays Using Ionic Glasses

Abstract

The gating of nanocrystal films is currently driven by two approaches: either the use of a dielectric such as SiO2 or the use of electrolyte. SiO2 allows fast bias sweeping over a broad range of temperatures but requires a large operating bias. Electrolytes, thanks to large capacitances, lead to the significant reduction of operating bias but are limited to slow and quasi-room-temperature operation. None of these operating conditions are optimal for narrow-band-gap nanocrystal-based phototransistors, for which the necessary large-capacitance gate has to be combined with low-temperature operation. Here, we explore the use of a LaF3 ionic glass as a high-capacitance gating alternative. We demonstrate for the first time the use of such ionic glasses to gate thin films made of HgTe and PbS nanocrystals. This gating strategy allows operation in the 180 to 300 K range of temperatures with capacitance as high as 1 μF·cm–2. We unveil the unique property of ionic glass gate to enable the unprecedented tunability of both magnitude and dynamics of the photocurrent thanks to high charge-doping capability within an operating temperature window relevant for infrared photodetection. We demonstrate that by carefully choosing the operating gate bias, the signal-to-noise ratio can be improved by a factor of 100 and the time response accelerated by a factor of 6. Moreover, the good transparency of LaF3 substrate allows back-side illumination in the infrared range, which is highly valuable for the design of phototransistors.

Reconfigurable 2D/0D p–n Graphene/HgTe Nanocrystal Heterostructure for Infrared Detection

“…This requires to make the conduction within the nanocrystal array more efficient using a ligand exchange step to get high carrier mobility. In this manuscript, we report about a way to induce p-n junction directly into the nanocrystal thin film by combining three key elements: (i) the unique electronic properties of graphene electrodes,(ii) the recent developments of HgTe NCs-based inks 15 leading to films with relatively high carrier mobility 34 (>1 cm 2 v -1 s -1 ), and (iii) the use of high capacitance ionic glass gating technology [35][36][37] that enables to reach high carrier density and to spatially tune the doping profile through the whole 2D/0D heterostructure. Our study demonstrates that the built-in electric field of the p-n junction formed into the nanocrystal film allows for enhancing the charge dissociation and unlock photovoltaic functionality.…”

Designing Photovoltaic Devices Using HgTe Nanocrystals for Short and Mid‐Wave Infrared Detection

“…Significant improvements were also obtained regarding the integration of the material into devices. Recent device developments include the demonstration of HgTe‐based field‐effect transistor and phototransistor, introduction of resonators to enhance the device light absorption, achieve pixel‐level spectral filtering or to achieve polarization‐sensitive detector . Devices with multicolor detection have been demonstrated either in the visible and in the IR, or in different IR fields such as SWIR/MWIR and MWIR/LWIR .…”

Ferroelectric Gating of Narrow Band-Gap Nanocrystal Arrays with Enhanced Light–Matter Coupling

“…When this dielectric is silica 21,22 , the capacitance value is generally a tradeoff between leakage and breakdown. Electrolyte [23][24][25][26][27][28][29] and ionic glasses [30][31][32][33] can be used to obtain higher gate capacitances (>1 µF. cm -2 ).…”