2 research outputs found
Coupled HgSe Colloidal Quantum Wells through a Tunable Barrier: A Strategy To Uncouple Optical and Transport Band Gap
Among
semiconductor nanocrystals (NCs), 2D nanoplatelets (NPLs)
are a special class of nanomaterials with well controlled optical
features. So far, most of the efforts have been focused on wide band
gap materials such as cadmium chalcogenide semiconductors. However,
optical absorption can be pushed toward the infrared (IR) range using
narrow band gap materials such as mercury chalcogenides. Here we demonstrate
the feasibility of a core/shell structure made of a CdSe core with
two HgSe external wells. We demonstrate that the optical spectrum
of the heterostructure is set by the HgSe wells and this, despite
the quasi type II band alignment, makes the band edge energy independent
of the inner core thickness. On the other hand, these core/shell NPLs
behave, from a transport point of view, as a wide band gap material.
We demonstrate that the introduction of a wide band gap CdSe core
makes the material less conductive and with a larger photoresponse.
Hence, the heterostructure presents an effective electric band gap
wider than the optical band gap. This strategy will be of utmost interest
to design infrared effective colloidal materials for which the reduction
of the carrier density and the associated dark current is a critical
property
Intraband Mid-Infrared Transitions in Ag<sub>2</sub>Se Nanocrystals: Potential and Limitations for Hg-Free Low-Cost Photodetection
Infrared photodetection based on
colloidal nanoparticles is a promising
path toward low-cost devices. However, mid-infrared absorption relies
on interband transitions in heavy metal-based materials, which is
a major flaw for the development toward mass market. In the quest
of mercury-free infrared active colloidal materials, we here investigate
Ag<sub>2</sub>Se nanoparticles presenting intraband transition between
3 and 15 μm. With photoemission and infrared spectroscopy, we
are able to propose an electronic spectrum of the material in the
absolute energy scale. We also investigate the origin of doping and
demonstrate that it results from a cation excess under the Ag<sup>+</sup> form. We demonstrate photoconduction into this material under
resonant excitation of the intraband transition. However, performances
are currently quite weak with (i) a slow photoresponse (several seconds)
and (ii) some electrochemical instabilities at room temperature