Quantum-Confined Mercury Telluride Nanocrystals and Their Application to Infrared Optoelectronics

Colloidal nanocrystals are versatile building blocks to design infrared optoelectronic devices. When their dimension is reduced below the Bohr radius, quantum confinement occurs, thus providing size-tunable optoelectronic properties. In particular, mercury telluride nanocrystals offer a broadly tunable absorption, going from 1.5 eV to 20 meV. Recent progress in material growth and in surface chemistry has allowed to enhance IR detectors performances. Still, advancement in several aspects is needed to further improve performance, maximize signal-to-noise ratio and speed up the photoresponse time. The need for such improvements has led to a variety of designs for IR detectors, ranging from photoconductive to photovoltaic devices. Here, the design of a HgTe nanocrystal-based sensor operating in the short-wave infrared and with a very fast time response is explored. The design relies on a planar geometry based on a dual gated field effect transistor. Device characterization shows that a diode operation mode is induced by the presence of the two gates, while graphene electrodes optimize the control on the electrostatic design of the p-n junction inside the nanocrystal arrays. Photo-response times as short as 3 ns are obtained when the device is operated in the diode mode, the fastest reported for an HgTe NC-based device, while still maintaining a very competitive gain band width product.