Ultrahigh-gain colloidal quantum dot infrared photodetectors: Unraveling the potential of electro-kinetically pumped charge multiplication

Abstract

Colloidal quantum dots (CQDs) are promising candidates for infrared photodetectors (IRPDs) with high detectivity (D*) and low-cost production. However, the incoherent hopping of charge carriers often causes low carrier mobility and inefficient charge extraction, leading to low detectivity in CQD-based IRPDs. Although photo-induced charge multiplication, in which high-energy photons create multiple electrons, is a viable alternative for enhancing the signal amplitude and detectivity, its capability is limited in IR detectors because of its susceptibility to thermal noise in low-bandgap materials. Herein, we present, for the first time, a pioneering architecture of a CQD-based IRPD that employs kinetically pumped charge multiplication. This is achieved by employing a thick CQD layer (> 540 nm) and subjecting it to a strong electric field. This configuration accelerates electrons to acquire kinetic energy, surpassing the bandgap of the CQD material, thereby initiating kinetically pumped charge multiplication. We also demonstrate that optimizing the dot-to-dot distance to approximately 4.1 nm yields superior device performance because of the tradeoff between increased impact ionization rates and diminished electron-hopping probabilities with increasing dot-to-dot distance. The optimal CQD-based IRPD exhibited a maximum multiplication gain of 85 and a peak detectivity (D*) of 1.4×1014 Jones at a wavelength of 940 nm.