Development and Characterization of Mercury Cadmium Telluride Colloidal Quantum Dot Based Infrared Optical Sensor

Abstract

Motivation of this thesis is to synthesize HgCdTe quantum dots responsive in MWIR spectral range using chemical synthesis method and develop room temperature operated MWIR focal plane array using commercial silicon ROIC and HgCdTe CQD layer. MWIR region of electromagnetic spectrum is an important spectral range for both space and civil applications. It is extremely important in the remote sensing point of view especially for imaging earth surface from space due to existence of atmospheric transmission window in this spectral band. The dominant photodetectors in this range are single crystal InSb and HgCdTe, while the cost of these detectors is high and requires cooling around 80 K to reduce the dark current. Infrared detectors made out of epitaxial growth of HgCdTe material grown on lattice matched substrates such as CdZnTe, which is in normal practice are prohibitively costly and lot of research is going on in the developed countries to find a better alternative for the material. In the last decade colloidal quantum dots (CQD) are emerged as a better alternative for the detection of electromagnetic spectrum due to their feasible synthesis as well as tuneable electrical and optical properties. Among the available IR absorbing QD materials, HgCdTe is of special interest due to the bandgap tuneability over the wide range, which covers SWIR-LWIR regions. Its large bulk Excitonic Bohr radius (40 nm in HgTe) further helps in better control over the bandgap engineering. This thesis investigates physical properties of synthesized quantum dots, development and characterization of heterojunction IR detector and finally development and study of 320×256 pixels MWIR FPA. Significant amount of efforts have been made to understand the performance of photo-induced charge generation and electron-hole pair separation in HgCdTe QDs-Silicon heterojunction and interdigitated photoconductive devices. Several Focal Plane Array (FPA) devices are fabricated by directly dispersing these QDs onto the Si ROICs. Single pixel junction and FPA devices are characterized and their figure of merit, Specific Detectivity (D*) has been evaluated. Room temperature imaging of various MWIR emitting targets has been carried out using above FPAs. The photographs taken with the devices indicate the real time demonstration of these room temperature operated CQD based IRFPA as highly cost effective alternative for commercially available IRFPA. This thesis work is presented in six chapters including conclusion and directions towards future work.