(358b) Colloidal Quantum Dots for X-Ray Detectors

The growing demand for creating smart and enabling devices in health, energy, information, and communication sectors requires design of novel semiconductor materials that exhibit application-specific engineered electronic properties with the potential for low-cost, large-area, and flexible devices. Colloidal quantum dots (QDs), which are nanoscale analogues of bulk crystals, offer a powerful platform for device engineers through their size-, shape-, and composition-tunable electronic and optical properties. Additionally, their surfaces can be functionalized with molecular ligands that allow bottom-up assembly into QD solids as well as impart diverse chemistry. To- date, QD solids have been used in a wide array of devices ranging from solar cells, light emitting diodes and field-effect transistors but most of these success stories have primarily been limited to the visible and near infrared region of the electromagnetic spectrum.

In this talk, I will present our recent efforts to push the envelope of the applicability of these colloidal QDs towards high energy (X-ray) applications. I will highlight some of our recent results that show the potential of oxide and chalcogenide nanocrystals as efficient hole-blocking and photon conversion interlayers in state-of-the-art amorphous-selenium based X-ray detectors and imagers for mammography. Specifically, we reported the lowest dark current density (30 pA/cm²) ever measured for any solid-state avalanche sensor at room temperature using CeO₂ colloidal quantum dot blocking layers. Secondly, we extended the approach to fabricate hybrid amorphous-selenium and CdSe colloidal QD based hybrid devices with enhanced charge extraction capabilities coupled efficiently to state-of-the-art scintillators demonstrating extremely high specific detectivity (~5*10¹² Jones), fast photo-response with megahertz 3-dB electrical bandwidth (~25 MHz), ultra-low dark current density (~10 pA/cm²), low noise current (~20 fW/Hz^1/2) and high linear dynamic range (~150 dB).