Integrated Semiconductor Quantum Dot Scintillation Detector: Ultimate Limit for Speed and Light Yield

A picosecond-range timing of charged particles and photons is a long-standing challenge for many high-energy physics, biophysics, medical and security applications. We present a design, technological pathway and challenges, and some properties important for realization of an ultrafast high-efficient room-temperature semiconductor scintillator based on self-assembled InAs quantum dots (QD) embedded in a GaAs matrix. Low QD density ( $ ), fast ( $\sim 5~\hbox{ps}$ ) electron capture, luminescence peak redshifted by 0.2-0.3 eV from GaAs absorption edge with fast decay time (0.5-1 ns) along with the efficient energy transfer in the GaAs matrix (4.2 eV/pair) allows for fabrication of a semiconductor scintillator with the unsurpassed performance parameters. The major technological challenge is fabrication of a large volume ( $ > 1~\hbox{cm}^{3}$ ) of epitaxial QD medium. This requires multiple film separation and bonding, likely using separate epitaxial films as waveguides for improved light coupling. Compared to traditional inorganic scintillators, the semiconductor-QD based scintillators could have about 5x higher light yield and 20x faster decay time, opening a way to gamma detectors with the energy resolution better than 1% and sustaining counting rates $ > 100~\hbox{MHz}$ . Picosecond-scale timing requires segmented low-capacitance photodiodes integrated with the scintillator. For photons, the proposed detector inherently provides the depth-of-interaction information.