We propose a true solid-state alternative to the vacuum photomultiplier tube using amorphous selenium (a-Se) as the bulk avalanche i-layer. A-Se is a unique photosensing material in which carrier transport can be shifted entirely from localized to extended states where only holes get hot and undergo impact ionization, resulting in deterministic and non-Markovian avalanche gain. To achieve reliable and repeatable impact ionization gain without irreversible breakdown, a non-insulating metal oxide ntype hole-blocking/electron-transporting layer is needed. For the first time, we have deposited a solution-processed quantum dot (QD) hole blocking layer over an a-Se film at room temperature, without any surface or bulk crystallization. We have measured the lowest dark current density ever reported (30 pA/cm 2 at the onset of avalanche) compared to any other solid-state avalanche sensor at room temperature. Our results provide new strategies for the development of advanced solid-state photomultipliers via efficient QD-based interface layers to fully exploit the deterministic avalanche properties of a-Se.

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Colloidal quantum dots (CQDs) provide wide spectral tunability and high absorption coefficients owing to quantum confinement and large oscillator strengths, which along with solution processability, allow a facile, low-cost, and roomtemperature deposition technique for the fabrication of photonic devices. However, many solution-processed CQD photodetector devices demonstrate low specific-detectivity and slow temporal response. To achieve improved photodetector characteristics, limiting carrier recombination and enhancing photogenerated carrier separation are crucial. In this study, we develop and present an alternate vertical-stack photodetector wherein we use a solution-processed quantum dot photoconversion layer coupled to an amorphous selenium (a-Se) wide-bandgap charge transport layer that is capable of exhibiting single-carrier hole impact ionization and is compatible with active-matrix readout circuitry. This a-Se chalcogenide transport layer enables the fabrication of highperformance and reliable solution-processed quantum dot photodetectors, with enhanced charge extraction capabilities, high specific detectivity (D* ∼ 0.5−5 × 10 12 Jones), fast 3 dB electrical bandwidth (3 dB BW ∼ 22 MHz), low dark current density (J D ∼ 5−10 pA/cm 2 ), low noise current (i n ∼ 20−25 fW/Hz 1/2 ), and high linear dynamic range (LDR ∼ 130−150 dB) across the measured visible electromagnetic spectrum (∼405−656 nm).

The chemical versatility and rich phase behavior of tin phosphides have led to interest in their use for a wide range of applications including optoelectronics, thermoelectrics, and electrocatalysis. To date,...

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