We demonstrated an ultrahigh-performance and self-powered β-Ga2O3 thin film solar-blind photodetector fabricated on a cost-effective Si substrate using a high-temperature seed layer (HSL). The polycrystalline β-Ga2O3 thin film deposited with HSL shows high performance in the solar-blind region in comparison to the amorphous Ga2O3 thin film deposited without HSL. The zero-bias digitizing sensor prototype with an HSL produces a digitized output bit with deep UV (DUV) light that exhibits a high on/off (I 254 nm/I dark) ratio of >103, a record-low dark current of 1.43 pA, and high stability and reproducibility over 100 cycles even after >2100 h. The photodetector shows minimum persistent photoconductivity and fast response in milliseconds. The photodetector yields a responsivity of 96.13 A W–1 with an external quantum efficiency of 4.76 × 104 at 5 V for 250 nm monochromatic light. The photodetector shows a high response to even a rare weak signal of DUV (44 nW/cm2). These values are the highest reported to date for a planar β-Ga2O3 thin film based photodetector despite the use of the cost-effective substrate. The asymmetric I–V curve indicates a dissimilar Schottky barrier height at the two ends of the MSM photodetector, which is discussed as the main reason for the high response even at zero bias. This work provides the guidelines to develop a β-Ga2O3-based cost-effective, self-powered, high-performance, and fast DUV photodetector that possesses a high potential for next-generation practical solar-blind photodetector application.

Traditional photodetectors generally show a unipolar photocurrent response when illuminated with light of wavelength equal or shorter than the optical bandgap. Here, it is reported that a thin film of gallium oxide (GO) decorated with plasmonic nanoparticles, surprisingly, exhibits a change in the polarity of the photocurrent for different UV bands. Silver nanoparticles (Ag NPs) are vacuum‐deposited onto β‐Ga2O3 and the AgNP@GO thin films show a record responsivity of 250 A W−1, which significantly outperforms bare GO planar photodetectors. The photoresponsivity reverses sign from +157 µA W−1 in the UV‐C band under unbiased operation to −353 µA W−1 in the UV‐A band. The current reversal is rationalized by considering the charge dynamics stemming from hot electrons generated when the incident light excites a local surface plasmon resonance in the Ag nanoparticles. The Ag nanoparticles improve the external quantum efficiency and detectivity by nearly one order of magnitude with high values of 1.2 × 105 and 3.4 × 1014 Jones, respectively. This plasmon‐enhanced solar blind GO detector allows UV regions to be spectrally distinguished, which is useful for the development of sensitive dynamic imaging photodetectors.

Although fast-scan cyclic voltammetry (FSCV) has contributed to important advances in neuroscience research, the technique is encumbered by significant analytical challenges. Confounding factors such as pH change and transient effects at the microelectrode surface make it difficult to discern the analytes represented by complex voltammograms. Here we introduce paired-pulse voltammetry (PPV), that mitigates the confounding factors and simplifies the analytical task. PPV consists of a selected binary waveform with a specific time gap between each of its two comprising pulses, such that each binary wave is repeated, while holding the electrode at a negative potential between the waves. This allows two simultaneous yet very different voltammograms (primary and secondary) to be obtained, each corresponding to the two pulses in the binary waveform. PPV was evaluated in the flow cell to characterize three different analytes, (dopamine, adenosine, and pH changes). The peak oxidation current decreased by approximately 50%, 80%, and 4% for dopamine, adenosine, and pH, in the secondary voltammogram compared with primary voltammogram, respectively. Thus, the influence of pH changes could be virtually eliminated using the difference between the primary and secondary voltammograms in the PPV technique, which discriminates analytes on the basis of their adsorption characteristics to the carbon fiber electrode. These results demonstrate that PPV can be effectively used for differentiating complex analytes.

The quest for flexible and completely visible transparent solar-blind photodetector is the great motivation for next generation invisible security and photo-sensor application. Here, we have developed high performance and completely flexible solar blind photodetector using room temperature grown amorphous Ga 2 O 3 thin film and unconventional amorphous indium-zincoxide (a-IZO) transparent conducting electrodes. The a-IZO transparent conducting electrodes are deposited using an optimized and unique RF superimposed DC sputtering which helps to achieve high optoelectronic properties with excellent mechanical flexibility. In contrast to conventional and highly reflective silver (Ag) metal electrodes, IZO offers transparency >85% in visible-IR. The solar-blind photodetector with a-IZO electrode shows high responsivity of 43.99 A W −1 and high external quantum efficiency of 2.18 × 10 4 % in contrast to conventional Ag metal electrodes. The performance of the a-IZO/a-Ga 2 O 3 photodetector is the highest among the reported amorphous Ga 2 O 3 photodetector. Moreover, the flexibility of a-IZO electrode and conventional Ag metal electrode on a-Ga 2 O 3 photodetector is investigated under repeated bending cycle. The a-IZO electrode shows excellent flexibility of the solarblind photodetector and demonstrated a decrease in photocurrent by 28.6% under 30 cm bending radius and a 38.8% decrease in photocurrent even after 500 stretch/release cycles at 30 cm bending radius. However, the conventional Ag electrode shows complete failure on bending with 30 cm bending radius even on single cycle. The results demonstrated a-IZO thin film as a potential electrode for next generation flexible and visible transparent solar-blind photodetector.

Efficiency of earth abundant and pure sulfide kesterite Cu-Zn-Sn-S (CZTS) solar cell has been stagnant around 9.4% for years, while its counterpart Cu-In-Ga-Se (CIGS) reports an efficiency of more than 22%. Low open circuit voltage (VOC) is the major challenging factor for low efficiency due to severe nonradiative interface recombinations. The existence of higher defect states at the conventional CZTS-CdS interface due to undesirable energy level alignment and lattice misfit promotes trap-assisted recombinations and results in low VOC. In this work, amorphous TiO2 (Eg=3.8eV) is proposed as a promising substitute to the conventional and low bandgap CdS (Eg=2.4eV) layer. The surface and interface of the CZTS-TiO2 layer were investigated using X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). The result reveals favorable “spike”-like conformations at the CZTS-TiO2 interface with a conduction band offset value of 0.17 eV. The nanoscale probing of the interface by Kelvin probe force microscopy across CZTS-TiO2 layers shows a higher potential barrier for interface recombination at CZTS-TiO2 in contrast to the conventional CZTS-CdS interface. Finally, the fast decay response and lower persistent photoconductivity of photogenerated carriers for CZTS-TiO2 heterojunction based photodetectors further validate our results. The energy level alignment and nanoscale interface studies signify TiO2 as a promising alternate buffer layer for earth abundant CZTS solar cells.