Study of charge carrier transport properties and lifetimes in HR GaAs:Cr with Timepix3

The response of a Timepix3 (256 × 256 pixels, pixel pitch 55 μm) detector with a 500 μm thick HR GaAs:Cr sensor was studied in proton beams of 125 MeV at the Danish Centre for Particle Therapy in Aarhus, Denmark and in a 120 GeV/c pion beam at the Super-Proton Synchrotron (SPS) at CERN. The sensor was biased at different voltages and irradiated at different angles. The readout chip was configured to operate in electron and hole collection modes. Measurements at grazing angles allowed to see elongated tracks with well-defined impact and exit points, so that charge carrier production depths could be determined in each pixel. We extracted the charge collection efficiencies and the charge carrier drift times as a function of the distance to the pixel plane. It was found that measured proton tracks are shorter in hole collection than in the case of electron collection, which is explained by the shorter lifetime of holes. At an angle of 60 degrees with respect to the sensor normal, the average track length in hole collection was ∼700 μm and 950 μm in electron collection mode. To understand the experimental findings, models describing the properties of HR GaAs:Cr were implemented into the Allpix2 simulation framework. We added previously presented experimental results describing the dependence of the electron drift velocity on the electric field and validated the response by comparing measurement and simulation for various X- and gamma-ray sources in the energy range of 10–60 keV. By comparison of the experimental and the simulated results, the mobility μ h and the lifetime of holes τ h were estimated as μ h = (320 ± 10) cm2/V/s and τ h = (4.5 ± 0.5) ns.

Exploration of grid scheme for Frisch-grid ionization chamber

A new Frisch-grid ionization chamber has been built to explore the appropriate choice of Frisch-grid. Detailed studies of the relationship between grid geometries and detector performance have been performed with an $$^{241}$$ 241 Am source. This paper describes and compares the energy resolution of ionization chambers with parallel-wire and mesh grids of different grid parameters. Some specific recommendations for grid selection are provided based on the data currently available. To obtain optimal energy resolution, the operating voltage of the chamber must satisfy the condition of minimum electron collection on the grid with distinct geometries and parameters, respectively. Since there is no established theory applicable to both types of grids, we have devised a careful simulation procedure incorporating the COMSOL and Garfield++ codes to search for the conditions of the minimum electron collection on the grid. The simulation results fit the experimental data well, suggesting that this simulation method successfully predicts the suitable voltage setting when using a mesh grid or parallel wires grid as the shielding electrode.

Planar narrowband Tamm plasmon-based hot-electron photodetectors with double distributed Bragg reflectors

Hot-electron photodetectors (HE PDs) are attracting a great deal of attention from plasmonic community. Many efficient HE PDs with various plasmonic nanostructures have been demonstrated, but their preparations usually rely on complicated and costly fabrication techniques. Planar HE PDs are viewed as potential candidates of cost-effective and large-area applications, but they likely fail in the simultaneous achievement of outstanding optical absorption and hot-electron collection. To reconcile the contradiction between optical and electrical requirements, herein, we propose a planar HE PD based on optical Tamm plasmons (TPs) consisted of an ultrathin gold film (10 nm) sandwiched between two distributed Bragg reflectors (DBRs). Simulated results show that strong optical absorption (>0.95) in the ultrathin Au film is realized. Electrical calculations show that the predicted peak photo-responsivity of proposed HE PD with double DBRs is over two times larger than that of conventional single-DBR HE PD. Moreover, the planar dual-DBR HE PDs exhibit a narrowband photodetection functionality and sustained performance under oblique incidences. The optical nature associated with TP resonance is elaborated.

Preparation by Hydrothermal Method of TiO2-RGO Nanocomposite and Using as Photoanode of Dye-Sensitized Solar Cell

We explored the photoanode properties of DSSCs by used RGO and TiO2 nanoparticles as an optical electrode (we used the doctor's blade method). Using the hydrothermal process, we prepared a nanocomposite of TiO2/RGO. SEM and XRD, tests were used to study the structural properties of TiO2 and TiO2/RGO. When compared the J-V properties of the integrated devices made to those made, the J-V properties of the integrated devices came out on top of used TiO2/RGO as the photoanode in a solar cell for TiO2/RGO, which increased the PCE (8.674±0.063%). We were able to improve the short circuit current density (Jsc) and the power conversion efficiency (PCE) for the effective region by adding RGO to the TiO2. The PCE has improved due to better electron transport, improved electron collection in photoanode, and increased light-harvesting performance. As a result, RGO with distinct structural and optical properties is a viable choice in DSSC.

Charge Transporting Materials Grown by Atomic Layer Deposition in Perovskite Solar Cells

Charge transporting materials (CTMs) in perovskite solar cells (PSCs) have played an important role in improving the stability by replacing the liquid electrolyte with solid state electron or hole conductors and enhancing the photovoltaic efficiency by the efficient electron collection. Many organic and inorganic materials for charge transporting in PSCs have been studied and applied to increase the charge extraction, transport and collection, such as Spiro-OMeTAD for hole transporting material (HTM), TiO2 for electron transporting material (ETM) and MoOX for HTM etc. However, recently inorganic CTMs are used to replace the disadvantages of organic materials in PSCs such as, the long-term operational instability, low charge mobility. Especially, atomic layer deposition (ALD) has many advantages in obtaining the conformal, dense and virtually pinhole-free layers. Here, we review ALD inorganic CTMs and their function in PSCs in view of the stability and contribution to enhancing the efficiency of photovoltaics.

Photo-absorption and electron collection of field-assisted GaN nanohole array photocathode

The light absorption and photo-generation rate under different periods, filling factors (FF), hole depth and inclination angles are studied. The NHA exhibits a larger light absorption compared with the planar film, which is about 99.99973%. Based on the three-dimensional continuity equation, the quantum efficiency (QE) and collection efficiency (CE) of the field-assisted GaN NHA and the graded compositional AlGaN NHA are calculated. The QE and CE of the GaN NHA with a period of 200 nm, a filling factor of 0.05, an inclined angle of 10°, and a field intensity of 2 V/µm are 62.7% and 62.6%, respectively. In addition, the graded compositional AlGaN structure has a more improved effect on the vertical NHA. Compared with the uniform GaN NHA, the electron collection of AlGaN NHA ratio is increased by 2.4 times. The design principles proposed in this work provide guidance to reasonable parameters for the application of NHA photocathodes.