Microwave plasma-assisted reactive HiPIMS of InN films: Plasma environment and material characterisation

This work focuses on the low temperature fabrication process of InN thin films via microwave plasma-assisted reactive high power impulse magnetron sputtering (MAR-HiPIMS). The influence of microwave plasma on the HiPIMS discharge process at various nitrogen flows and microwave powers was monitored and characterised through in situ diagnostics, including following HiPIMS I(V,t) curves, optical emission spectroscopy (OES), as well as performing time-resolved Langmuir probe and time-of-flight mass spectroscopy (ToF-MS) measurements. This was followed by the deposition of InN films via standard reactive HiPIMS (reference sample) and MAR-HiPIMS and their characterisation via X-ray diffraction (XRD), reflectometry (XRR), as well as scanning and transmission electron microscopy (SEM, TEM). It was found that the microwave plasma facilitates the dissociation/activation of nitrogen species and supplies seed electrons to the magnetron discharge plasma. Furthermore, the energy of the incoming ions was determined via ToF-MS, and it was possible to identify their plasma origin and temporal behaviour. The produced R-HiPIMS sample was highly metallic, with no nitride phase detected. The MAR-HiPMS film, however, was stoichiometric and exhibited (0002) direction texturing, with an optical bandgap of approx. 1.5 eV, electron concentration of 2.72 × 1020 cm−3 and electron mobility of 7.16 cm2V−1 s−1 (in the range for polycrystalline InN)

Dosimetry of microbeam radiotherapy by flexible hydrogenated amorphous silicon detectors

Objective. Detectors that can provide accurate dosimetry for microbeam radiation therapy (MRT) must possess intrinsic radiation hardness, a high dynamic range, and a micron-scale spatial resolution. In this work we characterize hydrogenated amorphous silicon detectors for MRT dosimetry, presenting a novel combination of flexible, ultra-thin and radiation-hard features. Approach. Two detectors are explored: an n-type/intrinsic/p-type planar diode (NIP) and an NIP with an additional charge selective layer (NIP + CSC). Results. The sensitivity of the NIP + CSC detector was greater than the NIP detector for all measurement conditions. At 1 V and 0 kGy under the 3T Cu-Cu synchrotron broadbeam, the NIP + CSC detector sensitivity of (7.76 +/- 0.01) pC cGy-1 outperformed the NIP detector sensitivity of (3.55 +/- 0.23) pC cGy-1 by 219%. The energy dependence of both detectors matches closely to the attenuation coefficient ratio of silicon against water. Radiation damage measurements of both detectors out to 40 kGy revealed a higher radiation tolerance in the NIP detector compared to the NIP + CSC (17.2% and 33.5% degradations, respectively). Percentage depth dose profiles matched the PTW microDiamond detector's performance to within +/- 6% for all beam filtrations except in 3T Al-Al due to energy dependence. The 3T Cu-Cu microbeam field profile was reconstructed and returned microbeam width and peak-to-peak values of (51 +/- 1) mu m and (405 +/- 5) mu m, respectively. The peak-to-valley dose ratio was measured as a function of depth and agrees within error to the values obtained with the PTW microDiamond. X-ray beam induced charge mapping of the detector revealed minimal dose perturbations from extra-cameral materials. Significance. The detectors are comparable to commercially available dosimeters for quality assurance in MRT. With added benefits of being micron-sized and possessing a flexible water-equivalent substrate, these detectors are attractive candidates for quality assurance, in-vivo dosimetry and in-line beam monitoring for MRT and FLASH therapy

Music sequencer with wireless control panel made of LEDs

International audienc

ZnSnxGe1-xN2 as electron-selective contact for silicon heterojunction solar cells

This work reports the electrical characterization of ZnSnxGe1-xN2 (ZTGN) layers deposited on glass by sputtering and further assesses for the first time the performance of SHJ solar cells featuring them as electron-selective contacts. Bandgap, conductivity, and activation energy were found to significantly change between Sn and Ge-rich samples, but poor performance was observed when ZTGN layers were employed as electron-selective contacts for SHJ solar cells, with similar results despite changes in material properties. A non-moving Fermi level around mid-gap silicon, strong limitation due to series resistance, and poor conductivity of Ge-rich samples can account for the observed behavior. Doping of Ge-rich ZTGN appears thus necessary to build efficient devices with a ZTGN contact layer. Using an ex-situ phosphine palsma followed by annealing did not prove successful to this regard, making in-situ doping probably necessary

A comprehensive analysis of electron emission from a-Si:H/Al2O3 at low energies

Recently developed microchannel plates based on amorphous silicon offer potential advantages with respect to glass based ones. In this context, secondary electron emission at very low energies below 100 eV has been studied for relevant materials for these novel devices. The aim of this work was to quantify the low energy electron emission - secondary emission and elastic scattering - from amorphous silicon and alumina and the dependence of the emission energy distribution on the primary electron energy, which was previously unknown. Secondary emission and energy distribution were both modelled and measured using equipment particularly designed for this energy range. The effects of roughness, angle of incidence and surface composition were analysed. We show crossover energies as well as the angular dependence of electron emission from amorphous silicon and alumina, with a maximum experimental emission yield value of 2 and 2.8, respectively, at an incident angle of 75°. A parameterization for the energy dependence of the emission energy spectrum at low energies was derived. This extensive analysis is fundamental for a comprehensive understanding of the performance of amorphous silicon-based microchannel plate detectors. It provides a complete model for secondary electron emission for a detailed description of the detector operation. The present results thus set the basis for a simulation framework, which is an essential element to increase the performance of these detectors and enable further developments

Effects of Work Function and Electron Affinity on the Performance of Carrier-Selective Contacts in Silicon Solar Cells Using ZnSnx Ge-1 (-) N-x(2) as a Case Study

This work reports the electrical characterization of ZnSnx Ge1 - xN2 (ZTGN) layers (10% < x < 90%) deposited on glass by combinatorial sputtering and further assesses the performance of silicon heterojunction (SHJ) solar cells featuring them as electron-selective contacts. Bandgap, dark conductivity, and the activation energy of the latter were found to significantly change between Sn- and Ge-rich samples. When applying ZTGN layers as electron-selective contacts for SHJ solar cells, poor solar cell performance was observed, with surprisingly similar results despite changes in material properties. From analysis and modeling of the current-voltage characteristics using several device structures, we show that the work function of the electron-selective contact lies around 4.35 eV for all investigated Sn and Ge contents, which is too high to form an excellent electron-selective contact. By comparing different solar cell architectures, we could further identify that the Ge-rich layer imposes an additional barrier to electron extraction, independently of its poor selectivity, due to its low conductivity. Doping of Ge-rich ZTGN, thus, appears as the most relevant approach to build efficient devices with a ZTGN contact layer.PV-LA

Amorphous silicon detectors for proton beam monitoring in FLASH radiotherapy

Ultra-high dose rate radiation therapy (FLASH) based on proton irradiation is of major interest for cancer treatments but creates new challenges for dose monitoring. Amorphous hydrogenated silicon is known to be one of the most radiation-hard semiconductors. In this study, detectors based on this material are investigated at proton dose rates similar to or exceeding those required for FLASH therapy. Tested detectors comprise two different types of contacts, two different thicknesses deposited either on glass or on polyimide substrates. All detectors exhibit excellent linear behaviour as a function of dose rate up to a value of 20 kGy/s. Linearity is achieved independently of the depletion condition of the device and remarkably in passive (unbiased) conditions. The degradation of the performance as a function of the dose rate and its recovery are also discussed

Bandgap engineering of indium gallium nitride layers grown by plasma-enhanced chemical vapor deposition

This paper reports on the fabrication of In xGa 1 - xN (InGaN) layers with various compositions ranging from InN to GaN using a cost-effective low-temperature plasma-enhanced chemical vapor deposition (PECVD) method and analyzes the influence of deposition parameters on the resulting films. Single-phase nanocrystalline InGaN films with crystallite size up to 30 nm are produced with deposition temperatures in the range of 180-250 ? using the precursors trimethylgallium, trimethylindium, hydrogen, nitrogen, and ammonia in a parallel-plate type RF-PECVD reactor. It is found that growth rate is a primary determinant of crystallinity, with rates below 6 nm/min producing the most crystalline films across a range of several compositions. Increasing In content leads to a decrease in the optical bandgap, following Vegard's law, with bowing being more pronounced at higher growth rates. Significant free-carrier absorption is observed in In-rich films, suggesting that the highly measured optical bandgap (about 1.7 eV) is due to the Burstein-Moss shift. (C) 2022 Author(s).PV-LA