Single ion implantation using focused ion beam systems enables high spatial resolution and maskless doping for rapid and scalable engineering of materials for quantum technologies, particularly for the generation of qubits and colour centres in solid-state hosts. In these applications, the confidence with which a single ion can be deterministically implanted is critical, and so the efficiency of the detection mechanism is a vital parameter to understand. Here, we present a study of the single ion detection efficiency for a variety of ion species (Si, P, Mn, Co, Ge, Sb, Au, and Bi) into various hosts (Si, SiO2, Al2O3, GaAs, diamond, and SiC). The effect of varying ion mass, charge, and kinetic energy is studied, in addition to the cluster implantation of Sb, Au, and Bi. The detection efficiencies measured vary from 40% to 100%, based on the substrate and ion beam combination.We demonstrate that it is possible to achieve detection efficiencies >90% for a wide range of ion species and substrate combinations through selection of the implantation parameters. Furthermore, detection efficiencies of 100% are found for the doping of Sb clusters, which is of direct relevance for the future fabrication of quantum devices.

Deep-level transient spectroscopy (DLTS) and Laplace-DLTS were used to investigate electrically active defects in (010)-oriented beta-Ga2O3 epilayers grown via metal-organic chemical vapor deposition and doped with Si during growth. The impact of isochronal rapid thermal annealing in N-2 on the electrical characteristics of Pt Schottky barrier diodes and on defect concentrations was examined by annealing at temperatures from 150 to 450 degrees C with 100 degrees C increments. Four deep levels were detected, with concentrations in the range of 10(13)-10(14) cm(-3) and activation energies of electron emission to the conduction band (Delta E-c) of 0.06, 0.40, 0.55, and 0.62 eV. The E-c-0.06 eV trap was no longer observed in DLTS measurements after heating to 400 K, and the E-c-0.62 eV trap was suppressed after annealing at 350 degrees C. In contrast, the E-c-0.40 eV trap progressively reduced in concentration, while the trap density of the E-c-0.55 eV level increased with each rapid thermal annealing step, suggesting defect redistribution along the [010] direction. The electric field dependence of the electron emission rates indicates acceptor-like behavior for the E-c-0.55 eV state and donor-like behavior for the E-c-0.62 eV state. As both states exhibit activation energies consistent with the commonly reported E1 defect, we propose the following labelling conventions: E1a (E-c-0.55 eV) and E1b (E-c-0.62 eV). The nature and potential origins for each of the observed defects are discussed.

Deep-level defects in Ta-doped β-Ga2O3 single crystals grown using the optical floating zone method are investigated. Deep-level transient spectroscopy (DLTS) in conjunction with Laplace-DLTS (L-DLTS) and photoluminescence (PL) has been applied to (100) oriented β-Ga2O3:Ta bulk crystals. The temperature dependence of the bias capacitance of diodes indicates no significant sign of carrier freeze-out down to 20 K. This confirms the predicted shallow donor behavior of Ta impurity atoms in β-Ga2O3 samples with a carrier concentration of (1.0–1.2) × 1018 cm−3. DLTS and L-DLTS analysis show six traps with activation energies of electron emission of 0.28 (Es), 0.46 (E9), 0.52 (E1), 0.69 (E2a), 0.75 (E2b), and 0.97 (E3) eV, with trap concentrations in the range of 1015–1017 cm−3. In addition, temperature-dependent PL has been used to study the broad luminescence bands with their maxima at 3.10 and 3.40 eV. Subsequent Arrhenius analysis extracted activation energy values (EA of 20 ± 1 and 79 ± 4 meV for quenching of the PL peaks at 3.10 and 3.40 eV, respectively.

Mesoporous titanium dioxide (m-TiO2) has gained significant attention in photocatalytic, photoelectrochemical, energy storage, and photovoltaic applications. However, the performance of m-TiO2-based devices is often hindered by their poor electrical conductivity, low electron mobility, and high electronic trap density. Doping m-TiO2 with alkali-metal elements is a promising method to tackle these issues. Herein, an ultrafast laser treatment is presented to introduce lithium (Li) doping into m-TiO2 (Li-doped m-TiO2) to enhance its charge transport ability for mesoscopic perovskite solar cells (PSCs). Remarkably, the laser treatment only needs 42 s irradiation in total at the highest temperature of 800-850 degrees C to prepare the Li-doped m-TiO2, compared to the traditional furnace treatment at a temperature of 500 degrees C for 60 min. Consequently, PSCs assembled under high relative humidity (60-75%) using the laser treatment exhibited a power conversion efficiency (PCE) of 19.15%, higher than that of the furnace treatment of 18.10%. The improvement is due to the enhanced interconnection between the Li-doped m-TiO2 nanoparticles, reduced oxygen vacancies, and improved interfacial contact at m-TiO2/perovskite, resulting from the laser treatment. These factors contribute to an improved electron transport capability, reduced charge recombination, and suppressed hysteresis behaviour in the PSCs. The ultrafast laser treatment introduced here offers a novel path for rapid manufacturing of metal-doped m-TiO2 materials for PSCs and other related applications.

Increasing the understanding of the electronic properties of gallium (Ga) in silicon (Si) used nowadays to manufacture p‐type Si solar cells is of key technological importance. In this contribution, the results of the effect of Ga concentration on the low‐temperature photoluminescence (PL) spectra in crystalline Si are reported. The Ga‐doped Si samples studied have negligible boron concentrations, which can complicate spectral analysis of the bound exciton (BE) lines. The split Ga BE ground state at T = 10 K is analyzed and the PL intensity ratios for the BE to free exciton peaks are compared. By comparing these to known Ga concentrations, derived from capacitance–voltage measurements, an all‐optical (PL) calibration curve for the quantification of Ga concentration in Si is established. The effects of both temperature and excitation power on the PL intensity ratios are also studied. By combining the temperature‐induced changes in the PL intensity ratios with the calibration curve at 10 K, a calibration function has been determined. It is found that the decay rates of the PL intensity ratios as a function of excitation power are independent of the chosen (split) BE peak. The major benefits of this method and its limitations are discussed.

We use insulating polystyrene colloid particles to selectively cover the electron transport layer of n-i-p perovskite solar cells and investigate the effects of the coverage and lateral blocking distance on device performance.

Abstract Solid-state spin qubits within silicon crystals at mK temperatures show great promise in the realisation of a fully scalable quantum computation platform. Qubit coherence times are limited in natural silicon owing to coupling to the 29Si isotope which has a non-zero nuclear spin. This work presents a method for the depletion of 29Si in localised volumes of natural silicon wafers by irradiation using a 45 keV 28Si focused ion beam with fluences above 1 × 1019 ions cm−2. Nanoscale secondary ion mass spectrometry analysis of the irradiated volumes shows residual 29Si concentration down to 2.3 ± 0.7 ppm and with residual C and O comparable to the background concentration in the unimplanted wafer. After annealing, transmission electron microscopy lattice images confirm the solid phase epitaxial re-crystallization of the as-implanted amorphous enriched volume extending over 200 nm in depth.

Carbon-based hole-transport-layer-free perovskite solar cells (HTL-free C-PSCs) have gained tremendous attention due to their low cost, ease of fabrication, low-temperature processability, and excellent long-term stability. However, HTL-free C-PSCs suffer from poor interfacial contact at the carbon/perovskite and limited hole extraction ability, thereby limiting the device's performance. Herein, an in situ one-step synthesis strategy is presented to simultaneously generate laser-induced graphene flakes (LIG) embedded with the uniformly distributed fine NiOX nanoparticles (LIG@NiOX) as the electrode for HTL-free C-PSCs. Due to the desired morphology of the LIG flakes, it enables the formation of a compact LIG@NiOX electrode without a post-heat treatment or hot-pressing process. As a result, the fully ambient-processed HTL-free C-PSCs prepared under a high relative humidity of around 50-70% based on the LIG@NiOX achieve a power conversion efficiency (PCE) of up to 14.46%, compared to a PCE of 10.36% for the PSCs based on the commercial graphite/carbon black. This is due to a remarkable improvement in the physical contact at the carbon/perovskite interface using LIG@NiOX. Moreover, the PSCs based on LIG@NiOX retained 94% of their initial PCEs after 185 days of storage in ambient air, compared to those based on the Spiro-OMeTAD/Au that only retained 78% of their initial PCEs after 84 days of storage under the same ambient condition. The laser process opens a new avenue for simultaneous forming LIG embedded with the in situ formed metal oxide nanoparticles for various applications.

The contradictory reports in the literature about the stability of Ga-doped silicon (Si) material for photovoltaic applications, in comparison to those doped with B, necessitate a more detailed understanding of the characteristics of this material before solid conclusions about degradation mechanisms can be made. In this work, high-resolution low-temperature photoluminescence (PL) has been used to investigate and analyze the luminescence from Ga-doped and P+Ga co-doped Czochralski-grown silicon (Cz-Si) materials. Comparison of thermally induced changes in luminescence features for these materials are compared to those occurring in B-doped and P+B co-doped Si materials. It has been found that the Ga bound exciton (BE) exhibits a triplet luminescence structure which is preserved in the co-doped material, explained by the splitting of the exciton ground state. A similar effect does not occur for the BE-related PL signal in B-doped silicon material. A low temperature (10–20 K) range was then used to investigate the temperature-induced changes in impurity related photon emission lines in the PL spectra of the studied materials. The effect of thermal energy on the PL intensity of different radiative recombination channels is elucidated. It has been argued that the presence of compensating impurities causes enhanced radiative recombination of some excitonic emissions while others behave in a similar way as in a single-doped material. The possible relationship of the observed effects on electron-hole recombination at room temperature is discussed.

Before lower purity, lower cost silicon (Si) materials, such as compensated Si, can play a role in the terawatt-level (TW) capacity of photovoltaics, a better understanding of the fundamental properties of impurities in compensated Si is essential. In this work, high-resolution photoluminescence (PL) has been used to study the charge carrier radiative recombination through Donor-Acceptor pairs (DAPs) in phosphorus (P) and gallium (Ga) co-doped Si material grown for solar cell applications. The high spectral resolution of our PL system, 0.06 meV, enables us to overcome hitherto prior issues of overlapping spectral lines, giving access to extremely fine structures associated with DA pair (DAP) recombination. Our results confirm the presence of three broad bands and a discrete line structure related to DAP luminescence. The comparison of the discrete line structure due to DAPs recombination in the PL spectra with the theoretically predicted one allows the accurate determination of the Ga ionization energy. Temperature-dependent PL is then used to understand the thermally-induced changes in the DAP luminescence. In particular, we observe that the radiative recombination channel remains active for distant DAPs up to-40 K, unlike that for close-range DAPs for which the radiative channel is quenched after only slight increases in the temperature range 10e25 K. Furthermore, the analysis of the temperature dependent changes in the PL intensity of the broad DAP bands up to-200 K is used to derive the ionization energy of P donors in compensated Si material. In light of this important information, the significance of using high resolution PL to analyse spectral features in compensated Si is demonstrated.(c) 2023 Vietnam National University, Hanoi. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Semitransparent perovskite solar cells are prepared using colloidal scale polymer sponge-like particle additives that spontaneously form 2D nanopore arrays whilst increasing the power conversion efficiency.

Perovskite solar cells continue to attract interest due to their facile preparation and high power conversion efficiencies. However, the highest efficiency perovskite solar cells inevitably contain lead, which raises concerns over contamination of drinking water when a solar module is broken and then flooded. We previously showed that conventional synthetic hydroxyapatite (HAP) nanoparticles could capture some of the lead from broken solar cells, but the amount of lead released was well above the safe drinking water level. Here, we modify the HAP synthesis to prepare new spherical-HAP (s-HAP) nanoparticles with a 60% increase in the Pb absorption capacity. We blend s-HAPs with TiO 2 nanoparticles to construct mixed scaffolds and investigate their effect on (FAPbI 3 ) 0.97 (MAPbBr 3 ) 0.03 solar cell performance and lead capture. Replacement of 80% of the TiO 2 nanoparticles with s-HAP causes the power conversion efficiency to increase from 18.61% to 20.32% as a result of decreased charge carrier recombination. Lead contamination of water from devices subjected to simulated hail damage followed by flooding is shown to decrease exponentially with increasing s-HAP content. The lead concentration in water after 24 h is below the US safe water drinking limit.

A combination of KBr modification and laser processing is utilized to prepare SnO2 films for rigid and flexible perovskite solar cells (PSCs). The KBr modification effectively passivates the defects at the interface between SnO2 and perovskite as well as grain boundaries of the perovskite film. A power conversion efficiency (PCE) of 20.14% is achieved with the KBr‐modified SnO2 for the rigid PSCs fabricated under a relative humidity of around 65–75%, compared to the pristine SnO2 films with a PCE of 18.66%. Then, a picosecond ultraviolet laser is employed to process KBr‐modified SnO2 films on flexible substrates with a rapid scanning rate of 100 mm s−1. The laser process improves the PCEs and durability of the PSCs. The flexible PSCs fabricated by the laser remain over 80% of their initial PCEs after 1000 bending cycles, higher than those fabricated by the hot plate showing 40% of their initial PCEs after the same bending cycles.

A conventional annealing method to fabricate metal oxide films used for perovskite solar cells (PSCs) is a time‐consuming batch process. Herein, a near‐IR fiber laser process with a unique design of power ramping program and beam configuration is developed to achieve ultrafast and scalable processing of TiO 2 films for PSCs. Highly crystalline anatase TiO 2 films can be synthesized in only 18.5 s by the laser process with a peak annealing temperature up to 800–850 °C, compared with that of the furnace‐annealing at 500 °C for 30 min and an overall processing time of 3 h. Then, a unique capability of using this laser process is presented to anneal stacked layers of substrates coated with the TiO 2 films simultaneously, with a uniform annealing area up to 15.2 cm 2 , thereby potentially achieving an in‐line production rate of over 43 cm 2 min −1 (1 cm 2 in ≈1.4 s). Planar PSCs fabricated under a high relative humidity of 60–70% based on the TiO 2 films annealed under optimal laser conditions show enhanced photovoltaic performance than the furnace‐annealed samples. This laser process potentially opens a new avenue for scalable annealing and rapid production of thin films.

We report the manufacture of fully solution processed photodetectors based on two-dimensional tin(ii) sulfide assembled via the Langmuir-Blodgett method. The method we propose can coat a variety of substrates including paper, Si/SiO2 and flexible polymer allowing for a potentially wide range of applications in future optoelectronic devices.

The air stability of PSCs is enhanced by employing a TiO2/Al2O3 bilayer mesoporous scaffold.

The mesoporous (meso)-TiO2 layer is a key component of high-efficiency perovskite solar cells (PSCs). Herein, pore size controllable meso-TiO2 layers are prepared using spin coating of commercial TiO2 nanoparticle (NP) paste with added soft polymer templates (SPT) followed by removal of the SPT at 500 °C. The SPTs consist of swollen crosslinked polymer colloids (microgels, MGs) or a commercial linear polymer (denoted as LIN). The MGs and LIN were comprised of the same polymer, which was poly(N-isopropylacrylamide) (PNIPAm). Large (L-MG) and small (S-MG) MG SPTs were employed to study the effect of the template size. The SPT approach enabled pore size engineering in one deposition step. The SPT/TiO2 nanoparticle films had pore sizes > 100 nm, whereas the average pore size was 37 nm for the control meso-TiO2 scaffold. The largest pore sizes were obtained using L-MG. SPT engineering increased the perovskite grain size in the same order as the SPT sizes: LIN < S-MG < L-MG and these grain sizes were larger than those obtained using the control. The power conversion efficiencies (PCEs) of the SPT/TiO2 devices were ∼20% higher than that for the control meso-TiO2 device and the PCE of the champion S-MG device was 18.8%. The PCE improvement is due to the increased grain size and more effective light harvesting of the SPT devices. The increased grain size was also responsible for the improved stability of the SPT/TiO2 devices. The SPT method used here is simple, scalable, and versatile and should also apply to other PSCs.

Stabilised amorphous selenium (a-Se) is currently used in the majority of direct conversion mammographic X-ray imaging detectors due to its X-ray photoconductivity and its ability to be uniformly deposited over large area TFT substrates by conventional vacuum deposition. We report experimental results on photocurrent spectroscopy (frequency-resolved spectroscopy (FRS) and single-time transients), on vacuum-deposited a-Se films. We show that all measured photocurrents depend critically on the relative time spent by the material in the light and in the dark. We identify that the observed pronounced variation in optical response depends on the density of trapped (optically injected) charge within 200 nm of the surface and show that it is the ratio of dark and light exposure time that controls the density of such charge. Our data confirm that the localised charge radically influences the photocurrent transient shape due to the effective screening of the applied field within 200 nm of the surface. The field modification occurs over the optical extinction depth and changes both the photogeneration process and the drift of carriers. Many aspects of our data carry the signature of known properties of valence alternation pair (VAP) defects, which control many properties of a-Se. Modelling in the time domain shows that light generation of VAPs followed by optically triggered VAP defect conversion can lead to near-surface charge imbalance, demonstrating that VAP defects can account for the unusual optical response. The stabilised a-Se films were deposited above the glass transition temperature of the alloy with composition a-Se:0.3% As doped with ppm Cl. Electron paramagnetic resonance measurements at temperatures down to 5 K did not detect any spin active defects, even under photoexcitation above band gap.

We investigate the atomic scale structure of m-plane InGaN quantum wells grown on bulk m-plane GaN templates and reveal that as the indium content increases there is an increased tendency for nonrandom clustering of indium atoms to occur. Based on the atom probe tomography data used to reveal this clustering, we develop a k · p model that takes these features into account and links the observed nanostructure to the optical properties of the quantum wells. The calculations show that electrons and holes tend to colocalize at indium clusters. The transition energies between the electron and hole states are strongly affected by the shape and size of the clusters. Hence, clustering contributes to the very large line widths observed in the experimental low temperature photoluminescence spectra. Also, the emission from m-plane InGaN quantum wells is strongly linearly polarized. Clustering does not alter the theoretically predicted polarization properties, even when the shape of the cluster is strongly asymmetric. Overall, however, we show that the presence of clustering does impact the optical properties, illustrating the importance of careful characterization of the nanoscale structure of m-plane InGaN quantum wells and that atom probe tomography is a useful and important tool to address this problem.

This paper is concerned with the scanning tunnelling microscope tunnelling conditions needed to produce constant current images dominated either by surface topology or by electronic effects. A model experimental structure was produced by cleaving a GaAs multi δ-doped layer in UHV and so projecting a spatially varying electron gas density onto the (110) surface. This cross sectional electron density varies on a nanometre scale in the growth direction. The electronic structure and tunnelling properties of this system were modelled, and the tunnelling conditions favouring sensitivity to the surface electron gas density determined.