Arsenic Doping Research Articles

Arsenic-doped HgCdTe: FTIR photoluminescence and photoreflectance spectroscopy study

Photoluminescence (PL) and photoreflectance (PR) spectroscopy were used for the optical study of arsenic doping of HgCdTe grown by molecular beam epitaxy (MBE). Un-doped and arsenic-doped material with cadmium telluride molar fraction x = 0.29 grown under similar conditions and subjected to similar types of annealing was studied. The PL spectra of the un-doped material featured signatures of intrinsic defects associated with mercury vacancy, excessive tellurium, and related complexes. In the arsenic-doped material, optical signatures of these defects appeared to be suppressed. After arsenic activation, shallow (7–8 meV) acceptor levels were found in the material. These were attributed to the dopant activation, which was confirmed with electrical studies showing p-type conductivity with hole concentration ∼1016 cm−3. The studies showed that the actual pattern of arsenic doping in HgCdTe can be indeed screened by intrinsic defects, which are inherent to MBE-grown HgCdTe and tend to interact with the dopant.

Photovoltaic performance of pristine and arsenic doped hybrid perovskite

Under the scope of all-solid-state perovskite solar cells, the important role of methylammonium lead halide film lies in facilitating the formation of a photo-generated electronrich film, which directly affects the overall photovoltaic performance. This study introduces a novel chemical strategy aimed at increasing the quality of perovskite film through minimal arsenic doping. The result of the inclusion of arsenic is characterized by high crystalline grains in the attainment of a homogeneous, uniform and ancient perovskite film. The analysis of the UV-Visible spectra indicates that the perovskite film, which is produced under sequential conditions, displays light extraction of electrons for light absorption, more effective electron transport, and adjacent electron transport layer. Different morphology obtained through customized perovskite conditions contribute to a better short-circuits current, which improves overall cell performance. Arsenic-doped perovskite-based solar cells demonstrate a 1.55% increase in power conversion efficiency compared to their nondecorated counterparts, exhibiting 0.20% efficiency. The outcomes not only offer a straightforward method for enhancing perovskite films but also introduce an innovative perspective on constructing high-performance perovskite solar cells using minimal amounts of arsenic, thereby minimizing toxicity in the fabricated solar cells.

Investigating the optical properties and electronic structure of gallium phosphide nanotubes doped with arsenic via implementing first-principles calculations.

This study investigates the impact of arsenic doping on the optical characteristics and electronic structure of zigzag (8, 0) and armchair (4, 4) gallium phosphide nanotubes using first-principles calculations based on the GaP1-xAsx system, where x = 0, 0.25, 0.5, 0.75, and 1. The electronic calculations showed that doping more arsenic atoms reduces the energy band gap for zigzag and armchair GaPAs nanotubes. PDOS analysis indicates that Ga-4p and P-3p orbitals play a significant role in determining the electronic properties of the GaP nanotube. The dominance of Ga-4p and P-3p orbitals in both the valence and conduction bands indicates their importance across the energy spectrum of the material. The complex dielectric function and absorption coefficient of zigzag and armchair GaP1-xAsx nanotubes are calculated for incident radiation with energies ranging from 1 to 6.2eV. Optical results revealed that both zigzag and armchair GaPNTs exhibit strong absorption in the UV-visible regions due to electronic transitions between different Van Hove singularities. Also, due to quantum confinement effects, pure zigzag gallium phosphide nanotube exhibited two absorption edges at wavelengths (273 and 375nm). These edges stand from the energy level's quantization in the nanotube construction, affecting the absorption characteristics. Substitutional doping by arsenic atoms changes the absorption edge to the long wavelengths due to decreased bandgap energy. Investigating electronic structures and optical properties of nanotubes proposes several advantages, such as understanding the doping effects on the nanotube structure and contributing to the direction of the experimental studies. These computational studies play a key role in developing the applications of nanomaterials. Calculations of density functional theory (DFT) are achieved via the SIESTA package. SIESTA is a powerful and effective tool for executing DFT calculations on a large system of atoms. It generates numerous output files covering detailed information about the electronic structure, optical properties, total energy, optimized geometry, and other computed properties. The generalized gradient approximation GGA with Perdew-Burke-Ernzerhof PBE functional was used. A vacuum region of 10 A0 was applied to avoid the interactions of adjacent nanotubes.

Optical properties of HgCdTe epitaxial films doped with arsenic

Subject of study. Epitaxial films of Hg0.7Cd0.3Te solid solutions grown by molecular beam epitaxy and doped with arsenic to obtain hole-type conductivity in order to form p-n junctions for the production of infrared photodetector structures are studied. Aim of study. The types and characteristics of defects formed during arsenic doping of epitaxial films of Hg0.7Cd0.3Te solid solutions grown by molecular beam epitaxy and the effect of doping on the level of disorder in the solid solution are determined. Method. Ellipsometry, optical transmittance, photoluminescence, and photoreflectance are used. Main results. The initial material is shown to have high quality in terms of film bulk and surface quality, and the quality was found to improve after two-stage activation thermal annealing. Annealing has been shown to activate the arsenic with the formation of shallow (7–8 meV) acceptor levels. No side defects were found to occur as a result of the introduction of arsenic into the films during growth and annealing. Practical significance. This research demonstrated the effectiveness of doping epitaxial films of Hg0.7Cd0.3Te solid solutions with arsenic as an acceptor impurity in order to produce layers with hole conductivity during the production of photodiode structures.

Single-Atom Control of Arsenic Incorporation in Silicon for High-Yield Artificial Lattice Fabrication.

Artificial lattices constructed from individual dopant atoms within a semiconductor crystal hold promise to provide novel materials with tailored electronic, magnetic, and optical properties. These custom-engineered lattices are anticipated to enable new, fundamental discoveries in condensed matter physics and lead to the creation of new semiconductor technologies including analog quantum simulators and universal solid-state quantum computers. This work reports precise and repeatable, substitutional incorporation of single arsenic atoms into a silicon lattice. A combination of scanning tunneling microscopy hydrogen resist lithography and a detailed statistical exploration of the chemistry of arsine on the hydrogen-terminated silicon (001) surface are employed to show that single arsenic dopants can be deterministically placed within four silicon lattice sites and incorporated with 97 ± 2% yield. These findings bring closer to the ultimate frontier in semiconductor technology: the deterministic assembly of atomically precise dopant and qubit arrays at arbitrarily large scales.

Process optimization of titanium self-aligned silicide formation through evaluation of sheet resistance by design of experiment methodology

A low-resistivity titanium silicide (TiSi2) is crucial as a gate and source/drain material in microelectronic device fabrication, offering notable properties to enhance device performance. This study aims to experimentally determine the optimum process parameters, including arsenic doping dosage, titanium thickness, and two-step rapid thermal process (RTP) temperature, for the sheet resistance of titanium self-aligned silicide process using a design of experiment methodology. The results demonstrate that both the thickness of the titanium and the temperature of the RTP play crucial roles in determining the sheet resistance of TiSi2. Statistical analysis reveals that increasing the titanium thickness or the temperature of the first-step RTP (RTP-1) could reduce the sheet resistance. Additionally, an optimal second-step RTP (RTP-2) temperature is critical to yield low-resistivity TiSi2 by completely converting C49- to C54-phase. The optimum process conditions for obtaining low sheet resistance are a titanium thickness of 32–35 nm, RTP-1 temperature of 720–750 °C for 75 s, and RTP-2 temperature of 860 °C for 20 s. Moreover, surface amorphization of the polysilicon by arsenic ion implantation before the deposition of Ti/TiN films also plays a crucial role in the formation of C54-TiSi2. The lowest sheet resistance achieved was 3.91 Ω/sq with an arsenic dosage of 1 × 1014 cm−2. The optimum condition was adopted for forming a submicron polysilicon gate, providing a promising approach for designing the process parameters for titanium self-aligned silicide formation to achieve low resistance in nanoscale electronic devices.

Surface engineered phosphorene using boron and arsenic doping/Co-doping for Co-optimizing the adsorption stability, transduction, and recovery of CO, NO, and SO gases – A density functional theory perspective

In this work, for the first time, the effects of non-metallic Boron (B), Arsenic (As) substitutional doping as well as co-doping at different lattice positions of monolayer Phosphorene (Ph) have been extensively investigated for Carbon Monoxide (CO), Sulphur Monoxide (SO), and Nitrogen Monoxide (NO) adsorption using first principle calculation. The electronic configurations and effects of relative dopant positions (for co-doping) on atomic sub-planes of Ph significantly influence the molecular adsorptions of these monoxides, whereas the charge transfer is dominated by the molecular orientations and charge distributions of the gas molecule and host atoms near adsorption sites. The B doping notably increases the adsorption strength for each monoxide, wherein As doping increases the adsorption for CO and NO adsorption and reduces the strength for SO compared to pristine Ph. In contrast, B/As co-doping significantly and moderately increases the strength of CO/NO and SO adsorption, respectively. The co-doping exhibits a shorter recovery time while retaining adsorption stability for CO and NO. Moreover, doping/co-doping notably increases the charge transfer after NO adsorption. Finally, the NO and SO adsorptions severely alter the distribution of electronic states near the band edges, which results in significant modulations in the energy band structure of the co-doped lattice.

Creating metal saturated growth in MOCVD for CdTe solar cells

Determining the thermodynamic conditions in MOCVD growth of II-VI semiconductor materials is not as straightforward as in III-V growth where Group V hydrides are generally used. This paper establishes a technique, using in situ laser reflectometry, to ensure that the thermodynamic equilibrium is under metal saturated growth. This has been applied to the arsenic doping of CdTe solar cells where it was shown that increasing the II/VI precursor ratio resulted in an increase in As dopant incorporation. The growth kinetics were determined by the diisopropyl tellurium (DIPTe) concentration for II/VI precursor ratios above 2. A method is presented where the change in II/VI precursor ratio can be predicted for different positions in a horizontal MOCVD chamber that has, in turn, enabled variation in NA and the solar cell open circuit voltage (Voc) to be determined as a function of the II/VI precursor ratio. This gives new insight to the thermodynamic drivers in MOCVD growth for improved solar cell Voc and is a method that could be applied to MOCVD of other II-VI semiconductors.

Arsenic doping and diffusion in CdTe: a DFT study of bulk and grain boundaries

The doping of CdTe with As is a method which is thought to increase cell efficiency by increasing electron hole concentrations. This doping relies on the diffusion of As through CdTe resulting in AsTe substitution. The potential effectiveness of this is considered through kinetic and electronic properties calculations in both bulk and Σ3 and Σ9 grain boundaries using Density Functional Theory. In bulk zinc-blende CdTe, isolated As diffuses with barriers <0.5 eV and with similar barriers through wurtzite structured CdTe, generated by stacking faults, suggesting that As will not be trapped at the stacking faults and hence the transport of isolated As will be unhindered in bulk CdTe. Substitutional arsenic in bulk CdTe has little effect on the band gap except when it is positively charged in the AX-centre position or occurring as a di-interstitial. However in contrast to the case of chlorine, arsenic present in the grain boundaries introduces defect states into the band gap. This suggests that a doping strategy whereby the grain boundaries are first saturated with chlorine, before single arsenic atoms are introduced, might be more beneficial.

Investigating the role of copper in arsenic doped Cd(Se,Te) photovoltaics

The open circuit voltage (VOC) deficit in Cd(Se,Te)-based photovoltaics remains a critical obstacle for pushing the technology closer to theoretical performance limits. Arsenic doping has become a dominant and promising route to achieve the higher p-type carrier concentrations necessary for higher VOC, but challenges associated with this alternate defect chemistry and higher doping density have hindered progress. Here we show that while arsenic doping enables high carrier concentrations (>1016 cm−3), co-doping with copper can provide a boost to VOC without a significant change to carrier concentration. A large data set is initially used to explore current-voltage and capacitance-voltage trends associated with arsenic doped devices with and without copper. A smaller subset is then used to probe these trends using a wide variety of characterization techniques. Copper is found to facilitate reduced interface recombination and potentially improved bulk absorber characteristics, though the mechanisms for these improvements are not yet clear. Despite the improved performance of co-doped devices, VOC is still far below its potential especially for highly doped devices. Low emitter doping in conjunction with high absorber doping seems to be a plausible cause for this significant deficit, though other device properties may exacerbate this problem.

Superconductivity Induced by Site-Selective Arsenic Doping in Mo5Si3.

Arsenic doping in silicides has been much less studied compared with phosphorus. In this study, superconductivity is successfully induced by As doping in Mo5Si3. The superconducting transition temperature (Tc) reaches 7.7 K, which is higher than those in previously known W5Si3-type superconductors. Mo5Si2As is a type-II BCS superconductor with upper and lower critical fields of 6.65 T and 22.4 mT, respectively. In addition, As atoms are found to selectively take the 8h sites in Mo5Si2As. The emergence of superconductivity is possibly due to the shift of Fermi level as a consequence of As doping, as revealed by the specific heat measurements and first-principles calculations. Our work provides not only another example of As doping but also a practical strategy to achieve superconductivity in silicides through Fermi level engineering.

Development of arsenic doped Cd(Se,Te) absorbers by MOCVD for thin film solar cells

Recent developments in CdTe solar cell technology have included the incorporation of ternary alloy Cd(Se,Te) in the devices. CdTe absorber band gap grading due to Se alloying contributes to current density enhancement and can result in device performance improvement. Here we report Cd(Se,Te) polycrystalline thin films grown by a chamberless inline atmospheric pressure metal organic chemical vapour deposition technique, with subsequent incorporation in CdTe solar cells. The compositional dependence of the crystal structure and optical properties of Cd(Se,Te) are examined. Selenium graded Cd(Se,Te)/CdTe absorber structure in devices are demonstrated using either a single CdSe layer or CdSe/Cd(Se,Te) bilayer (with or without As doping in the Cd(Se,Te) layer). Cross-sectional TEM/EDS, photoluminescence spectra and secondary ion mass spectroscopy analysis confirmed the formation of a graded Se profile toward the back contact with a diffusion length of ~1.5 μm and revealed back-diffusion of Group V (As) dopants from the CdTe layer into Cd(Se,Te) grains. Due to the strong Se/Te interdiffusion, CdSe in the Se bilayer configuration was unable to form an n-type emitter layer in processed devices. In situ As doping of the Cd(Se,Te) layer benefited the device junction quality with current density reaching 28.3 mA/cm 2 . The results provide useful insights for the optimisation of Cd(Se,Te)/CdTe solar cells. Compositional control of optical band gap in Cd(Se,Te) thin films (0 ≤ x ≤ 1) (left) and the Se profile in finished Cd(Se,Te) devices (right) fabricated by MOCVD. • Cd(Se,Te) thin films (0 ≤ x ≤ 1) deposited with linear compositional control using a chamber-less MOCVD process. • CdSe-only and CdSe/CdSe 0.2 Te 0.8 bilayers utilised for Cd(Se,Te) grading in devices. • In-situ and ex-situ group V (arsenic) doping of the graded Cd(Se,Te) obtained. • Device performance improved for thinner CdSe layers and in-situ doped bilayers. • Good control of Se profile achieved via CdSe and CdSe/CdSe 0.2 Te 0.8 properties.

Comparative study of As and Cu doping stability in CdSeTe absorbers

The reasons behind the long-term degradation of Cu-doped CdTe thin-film solar cells have been a topic of discussion for almost two decades. Yet the underlying mechanisms of such degradation, especially interactions of Cu doping with Cl in high-performance CdSeTe devices, still lack detailed understanding. In this study, we provide a consistent theoretical analysis of the fundamental physics behind this phenomenon. We then identify the dominant device degradation mechanism that cannot be completely eliminated in Cu-doped chlorinated CdSeTe-based PV. Finally, we conclude that this key mechanism is absent in CdSeTe PV when using arsenic absorber doping, which explains the remarkable stability demonstrated by this new technology. Theoretical conclusions are supported by the results of accelerated life tests on Cu- and As-doped chlorinated CdSeTe cells.

Segregation mechanism of arsenic dopants at grain boundaries in silicon

Three-dimensional distribution of arsenic (As) dopants at Σ3{111}, Σ9{221}, Σ9{114}, and Σ9{111}/{115} grain boundaries (GBs) in silicon (Si) is examined by correlative analytical methods using ato...

Gate-controlled ambipolar transport in b-AsP crystals and their VIS-NIF photodetection.

As a new two-dimensional elemental layered semiconductor, black phosphorus (b-P) has received tremendous attention due to its excellent physical and chemical properties and has potential applications in the fields of catalysis, energy, and micro/nano-optoelectronic devices. However, studies have found that b-P is very unstable and will decompose within a few minutes under humid air conditions. Element doping is an effective method for adjusting the physical and chemical properties of crystals. Theoretical and experimental studies have confirmed that the stability of b-P crystals is significantly improved after arsenic doping, and the crystals also exhibit excellent photoresponse and electrical transport performances. In this work, we investigate the physical properties of a component of black arsenic phosphorus crystals (b-As0.084P0.916) and the potential applications in field effect transistors (FETs) and broadband photodetectors. An obvious ambipolar behavior is observed in the transfer characteristics of b-As0.084P0.916 based FETs, with drain current modulation on the order of 105 and the highest charge-carrier mobility of up to 147 cm2 V-1 s-1. The physisorption of atmospheric species on the surface of the FETs is the main factor for the formation of Schottky contacts between the Au electrodes and the b-As0.084P0.916 crystal. Temperature-dependent electrical characteristics show that the Fermi level shifts from the valence band to the middle level between the conduction band and valence band as the temperature decreases. In addition, the FETs also exhibit excellent photoresponse properties from the visible to near-infrared region (450-2200 nm), with a responsivity of 37 A W-1, a specific detectivity of 7.18 × 1010 Jones, and a fast response speed (τrise ≈ 0.04 s and τdecay ≈ 0.14 s). These results suggest that b-As0.084P0.916 crystals are a promising candidate for future electronic and optoelectronic devices.

Arsenic Doping Upon the Deposition of CdTe Layers from Dimethylcadmium and Diisopropyltellurium

The incorporation and activation of arsenic from tris(dimethylamino)arsine in CdTe layers grown by metal-organic chemical vapor deposition from dimethylcadmium and diisopropyltellurium on GaAs substrates are investigated. The incorporation of arsenic into CdTe depends on the crystallographic orientation of the layers and increases in the series (111)B → (100) → (310). The arsenic concentration in the CdTe layers is proportional to the tris(dimethylamino)arsine flow rate at a power of 1.4 and increases with decreasing diisopropyltellurium/dimethylcadmium ratio from 1.4 to 0.5. After deposition, the CdTe:As layers have p-type conductivity with an arsenic concentration of 1 × 1017–7 × 1018 cm–3 and a hole concentration of 2.7 × 1014–4.6 × 1015 cm–3, respectively; the fraction of electrically active arsenic does not exceed ~0.3%. After annealing in argon (250–450°C), the highest hole concentration is 1 × 1017 cm–3, and the arsenic activation efficiency is ~4.5%. The ionization energy of arsenic determined from the temperature dependence of the hole concentration is in the range of 98–124 meV. The low-temperature photoluminescence spectra of the layers have an emission peak with an energy of ~1.51 eV, which can be attributed to donor–acceptor recombination, where AsTe is an acceptor with an ionization energy of ~90 meV.

Complementary characterization method of 3D arsenic doping by using medium energy ion scattering

We report on a new characterization method of 3D—doping performed by arsenic implantation into FinFET—like nanostructures by using Medium Energy Ion Scattering. Because of its good depth resolution (0.25 nm) at the surface, it is one of techniques of choice suitable to analyse the ultra-shallow doping of thin crystal films. However, with the constraints related to the nanostructures’ geometry and the low lateral resolution of the MEIS beam (0.5 × 1 mm2), we developed an adequate protocol allowing their analysis with this technique. It encompasses three different geometries to account for the MEIS spectra of the arsenic implanted in each part of the nanostructures. The originality of the protocol is that, according to the chosen analysis geometry, the overall spectrum of arsenic is not the same because the contributions of each part of the patterns to its formation are different. By using two of them, we observed double peaks of arsenic. Thanks to 3D deconvolutions performed with PowerMEIS simulations, we were able to identify the contribution of the tops, sidewalls and bottoms in their formation. Thus, by separating the spectrum of the dopants implanted in the Fins (tops + sidewalls) from that of the bottoms, we were able to characterize the 3D doping conformity in the patterns. Two different implantation methods with the associated local doses computed in each single part were investigated. We found that the distribution of the dopants implanted by using the conventional implanter method is very different from that of plasma doping.

Electrical and thermal transport properties of natural and synthetic FeAsxS2-x (x ≤ 0.01)

The combined powder X-ray diffraction, microstructural, local and bulk chemical analyses of natural pyrite single crystals from Reiche Zeche, Johangeorgenstadt and Pretzchendorf (Erzgebirge, Saxony, Germany) showed compositions FeAs0.002(1)S1.998(9), FeAs0.004(1)S1.996(9) and FeAs0.005(1)S1.995(9), respectively. The arsenic doping leads to smaller semiconducting energy gaps (Eg ~0.1–0.2 eV) in comparison with binary FeS2 (Eg = 0.96 eV), as well as switching of conduction type mechanism from n-to the p-type. These findings are supported by the measurements of the electrical resistivity and Seebeck coefficient of the synthetic FeAsxS2-x series (maximal As-content x = 0.01 at 773 K). The investigations of sintered FeS2 + MO2 (M = Si, Ti, Zr) composites indicate that some insulating metal oxides as impurities influence less the electrical transport properties of pyrite. All performed studies unambiguously confirmed that p-type conductivity for T > 300 K is a hallmark of the ternary As-doped FeAsxS2-x (x ≥ 0.002) pyrites.

Monolayer Doping of Germanium with Arsenic: A New Chemical Route to Achieve Optimal Dopant Activation.

Reported here is a new chemical route for the wet chemical functionalization of germanium (Ge), whereby arsanilic acid is covalently bound to a chlorine (Cl)-terminated surface. This new route is used to deliver high concentrations of arsenic (As) dopants to Ge, via monolayer doping (MLD). Doping, or the introduction of Group III or Group V impurity atoms into the crystal lattice of Group IV semiconductors, is essential to allow control over the electronic properties of the material to enable transistor devices to be switched on and off. MLD is a diffusion-based method for the introduction of these impurity atoms via surface-bound molecules, which offers a nondestructive alternative to ion implantation, the current industry doping standard, making it suitable for sub-10 nm structures. Ge, given its higher carrier mobilities, is a leading candidate to replace Si as the channel material in future devices. Combining the new chemical route with the existing MLD process yields active carrier concentrations of dopants (>1 × 1019 atoms/cm3) that rival those of ion implantation. It is shown that the dose of dopant delivered to Ge is also controllable by changing the size of the precursor molecule. X-ray photoelectron spectroscopy (XPS) data and density functional theory (DFT) calculations support the formation of a covalent bond between the arsanilic acid and the Cl-terminated Ge surface. Atomic force microscopy (AFM) indicates that the integrity of the surface is maintained throughout the chemical procedure, and electrochemical capacitance voltage (ECV) data shows a carrier concentration of 1.9 × 1019 atoms/cm3 corroborated by sheet resistance measurements.

A Multi-Electrode System for the Implementation of Solid-State Quantum Devices Based on a Disordered System of Dopant Atoms in Silicon

In this work, we present a nanoscale solid state structure, which is a 3D-array of tunnel-coupled arsenic dopants in silicon with a system of metallic electrodes leading to them. The structures of eight metal electrodes were fabricated on the inhomogeneously in depth doped with arsenic silicon surface, four of which converge to a region 50 nm in diameter, and four to a region of 200 nm. After removal of a thin highly conducting upper silicon layer, single-electron transport in an array (reservoir) of arsenic impurity atoms located between the electrodes is demonstrated. The Coulomb blockade was $${\sim}100$$ mV at a temperature of 4.2 K. The proposed structure can be used as a reservoir neural network, where single impurity atoms act as neurons, and electrodes will act as input and output terminals of the device, and also be used to configure the neural network. The operating temperature of such devices can be significantly increased due to the relatively small effective size of impurity arsenic atoms in silicon (3–5 nm).