MD Simulations based on force fields and first-principles calculations based on density functional theory have been employed to investigate the initial stages of oxidation on silicon (100) surfaces exhibiting a p(2 x 2) reconstruction when exposed to atomic oxygen. Our results reveal that, when oxygen atoms are sequentially added to energetically preferred sites on the p(2 x 2) reconstructed Si(100) surface, the lattice maintains its crystallinity for up to three layers, in contrast to the typically observed disordered surface oxide. Detailed atomic and electronic structures of the crystalline SiOx/Si are presented, which provide a starting point model for the recent measurements of crystalline SiOx/Si formed under controlled oxidation conditions.

Germanium's compatibility with Complementary Metal-Oxide-Semiconductor (CMOS) and strong near-infrared response make it an attractive platform for infrared photonics, but its intrinsic material properties hinder straightforward extension of absorption beyond the band edge. In this perspective, we synthesize recent and new experiments and analyses on femtosecond-laser approaches that attempt to combine surface microstructuring and hyperdoping of Ge in a single step. We argue that, unlike silicon, Ge's high optical absorption at visible/green wavelengths, shallow energy deposition, lower melting point, and reduced thermal conductivity favor intense localized heating, evaporation, and redeposition-conditions that both produce high baseline sub-bandgap absorption from damage and prevent effective incorporation of thin-film dopant precursors. In a case example, Ti shows only trace incorporation from qualitative measurements. We discuss why laser-induced structural disorder, rather than stable deep dopant incorporation, dominates the optical response, and we outline practical pathways forward: exploring longer wavelengths or gas-phase chemistries, applying separate in situ heating, or decoupling texturing from heavy doping.

Epitaxially grown lattice-matched GaInP on a GaAs crystal is a common part in semiconductor devices such as bipolar junction transistors and space solar cells. Due to the larger band gap of GaInP, it provides also high-quality passivation for GaAs surfaces. Therefore, the photoluminescence (PL) intensity measured from GaInPcapped GaAs is among the strongest intensities obtained from GaAs crystals having different surface passivation layers. Here we demonstrate that a facile wet chemical treatment, including immersions in two solutions: first in hot hydrogen peroxide (H2O2) and then in hot water (H2O), increases the PL intensity from epitaxial GaInP/GaAs. Concomitantly, the GaInP surface is further oxidized according to x-ray photoelectron spectroscopy results. Particularly, arsenic impurities and indium at the surface become oxidized. Finally, the H2O2-* H2O treatment combination is used to modify the n-type GaAs contact layer (150 nm), deposited on the top of epitaxial GaInP/GaAs such that the PL intensity from GaAs increases by factor of two as compared to PL from the high-quality GaInP/GaAs reference. The H2O2-* H2O treatment is discussed to transform an initial n-type GaAs contact layer, which degrades the PL intensity, to an antireflective and less absorptive layer which resembles a recently reported black GaAs surface.

We show that the broad X-ray photoelectron lines of silicon oxide on silicon arise from a continuous statistical distribution of core-level binding energies. Statistical simulations spanning compositions from Si to SiO_2 reproduce the full extent of this broadening, reaching 5 eV for SiO_1.0 , in quantitative agreement with 0.23 nm layer-resolved spectra reconstructed from Ar^+ sputtering data. This continuous distribution blurs distinct spectral fingerprints of local structural motifs, thereby challenging conventional chemical state assignment in oxide X-ray photoelectron spectra.

This study explores the area-dependent resistive switching (RS) characteristics of Gd0.2Ca0.8MnO3 (GCMO)-based memristors with aluminum (Al) and gold (Au) electrodes, emphasizing their potential for neuromorphic computing applications. Using a combination of electrical measurements and X-ray photoelectron spectroscopy (XPS), we demonstrate that the high-resistance (HRS) and low-resistance (LRS) states exhibit predictable scaling with device area, with HRS resistances ranging from 107 to 108 Ω and LRS from 105 to 107 Ω, supporting the hypothesis of interface-type RS. XPS depth profiling revealed notable differences in AlO x interfacial layer composition between HRS and LRS, with a higher oxide content and a widened interfacial region in HRS. Additionally, the multistate RS capability of up to ten distinct levels was achieved by modulating applied voltages, highlighting GCMO's suitability as a material for synaptic weight storage in artificial neural networks. Our findings underscore GCMO's promise for energy-efficient, scalable memristor-based systems.

Promising intrinsic electronic properties, such as narrow bandgap and high charge carrier mobilities, make germanium (Ge) a good replacement for silicon in optoelectronic applications (e.g., photodetectors). However, successful fabrication of efficient Ge devices requires minimization of both reflectance and surface recombination losses. This work begins with an observation that metal‐assisted chemical etching (MACE) of Ge surfaces, used for optics improvement, reduces surface recombination without application of any intentional passivation. We proceed with investigation of the effect of MACE solution components and their mixtures on Ge surface passivation. The results demonstrate that HF:H 2 O 2 aqueous solution leads to efficient and stable passivation. The film formed in this solution secures surface recombination velocity ( S eff ) of 14 cm s −1 . Morphological and chemical characterization of the structure reveals porous germanium (PGe) layer with some GeO x included. Finally, we propose several hypotheses on a mechanism behind this passivation, among which are the presence of GeO 2 at the film‐bulk Ge interface and appearance of a potential barrier due to the heterojunction formation. The presented Ge passivation with PGe layer provides a simple and cost‐efficient alternative to existing state‐of‐the‐art passivation schemes.

To increase performance of many photonic devices (e.g., solar cell, light emitting diode (LED), photodetector), it is essential to decrease light reflection at device interfaces. Sustainable and scalable methods have been intensively developed for manufacturing nanostructured antireflection coatings at device surfaces to reduce the reflection‐induced losses in them. In this work, a novel wet chemical method is demonstrated to prepare black nanostructured GaAs surfaces in scalable manner. This facile method includes two steps: immersion of GaAs in hot H 2 O 2 solution followed by immersion in hot H 2 O both at around 80 °C. Microscopy, spectroscopy, and diffraction measurements reveal that the H 2 O 2 immersion increases a surface porosity at GaAs while the hot‐water treatment causes the formation of GaOOH nanocrystals. Reflectivity at the resulting black GaAs surface is decreased even below 1% in a broadband. Photoluminescence intensity measurements are used to study whether the presented top‐to‐down method increases harmful non‐radiative recombination, as compared to the initial GaAs surface. Integration of the found black‐GaAs method with device manufacturing is presented by means of planar metal–GaAs–metal photodetectors, of which external quantum efficiency increases due to the method.

Most electronic and photonic devices include ohmic metal-semiconductor junction(s), of which contact resistivity needs to be minimized for best efficiency of the devices. Interface defects in the junction usually degrade the junction's performance, thus cleaning and passivation of semiconductor surface is crucial during contact fabrication. For silicon devices the RCA (Radio Corporation of America) cleaning has been the most known method. Here we have addressed the question whether it is still possible to develop Si surface treatments to decrease the contact resistivity. We have combined wet chemistry and ultra-high vacuum (UHV) heating for two cases: low and highly phosphorus-doped n-type Si. As compared to silicon surfaces treated only with wet chemistry, the contact resistivity is lowered when (i) lowly doped n-Si is rapidly heated at temperature around 1200 degrees C in UHV followed by hydrofluoric (HF) acid dip before Ni sputtering; (ii) p-Si substrate with highly n-type surface is first immersed in HF, then UHV heated at 400 degrees C followed by immersion to HF. Our results show that the final HF dip decreases surface oxide formation in air during sample transfer to the metal deposition, and that surface phosphorus concentration decreases at highly doped n-Si surfaces during elevated temperature UHV heating.

Low-resistive Ohmic contacts are needed in most microelectronics and photonics devices to connect a device to the electric circuit. Manufacturing of Ohmic contacts typically requires the doping of a semiconductor surface region as n-type or p-type (i.e., electron- or hole-doped, respectively). This task has, however, become challenging when the doping needs to be controlled with nanometer or even atomic level precision at lowered processing temperatures. In this work, we demonstrate a low-temperature method to tackle this contact manufacturing challenge using ultrathin antimony (Sb) doped germanium (Ge) nanolayers. We have integrated the method with the common lift-off processing to make Ohmic nickel (Ni) contacts on low-doped n-type Ge and Si substrates and on semi-insulating GaAs, which initially show the Schottky contacts. A proper combination of wet chemical cleaning plus depositing Sb and Ge atomic layers on the substrates, kept at room temperature, in a very clean environment of ultrahigh vacuum before the Ni-film deposition and postmetallization heating changes the Schottky contacts to Ohmic ones. Complementary methods are used to probe the physicochemical properties of interfaces during the manufacturing process to clarify the mechanisms behind the Ohmic-contact formation.

Current transport in polysilicon is a complicated process with many factors to consider. The inhomogeneous nature of polysilicon with its differently shaped and sized grains is one such consideration. We have developed a method that enhances existing resistivity models with a 2-D extension that incorporates the grain size distribution using a Voronoi-based resistor network. We obtain grain size distributions both from our growth simulations (700, 800, and 900 K) and experimental analysis. Applying our method, we investigate the effect that variation in grain size produces with cases of different average grain sizes (2 nm-3 $\mu$m). For example, the resistivity of polysilicon with an average grain size of 175 nm drops from 11 to 4.5 k$\Omega\cdot$cm when compared with conventional 1-D modeling. Our study highlights the strong effect of grain size variation on resistivity, revealing that wider distributions result in significant resistivity reductions of up to more than 50%. Due to larger grains present with a grain size distribution, current transport encounters fewer grain boundaries while the average grain size remains the same resulting in fewer barriers along the current transport path. Incorporating the grain structure into the resistivity modeling facilitates a more detailed and comprehensive characterization of the electrical properties of polysilicon.

Nickel (Ni) is the key component in ohmic contacts for Mg‐doped p‐GaN, but the detailed formation mechanisms of the ohmic contact have not yet been understood. In this work, the effect of potassium hydroxide (KOH)‐based chemical treatment on the surface of p‐GaN is investigated using X‐ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and low‐energy electron diffraction (LEED). Ni metal contacts on the chemically treated p‐GaN surface are studied using transfer length method (TLM) and synchrotron radiation photoelectron spectroscopy (SR‐XPS). The chemical treatment of p‐GaN improves the brightness of the (1x1) hexagonal diffraction pattern in LEED and keeps the 2D terrace structure in STM visible. Concomitantly, XPS shows that the amount of O, C, and Mg–O bonds at the surface were reduced. Ni/p‐GaN provided an ohmic contact after annealing in ultra‐high vacuum (UHV) at 500 °C. Simultaneously, SR‐XPS shows the diffusion of Ga to Ni and the formation of a previously unreported Ga 3d component, which has a surprisingly narrow line shape, indicating that it originates from a crystalline interface phase. Diffusion of Ga is discussed to cause Ga vacancies and acceptor levels in the bandgap increasing carrier tunneling, thus enabling ohmic contact.

Cleaning semiconductor surfaces by atomic hydrogen or hydrogen plasma has gained significant interest because such a dry-cleaning method enables to reduce consumption of chemicals and pure water, and to treat challenging surfaces of three-dimensional semiconductor nanostructures. We have studied effects of mere H2 2 molecule exposures on (111)B and (110) surfaces of InSb with native oxides in an ultrahigh-vacuum (UHV) chamber. Without any hydrogen cracking, exposure of native-oxide covered InSb(111)B, heated simultaneously at 350 degrees C, to H2 2 with a partial pressure of 5 center dot 10-- 5 mbar decreases amount of surface oxides and carbon, according to x-ray photoelectron spectroscopy, and provides (2x2) low-energy electron diffraction (LEED) pattern. Scanning tunneling microscopy indicates that this InSb(111)B(2x2) surface contains still extra Sb. When the InSb temperature increases to 400 degrees C during the H2 2 exposure, LEED changes to (3x3) pattern, which is known to arise from a less Sb-rich surface compared to InSb(111)B(2x2). When InSb(111)B(3x3) is exposed to H2 2 at the lowered temperature of 300 degrees C, LEED changes back to (2x2), which is discussed to arise from that InSb(111)B (3x3) contains still oxygen. Experiments for InSb(110) support that the found H2 2 exposure effects apply to different crystal faces of InSb.

Polycrystalline silicon (poly-Si) is an excellent material for use in microelectronic devices, both in electrical and mechanical applications. Its mechanical and electrical properties are widely adjustable, its processing technology is compatible with existing microcircuit manufacturing technology, and its availability and recyclability are at a high level. Here, we focus on investigating the properties of poly-Si that distinguish it from other forms of silicon, that is, grains, grain boundaries, and the conditions and treatments that determine grain and grain boundary properties. Starting from the molecular dynamics simulations of the deposition of thin poly-Si films under different growth conditions we study the properties of the films, grains, and grain boundaries as a function of growth time, growth temperature, and post-annealing. We aim to get data and information that will form the essential basis for future research on the electrical properties of poly-Si. The main results are: (i) the effect of post-annealing on the distribution of the grain size and grain boundary thickness (ii) the distribution of the grain orientations, and (iii) the density of the 3- and 5-bonded atoms as a function of deposition temperature.

Polycrystalline silicon (poly-Si) significantly expands the properties of the ICT miracle material, silicon (Si). Depending on the grain size and shape and grain boundary structure, the properties of poly-Si exceed what single-crystal (c-Si) and amorphous (a-Si) silicon can offer, especially for radio frequency (RF) applications in microelectronics. Due to its wide range of applications and, on the one hand, its theoretically and technologically challenging microstructure, poly-Si research is the most timely (Ding et al 2020 Mater. Charact. 161 110174; Zhao and Li 2019 Acta Mater. 168 52-62). In this report, we describe how we simulate and analyse the phenomena and mechanisms that control the effect of poly-Si deposition parameters on the structure of the deposited poly-Si films using classical molecular dynamics simulations. The grain shape and size, degree of crystallinity, grain boundary structure and the stress of poly-Si films are determined depending on the growth temperature, temperature distribution in the growing film, deposition flux, flux variation and the energy transferred to the film surface due to the deposition flux. The main results include: (i) the dependence of the crystallinity profile of the deposited poly-Si films on the stress, temperature and the different parameters of the deposition flux, (ii) growth modes at the early stages of the deposition, (iii) interaction and stability of seed crystallites at the early stage of the deposition of poly-Si films and the transition from the isolated crystallite growth to the poly-Si growth, (iv) interplay of the temperature, crystallinity, crystal shape and heath conductivity of different Si phases, (v) four different stages of crystallite growth are described: nucleation, growth, disappearance and retardation.

Use and performance criteria of photonic devices increase in various application areas such as information and communication, lighting, and photovoltaics. In many current and future photonic devices, surfaces of a semiconductor crystal are a weak part causing significant photo-electric losses and malfunctions in applications. These surface challenges, many of which arise from material defects at semiconductor surfaces, include signal attenuation in waveguides, light absorption in light emitting diodes, non-radiative recombination of carriers in solar cells, leakage (dark) current of photodiodes, and light reflection at solar cell interfaces for instance. To reduce harmful surface effects, the optical and electrical passivation of devices has been developed for several decades, especially with the methods of semiconductor technology. Because atomic scale control and knowledge of surface-related phenomena have become relevant to increase the performance of different devices, it might be useful to enhance the bridging of surface physics to photonics. Toward that target, we review some evolving research subjects with open questions and possible solutions, which hopefully provide example connecting points between photonic device passivation and surface physics. One question is related to the properties of the wet chemically cleaned semiconductor surfaces which are typically utilized in device manufacturing processes, but which appear to be different from crystalline surfaces studied in ultrahigh vacuum by physicists. In devices, a defective semiconductor surface often lies at an embedded interface formed by a thin metal or insulator film grown on the semiconductor crystal, which makes the measurements of its atomic and electronic structures difficult. To understand these interface properties, it is essential to combine quantum mechanical simulation methods. This review also covers metal-semiconductor interfaces which are included in most photonic devices to transmit electric carriers to the semiconductor structure. Low-resistive and passivated contacts with an ultrathin tunneling barrier are an emergent solution to control electrical losses in photonic devices.

Polycrystalline silicon (poly-Si) has been and still is a pivotal material, particularly in the electronics and solar energy industries. Controlling crystallization is one of the challenges, e.g., in producing poly-Si films for radio frequency applications. Since film growth by deposition is a random process, producing a specific grain size distribution for poly-Si is challenging. By combining molecular dynamics simulation data with surface diffusion physics, novel transparent models are constructed that shed light on the physics behind the deposition of poly-Si thin films and assist the selection of simulation parameters. Both probabilistic and geometric approaches are used to find relevant simulation parameters and their bounds to describe the complex grain-grain boundary interactions in the growth of poly-Si thin films. Poly-Si growth simulations provide valuable information to better understand the features of optimal growth conditions. The constructed parameterized deposition model is fitted to the simulation data. In addition to further refining the simulation of customized poly-Si films, the presented modeling concept can also be used more generally in the analysis of physical vapor deposition.

Manufacturing a low‐resistive Ohmic metal contact on p‐type InP crystals for various applications is a challenge because of the Fermi‐level pinning via surface defects and the diffusion of p‐type doping atoms in InP. Development of wet‐chemistry treatments and nanoscale control of p‐doping for InP surfaces is crucial for decreasing the device resistivity losses and durability problems. Herein, a proper combination of HCl‐based solution immersion, which directly provides an unusual wet chemical‐induced InP(100)c(2 × 2) atomic structure, and low‐temperature Mg‐surface doping of the cleaned InP before Ni‐film deposition is demonstrated to decrease the contact resistivity of Ni/p‐InP by the factor of 10 approximately as compared to the lowest reference value without Mg. Deposition of the Mg intermediate layer on p‐InP and postheating of Mg/p‐InP at 350 °C, both performed in ultrahigh‐vacuum (UHV) chamber, lead to intermixing of Mg and InP elements according to X‐ray photoelectron spectroscopy. Introducing a small oxygen gas background (O 2 ≈ 10 −6 mbar) in UHV chamber during the postheating of Mg/p‐InP enhances the indium outdiffusion and provides the lowest contact resistivity. Quantum mechanical simulations indicate that the presence of InP native oxide or/and metal indium alloy at the interface increases In diffusion.

Properties of oxidized InP surfaces, which are known to cause less electrical and optical losses than other III–V oxides, are relevant to develop the passivation of current and future applications of III–V crystals (e.g. lasers, detectors). We report that a proper low-temperature (LT) (<400 °C) gas exposure with NH 3 or O 2 enables beneficial modifications of InP native oxides, of which formation is difficult to avoid in devices. Effects of the gas exposure depend on the doping of InP. NH 3 exposure without a plasma source at 250 °C or lower temperature increases photoluminescence (PL) intensity of native-oxide covered n-InP crystals, which interestingly provide a stronger PL signal than n-InP with the HCl-cleaned surface. In contrast, O 2 exposure around 300 °C increases PL signal of native-oxide covered p-type InP. Core-level photoelectron spectra reveal that N atoms are incorporated into the native oxide system of InPO 4 /InP during LT NH 3 exposures. Scanning tunneling microscopy shows a band bending and a tendency to crystallization at native-oxide covered InP surfaces. Photoelectron spectra, which are analyzed with recent calculations, show larger variation in the bonding environment for the host In atoms and for incorporated N atoms, as compared to the P bonding sites in the InPO 4 native oxide.

Modified group-IV(1 00) surfaces have been successfully utilized as a template for growing crystalline oxide films, e.g., BaO. Knowledge of structural and electronic properties of surface reconstructions on group-IV(100) substrates can be used for the control of abruptness and electric properties of oxide/group-IV interfaces. In the present study, reversible Ba/Ge(100) c(4 x 4) <-> (1 x 2) phase transition, governed by the adsorption of oxygen at room temperature, as well as structural properties of both surface phases have been studied in detail by low -energy electron diffraction, scanning tunneling microscopy, and core-level photoemission using the synchrotron radiation. An atomic model is proposed for the c(4 x 4) reconstruction, and it is shown how this structure is modified upon the interaction with oxygen. Finally, the useful properties of O-containing (1 x 2) reconstruction, which allow one to optimize the growth of crystalline oxide films, are discussed.