Dopant Atoms In Semiconductors Research Articles

Doped semiconductor devices for sub-MeV dark matter detection

Dopant atoms in semiconductors can be ionized with ∼10 meV energy depositions, allowing for the design of low-threshold detectors. We propose using doped semiconductor targets to search for sub-MeV dark matter scattering or sub-eV dark matter absorption on electrons. Currently unconstrained cross sections could be tested with a 1 g-day exposure in a doped detector with backgrounds at the level of existing pure semiconductor detectors, but improvements would be needed to probe the freeze-in target. We discuss the corresponding technological requirements and lay out a possible detector design. Published by the American Physical Society 2024

Hyperfine-assisted fast electric control of dopant nuclear spins in semiconductors

Nuclear spins of dopant atoms in semiconductors are promising candidates as quantum bits, due to the long lifetime of their quantum states. Conventionally, coherent control of nuclear spins is done using ac magnetic fields. Using the example of a phosphorus atom in silicon, we theoretically demonstrate that hyperfine interaction can enhance the speed of magnetic control: the electron on the donor amplifies the ac magnetic field felt by the nuclear spin. Based on that result, we show that hyperfine interaction also provides a means to control the nuclear spin efficiently using an ac electric field, in the presence of intrinsic or artificial spin-orbit interaction. This electric control scheme is especially efficient and noise-resilient in a hybrid dot-donor system holding two electrons in the presence of an inhomogeneous magnetic field. The mechanisms proposed here could be used as building blocks in nuclear-spin-based electronic quantum information architectures.

Approaching the quantum limit for plasmonics: linear atomic chains

Optical excitations in atomic-scale materials can be strongly mixed, with contributions from both single-particle transitions and collective response. This complicates the quantum description of these excitations, because there is no clear way to define their quantization. To develop a quantum theory for these optical excitations, they must first be characterized so that single-particle-like and collective excitations can be identified. Linear atomic chains, such as atom chains on surfaces, linear arrays of dopant atoms in semiconductors, or linear molecules, provide ideal testbeds for studying collective excitations in small atomic-scale systems. We use exact diagonalization to study the many-body excitations of finite (10 to 25) linear atomic chains described by a simplified model Hamiltonian. Exact diagonalization results can be very different from the density functional theory (DFT) results usually obtained. Highly correlated, multiexcitonic states, strongly dependent on the electron–electron interaction strength, dominate the exact spectral and optical response but are not present in DFT excitation spectra. The ubiquitous presence of excitonic many-body states in the spectra makes it hard to identify plasmonic excitations. A combination of criteria involving a many-body state’s transfer dipole moment, balance, transfer charge, dynamical response, and induced-charge distribution do strongly suggest which many-body states should be considered as plasmonic. This analysis can be used to reveal the few plasmonic many-body states hidden in the dense spectrum of low-energy single-particle-like states and many higher-energy excitonic-like states. These excitonic states are the predominant excitation because of the many possible ways to develop local correlations.

The effect of oxidation and carbon contamination on SEM dopant contrast

Dopant contrast in the scanning electron microscope (SEM) has the potential to provide rapid and quantitative information about the distribution of dopant atoms in semiconductors providing that a robust quantification procedure can be developed. When silicon is exposed to air, it rapidly forms a native oxide on its surface which inevitably affects dopant contrast. In this paper we compare the dopant contrast observed on an in-situ cleaved specimen and an air-cleaved specimen and further examine the influence of prolonged electron exposure on dopant contrast.

Mössbauer study of 57Fe in GaAs and GaP following 57Mn+ implantation

Ion implantation provides a precise method of incorporating dopant atoms in semiconductors, provided lattice damage due to the implantation process can be annealed and the dopant atoms located on regular lattice sites. We have undertaken 57Fe emission Mossbauer spectroscopy measurements on GaAs and GaP single crystals following implantation of radioactive 57Mn + ions, to study the lattice sites of the implanted ions, the annealing of implantation induced damage and impurity–vacancy complexes formed. The Mossbauer spectra were analyzed with four spectral components: an asymmetric doublet (D1) attributed to Fe atoms in distorted environments due to implantation damage, two single lines, S1 assigned to Fe on substitutional Ga sites, and S2 to Fe on interstitial sites, and a low intensity symmetric doublet (D2) assigned to impurity–vacancy complexes. The variations in the extracted hyperfine parameters of D1 for both materials at high temperatures (T > 400 K) suggests changes in the immediate environment of the Fe impurity atoms and different bonding mechanism to the Mossbauer probe atom. The results show that the annealing of the radiation induced damage is more prominent in GaAs compared to GaP.

Scanning-probe spectroscopy of semiconductor donor molecules

Semiconductor devices continue to press into the nanoscale regime, and new applications have emerged for which the quantum properties of dopant atoms act as the functional part of the device, underscoring the necessity to probe the quantum structure of small numbers of dopant atoms in semiconductors[1-3]. Although dopant properties are well-understood with respect to bulk semiconductors, new questions arise in nanosystems. For example, the quantum energy levels of dopants will be affected by the proximity of nanometer-scale electrodes. Moreover, because shallow donors and acceptors are analogous to hydrogen atoms, experiments on small numbers of dopants have the potential to be a testing ground for fundamental questions of atomic and molecular physics, such as the maximum negative ionization of a molecule with a given number of positive ions[4,5]. Electron tunneling spectroscopy through isolated dopants has been observed in transport studies[6,7]. In addition, Geim and coworkers identified resonances due to two closely spaced donors, effectively forming donor molecules[8]. Here we present capacitance spectroscopy measurements of silicon donors in a gallium-arsenide heterostructure using a scanning probe technique[9,10]. In contrast to the work of Geim et al., our data show discernible peaks attributed to successive electrons entering the molecules. Hence this work represents the first addition spectrum measurement of dopant molecules. More generally, to the best of our knowledge, this study is the first example of single-electron capacitance spectroscopy performed directly with a scanning probe tip[9].

Dopant atoms in semiconductors: state and behavior, by V. I. Fistul?, Moscow: Fizmatlit, 2004

Dopant atoms in semiconductors: state and behavior, by V. I. Fistul?, Moscow: Fizmatlit, 2004

Simulations of the electrostatic potential in a thin silicon specimen containing a p-n junction

ABSTRACTThe measurement of potentials associated with dopant atoms in semiconductors at nanometer spatial resolution using off-axis electron holography is known to be affected by the presence of the surfaces of thin specimens. In particular, the potential across a p-n junction is often found to be lower than would be expected from predicted properties of bulk devices. Here we present simulations of two-dimensional potential profiles within a thin (<1 µm) parallel-sided specimen containing a p-n junction. We find that the potential across the p-n junction is always smaller, when projected through the specimen, than would be expected from the properties of the bulk material. Crucially, the step in potential across the junction is independent of the value of the potential on the surface of the specimen for high dopant concentrations (>1017 cm−3). The simulations are compared with experimental data. Although they can account for some of the reduction in the observed potential, they do not fully explain the experimental results.

Incorporation of dopant atoms and defects in semiconductors: a microscopic view

We demonstrate that scanning tunneling microscopy is an ideal tool for the investigation of individual bulk defects and dopant atoms in semiconductors. This technique allows not only an atomically resolved imaging of individual defects and dopant atoms, but rather a detailed determination of their nanoscale electronic as well as structural properties and their concentrations. The capacities of scanning tunneling microscopy for defect investigations will be presented with help of selected examples.

Imaging defects and dopants

The electrical properties of semiconductor materials are, to a large degree, governed by defects and dopant atoms incorporated during growth and production processes. Unfortunately, direct experimental access to such bulk point defects is very difficult. In recent years, however, scanning tunneling microscopy has developed into an ideal tool for the investigation of individual bulk defects and dopant atoms in semiconductors. This technique allows not only atomically resolved imaging of individual defects and dopant atoms, but also detailed determination of nanoscale electronic as well as structural properties and their concentrations. This provides new access to the physical mechanisms involved in the incorporation and interaction of defects and dopant atoms in semiconductors, leading eventually to an atomic level understanding of materials’ properties.With the invention of the transistor, a revolution in the development of semiconductor-based electronic devices began. However, even in the very early stages, the importance of defects and dopant atoms became obvious. In fact, if one incorporates the right defects and dopant atoms into semiconductor materials, one can tune their electrical properties such that optimal device characteristics are achieved. Unfortunately, counteractive defects are often also formed unintentionally during semiconductor<@> <@$p>processing, leading to unfavorable electronic properties. Considerable research efforts have, therefore, focused on understanding the nanoscale physics that governs the formation of point defects, the incorporation behavior of impurities, and their respective electronic properties.

Dopant mapping for the nanotechnology age.

The push for smaller microelectronics poses many challenges, such as locating dopant atoms in semiconductors with ever-increasing precision. The ideal technique must be able to detect single dopants with atomic resolution, and identify their electronic state. Neither is an easy task.

Scaling, small numbers and randomness in semiconductors

The randomness in the distribution of dopant atoms in semiconductors becomes increasingly important as devices are miniaturized and voltages are reduced. Fluctuations in the distribution have serious effects on noise margins in advanced devices and constitute a limit to the size of transistors built with present fabrication methods. In this article, the author explores ways to avoid those limits. >