Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session L14: Focus Session: Dopants and Defects in Group IV Semiconductors |
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Sponsoring Units: DMP FIAP Chair: Peihong Zhang, University of Buffalo Room: 008A |
Wednesday, March 4, 2015 8:00AM - 8:12AM |
L14.00001: BSE calculations of color center defects in diamond S. Vimolchalao, W.H. Liang, F.D. Vila, J.J. Kas, J.J. Rehr, F. Farges Colored diamonds are both of fundamental and commercial interest. Several recent efforts have focused on determining the origin of their color. For example, experiments show that the color of blue diamonds is associated with isolated boron impurities\footnote{J.Walker, Rep. Prog. Phys. {\bf 42} 1605 (1979).} while nitrogen impurities are responsible for yellow diamonds. It has previously been shown \footnote{F.Farges \textit{et al.}, Europhysics News {\bf43}, 20 (2012).} that theoretical Bethe-Salpeter Equation (BSE) simulations of boron-doped diamond yield a dark-blue diamond in good agreement with that observed. However, the structure of the nitrogen defects is not well understood. Here we present BSE calculations of the optical response of nitrogen-doped diamonds using relaxed 64-atom unit cells. We focus on N$_x$V$_y$ defect sites, where $x$ is the number of substitutional nitrogen atoms and $y$ is the number of carbon vacancies. We find that the most likely candidates are the N$_3$V$_1$ and N$_2$V$_0$ defects, which show absorption in the 2.5-3.2 eV range, consistent with yellow color. Our results also rule out the N$_1$V$_0$ and N$_4$V$_1$ defect types as possible yellow centers. [Preview Abstract] |
Wednesday, March 4, 2015 8:12AM - 8:24AM |
L14.00002: Structure and electronic properties of nanodiamond and its fluorination effect Kazuyuki Takai, Kenta Kogane, Hidekazu Touhara, Yoshiyuki Hattori Fluorination of nano-sized diamond (ND) is expected not only to stabilize the surface structure, but also to introduce functional groups on the surface, the conduction carriers, and so on. In this study, we evaluate the structure and magnetic properties of ND and fluorinated ND (FND) in order to consider the change in the electronic state and the surface structure by fluorination. Fluorination of ND was carried out by the direct reaction between gaseous fluorine (1 atm) and commercially available detonation diamond at 623 -- 873 K. X-ray Diffraction study reveals the structural stability of core part of ND during fluorination. X-ray photoemission spectroscopy exhibits F1s peak at the lower binding energy region than that for physisorbed molecular fluorine, indicating the formation of the chemical bonding between C and F in the sample. The Electron Paramagnetic Resonance results suggest that fluorination induces not only changes in the surface structure but also relaxation of defects in the core part. [Preview Abstract] |
Wednesday, March 4, 2015 8:24AM - 8:36AM |
L14.00003: Determine the number of nitrogen vacancy color centers in the nano-diamond particles with large size difference Jui-Hung Hsu, Long-Jyun Su, Huan-Cheng Chang The number of emitters in a nano-particle is usually determined by the photon correlation using the Hanbury Brown and Twiss configuration. However, limited to the photon statics, this method is only valid for the small numbers. It would be difficult to measure the number of emitters, if individual nano-particles contain more than several tens or hundreds of emitters. In this contribution, we present a work to quantitatively determine the number of nitrogen-vacancy (NV) centers in the individual nano-diamond (ND) particles. Our previous work (Nanotechnology 24, 315702) suggests that the density of NV centers would be significantly decreased while reducing ND particle size from 100 nm to 30 nm. It thus motivates us to measure the number of NV centers of individual ND particles with large size difference. Under saturated the pulse excitation, the emission intensity from individual ND particle is proportional to the number of NV centers and the fluorescence quantum yield, which are able to be determined independently. [Preview Abstract] |
Wednesday, March 4, 2015 8:36AM - 9:12AM |
L14.00004: Designing shallow donors in diamond Invited Speaker: Jonathan Moussa The production of $n$-type semiconducting diamond has been a long-standing experimental challenge. The first-principles simulation of shallow dopants in semiconductors has been a long-standing theoretical challenge. A desirable theoretical goal is to identify impurities that will act as shallow donors in diamond and assess their experimental viability. I will discuss this identification process for the LiN$_4$ donor complex. It builds a scientific argument from several models and computational results in the absence of computational tools that are both trustworthy and computationally tractable for this task. I will compare the theoretical assessment of viability with recent experimental efforts to co-dope diamond with lithium and nitrogen. Finally, I discuss the computational tools needed to facilitate future work on this problem and some preliminary simulations of donors near diamond surfaces. [Preview Abstract] |
Wednesday, March 4, 2015 9:12AM - 9:24AM |
L14.00005: Carbon-antisite vacancy defect in 4H silicon carbide for realizing solid state qubit Adam Gali, Kriszti\'an Sz\'asz, Viktor Iv\'ady, Igor Abrikosov, Michel Bockstedte, Erik Janz\'en Dopants in solids are promising candidates for implementations of quantum bits for quantum computing. Silicon carbide (SiC) with engineered point defects is considered as very promising material for the next generation devices, with applications ranging from electronics and photonics to quantum computing. Employing density functional theory and many body perturbation theory, we show that the neutral carbon antisite-vacancy pair (CAV) has high spin ground state, and that its spin may be coherently manipulated by optical excitation in n-type 4H SiC. As the positively charged CAV defect in 4H SiC has been recently engineered to act as single photon source [1], our finding brings a hope that optically addressed quantum bits can be realized by the neutral CAV defects in 4H SiC, and provide an additional target for researchers seeking for solid state single color centers for quantum information processes and metrology. The calculated zero-phonon line of the optically excited state is about 1550 nm (0.8 eV) which perfectly fits to the telecom wavelengths, that makes this qubit candidate very promising for integration of quantum optics devices with existing fiber optics technology. [1] S. Castelletto et al., Nature Materials, 13, 151-156 (2014) [Preview Abstract] |
Wednesday, March 4, 2015 9:24AM - 9:36AM |
L14.00006: Determining exact location of Group V dopants below the Si(001):H surface from scanning tunnelling spectroscopy and density functional theory Veronika Brazdova, Kitiphat Sinthiptharakoon, Philipp Studer, David R. Bowler, Adam Rahnejat, Neil J. Curson, Steven Schofield, Andrew J. Fisher Group V impurities in silicon provide a way to tailor properties of electronic materials. The magnetically quiet environment that silicon provides for the impurity spins has also lead to new applications in coherent quantum devices. In both the ultimate classical devices and in future quantum computers the exact position of the dopants near surfaces and interfaces will determine the functionality: the ability to control and monitor those positions is key in these technologies. We precisely determine the substitutional sites of neutral As dopants that lie between 4.2 A and 15.0 A below the hydrogenated Si(001) surface, using a combination of density functional theory and low-temperature scanning tunnelling microscopy. We describe the interaction of the donor-electron state with the surface. [Preview Abstract] |
Wednesday, March 4, 2015 9:36AM - 9:48AM |
L14.00007: Towards bipolar atomic scale dopant devices defined by STM-lithography Andreas Fuhrer, Sigrun K{\"o}ster, Nikola Pascher Dopant device fabrication with hydrogen resist lithography has been demonstrated only for n-type dopants. The reason for this is the ease with which phosphorus can be incorporated and activated after gas phase doping with phosphine. Specifically, incorporation on the silicon (001) surface can be achieved at $350^\circ$C while keeping the hydrogen resist intact and thus avoiding surface diffusion of the dopants. Here, we present new results on p-type $\delta$-doping of silicon, towards the fabrication of bipolar dopant devices with hydrogen resist lithography. Using diborane as a gas-phase dopant source, Hall bar devices were fabricated to extract hole densities and mobilities in cryogenic magneto-transport experiments. Furthermore, the dependence of these parameters on diborane dose and dopant activation temperatures is investigated. We find that gas-phase doping with diborane is compatible with hydrogen resist lithography and dopant structures can be patterned using the STM. However, activation of the boron dopants currently still leads to significant diffusion and therefore blurring of the patterned devices. We will discuss the prospects of further optimising this and present a possible path forward towards bipolar atomic scale device fabrication with the STM. [Preview Abstract] |
Wednesday, March 4, 2015 9:48AM - 10:00AM |
L14.00008: Suppressed Incomplete Ionization of Shallow Donors in Germanium Jose Menendez, Chi Xu, Charutha Senaratne, John Kouvetakis For doping levels $N_{d}$ \textgreater 10$^{\mathrm{17}}$ cm$^{\mathrm{-3}}$, an elementary analysis indicates that shallow donors should not be completely ionized in germanium at room temperature. The predicted degree of incomplete ionization (I.I.) represents a fundamental limitation in the quest for ultra-low sheet resistances, as required in Ge-based nMOS devices. Unfortunately, the experimental verification of the predictions is made difficult by the possible presence of inactive dopants, which also lead to free carrier concentrations $n$ \textless $N_{d}$. In this work, we prepared $n$-type Ge films on Ge-buffered Si substrates using novel synthetic approaches that are expected to minimize the presence of inactive dopants. Higher-order germanes (Ge$_{\mathrm{3}}$H$_{\mathrm{8}}$ and Ge$_{\mathrm{4}}$H$_{\mathrm{10}})$ were used as the source of Ge for growth at low temperatures. Phosphorus atoms were furnished via P(MH$_{\mathrm{3}})_{\mathrm{3}}$ (M $=$ Ge, Si) compounds in which the P atom is already bonded to three group-IV atoms in a way that is expected to promote substitutional incorporation. Spectroscopic ellipsometry and SIMS were used to determine $n$ and $N_{d}$, respectively. The results indicate no observable I.I. Within experimental error, $n=N_{d}$, in contradiction with the elementary theory. These findings are compatible with the model developed by Altermatt \textit{et al}. to explain I.I. phenomena in silicon. [Preview Abstract] |
Wednesday, March 4, 2015 10:00AM - 10:12AM |
L14.00009: Band Structure and Optical Properties of Dilute Ge:C Alloys Chad Stephenson, William O'Brien, Meng Qi, Michael Penninger, William Schneider, Miriam Gillett-Kunnath, Jaroslav Zajicek, Mark Wistey The last major missing piece to achieving integrated Si photonics is an efficient light emitter. Dilute Ge:C alloys offer a new route to create efficient lasers directly within conventional CMOS electronics. Although neither Ge nor C emits light, Ge:C is a highly mismatched alloy, similar to GaAsN, in which band anticrossing is expected to create a direct bandgap. We have performed ab initio band structure simulations using hybrid functionals and spin-orbit coupling that show a sharp decrease in bandgap at the direct conduction band valley with C incorporation, turning Ge:C into a direct bandgap semiconductor and even a semi-metal. We report on the optical properties, highlighting the strength of free carrier absorption due to the changes in the band structure. Some of its potential applications include integrated light emitters, modulators, and photodetectors. With the three-band system, Ge:C also has potential for use in upconverting structures. We also report successful incorporation of C in Ge using hybrid gas+solid source molecular beam epitaxy (MBE) using a precursor gas, tetra(germyl)methane (4GeMe), that prevents undesirable C-C bonds and interstitial incorporation. [Preview Abstract] |
Wednesday, March 4, 2015 10:12AM - 10:24AM |
L14.00010: GeSn \textit{pin} diodes: from pure Ge to direct-gap materials James Gallagher, Charutha Senaratne, Chi Xu, Toshihiro Aoki, John Kouvetakis, Jose Menendez Complete $n-i-p$ Ge$_{\mathrm{1-y}}$Sn$_{y}$ diode structures (y$=$0-0.09) were fabricated on Si substrates with Sn concentrations covering the entire range between pure Ge and direct-gap materials. The structures typically consist of a thick ( \textgreater 1 $\mu $m) $n++$ Ge buffer layer grown by Gas Source Molecular Epitaxy using Ge$_{4}$H$_{10}$ and either P(SiH$_{3})_{3}$ or P(GeH$_{3})_{3}$, followed by a GeSn intrinsic layer ($\sim$ 500 nm), grown by Chemical Vapor Deposition (CVD) using Ge$_{3}$H$_{8}$ and SnD$_{4}$, and a GeSn $p$-type top layer ($\sim$ 200 nm) grown by CVD using Ge$_{3}$H$_{8}$, SnD$_{4}$ and B$_{2}$H$_{6}$. Temperature-dependence of the $I-V$ characteristics of these diodes as well as the forward-bias dependence of their electroluminescence (EL) signal were investigated, making it possible for the first time to extract the compositional dependence of parameters such as band gaps, activation energies, and dark currents. The EL spectra are dominated by direct-gap emission, which shifts from 1590 nm to 2300 nm, in agreement with photoluminescence results. [Preview Abstract] |
Wednesday, March 4, 2015 10:24AM - 10:36AM |
L14.00011: Doping and strain dependence of the electronic band structure in Ge and GeSn alloys Chi Xu, James Gallagher, Charutha Senaratne, Christopher Brown, Nalin Fernando, Stefan Zollner, John Kouvetakis, Jose Menendez A systematic study of the effect of dopants and strain on the electronic structure of Ge and GeSn alloys is presented. Samples were grown by UHV-CVD on Ge-buffered Si using Ge3H8 and SnD4 as the sources of Ge and Sn, and B2H6/P(GeH3)3 as dopants. High-energy critical points in the joint-density of electronic states were studied using spectroscopic ellipsometry, which yields detailed information on the strain and doping dependence of the so-called $E_{1}$, $E_{1}+\Delta_{1}$, $E_{0}'$ and $E_{2}$ transitions. The corresponding dependencies of the lowest direct band gap $E_{0}$ and the fundamental indirect band gap $E_{ind} $were studied via room-T photoluminescence spectroscopy. Of particular interest for this work were the determination of deformation potentials, band gap renormalization effects, Burstein-Moss shifts due to the presence of carriers at band minima, and the dependence of other critical point parameters, such as amplitudes and phase angles, on the doping concentration. The selective blocking of transitions due to high doping makes it possible to investigate the precise $k$-space location of critical points. These studies are complemented with detailed band-structure calculations within a full-zone $k$-dot-$p$ approach. [Preview Abstract] |
Wednesday, March 4, 2015 10:36AM - 10:48AM |
L14.00012: First-principles Study of the NiGe/Ge Schottky Barrier Height under Dopant Segregation Chiung-Yuan Lin, Han-Chi Lin Traditional Si-based MOSFETs are approaching its fundamental scaling limits, and Ge has been comprehensively explored as a potential channel material to replace Si due to its high intrinsic carrier mobility for further performance enhancement. Nevertheless, strong Fermi-level pinning near the valence band edge of Ge leads to high electron Schottky barrier height. Dopant segregation technique has been proposed to achieve shallower junction depth and heavier dopant concentration for NiGe/Ge. However, the role of dopants at the NiGe/Ge interface is not clear. In this study, first-principles calculations are employed to nail down the most stable dopant position and to obtain the physical Schottky barrier height (by HSE06 hybrid functional) of the NiGe/Ge contact. For the conventional n-type dopant such as phosphorous and arsenic, our calculations show that those two elements may be segregated at the interface, while the reduction of the Schottky barrier height is insignificant. This implies that the experimental improvement of the NiGe/n-type Ge junction by dopant are mainly attributed to the increased dopant concentration around the interface. [Preview Abstract] |
Wednesday, March 4, 2015 10:48AM - 11:00AM |
L14.00013: Quantum dynamics of electric-dipole coupled nitrogen-vacancy centers in diamond and possible applications Lei-Ming Zhou, Fang-Wen Sun, Nan Zhao, Guang-Can Guo Nitrogen-Vacancy (NV) center in diamond is a popular platform for quantum information, quantum metrology and quantum physics research. Single NV centers and their quantum dynamics were well-studied in the past decade. Magnetic-dipole coupling between NV center pairs was also implemented, very recently, to realize spin entanglement. Here, we theoretically investigate the quantum dynamics of electric-dipole coupled NV centers in low temperature. With quantum electrodynamics method, we establish master equations to describe the quantum dynamics of the coupled NV center pairs. The collective behaviors induced by the common photon bath, including super-radiance, coherent coupling and cross-relaxation are discussed. We also predict several experimentally observable effects, such as photon polarization transfer, which have potential application in nano-photonics. [Preview Abstract] |
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