Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session P12: Focus Session: Dopants and Defects in Semiconductors: Hyper Doping |
Hide Abstracts |
Sponsoring Units: DMP Chair: Jeff Grossman, Massachusetts Institute of Technology Room: D223/224 |
Wednesday, March 23, 2011 8:00AM - 8:12AM |
P12.00001: Limits of doping In$_{0.53}$Ga$_{0.47}$As with Si and Be Sangeetha Vijeyaragunathan, Tetsuya D. Mishima, Michael B. Santos We report on a study of doping efficiency in In$_{0.53}$Ga$_{0.47}$As layers grown on InP (001) substrates by molecular beam epitaxy. Si and Be effusion cells were used to provide n- and p-type dopants, respectively. In epilayers grown at 0.63 monolayers per second with a substrate temperature of 500\r{ }C, doping cell temperatures below T$_{Si}$=1260\r{ }C (T$_{Be}$=907\r{ }C) resulted in electron (hole) concentrations that followed an Arrhenius relation with an activation energy of 5.0 eV (4.0 eV). At higher cell temperatures, the carrier concentration saturated at approximately n=3.1$\times $10$^{19}$cm$^{{\-}3}$ (p=2.6$\times $10$^{19}$cm$^{{\-}3})$. For T$_{Si}$=1300\r{ }C (T$_{Be}$=928\r{ }C), the carrier concentration was increased to n=4.2$\times $10$^{19}$cm$^{{\-}3}$ (p=3.3$\times $10$^{19}$cm$^{{\-}3})$ through use of a lower substrate temperature of 400\r{ }C (470\r{ }C). The maximum carrier concentration achieved through lowering the substrate temperature was n=4.8$\times $10$^{19}$cm$^{{\-}3}$ (p=9.1$\times $10$^{19}$cm$^{{\-}3})$. For Be doping, the maximum hole concentration was increased to 1.3$\times $10$^{20}$cm$^{{\-}3}$ by using a lower growth rate. We will compare our results with the doping of GaSb and InAs, and discuss attempts to increase the maximum concentration through delta-doping and migration enhanced epitaxy. [Preview Abstract] |
Wednesday, March 23, 2011 8:12AM - 8:24AM |
P12.00002: Se-precipitation in ZnSe under moderate-power laser-irradiation at high-pressure G.P. Lindberg, R.E. Tallman, R. Lauck, M. Cardona, B.A. Weinstein We report evidence for the formation of Se inclusions in ZnSe under laser-irradiation during pressure-Raman experiments. Spectra of high-quality $^{68}$Zn$^{76}$Se crystals are recorded at 300K for pressures of 0-13GPa using 647nm excitation at powers of 10 and 100 mW (focal spot $\sim $ 50$\mu $m.) For runs at the higher power a new Raman peak appears at 1.8 GPa, and shifts to lower energy at the rate --3.5 cm$^{-1}$/GPa with further increase of pressure. Its frequency, 228cm$^{-1}$ at 1.8GPa, is within 7 cm$^{-1}$ of the A1 and E$^{\mbox{'}\mbox{'}}$ Raman peaks in trigonal Se, which both exhibit negative, strongly non-linear, pressure shifts.\footnote{W. Richter, \textit{et. al.}, phys. stat. sol. (b)\underline {56}, 223(1993); K. Aoki, \textit{et. al.}, J. Phys. Soc. Japan \underline {48}, 906 (1980).} In particular, the pressure-shift of the new ZnSe peak gives a reasonable fit to the average dependence of the Se A1 peak over the range 2-8 GPa. No assignment to any of the ZnSe acoustic modes (one- or two- phonon) that also soften with pressure is feasible for the new peak. It is most likely related to the Se A1-mode in Se-inclusions, whose tendency to precipitate appears to increase with pressure. [Preview Abstract] |
Wednesday, March 23, 2011 8:24AM - 8:36AM |
P12.00003: Band Renormalization in Mn Doped TiS$_{2}$ Timothy Kidd, Paul Shand, Laura Strauss, Jon Rameau, Tonica Valla, Peter Johnson Titanium disulphide is a narrow gap semiconductor with a highly 2D layered structure. Mn dopants can be used to transform the band structure into being truly metallic via a rigid band shift of the electronic states. The system also begins to exhibit a variety of low temperature magnetic phases at Mn concentrations above 5{\%}. We have performed angle resolved photoemission measurements of this system that clearly the transformation of the band structure from semiconducting to metallic. Furthermore, it can be seen that states near the valence band maxima become strongly modified beyond the rigid band shift approximation. The degeneracy of these states is lifted and they show behavior much like the spin splitting classically seen in surface states of gold and more recently in those of topological insulators. This behavior was quite unexpected as the states probed should be essentially bulk bands for this inert material. While no signs of temperature dependence were found to correlate these changes in electronic structure with any magnetic phase transition, it seems likely that this novel behavior arises from magnetic interactions with the Mn dopants. [Preview Abstract] |
Wednesday, March 23, 2011 8:36AM - 8:48AM |
P12.00004: Persistent Photoconductivity and Magnetotransport in Dilute Nitride Semiconductor Alloys R.L. Field III, Y. Jin, C. Kurdak, R.S. Goldman Nitrogen related defects, such as N interstitials and Si-N complexes, are known to dominate electrical and optical properties of dilute nitride semiconductor alloys [1,2]. We investigate the dependence of these defects on N incorporation for MBE grown Si and Te-doped dilute GaAs$_{1-x}$N$_x$ ($x$ = 0.75-1.9) alloys. Persistent photoconductivity was observed for these heterostructures as high as 160 K, with photo-capture barriers from 216-350 meV. Also, carrier concentrations extracted from Hall measurements reveal a T-independent regime above 150 K and a strong thermally-activated regime below 150 K. These two phenomena are reminiscent of the behavior of n- type AlGaAs, suggesting the presence of similar N-induced DX- center-like states in GaAsN. We will discuss the dependence of these energies on both N composition and annealing temperature. \\[4pt] [1] Y. Jin \emph{et al.}, Appl. Phys. Lett. 95, 092109 (2009).\\[0pt] [2] Y. Jin \emph{et al.}, Appl. Phys. Lett. 95, 062109 (2009). [Preview Abstract] |
Wednesday, March 23, 2011 8:48AM - 9:00AM |
P12.00005: ABSTRACT WITHDRAWN |
Wednesday, March 23, 2011 9:00AM - 9:12AM |
P12.00006: Magnetic properties of Mn doped zinc selenide clusters: First principles calculations Sachin Nanavati, Sundararajan V., Shailaja Mahamuni, Subhash Ghaisas, Vijay Kumar We report the result of our study on magnetic properties of Mn doped ZnSe clusters within the pseudopotential based density functional theory (DFT). In the present work, we substituted one or two Mn atoms at different cationic sites of small ZnSe clusters and the corresponding stable geometrical configurations are obtained. In general, we find a large magnetic moment of 5 $\mu _{B }$ magnetic moment when one Mn atom is substituted. For the case of doping of two Mn atoms, calculations were performed for both parallel and anti-parallel spin-configurations. The variations in the density of state (DOS), the gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), the binding energy, and the magnetic moment have been analyzed as a function of the cluster size. This paper will discuss the preferred sites of the dopants, type of magnetization and their bonding characteristics for the above mentioned clusters. [Preview Abstract] |
Wednesday, March 23, 2011 9:12AM - 9:48AM |
P12.00007: Sub-bandgap absorptance in chalcogen-hyperdoped silicon Invited Speaker: ~It has been shown that optical doping with pulsed lasers~can achieve non-equilibrium concentrations up to one atomic {\%} of heavy chalcogens in silicon.~~Compared to intrinsic silicon, this material exhibits near-unity absorption of sub-bandgap photons and has potential use in silicon infrared photodetectors and high-efficiency photovoltaics.~~Successful application of this material, however, requires better understanding of the exact mechanism responsible for sub-bandgap absorptance.~~Using a variety of techniques, we probe the chemical structure of this material system.~~We find that the short range structure of the dopant atom is correlated to the amount of sub-bandgap absorptance.~~We also compare the structure of different dopant species (S and Se) as well as different hyperdoping mechanisms (fs-laser doping vs. ion implantation followed by pulsed laser melting).~~In conjunction with theoretical modeling of expected chalcogen defect states, we identify dominant structural characteristics related to the observation of sub-bandgap absorptance. ~ Expanding on previous results, we demonstrate control of sub-bandgap absorptance through thermal processing. ~~In addition to suggesting a method to engineer the optical properties of the material, this result provides further insight into the thermodynamics of formation of a possible dopant-related defect state.~~We compare the thermodynamics measurements to the dopant structural measurements and posit a model of sub-bandgap absorptance and defect dynamics. ~These results provide a better understanding of the phenomena of sub-bandgap absorptance in chalcogen-hyperdoped silicon and a pathway to explore other hyperdoped semiconductors. ~~ [Preview Abstract] |
Wednesday, March 23, 2011 9:48AM - 10:00AM |
P12.00008: Supersaturated Silicon-Chalcogen Alloys for Thin-film Photodetectors Daniel Recht, Aurore Said, Si Hui Pan, Michael Aziz, Jeffery Warrender, Thomas Cruson, David Hutchinson, Peter Persans, Joseph Sullivan, Mark Winkler, Tonio Buonassisi Supersatured silicon-chalcogen alloys are known to have strong infrared optical absorption and the ability to detect light with energy less than silicon's bandgap. The range of infrared wavelengths these alloys absorb is much broader than the range over which photodiodes made from these alloys respond. We have recently performed several experiments to understand the disconnect between optical absorption and photodetection in thin, monocrystalline films of these alloys fabricated by ion implantation followed by nanosecond laser melting. When subjected to sensitive tests of photoconductivity, these alloys show no optoelectronic response at several absorbed sub-bandgap wavelengths. Furthermore, measurements on photodiodes made from silicon chalcogen alloys suggest that these materials are in fact a potent low-voltage photodetection gain medium. These results, along with temperature dependent transport measurements and sensitive optical spectroscopy, indicate that the mechanism of sub-bandgap response could be substantially more complex than is commonly thought. [Preview Abstract] |
Wednesday, March 23, 2011 10:00AM - 10:12AM |
P12.00009: Non-radiative Recombination in Intermediate Band Photovoltaics Jacob Krich, Al\'an Aspuru-Guzik Intermediate band photovoltaics (IBPV) promise to absorb low energy photons while maintaining large open circuit voltages, breaking the Shockley-Queisser efficiency limit. Proposals for IBPV include hyperdoping semiconductors with impurities forming mid-gap states, creating a band entirely contained inside the larger semiconductor bandgap. For such devices to function, the electronic states in the middle of the band gap must be extended and thus not contribute to multiphonon recombination. Since the intermediate band is produced by randomly placed impurities, however, there is an inherent disorder in the electronic structure, which produces localized states inside the band gap due to Anderson localization, even at high impurity concentrations. We use a finite size scaling analysis to find the localization properties of a non-interacting intermediate band and its resultant contribution to non-radiative recombination. [Preview Abstract] |
Wednesday, March 23, 2011 10:12AM - 10:24AM |
P12.00010: A Metal-Insulator Transition in Silicon Hyperdoped with Chalcogens Elif Ertekin, Mark Winkler, Aurore Said, Michael Aziz, Tonio Buonassisi, Jeffrey Grossman Hyperdoped Silicon, the material resulting from the laser doping of Silicon to impurity concentrations orders of magnitude beyond the room temperature solubility limit, can exhibit unique properties. For example, ``Black Silicon'', formed from laser doping with chalcogens S, Se, or Te, exhibits anomalous sub band gap optical absorption at photon energies as low as 0.5 eV and a flat absorption spectrum. While this has piqued interest in the use of Black Silicon for optoelectronics and photovoltaics, there has not yet been a clear explanation for the enhanced optical properties. Focusing on the Se doped systems, we use Density Functional Theory to show that the optical absorption results from an impurity induced insulator to metal transition. Our calculations indicate that an isolated Se impurity introduces a localized electronic state in the band gap. At higher defect concentrations, the transition to the metallic state is demonstrated by an increase in the defect level bandwidth and the eventual merging of the defect state with the conduction bands. The concentration at which this occurs corresponds very well with experimental low temperature Hall effect measurements. [Preview Abstract] |
Wednesday, March 23, 2011 10:24AM - 10:36AM |
P12.00011: Dopant effects on dislocation width of dislocations in Si Yutaka Ohno, Toshinori Taishi, Yuki Tokumoto, Ichiro Yonenaga Impurities interact with dislocations in semiconductor crystals, resulting in variations of dynamical activities of dislocations such as mobility and immobilization, and also in leading to inhomogeneity of electrical and optical properties of microelectronic and PV devices. Especially in Si in demanded trend of heavily doping for miniaturized transistors, basic knowledge of dislocation-dopant impurity interaction increases the importance. In CZ-Si doped with $n$-type impurities of P, As, and Sb, dislocations freshly induced at 1173 K extended their dissociation width with increasing duration of subsequent annealing at the same temperature. The width increased by annealing when the concentration of $n$-type impurities was high. On the other hand, the dissociation width was unchanged during annealing in Si undoped and doped with $p$-type impurities of B and Ga. These results suggest that the energy of stacking fault bound to partial dislocations is strongly affected by the number of $n$-dopant impurities segregated nearby them via their thermal migration, irrespective of atomic size of the dopant impurities; i.e., $n$-dopant impurities segregate nearby a stacking fault so as to reduce the stacking fault energy. [Preview Abstract] |
Wednesday, March 23, 2011 10:36AM - 10:48AM |
P12.00012: Entropic Influence on the Aggregation Physics of Interstitial Point Defects in Silicon Talid Sinno, Sumeet Kapur, Alex Nieves The evolution of self-interstitials and their aggregates during the annealing of ion-implanted silicon has received a tremendous amount of attention because of their strong, non-linear effects on the diffusion of dopants. The implantation process leads to extensive lattice damage, which must be healed by thermal annealing. Also generated by the implantation process is a large number of self-interstitials which lead to enhanced dopant diffusion during annealing known as Transient Enhanced Diffusion, or TED. A major obstacle to understanding and quantitatively predicting TED is the formation of a variety of self-interstitial aggregates, which range from small amorphous three-dimensional clusters, to planar stacking-faults with various crystallographic orientations. In the present study, we use large-scale constant-stress MD simulations to dynamically simulate the evolution of an ensemble of highly supersaturated self-interstitials at various temperatures and pressures. We show that the simulated interstitial clustering into various types of planar structures exhibits a complex thermodynamic-kinetic phase diagram that is sensitively controlled by entropic factors. The observations are studied with a recently developed approach that maps out the potential energy landscape in the vicinity of the defect cluster and allows for the total (classical) free energy to be analyzed. [Preview Abstract] |
Wednesday, March 23, 2011 10:48AM - 11:00AM |
P12.00013: The chemical trends of a new defect cluster: DDX centers Jie Ma, Su-Huai Wei DX center is a major ``killer'' defect limiting n-type doping in group II-VI and III-V semiconductors. It converts a shallow donor to deep one, which is a major reason for the saturation of free-electron carriers in the doping process. Several structure models of isolated DX centers have been proposed in the literatures, such as the broken-bond model (BB-DX), and the $\alpha $ and $\beta $ cation-cation bond model (CCB-DX). All these DX centers can be stabilized with hydrostatic pressure or reduced dimensionality and size. In group III-V and II-VI semiconductors, it has been common believe that cation-site induced DX centers are easier to form than anion-site induced ones. Because DX centers trap an extra electron, therefore, another defect in the system must donate the electron and form a positive charged defect. We show, using GaAs as an example, that in heavily doped semiconductor, the negative charged DX center and positive charged donor can couple strongly through the Coulomb interaction, forming the dominant DDX center. The DDX centers are still deep level defects. However, unlike the DX center, the DDX centers have different chemical trends, i.e., anion-site DDX center is easier to form than cation-site DDX centers. A simple model is proposed to explain the new trends. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2025 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700