Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session S44: Focus Session: Defects in Semiconductors: Defects Engineering |
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Sponsoring Units: FIAP Chair: Andriy Zakutayev, National Renewable Energy Laboratory Room: Mile High Ballroom 4C |
Thursday, March 6, 2014 8:00AM - 8:12AM |
S44.00001: Bipolar Doping Control in Sputter-deposited Cu$_{3}$N Thin Films as a Function of Growth Conditions Angela Fioretti, Steven Christensen, David S. Ginley, Eric S. Toberer, Andriy Zakutayev Experimental evidence of Cu$_{3}$N defect-tolerance has been observed in that it can be doped either n-type or p-type based solely on growth conditions. In this presentation, the control of bipolar doping behavior as a function of growth conditions in Cu$_{3}$N is demonstrated, and hypotheses as to the underlying physics of this behavior are explored. Thin films of Cu$_{3}$N were deposited using reactive RF-magnetron sputtering. Growth temperature and target power density were varied respectively in two sets of experiments. For both sets, Hall effect and Seebeck coefficient measurements were used to characterize carrier type. Furthermore, NEXAFS measurements were performed to investigate the fundamental differences in structure that may give rise to Cu$_{3}$N bipolar doping. Cu$_{3}$N grown under conditions in which the activity of nitrogen was low exhibited n-type conductivity, while films grown under conditions in which the activity of nitrogen was high exhibited p-type conductivity. NEXAFS measurements revealed the presence of mixed Cu valence (both Cu$^{+1}$ and Cu$^{+2})$, and this discovery helped to shed light on the underlying physics behind Cu$_{3}$N bipolar doping behavior. [Preview Abstract] |
Thursday, March 6, 2014 8:12AM - 8:24AM |
S44.00002: Effect of annealing on electronic carrier transport properties of gamma-irradiated AlGaN/GaN high electron mobility transistors Anupama Yadav, Casey Schwarz, Max Shatkhin, Luther Wang, Elena Flitsiyan, Leonid Chernyak, Lu Liu, Ya Hwang, Fan Ren, Stephen Pearton AlGaN/GaN High Electron Mobility Transistors were irradiated with $^{\mathrm{60}}$Co gamma-ray doses from 100Gy to 1000Gy, in order to analyze the effects of irradiation on the devices' transport properties. Temperature dependent Electron Beam Induced Current (EBIC) measurements, conducted on the devices before and after exposure to gamma-irradiation, allowed for the obtaining of activation energy related to radiation-induced defects due to nitrogen vacancies. Later, the devices were annealed at 200$^{\mathrm{o}}$ C for 25 minutes. All the measurements were performed again to study the effect of annealing on the gamma-irradiated devices. Annealing of gamma-irradiated transistors shows that partial recovery of device performance is possible at this temperature. DC current-voltage measurements were also conducted on the transistors to assess the impact of gamma-irradiation and annealing on transfer, gate and drain characteristics. [Preview Abstract] |
Thursday, March 6, 2014 8:24AM - 8:36AM |
S44.00003: Electronic and Optical Properties of ScN and (Sc,Mn)N Thin Films Deposited by DC-Magnetron Sputtering Bivas Saha, Gururaj Naik, Vladimir Drachev, Alexandra Boltasseva, Ernesto Marinero, Timothy Sands Scandium Nitride (ScN) is a rocksalt semiconductor with an interesting electronic structure for optoelectronic and dilute magnetic semiconductor applications. We present detailed studies of the electronic transport and optical properties of ScN and its alloys with manganese nitride (MnN). Our results suggest (a) dilute manganese doping in ScN compensates for the high $n$-type carrier concentrations arising due to oxygen impurities, and (b) an $n$-type to $p$-type carrier type transition occurs at a composition between 5.8{\%} and 11{\%} Mn on Sc sites. In terms of its optical properties, our analysis clearly indicates direct and indirect bandgap absorption edges of ScN located at 2.04 eV and 1.18eV respectively. In addition to the direct gap absorption edge, (Sc,Mn)N samples also show Mn-defect induced electronic absorption. Photoluminescence measurements at room temperature from ScN films exhibit a yellowish-green emission corresponding to direct gap radiative recombination. Direct gap recombination is not expected given the smaller indirect gap. A possible role of high excitation intensities in suppressing relaxation and recombination across the indirect bandgap is suspected.. [Preview Abstract] |
Thursday, March 6, 2014 8:36AM - 8:48AM |
S44.00004: Photonic Crystal Cavities in Cubic (3C) Silicon Carbide Marina Radulaski, Thomas Babinec, Sonia Buckley, Armand Rundquist, J Provine, Kassem AlAssaad, Gabriel Ferro, Jelena Vuckovic Silicon carbide (SiC) combines many of the outstanding material properties of other well-known optical and quantum optical materials, including strong optical nonlinearity, high Young's modulus, and a host of optically-active crystalline defects, in a single CMOS-compatible platform. For many applications in classical and quantum information processing, the material properties of the cubic silicon carbide polytype (3C-SiC) in particular are advantageous. We therefore present the design, fabrication, and characterization of high quality factor and small mode volume planar photonic crystal cavities in cubic 3C-SiC thin films (200 nm). We demonstrate cavity resonances across the infrared telecommunications band, with wavelengths from 1.25 - 1.6 $\mu $m. Finally, we highlight our progress developing higher Q/V nanobeam cavities, as well as extending this optical cavity platform towards integration with SiC color centers. [Preview Abstract] |
Thursday, March 6, 2014 8:48AM - 9:00AM |
S44.00005: Energy transfer among isoelectronic dopants in GaP Theresa Christian, Kirstin Alberi, Brian Fluegel, Angelo Mascarenhas Although GaP is an indirect-bandgap material, it can also be an efficient light-emitter at visible wavelengths when isoelectronic impurities mediate radiative recombination via states within the bandgap. Since these states also provide a medium for energy transfer via exciton hopping among localized isoelectronic trap sites, the carrier dynamics in doped GaP are strongly dependent on the distribution and density of impurity species. We present spectroscopic data demonstrating the role of energy transfer among isoelectronic states in GaP via temperature-dependent and time-resolved photoluminescence. Research was supported by the U. S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division under contract DE-AC36-08GO28308 and by the Department of Energy Office of Science Graduate Fellowship Program (DOE SCGF), made possible in part by the American Recovery and Reinvestment Act of 2009, administered by ORISE-ORAU under contract no. DE-AC05-06OR23100. [Preview Abstract] |
Thursday, March 6, 2014 9:00AM - 9:12AM |
S44.00006: Amphoteric Doping of GaAsBi alloys with Silicon R.L. Field III, T. Jen, B. Yarlagadda, M. Luengo-Kovac, V. Sih, C. Kurdak, R.S. Goldman Due to the significant bandgap reduction associated with bismuth incorporation, dilute bismuthide semiconductor alloys have been proposed for high-efficiency optoelectronic devices. Although Si and Be are the most common dopants for n- and p-type doping of GaAs and related materials during MBE growth, their use in high quality structures has limitations. For example, while Be has a high active solubility in GaAs, it is also a fast diffuser in GaAs. In this work, Si is found to be an amphoteric dopant in GaAsBi by varying the As$_{\mathrm{4}}$/Ga beam equivalent pressure ratio, resulting in n-type (p-type) films due to Si entering group III (group V) sites. The hole mobility is found to decrease with Bi composition, an indication that Bi-related defects are the main source of scattering in p-type GaAsBi. Yet, the electron mobility appears independent of Bi composition, at least in the range of compositions that have been fabricated and measured. To date, we have achieved Bi incorporation in excess of 6{\%} Bi substituting for As, with electron mobilities as high as 2500 cm$^{\mathrm{2}}$/V-s for Si-doped (n $\approx $ 10$^{\mathrm{18}}$ cm$^{\mathrm{-3}})$ GaAsBi. Using Si provides an alternative to the traditional use of C and Be as p-type dopants. [Preview Abstract] |
Thursday, March 6, 2014 9:12AM - 9:24AM |
S44.00007: Tunable threshold voltage via molecular doping of solution-processed organic field-effect transistors James Belasco, Swagat Mohapatra, Yadong Zhang, Stephen Barlow, Seth Marder, Antoine Kahn The threshold voltage, Vth, is a key parameter to control for proper circuit operation. We demonstrate the controlled tuning of Vth of solution processed, small molecule, organic field effect transistors (OFET) via molecular doping of the solution. A 1:1 blend solution containing the $\pi $-conjugated small molecule 6, 13-triisopropylsilylethynylpentacene (TIPS-pentacene) and polystyrene is used as the baseline solution for the OFETs. The organic p-dopant, molybdenum tris-[1-trifluoroethanoyl-2-trifluoromethylethane-1,2-dithiolene] [Mo(tfd-COCF3)3], a soluble version of Mo(tfd)3 [1], is added at various concentrations up to 0.3 wt{\%} to make bottom gate, bottom contact devices by spin coating on a SiO2 dielectric. IV-measurements on the resulting devices give baseline OFETs with an average mobility of 0.5 cm2/V.s and Vth of -1.5 V, while doped OFETs show the same average mobility with Vth shifted up to an average maximum of $+$2.5V. Overall, the various doping levels produce a gradual increase in the threshold voltage which we attribute in part to the filling of trap states that are known to exist in organic semiconductor films [2], and in part to effects related to the organic/dielectric interface. The direct correlation between Vth and doping concentration can be used to tune the threshold voltage in this system. [1] Y. Qi et. al. J. Am. Chem. Soc. 131, 12530 (2009) [2] H. Sirringhaus et. al. Adv. Mater. 21, 3859 (2009) [Preview Abstract] |
Thursday, March 6, 2014 9:24AM - 9:36AM |
S44.00008: Near-surface effects of transient oxidation and reduction on Nb-doped SrTiO3 epitaxial thin films C.F. Chang, Q.Y. Chen, P.V. Wadekar, O. Lozano, M.S. Wong, W.C. Hsieh, W.Y. Lin, H.H. Ko, Q.J. Lin, H.C. Huang, N.J. Ho, L.W. Tu, H.H. Liao, P.V. Chinta, W.K. Chu, H.W. Seo We studied the effects of transient oxidation and reduction of Nb-doped epitaxial thin films through variations of PAr and PO2. The samples were prepared by co-sputtering of Nb and SrTiO3 on LaAlO3 substrates. The Nb-content were varied from 0-33.7\%, as determined by PIXE. Contact resistance, sheet resistance, and optical properties are used to discriminate the effects. [Preview Abstract] |
Thursday, March 6, 2014 9:36AM - 9:48AM |
S44.00009: Role of iron impurity complexes in degradation of GaN/AlGaN HEMTs Yevgeniy Puzyrev, Sokrates Pantelides GaN/AlGaN high electron mobility transistors (HEMTs) are leading candidates for power RF devices, but they suffer from reliability issues, in particular, a current collapse. Experiments have shown that the current collapse is correlated with the presence of a Tp1 trap in either the GaN substrate or at the surface with an energy level at about 0.55 eV below the GaN conduction band. Recent experiments demonstrated that the $E_{c}$-0.55eV level increases with the decrease of the distance from the channel to the \textit{Fe}-doped GaN. Another study found a correlation between threading dislocation density (TDD) and the concentration of $E_{c}$-0.55eV trap. Drastic decrease of $E_{c}$-0.55eV trap concentration is observed after hydrogenation of the samples. During OFF state stress, the population of the generated Tp1 trap is proportional to the square root of the stress time, suggesting Tp1 generation is correlated to the diffusion of a point defect. We present results of first-principle calculations and show that degradation occurs by the dehydrogenation of Fe and Fe-vacancy complexes. Using these results we analyze available experimental data and provide a comprehensive picture of the generation of the $E_{c}$-0.55eV trap level. [Preview Abstract] |
Thursday, March 6, 2014 9:48AM - 10:00AM |
S44.00010: Modeling Quantum and Coulomb Effects in Nanoscale Enhancement-Mode Tri-Gate III-V MOSFETs Sameer Al-Sibiani, Khadija Khair, Shaikh Ahmed Because of limited benefits of strain engineering in extremely scaled silicon devices and lack of demonstration of a performance gain at the product level with nanowires, nanotubes, graphene, and other exotic channel materials, there is a strong motivation to continue device scaling using high-transport III-V (such as InGaAs and InAsSb) channel materials beyond the year 2020. However, there are several challenges with III-V MOSFETs prohibiting their use in high-performance and low-power logic applications. In this work, we investigate the performance of the tri-gate III-V FETs as compared to the planar counterpart, and show how quantum size quantization and random dopant fluctuations (RDF) affect the tri-gate FET characteristics and how to curb these issues. A 3-D fully \textit{atomistic} quantum-corrected Monte Carlo device simulator has been used in this work. Space-quantization effects have been accounted for via a \textit{parameter-free} effective potential scheme (and benchmarked against the NEGF approach in the ballistic limit). To treat full Coulomb (electron-ion and electron-electron) interactions, the simulator implements a real-space corrected Coulomb electron dynamics (ED) scheme. Also, the essential bandstructure parameters (bandgap, effective masses, and the density-of-states) have been computed using a 20-band nearest-neighbour \textit{sp}$^{3}d^{5}s^{\ast }$ tight-binding scheme. [Preview Abstract] |
Thursday, March 6, 2014 10:00AM - 10:12AM |
S44.00011: Fabrication of Si:P delta-doped layers with varying doping densities Tingbin Lim, Byron Villis, Samadhan Patil, Steven Schofield, Neil Curson, Gabriel Aeppli We are developing a programme to fabricate atomic scale device structures of phosphorus atoms in a silicon substrate. The first step in this process is the fabrication of 2D Si:P delta-doped layers in silicon, which have recently also been theoretically studied in terms of electrical transport by Hwang and Das Sarma (E. H. Hwang and S. Das Sarma, \textit{Phys. Rev. B}, \textbf{87}, 125411). The Si:P delta-doped layers are expected to exhibit interesting behaviors when the density of the P atom doping is varied through the metal-insulator transition, as well as for the high ($\sim$ 10$^{14}$ per cm$^{2})$ and low (below 10$^{13})$ doping regimes. We are fabricating Si:P delta-doped layers of varying densities from around 6 x 10$^{12}$ to 2 x 10$^{14}$ P atoms per cm$^{2}$, which we will use to experimentally assess the theoretical findings of Hwang and Das Sarma. Details of the fabrication process will also be discussed. [Preview Abstract] |
Thursday, March 6, 2014 10:12AM - 10:24AM |
S44.00012: Changes in surface chemical structure of BF$_{3}$ plasma doped Si$_{0.7}$Ge$_{0.3}$ films Jinwon Ma, Woo-Jung Lee, Jungmin Bae, Seunghoon Oh, Jeonghun Kim, Yuseon Kang, Mann-Ho Cho, Dae-Hong Ko, Yongseo Ahn, Hyungsub Kim, Snag-Il Seo, Nam-Hun Kim Ultra shallow junctions were formed using BF$_{3}$ plasma doping process in Si$_{0.7}$Ge$_{0.3}$ films. The damaged Si$_{\mathrm{x}}$Ge$_{\mathrm{y}}$ layer of a few {\AA} was observed in near surface region of doped Si$_{0.7}$Ge$_{0.3}$ films, which increased especially the interfacial germanium oxide states. While the surface oxide layer of as-grown Si$_{0.7}$Ge$_{0.3}$ film was mainly composed of silicon oxide, the oxide layers of doped Si$_{0.7}$Ge$_{0.3}$ films were largely composed of germanium oxide. It is reported that the interfacial GeO$_{\mathrm{2-x}}$ states are related with the interfacial defect states. In the doped films, however, GeO$_{\mathrm{2-x}}$ states were decreased after rapid thermal annealing (RTA) process. In especially, after RTA of doped sample with process conditions of 300 W and 30 s, it is shown that the formation of interfacial defect states were significantly decreased, which was caused by the Ge-F bond generated on the SiGe surface. [Preview Abstract] |
Thursday, March 6, 2014 10:24AM - 10:36AM |
S44.00013: Energetics and Diffusion of Gold in Bismuth Telluride Michael Shaughnessy, Norm Bartelt, Jonathan Zimmerman, Josh Sugar We investigate experimentally and theoretically the long-term chemical and morphological stability of Au contacts on Bi$_2$Te$_3$. Electron microscopy and energy dispersive spectroscopy experiments show that thermal annealing severely degrades the integrity of micron-thick Au films, eventually leading to their complete dissolution. To explain this result, we have used density functional theory to calculate defect formation energies and diffusion barriers of Au within Bi$_2$Te$_3$. We identify an interstitial binding site consistent with previous reports of (rapid) anisotropic diffusion of Au in Bi$_2$Te$_3$. We find, however, that substitutional Au has lower formation energies. We suggest that these substitutional defects may be active in our experiments and account for the relatively long time scale of the contact degradation. [Preview Abstract] |
Thursday, March 6, 2014 10:36AM - 10:48AM |
S44.00014: ABSTRACT WITHDRAWN |
Thursday, March 6, 2014 10:48AM - 11:00AM |
S44.00015: 1/f noise in micrometer-sized ultrathin ITO films Sheng-Shiuan Yeh, Wei-Ming Hsu, Jui-Kan Lee, Yao-Jen Lee, Juhn-Jong Lin By employing the ac bridge technique, we have measured the low frequency noises of micrometer-sized ultrathin indium tin oxide (ITO) films at room temperature to investigate the effect of post thermal annealing on the noise level. The noises in all the samples studied reveal an approximate $1/f$ form in the frequency range $f \approx$ 0.1--20 Hz. The microstructures and grain sizes of our films were altered by adjusting the thermal annealing conditions. An enhancement of the noise level was observed for those samples comprising smaller grains, where larger amounts of grain boundaries exist. This enhancement in the noise level may be ascribed to atomic diffusion along grain boundaries or dynamics of two-level-systems near the grain boundaries. [Preview Abstract] |
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