Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session P25: Focus Session: Dopants and Defects in Semiconductors - III-V's |
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Sponsoring Units: DMP Chair: Volkmar Dierolf, Lehigh University Room: D135 |
Wednesday, March 17, 2010 8:00AM - 8:12AM |
P25.00001: Symmetry of the H-N-H center in dilute III-N-V alloys determined by vibrational spectroscopy with applied stress M. Stavola, L. Wen, F. Bekisli, W.B. Fowler, R. Trotta, A. Polimeni, M. Capizzi, F. Martelli, S. Rubini The addition of a few percent of N to GaAs causes a large reduction in the band gap. The further addition of H causes the band gap to recover to the value of the N-free host [1]. IR spectroscopy and theory have found a canted H-N-H defect structure with C$_{1h}$ symmetry that is responsible for this surprising behavior caused by N and H [2-5]. A uniaxial-stress study of the IR lines of the H-N-H center has been performed. The splitting of the IR lines by stress confirms the C$_{1h}$ symmetry proposed by theory and yields an estimate of the canting angle of the center. The application of stress also gives rise to dichroism from which the lowering of the energy that results from the canting of the defect is determined. \\[4pt] [1] A. Polimeni \textit{et al}., Phys. Rev. B\textbf{63}, 201204 (2001). \\[0pt] [2] S. Kleekajai \textit{et al.}, Phys. Rev. B\textbf{77}, 085213 (2008). \\[0pt] [3] W. B. Fowler \textit{et al}., Phys. Rev. B\textbf{72}, 035208 (2005). \\[0pt] [4] M.-H. Du \textit{et al.}, Phys. Rev. B\textbf{72}, 073202 (2005). \\[0pt] [5] G. Ciatto \textit{et al.}, Phys. Rev. B\textbf{71}, 201301 (2005). [Preview Abstract] |
Wednesday, March 17, 2010 8:12AM - 8:24AM |
P25.00002: Probing the microstructure of the Si-N defect in GaAs John Buckeridge, Stephen Fahy The addition of N to Ga(In)As causes a dramatic decrease in the energy band gap. However Si doping of Ga(In)N$_{x}$As$_{1-x}$ after rapid thermal annealing results in a highly resistive material with an energy band gap governed by a net `active' N roughly equal to the total N content minus the Si concentration. In order to understand this mutual passivation effect two defect complexes have been proposed: (a) Si and N substituting on adjacent Ga and As sites, and (b) Si and N atoms forming a split-interstitial defect on an As site. We present results of density functional theory (DFT) calculations on the full spectrum of localized vibrational mode of these defects, which can be used as experimental probes in determining the presence of either defect complex. We also present results of DFT calculations of the formation energies of the defects, confirming previous calculations [A. Janotti \textit{et al.}, Phys. Rev. Lett. 100, 045505 (2008)]. We agree with their conclusions that the split-interstitial is the more likely configuration at the experimental annealing temperatures. [Preview Abstract] |
Wednesday, March 17, 2010 8:24AM - 8:36AM |
P25.00003: Origin of Persistent Photoconductivity Effect in GaAsN Alloys Yu Jin, Hailing Cheng, Ryan Jock, Cagliyan Kurdak, Rachel Goldman (In)GaAsN alloys with a few percent nitrogen have potential applications in many long wavelength optoelectronic devices. However, the formation of point defects, such as N interstitials and Si-N complexes, has been predicted to substantially limit the optical emission efficiency and minority carrier transport of (In)GaAsN. Here, we report a persistent photoconductivity (PPC) effect associated with N interstitial-related defects in GaAsN films. In our GaAsN films, PPC was observed up to 160K, with a photo-capture barrier of 350 - 400 meV. Meanwhile, low $T$ transport measurements reveal two regimes of carrier concentration, $n$, a $T$-independent regime above 150K and a thermally-activated regime below 150K. These two phenomena are reminiscent of the behavior of n-type AlGaAs due to the presence of DX-center levels, suggesting the presence of similar N-induced defect levels in GaAsN. Furthermore, after annealing, the PPC effect is suppressed and $n$ increases substantially. Our recent nuclear reaction analysis revealed that the interstitial N concentration is decreased by RTA. Therefore, the RTA-induced suppression of the PPC and the increase of $n$ in GaAsN suggest their association with N interstitials. [Preview Abstract] |
Wednesday, March 17, 2010 8:36AM - 8:48AM |
P25.00004: Measurement of [N] dependence of electron effective mass in GaAsN Tassilo Dannecker, Yu Jin, John Buckeridge, Ctirad Uher, Cagliyan Kurdak, Stephen Fahy, Rachel S. Goldman The electron effective mass of GaAs$_{1-x}$N$_{x}$ is predicted to be dependent on N-composition, x; however, conflicting results have been observed using cyclotron resonance and thermomagnetic measurements. Using room temperature thermopower and Hall measurements, in conjunction with assumptions of parabolic bands and Fermi-Dirac statistics, we determined the N composition dependence of the electron effective mass of GaAs$_{1-x}$N$_{x}$, in comparison with that of GaAs. Measurements of the Seebeck coefficient, S, for N compositions ranging from x=0 to 0.018, reveal a decrease in S with increasing x. The free carrier concentration, [n], for all GaAsN is lower than for GaAs. For GaAs, we extract an effective mass value of 0.052m$_{e}$, slightly lower than the literature value of 0.067m$_{0}$. For GaAsN, the effective mass apparently is in all cases greater than for GaAs but varies non-monotonically with x, revealing a minimum at x=0.010 and maxima at x=0.004 and 0.018. This non-monotonic dependence of m* on x cannot be explained with a simple band anti-crossing (BAC) model. Interestingly, this data is consistent with the predictions of Lindsay et al, suggesting the presence of resonances between N-related states and the GaAsN conduction band edge. [Preview Abstract] |
Wednesday, March 17, 2010 8:48AM - 9:00AM |
P25.00005: Deep Level Defects in Epitaxial GaAsBi/GaAs Zenan Jiang, D.A. Beaton, R.B. Lewis, I. Koslow, X.D. Chen, T. Tiedje, P.M. Mooney Bismuth incorporation in GaAs produces a much larger reduction in the band gap than In or Sb alloying, for the same increase in lattice constant. However, Bi is incorporated only at growth temperatures $<$400\r{ }C, making deep level defects a concern. Both GaAs layers and p-i-n structures containing a GaAsBi quantum well in the i-layer having a bismide fraction up to 4.7{\%} were grown by molecular beam epitaxy in the range 285-580\r{ }C. Deep level transient spectroscopy (DLTS) measurements of GaAs layers show several different traps, depending on the doping type and growth temperature, but all in concentration $<$5$\times $10$^{14}$ cm$^{-3}$. Similarly, the DLTS spectra from p-i-n devices vary with the growth conditions and with the bismide fraction and trap concentrations are $<$1$\times $10$^{15}$ cm$^{-3}$. These DLTS results are consistent with strong photoluminescence\footnote{X. Lu, et al., Appl. Phys. Lett. \textbf{95}, 041903 (2009).} and electroluminescence\footnote{R.B.Lewis, et al. J. Crystal Growth \textbf{311}, 1872-75 (2009)} from GaAsBi quantum wells having bismide fraction $\leq$5{\%}. The properties of these traps will be discussed. [Preview Abstract] |
Wednesday, March 17, 2010 9:00AM - 9:12AM |
P25.00006: Spectroscopic Evidence for ``Optically Relevant Defects'' in the Optically-Pumped NMR of Semi-Insulating GaAs Sophia Hayes, Kannan Ramaswamy, Xingyuan Pan, Christopher Stanton We probe the interaction of electrons localized at ``optically-relevant'' defect sites in GaAs on the surrounding Ga nuclear spins. Simulations of the spatial dependence of nuclear spin polarization have been employed to map the origin of the different lineshapes, and these follow the both the size and sign (spin orientation) of the electron spin polarization. Optically pumped NMR (OPNMR) provides information about electron-nuclear hyperfine interactions in such systems can be derived by measuring dynamic processes (e.g., nuclear spin relaxation) and static processes (e.g., hyperfine shifts). NMR lineshapes also provide insights into the spatial extent of such hyperfine interactions. In III-V cubic semiconductors, the broadening of conventional NMR spectra can arise from a number of factors. The lineshapes of $^{69}$Ga spectra of semi-insulating GaAs (si-GaAs) under optical pumping conditions exhibit additional broadening, which was theoretically predicted in earlier work, although not experimentally observed. In this presentation, we discuss the experimental observation of such OPNMR lineshapes, in addition to spatial mapping the nuclear polarization around the site of electron localization at an optically-relevant defect, such as substitutional defects in the si-GaAs lattice. [Preview Abstract] |
Wednesday, March 17, 2010 9:12AM - 9:24AM |
P25.00007: Charge Switching of Donor Ensembles in a Semiconductor Rainer G. Ulbrich, Karin Teichmann, Martin Wenderoth, Sebastian Loth, A.P. Wijnheijmer, J.K. Garleff, P.M. Koenraad We report charge switching of well-defined groups of individual donors in GaAs controlled by a scanning tunneling tip with atomic resolution [1,2]. Lateral positioning and voltage tuning of the band-bended region under the sharp tip allows to measure at low temperature, T = 5 K, the ionization threshold of each given donor site with high precision. The changing charge states of surrounding donors give rise to discrete ``Coulomb ladder'' steps in the screened electrostatic potential V(r) which is extracted for the nearest donor under the tip. In certain geometrical configurations we observe bias- and time-dependent flicker spectra. \\[4pt] [1] K.Teichmann et al., PRL 101, 076103 (2008)\\[0pt] [2] A.P.Wijnheijmer et al., PRL 102, 166101 (2009) [Preview Abstract] |
Wednesday, March 17, 2010 9:24AM - 9:36AM |
P25.00008: The density functional theory defect band gap in GaAs Peter A. Schultz Using a total energy method with detailed control of electrostatic boundary conditions, esp. the chemical potential for net charge, the computed charge transition levels of simple intrinsic defects in GaAs within density functional theory are presented. The levels are demonstrated to be converged with supercell size, and largely insensitive to the functionals and pseudopotentials used. The results accurately reproduce available experimental data. The range of defect levels, a defect band gap, spans a full experimental band gap regardless of the size of the Kohn-Sham gap of the underlying functional-pseudopotential context used. The defect band gap, based on extrapolated total energy differences, is a better predictor of the fundamental gap than the Kohn-Sham eigenvalue gap. Based on the quantitative predictions of the levels, these results lead to a reassessment of long-standing defect assignments in GaAs, reconciling seemingly contradictory observations. [Preview Abstract] |
Wednesday, March 17, 2010 9:36AM - 9:48AM |
P25.00009: Efficient $n$-type doping of zinc-blende III-V semiconductor quantum dots Lucas V. Besteiro, Luis Tortajada, Murilo L. Tiago, L.J. Gallego, James R. Chelikowsky, M.M.G. Alemany Semiconductors are intentionally doped $n$-type by replacing one host atom by an impurity atom that has one more electron. In the case of III-V semiconductors this can be done at both anion and cation sites. Here we show that III-V semiconductor nanocrystals with zinc-blende structure should not be doped by cation substitution, but rather by anion substitution. We found that, as result of quantum confinement, the formation of defects that affect the main characteristics of the dopants is favored when the nanocrystals are doped at the cation site. Our study is performed through first-principles calculations based on a real-space implementation of density-functional theory and pseudopotentials by using the PARSEC code. [Preview Abstract] |
Wednesday, March 17, 2010 9:48AM - 10:00AM |
P25.00010: Photoluminescence Microscopy of Defects in Ordered GaInP$_{2}$ Angelo Mascarenhas, Brian Fluegel The ternary semiconductor alloy GaInP$_{2}$ plays a very prominent role in High-Efficiency Multijunction Solar Cells as well as in Solid-State Lighting. The size-mismatch induced strain between the binary components leads to interesting phenomena such as spontaneous ordering. which result in dramatic changes to the electronic and optical properties of this alloy. In addition to bandgap lowering, spontaneous ordering is accompanied by defect-induced changes in the PL spectrum which are poorly understood. A broad band low energy band is uniformly present, and on a microscopic scale, extremely sharp emission lines (LEL) are seen in some samples. Attempts have been made to explain the LEL as transitions from regions where stacking faults induce quantum-confined heterostructures, however these fail to explain either the total dependence on sample growth, or the complete omnipresence of the LEL in samples where they do appear. A newly developed photoluminescence technique to probe the microstructure of these alloys will be discussed. [Preview Abstract] |
Wednesday, March 17, 2010 10:00AM - 10:12AM |
P25.00011: Microscopic crystalline stability of SiC, III-V, and II-VI crystals: generation of Frenkel pairs Piotr Boguslawski, Pawel Jakubas Applications of semiconductors in high-power/high-temperature devices require their structural robustness, which, at the microscopic level, is limited by generation of vacancy-interstitial Frenkel pairs (FPs). First principles calculations were used to analyze generation of FPs in SiC, GaN, ZnO, CdTe, ZnTe, and GaAs. Dramatic impact of injection currents on the process is stressed. We find that (i) in zinc blende crystals generation of FPs on cation sublattice is a few orders of magnitude more efficient than on the anion sublattice, while the opposite holds for GaN and ZnO, (ii) SiC, GaN, and GaAs are always structurally stable, with barriers of 5-10 eV. In contrast, in ZnTe and CdTe excess electrons reduce barriers from 3 to 1.4 eV, leading to degradation of II-VI light emitting diodes, (iii) in intrinsic ZnO the barriers are high, 5.5 eV. High p-type injection currents reduce the barrier to 3.5 eV, which is comparable to the band gap and may prevent high-power applications. A comprehensive analysis of the results is given. [Preview Abstract] |
Wednesday, March 17, 2010 10:12AM - 10:24AM |
P25.00012: InSb-based epilayers and quantum wells grown on off-axis and on-axis Ge(001) substrates by MBE Mukul Debnath, Tetsuya Mishima, Michael Santos, Khalid Hossain, Orin W Holland The highest electron and hole mobilities in quantum wells (QWs) at room temperature have been observed in QWs made of InSb and Ge, respectively. This provides a motivation for integrating InSb and Ge devices onto a single wafer. We report our investigation of the molecular beam epitaxy (MBE) of InSb epilayers and InSb/Al$_{x}$In$_{1-x}$Sb QWs on Ge(001) substrates that are on-axis or 6$^{o}$-off-axis. The formation of anti-phase domains (APDs) makes growth of high-quality InSb films on Ge a substantial challenge. Reflection high-energy electron diffraction patterns during growth indicate a two-domain and single-domain reconstruction for epilayers grown on on-axis and off-axis substrates, respectively. The narrowest X-ray rocking curve width is 215 arc sec for a 2.0-$\mu $m-thick InSb epilayer on an off-axis substrate. The room temperature electron mobility of a 4.0-$\mu $m-thick InSb epilayer was 1.5 times higher for growth on an off-axis Ge(001) substrate (53,500 cm$^{2}$/V-s) compared to growth on an on-axis substrate (34,500 cm$^{2}$/V-s). These data indicated that APDs are suppressed in the structures grown on off-axis Ge(001) substrates. [Preview Abstract] |
Wednesday, March 17, 2010 10:24AM - 10:36AM |
P25.00013: Dopant Induced Stress and Strain Enhanced Doping Junyi Zhu, Suhuai Wei, Gerald Stringfellow, Feng Liu We report an intriguing dopant induced electronic stress effect. A foreign dopant atom induces a lattice stress. Conventional dopant induced stress is due to the different atomic sizes between the dopant and host element. Here, we discovered an intriguing dopant induced electronic stress effect. First principles calculation reveals that even a dopant with the same atomic size as the host atom induces a lattice stress of electronic origin, because it has either one more or one less electron than the host. We also found that the electronic stress exhibits a nonlinear dependence on strain, different from the conventional atomic stress effect. In general, the competition between the atomic stress and electronic stress determines the overall stress induced by a dopant, which in turn determines how external strain will change the doping energy. [Preview Abstract] |
Wednesday, March 17, 2010 10:36AM - 10:48AM |
P25.00014: Ab-initio guided optimization of layered semiconductors (GaTe,GaSe) for Radiation Detection Applications Cedric Rocha Leao, Vincenzo Lordi The performance of high resolution semiconductor based radiation detectors at room temperature is hindered by intrinsic defects and accidental impurities. Experimental efforts to improve the properties of such materials are both time consuming and expensive, since they rely to a large extent on trial and error. In this talk, we show how a fully ab-initio approach allows ranking the most detrimental defects in a crystal in terms of carrier recombination and charge transport. The method was applied to gallium telluride and gallium selenide, both moderate gap layered semiconductors. Based on our results, we can tailor experimental processes to grow these semiconductors with optimal properties. This can be achieved by tuning the growth~ conditions to avoid the most harmful defects or by compensating them through the introduction of dopants that counteract their detrimental electronic behavior without adding significant scattering to propagating wavepackets in the material. [Preview Abstract] |
Wednesday, March 17, 2010 10:48AM - 11:00AM |
P25.00015: Tunneling Spectroscopy of GaAs Bilayer Hole System Nathaniel Bishop, YenTing Chiu, Mansour Shayegan, Emanuel Tutuc We measure tunneling between two two-dimensional (2D) GaAs (311)A hole layers with a density of about $3\!\times\! 10^{10} cm^{-2}$, and separated by about 23 nm (well width 15 nm, barrier width 8 nm). At very low interlayer biases, the tunneling data are similar to 2D GaAs electron samples. But at higher interlayer biases, typically in the range 400 to 600 and 1100 to 1200 $\mu$V, the spectra show additional conductance peaks. The side peaks move to higher bias at higher densities, and their positions also evolve with applied parallel magnetic field. We discuss possible origin of these anomalous side peaks. [Preview Abstract] |
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