Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session H21: Spectroscopic Studies of Semiconductors |
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Sponsoring Units: FIAP Chair: Norman Tolk, Vanderbilt University Room: 323 |
Tuesday, March 17, 2009 8:00AM - 8:12AM |
H21.00001: Two- and three-photon absorption of germanium in the mid-infrared Dongmin Seo, Leonard Feldman, Norman Tolk, Philip Cohen We have studied the nonlinear optical response of crystalline germanium using high-power infrared picosecond laser pulses at wavelengths ranging from 2.8 $\mu $m to 5.2 $\mu $m. Transmittance as a function of fluence at 2.8 $\mu $m and 4.4 $\mu $m were fitted by using two- and three-photon absorption, respectively. Data at 3.2, 3.6, and 4.0 $\mu $m, however, required consideration of simultaneous two- and three- photon absorptions in order to fit the experimental data. Transmittance as a function of wavelength further supports the onset of the two- and three-photon absorption at appropriate wavelengths. [Preview Abstract] |
Tuesday, March 17, 2009 8:12AM - 8:24AM |
H21.00002: Link between optical second-harmonic and reflectance-anisotropy spectroscopy of stepped Si(001) surfaces Robert Ehlert, Jinhee Kwon, Michael C. Downer Optical second-harmonic generation (SHG) and reflectance-anisotropy spectroscopy (RAS) are the two dominant noninvasive optical probes of electronic structure and chemical dynamics at surfaces, but underlying connections between these spectroscopies remain poorly understood. Here we combine spectroscopic SHG and RAS to characterize stepped Si(001) surfaces offcut toward [110] before and after dissociative adsorption of H$_2$ at the D$_B$ step edges. Such stepped surfaces provide attractive templates for self-directed growth of nanoscale structures, while SHG/RAS provide non-invasive in-situ sensors to guide and interpret step edge chemistry. Our major finding is that the broad negative step-induced feature of the RA spectrum around 3eV, and the spectrum of the step induced third order Fourier component of the SHG azimuthal anisotropy, show strikingly similar spectral shapes and dependencies on H$_2$ adsorption, suggesting that these features share a common microscopic origin in the step edges. Separate analysis with a simplified bond hyperpolarizability model indicates that chemically active step dangling bonds are dominant contributors to both SHG and RAS, and that hydrogen termination of the step edges alters both by redistributing oscillator strength from the dangling bond to step back bonds. [Preview Abstract] |
Tuesday, March 17, 2009 8:24AM - 8:36AM |
H21.00003: Photocurrent measurement on donor bound excitons in Si Na Young Kim, Darin Sleiter, Thaddeus Ladd, Katsuya Nozawa, Yoshihisa Yamamoto Donor bound excitons are formed when free excitons are captured by neutral donor impurities. Due to the spatial localization of exciton at the impurity site, the decay process of donor bound exciton state to neutral donor state features extremely narrow linewidth in energy. Utilizing this inherent feature, it would be feasible to identify nuclear spin states of the donor impurity resulting from the hyperfine interaction between phosphorus nucleus spin and electron spin. We study ensembles of phosphorus donor bound excitons in Si via photocurrent measurements at low temperatures since Auger non-radiative decay process is primarily dominant in an indirect band-gap semiconductor such as Si. We report electric and magnetic field effects on photocurrent signals of phosphorus donor bound excitons. [Preview Abstract] |
Tuesday, March 17, 2009 8:36AM - 8:48AM |
H21.00004: Polaronic effects in single doped GaAs quantum well . G. Martinez, M. Orlita, C. Faugeras, S. Deutschlander, P.Y. Yu, A. Riedel, R. Hey, K. Friedland Absolute magneto transmission experiments, for magnetic fields B up to 33 T, have been performed on a series of single GaAs quantum well with a width of 13nm, doped at a level Ns ranging from 2 to 7.5 10$^{11}$ cm$^{-2}$ and mobilities exceeding 10$^{6}$ cm$^{2}$/V/sec . The analysis of the spectra with a complete multi-dielectric model allows to extract the imaginary part of the electronic dielectric function which clearly exhibits different features for cyclotron energies higher than the phonon energies of GaAs. For the lower doped samples, the dependence on B of the damping parameter shows a pronounce increase when the energy exceeds the longitudinal optical phonon energy characteristic of polaronic effects. At higher fields this parameter increases once more resonantly showing a new interaction called ``X''. For Ns higher than 6 10$^{11}$cm$^{-2}$, only this new interaction is clearly visible though its amplitude decreases when increasing Ns. The origin of this new interaction is very likely related to mechanisms involving phonons. The different possibilities are discussed. [Preview Abstract] |
Tuesday, March 17, 2009 8:48AM - 9:00AM |
H21.00005: Anisotropy of plasmon-phonon coupling under intense optical excitation of GaAs. Amlan Basak, Hrvoje Petek The dependence of coherent optical processes in time-frequency domain on the polarization of pump and probe beams can shed light on different generation and detection mechanisms. Here, we report the response of (100) oriented n-doped GaAs (n$_{d}$=2x10$^{18 }$cm$^{-3})$ when excited to an e-h pair density n$_{exc}\sim $10$^{18}$-10$^{20}$ cm$^{-3}$ with a 10 fs laser pulse centered at 400 nm. Experiments are performed in the transient reflectivity and reflective electro-optic sampling geometries with various pump and probe orientations. Time domain signal showing plasmon-phonon oscillations has a weak pump polarization dependence indicating isotropic generation mechanism and strong probe polarization dependence revealing symmetry properties of various carrier-phonon interaction mechanisms. Fourier Transform analysis of the time domain signals at different probe orientations show both plasmon and phonon anisotropy. Results are discussed considering different possible carrier-phonon interaction mechanisms with different symmetry dependences. Frequency evolution of plasmon-phonon coupled mode with increasing photoexcited carrier density is consistent with the hole-phonon coupling in the high damping regime. [Preview Abstract] |
Tuesday, March 17, 2009 9:00AM - 9:12AM |
H21.00006: Photoluminescence of surface InAs quantum layer on GaAs(001) and the carrier dynamics Itaru Kamiya, Kosei Fukui The opto-electronic properties of self-assembled quantum dots (QDs) grown by epitaxial crystal growth, for instance InAs/GaAs(001) by MBE, have attracted great attention during the past few decades. Recently, there have been a number of reports on the properties of surface InAs QDs, where the QDs are not capped by GaAs and instead exposed to ambient, since such structure exhibits luminescence in the 1.5 micron regime. The growth of such QDs accompanies formation of a wetting layer (WL) which is typically a monolayer thick film of InAs. However, in the studies on InAs QDs, the contribution of the WL is often neglected, if not, not distinguished from those of the QDs. However, we find that surface WL exhibits unique properties, also providing information for better understanding those of the QDs. Here, using PL and PLE, we studied surface InAs WL and QDs grown on GaAs(001). We show that signals arising from the WL and QDs can be distinguished, and that they exhibit properties different from those of buried structures. Based on these results, we discuss the carrier dynamics in the near surface regime. [Preview Abstract] |
Tuesday, March 17, 2009 9:12AM - 9:24AM |
H21.00007: Determining the bandtail shape of highly Si-doped Al$_{0.3}$Ga$_{0.7}$As using persistent photoconductivity Jennifer Misuraca, Stephan von Molnar, Peng Xiong, Jelena Trbovic, Jun Lu, Jianhua Zhao, Hideo Ohno Highly Si-doped Al$_{0.3}$Ga$_{0.7}$As can be driven through the metal-insulator phase transition using persistent photoconductivity [1].~ Owing to the bi-stable nature of the Si donor, samples cooled in the dark are insulating. In the present work, an infrared LED is used to photodope the sample at 5K for a range of illumination times, which populates shallow states and provides a way to change the carrier concentration of the sample\textit{ in situ}.~ Measuring the carrier concentration as a function of temperature allows for the infinite temperature carrier concentrations and Hall activation energies to be extracted for various illumination times as the Fermi energy is tuned systematically.~ Application to Si- doped Al$_{0.3}$Ga$_{0.7}$As prepared by MBE allows one to infer the bandtail shape [2] in the energy range between the Fermi energy of the unilluminated sample and the mobility edge. [1] S. Katsumoto, et al. J. Phys. Soc. Jpn. 56, 2259 (1987) [2] I. Terry, et al. Solid State Commun. 84, 235 (1992) [Preview Abstract] |
Tuesday, March 17, 2009 9:24AM - 9:36AM |
H21.00008: Effect of order/disorder near the $\Gamma $-L and L-X crossovers in the conduction band of lattice-mismatched Ga$_{x}$In$_{1-x}$P alloys L. Bhusal, M. Steiner, J. Geisz, A. Mascarenhas In this work we have studied the effect of order/disorder on the $\Gamma $-L and L-X crossover points in the conduction band of Ga$_{x}$In$_{1-x}$P alloys, using polarized photoluminescence and electroreflectance techniques at various temperatures. Ga$_{x}$In$_{1-x}$P samples (x=0.25-0.78) were grown by atmospheric pressure organometallic vapor phase epitaxy (OMVPE). Some samples were grown directly on a miscut GaAs substrate while in other samples a thick GaAsP step-grade was grown first, to reduce the dislocation density. The significance of the crossover point in the conduction band of the alloy for the efficiency of devices such as multijunction high-efficiency solar cells and light emitting diodes will be discussed. [Preview Abstract] |
Tuesday, March 17, 2009 9:36AM - 9:48AM |
H21.00009: Intersubband absorption in InAlN/GaN heterostructures O. Malis, C. Edmunds, M. J. Manfra, D. L. Sivco, R. Molnar Nitride superlattices are promising for intersubband light emission and detection in the currently inaccessible near-infrared range (2-3 $\mu $m). Efforts to exploits the nitride properties have been hampered so far by difficulties related to the quality of the materials. Most studies to date have employed AlGaN/GaN heterostructures. However, the large lattice mismatch between AlGaN and GaN limits the total thickness of the structures. We are focusing on lattice-matched InAlN/GaN superlattices. InAlN has been less investigated due to the challenges in growing high-quality In-containing nitrides. Nevertheless, the large conduction band offset (1 eV) and lack of piezoelectric effect make the lattice matched nitrides ideally suited for near-infrared applications. We have performed a detailed intersubband absorption study of InAlN/GaN superlattices grown by MBE on HVPE GaN templates. X-ray diffraction analysis suggests that our samples are among the highest quality ever reported. The band structure of the materials was examined with Fourier-transform infrared spectroscopy. Strong intersubband absorption in the 430-530 meV energy range is reported for the first time for 2-4.5 nm-wide quantum wells. [Preview Abstract] |
Tuesday, March 17, 2009 9:48AM - 10:00AM |
H21.00010: Beryllium acceptor binding energy in AlN. Ashok Sedhain, T. M. Al Tahtamouni, Jing Li, Jingyu Lin, Hongxing Jiang The acceptor binding energy of an alternative dopant, Be, in AlN epilayers has been probed by time-resolved photoluminescence (PL) spectroscopy. The binding energy of excitons bound to Be acceptors in AlN is determined to be about 33 meV, which implies that the Be acceptor binding energy in AlN is about 0.33 eV in accordance with Haynes' rule. The measured PL decay lifetimes of the acceptor-bound exciton transitions in Be- and Mg-doped AlN (93 and 119 ps, respectively) also indicate that the binding energy of Be acceptor is smaller than that of the most common acceptor dopant in AlN, namely, Mg. The smaller activation energy of Be in AlN has the potential to partly address the critical $p$-type doping issue in AlN- and Al-rich AlGaN by increasing the room temperature free hole concentration by $\sim $10$^{3}$ compared to the case of Mg doping. [Preview Abstract] |
Tuesday, March 17, 2009 10:00AM - 10:12AM |
H21.00011: Estimation of third-order nonlinear optical susceptibility $\chi ^{(3) }$of synthetic Cu$_{2}$O crystal Shahin Mani, Joon Jang, John Ketterson High-quality crystals of Cu$_{2}$O were prepared by an improved method for thermally oxidizing metallic copper. We report the nonlinear refractive index (n$_{2})$ and the nonlinear two-photon absorption coefficient ($\beta )$ of the resultant crystals. The following techniques were utilized: i) Z-scan, ii) third-harmonic generation, and iii) intensity-dependent interferometry. The third-order susceptibility ($\chi ^{(3)})$ of a material plays important role in optical signal processing including switching, altering the frequency and the transmission characteristics. A comparison between the third-order nonlinear susceptibilities of a standard nonlinear reference material, carbon disulfide (CS$_{2})$ and Cu$_{2}$O will be made. [Preview Abstract] |
Tuesday, March 17, 2009 10:12AM - 10:24AM |
H21.00012: Anomalous Fresnel coefficients for quadrupole polaritons in Cu$_{2}$O Joon Jang, Yi Sun, Shahin Mani, John Ketterson In a direct-gap semiconductor, a polariton is a quantum superposition of an exciton and a photon, formed near the light cone. Unlike dipole polaritons that have been strongly confined in a 2D microcavity structure, a quadrupole polariton in a bulk Cu$_{2}$O is a coherently propagating bosonic state with an unusually long decoherence time owing to its unusual underlying electronic structure. Therefore, this unique semiconductor provides a model system for studying the theory of so-called additional boundary conditions at the vacuum-crystal boundary. Using resonant two-photon excitation, we create a coherently propagating polariton wave packet at 2 K and measure its reflectance (R) and transmittance (T) at the boundary opposite to the incoming surface. Surprisingly, we find an enhanced reflection of polaritons from sample surfaces such that the ratio T/R deviates significantly from the present theory. This anomalous boundary effect most likely arises from the quadrupole excitonic (matter) component of polaritons. Our experimental results have implications for the design of polariton-based waveguides and resonators in which traveling polaritons are effectively confined in the medium. [Preview Abstract] |
Tuesday, March 17, 2009 10:24AM - 10:36AM |
H21.00013: Photoluminescence Characteristics of Pulsed Laser Deposited ZnO Thin Films Grown in Nitrogen/Oxygen Ambients M.A. Thomas, J.B. Cui, Y.C. Soo, H. Kandel, T.P. Chen, C.P. Daghlian ZnO thin films were grown by pulsed laser deposition using a Zn target in different atmospheres. The samples were characterized by SEM, XRD, EDX, and temperature dependent photoluminescence (PL) measurements. The growth conditions were varied sequentially from a pure oxygen to a pure nitrogen atmosphere, and the resulting changes of the material properties were investigated. The presence of nitrogen during growth was found to have a strong impact on the materials. Samples grown with higher nitrogen concentrations showed weak PL characteristics at room temperature as well as a small temperature dependence of the near band edge emission. At temperatures below 40 K, a sharp and pronounced emission peak was present at 3.362 eV. In an attempt to understand the PL characteristics, the samples were annealed in both pure oxygen and pure nitrogen environments at 600\r{ }C. The samples grown with large nitrogen ratios exhibited a strong dependence on the annealing atmosphere; those annealed in nitrogen showed a strong increase in emissions in the 3.362 eV range compared to the same samples annealed in oxygen. In addition, the defect emissions of the samples were strongly affected by the presence of nitrogen during annealing. The possible role of nitrogen in ZnO growth and annealing is discussed. [Preview Abstract] |
Tuesday, March 17, 2009 10:36AM - 10:48AM |
H21.00014: Optical properties of epitaxial ZnGeAs$_{2}$ thin film S.G. Choi, D.E. Aspnes, M. Van Schilfgaarde, T.J. Peshek, T.J. Coutts, A.G. Norman, J.M. Olson, D.H. Levi Chalcopyrite ZnGeAs$_{2}$ lattice-matched to GaAs(001) is a promising 1.1 eV band gap semiconductor for applications in nonlinear photonic devices and multijunction solar cells. Knowledge of the optical functions of a material over a wide photon energy range is of importance to optimize photonic and photovoltaic device structures. We present room-temperature optical properties of a ZnGeAs$_{2}$ thin film grown epitaxially on a GaAs(001) substrate by metalorganic vapor phase epitaxy. Spectroscopic ellipsometry was employed to measure the pseudodielectric function of the ZnGeAs$_{2}$ thin film, and was compared with a theoretical calculation within the quasiparticle self-consistent GW approximation. The interband-transition critical-point energies were obtained from a standard lineshape analysis of the measured spectrum. We will also present a comparison of the optical properties of ZnGeAs$_{2}$ with those of other II-IV-V$_{2}$ chalcopyrite compounds as well as their corresponding III-V zincblende compounds. This abstract is subject to government rights. [Preview Abstract] |
Tuesday, March 17, 2009 10:48AM - 11:00AM |
H21.00015: Electronic and optical properties of dilute Bismide alloys Rajeev Kini, Angelo Mascarenhas, Ryan France, Aaron Ptak We will present photoluminescence measurements of GaAs$_{(1-x)}$Bi$_{x}$ thin films containing dilute concentration ($x \quad \le $ 0.045{\%}) of isoelectronic impurity Bi. We observe that Bi induces strong perturbation to the host band structure even at these low concentrations and see no spectral evidence for isolated Bi forming a bound state in GaAs. Very similar to the case of Bi in GaP, we observed no Bi-Bi pair states. An `undulation' spectrum is observed which we attribute to the vibronic levels of acceptors. [Preview Abstract] |
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