Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session B11: Compound and Oxide Semiconductors |
Hide Abstracts |
Sponsoring Units: FIAP Chair: Nelson Tansu, Lehigh University Room: D222 |
Monday, March 21, 2011 11:15AM - 11:27AM |
B11.00001: Terahertz radiation mechanism of native $n$-Type InN with different carrier concentrations Kuang-I Lin, Jung-Tse Tsai, Jenn-Shyong Hwang, Hon-Way Lin, Shangjr Gwo, Meng-Chu Chen InN has received considerable attention due to its lower effective mass, higher mobility, and higher velocity saturation compared with GaN or AlN. The fundamental band gap of InN has recently been reevaluated to be around 0.6--0.7 eV, being therefore a promising candidate for terahertz (THz) applications. In this study, the polarity and mechanism of THz radiation from native $n$-type InN excited by femtosecond optical pulses are investigated. The optical properties, electron concentrations, and crystalline quality are characterized by photoluminescence and Raman scattering spectra. The electron concentrations are estimated to be between 0.35$\times $10$^{19}$ and 3.87$\times $10$^{19}$ cm$^{-3}$. The intensity ratio of the $A_{1}$(LO) to $E_{2}$(high) mode increases with increasing electron concentration. The polarity of THz radiation field from the samples with higher electron concentrations is opposite to that from $p$-InAs, indicating that the dominant radiation mechanism is the drift current. However, the samples with lower electron concentrations show the same polarity as $p$-InAs. Under this condition, the radiation mechanism is dominated by the photo-Dember effect. [Preview Abstract] |
Monday, March 21, 2011 11:27AM - 11:39AM |
B11.00002: Self-confined GaN hetero-phased quantum wells Yu-Chi Hsu, Ikai Lo, Chia-Ho Hsieh, Wen-Yuan Pang, Mitch M.C. Chou, Yen-Liang Chen, Cheng-Hung Shih, Ying-Chieh Wang Wurtzite/zinc-blende/wurtzite GaN hetero-phased quantum wells (QWs) were grown by plasma-assisted molecular beam epitaxy. A self-assembling mechanism was used to simulate the hetero-phased QW, in which a wurtzite/zinc-blende phase transition was created by rotating the threefold symmetric N-Ga vertical bond of wurtzite 60$^{\circ}$. From the cathodoluminescence measurement, we observed an additional peak (energy $\sim $3.2eV) associated with GaN zinc-blende phase. From the transmission electron microscopy images and selective area electron diffraction patterns, we confirmed the formation of hetero-phased quantum wells with a transition of wurtzite/zinc-blende GaN [1]. \\[4pt] [1] I. Lo, Y.-C. Hsu, C.-H. Hsieh, W.-Y. Pang, M. M.C. Chou, Y.-L. Chen, C.-H. Shih, and Y.-C. Wang, Appl. Phys. Lett. \underline {\textbf{96}}, 222105 (2010). [Preview Abstract] |
Monday, March 21, 2011 11:39AM - 11:51AM |
B11.00003: Growths of InGaN Quantum Wells on GaN Micropyramids Renbo Song, Le Zhao, Guangyu Liu, Jing Zhang, Nelson Tansu Selective area epitaxy (SAE) of InGaN quantum wells on GaN micropyramids were grown by using metalorganic chemical vapor deposition (MOCVD). The pattern prepared for the SAE was fabricated by the deposition of 300 nm SiO$_{2}$ film on n-type GaN substrate by using plasma enhanced chemical vapor deposition (PECVD) and followed by photolithography. The grown micropyramid structures were characterized by scanning electron microscope (SEM) and photoluminescence (PL). Uniformly-distributed defect-free GaN micropyramids were observed by SEM. The growths of InGaN quantum wells were performed on the GaN micropyramids, and broadband luminescence were observed from the PL measurements applicable for white light-emitting diodes applications. [Preview Abstract] |
Monday, March 21, 2011 11:51AM - 12:03PM |
B11.00004: Charge Carriers in Boron Nitride Nanotubes Appear to confirm Quantum Capillary Action Richard Kriske A recent article in Physics Today confirmed a previous Theory put forward by this author in that electrons and perhaps other fundamental particles should find the easiest transmission path to be in the center of nanotubes not on the walls. Of course this is somewhat astonishing in that the center of the tube has nothing in it. This author had previously suggested that this might ultimately give a quantum mechanical explaination for capillary action. In any case a model could now be confirmed that this author previously put forward to show that in many cases the flow of particles should occur in the centers of nanotubes not on the walls and this would allow the exploration of the use of nanotubes as reaction devices, and transport devices with a general theory to show how molecules as well as elementary particles could be transported down the centers of these tubes and reacted in the tubes or in chambers attached to the tubes. This would also explain some vexing biological problems involving tubes and capillary action. [Preview Abstract] |
Monday, March 21, 2011 12:03PM - 12:15PM |
B11.00005: Transport Electron Scattering by Structural Defects in InSb Quantum Wells T.D. Mishima, M.B. Santos Among all the binary III-V semiconductors, InSb has the highest electron mobility and the narrowest band-gap. Field effect transistors and magnetic-field sensors are examples of devices based on InSb quantum wells (QWs) that exploit these material properties. In this study, we have investigated electron scattering due to two dominant structural defects, micro-twins (MTs) and threading dislocations (TDs), in InSb QWs grown on GaAs (001) substrates via AlInSb buffer layers. A linear regression analysis shows that the room-temperature electron mobility in InSb QWs has a strong correlation with the densities of both MTs and TDs, with an $R^{2}$ value of 0.9791. The MT-originated energy barrier and reflection coefficient for electron conduction in InSb QWs are estimated to be 0.09 eV and 0.33, respectively. The TD-limited electron mobility in InSb QWs is explained by electric charge with a density of 1.3 $\times$10$^{-10}$ C/m along a TD line. In addition to further discussion of the data, we will show the derivations of some key equations used for the mathematical analyses. This work was supported by the NSF under Grants Nos. DMR-0520550 and DMR- 0808086. [Preview Abstract] |
Monday, March 21, 2011 12:15PM - 12:27PM |
B11.00006: Strain, Confinement and Density Dependence of the Effective Mass of Holes in InSb Quantum Wells Chomani Gaspe, M. Edirisooriya, T.D. Mishima, R.E. Doezema, M.B. Santos, L.C. Tung, Y.J. Wang The valence band structure in a III-V quantum well (QW) is complicated by the presence of two highly non-parabolic bands. The lower (higher) energy band has a hole mass that is lighter (heavier) for motion in the plane of the QW. The energy separation between the two bands increases with increasing biaxial compressive strain and decreasing well width. An expected anticrossing between the two bands can add significantly to their non-parabolicity. We report an experimental study of the effective mass of 2D holes in a series of remotely doped InSb QWs under biaxial compressive strain. Only the lower energy band is occupied at low tempearture. Cyclotron resonance measurements at 4.2K show that the hole effective mass increases with increasing hole density from 0.045m$_{e}$ at 2.1$\times $10$^{11}$ cm$^{-2}$ to 0.083m$_{e}$ at 5.1$\times $0$^{11}$ cm$^{-2}$. The smallest effective mass of 0.017m$_{e}$ was observed in the QW with the largest compressive strain (1.06{\%}) and narrowest well width (7nm). This work was supported by the NSF Grants Nos. DMR-0520550 and DMR-088086. [Preview Abstract] |
Monday, March 21, 2011 12:27PM - 12:39PM |
B11.00007: Carrier and Spin Dynamics in Narrow Gap Parabolic Quantum Well Structures M. Bhowmick, T. Merritt, G.A. Khodaparast, T.D. Mishima, M.B. Santos, D. Saha, G.D. Sanders, C.J. Stanton Heterostructures with parabolic confinement potentials are important systems to study for many reasons. In a perfect Parabolic Quantum Well (PQW), the subbands are equally spaced and electron-electron interactions are virtually non-existent, allowing coupling of long-wavelength radiation only to the center-of-mass coordinate of the electron system. Narrow band PQW systems are well suited for THz devices because by careful design, one can tune the transition frequency, temperature stability, and narrow-band emission. In our studies, the parabolic confinement was created by an effective parabolic Al compositional gradient inside each well. We studied carrier/spin dynamics in an InSb/$Al_{x}In_{1-x}Sb$ multiple- PQW structure using several time resolved differential transmission schemes in the mid-infrared. Our results demonstrate the unique and complex dynamics in InSb heterostructures that can be important for electronic and optoelectronic devices. [Preview Abstract] |
Monday, March 21, 2011 12:39PM - 12:51PM |
B11.00008: Electrical characterization of GeSn grown on Si using ultra high vacuum chemical vapor deposition method Mo Ahoujja, S. Elhamri, J. Kouvetakis, J. Tolle, Mee Yi Ryu, Y.K. Yeo Recently, there has been considerable interest in growing Ge$_{1-x}$Sn$_{x}$ alloys on Si with x$<$ 0.2 for the purpose of developing optoelectronic devices that can be integrated with Si-based electronic technology. Here we report Hall coefficient and resistivity measurements as a function of temperature from thin epitaxial layers of GeSn grown on Si substrates using ultra high vacuum chemical vapor deposition. The Hall measurements show that GeSn samples with Sn concentrations of 1.5 and 2 {\%} are of high quality. The hole concentration for the boron doped Ge$_{0.98}$Sn$_{0.02}$ sample at room temperature is 7.1x10$^{18}$ cm$^{-3}$ while that of the as-grown undoped sample is 9.8x10$^{16}$ cm$^{-3}$. The measured hole mobility for Ge$_{0.98}$Sn$_{0.02}$ alloys with carrier concentrations greater than 10$^{18}$ cm$^{-3}$ are found to be comparable to those found in Ge samples with similar doping concentrations. [Preview Abstract] |
Monday, March 21, 2011 12:51PM - 1:03PM |
B11.00009: An extensive study to observe the effects of thermal annealing and ion fluences in the ion beam synthesis of $\beta $-SiC P.R. Poudel, B. Rout, D.R. Diercks, F.D. McDaniel, J.A. Paramo, Y.M. Strzhemechny A systematic study of the formation of $\beta $-SiC structures by low energy carbon ion (C$^{-})$ implantation into Si followed by high temperature thermal annealing will be presented. The effects of thermal annealing in the formation of $\beta $-SiC structures has been studied. It is observed that the thermal annealing of 1100\r{ }C for 1 hr is required to observe the formation of $\beta $-SiC. The quantitative analysis in the formation of $\beta $-SiC nanostructures has been performed by the implantation of various carbon ion fluences in the range of 1$\times $10$^{17}$ - 8$\times $10$^{17}$ atoms /cm$^{2}$ at an ion energy of 65 keV into Si. It is observed that the average size of $\beta $-SiC crystals decreases whereas the amount of $\beta $-SiC increases monotonically with ion fluence up to a fluence of 5 $\times $ 10$^{17}$ atoms/cm$^{2}$ and appears to saturate for a higher fluence of 8 $\times $ 10$^{17}$ atoms/cm $^{2}$ when the samples were annealed at 1100\r{ }C for 1 hr. The stability of graphitic C-C bonds at 1100\r{ }C limits the growth of SiC precipitates in the sample implanted at a fluence of 8$\times $10$^{17}$ atoms /cm$^{2}$ which results in the saturation behavior of SiC formation in the present study as predicted by various characterization techniques such as FTIR, Raman, XRD, XPS and Transmission electron microscopy. [Preview Abstract] |
Monday, March 21, 2011 1:03PM - 1:15PM |
B11.00010: Complimentary Ferromagnetic Mechanisms in Mn doped ZnO Thin films deposited using Pulsed Laser Ablation Devajyoti Mukherjee, Tara Dhakal, Hariharan Srikanth, Pritish Mukherjee, Sarath Witanachchi We show evidence through experiments and analysis that the ferromagnetism (FM) in 2{\%} Mn doped ZnO (ZMO) thin films is a combination of two complementary mechanisms - the bound magnetic polaron (BMP) percolation at low temperatures and the Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange interaction at higher temperatures. Pulsed laser deposition was used to grow ZMO thin films on c-cut sapphire substrates. Films were deposited at various temperatures and background oxygen pressures to study the effect of growth parameters on the FM. While no impurity-phase contributions were detected, a strong correlation between effective carrier densities and FM was established. FM in amorphous films with high defect densities were described by the BMP model whereas that in highly conducting films was consistent with the RKKY mechanism. Detailed characterization of the structural, electrical and magnetic properties of the as-deposited ZMO films will be presented. [Preview Abstract] |
Monday, March 21, 2011 1:15PM - 1:27PM |
B11.00011: Excitation of atomic zinc during excimer laser ablation of zinc oxide at 193 nm Enamul Khan, Stephen Langford, Thomas Dickinson Atomic excitations during UV laser ablation usually involve collisions with energetic electrons. When zinc oxide is ablated with a 193 nm excimer laser, we observe light emission at pulse energies ---well below the threshold for normal electron heating processes. At pulse energies near the threshold for visible light emission, the source is localized and moves away from the surface at a nearly constant velocity. Time-resolved quadrupole mass spectrometry confirms the presence of zinc atoms with velocities consistent with this motion. We propose that these excited zinc atoms are generated by two-photon excitation into the autoionizing 3d$^{10}$4p ($^{2}$P\r{ }$_{3/2})$ 5s~ $^{2}$[3/2]\r{ } state of atomic zinc at 103 001~cm$^{-1}$. The broad ``window resonance'' associated with this state in single-photon absorption is associated with a \textit{drop} in absorption, because the main decay channel (ionization) is hindered by destructive interference effects. We propose that radiative decay, which is otherwise a minor decay channel, produces bound excited states that subsequently decay to yield the observed light. [Preview Abstract] |
Monday, March 21, 2011 1:27PM - 1:39PM |
B11.00012: Role of ligands on the photoluminescence of colloidal CdSe quantum dots and enhancement of photoconductivity of ZnO nanowires by quantum dots Syamanta Kumar Goswami, Tae Soo Kim, Byoung Woo Lee, Eunsoon Oh, Ch. Kiran Kumar, Eui Tae Kim Colloidal core-shell CdSe/ZnS quantum dots (QDs) encapsulated by trioctylphosphine oxide ligand were synthesized via pyrolysis. Then the TOPO ligands by 3-mercaptopropionic acid ligands were replaced under Ar environment. ZnO nanowires were fabricated by sonochemical method on pre-patterned alumina electrodes. With increasing temperature above 220 K, the PL lifetime was found to be increased in case of the TOPO capped QDs, whereas for the MPA capped QDs, the lifetime was short and almost independent of temperature. The conductivity of ZnO nanorods was increased after the deposition of the QDs, which was further enhanced by the exposure of light. This increase in the conductivity with and without light can be explained by the photo-carrier transport and surface modification effect, respectively. The photo-generated electrons in the CdSe QDs will tend to move toward the ZnO nanowires, resulting in the enhancement of photo-conductivity in the ZnO nanowires. [Preview Abstract] |
Monday, March 21, 2011 1:39PM - 1:51PM |
B11.00013: Preparation and characterization of nanostructured ZIO thin films Vipin Kumar Jain, Praveen Kumar, Y.K. Vijay ZnO--In2O3 system has attracted much attention because of chemical and thermal stability in addition to properties comparable to those of ITO. In the present work Zinc indium oxide (ZIO) thin films were deposited on glass substrate with varying concentration (ZnO: In2O3 - 100:0, 90:10, 70:30 and 50:50 wt {\%}) at room temperature by flash evaporation technique. These deposited ZIO films were annealed in vacuum to study the thermal stability and to see the effects on the structural, chemical and electrical properties. Each film has been characterized ex-situ by XRD, XPS, XRF, AFM, SEM, optical band gap and Hall measurements. Results show the properties of the ZIO films strongly depend on the In2O3 concentration and also influenced by the post annealing of these films. XPS core level spectra of Zn(2p), O(1s) and In(3d) have been deconvoluted into their Gaussian components, while valence band spectra shows the change in electronic structures of the films. [Preview Abstract] |
Monday, March 21, 2011 1:51PM - 2:03PM |
B11.00014: M-plane ZnO grown on m-plane sapphire by radio-frequency magnetron sputtering Bi-Hsuan Lin, Wei-Rein Liu, Shao-Ting Hsu, Chin-Chia Kuo, Song Yang, Chia-Hung Hsu, Wen-Feng Hsieh High quality m-plane orientated ZnO films with in-plane epitaxial relationship of (0002)$_{ZnO}\vert \vert $(11-20)$_{sapphire}$ and (11-20)$_{ZnO}\vert \vert $(0006)$_{sapphire}$ have been successfully grown on m-plane sapphire by using radio-frequency magnetron sputtering. The introduction of a nanometer thick low temperature grown ZnO buffer layer effectively eliminated other undesirable orientations. The significant anisotropy of the strain field breaks the hexagonal symmetry and leads to the different physical properties from that of c-plane oriented ZnO films. The structural properties, including crystalline quality, strain state, and defect structures, of the m-plane ZnO layers are thoroughly examined by synchrotron x-ray scattering, transmission electron microscopy and atomic force microscopy. The optical properties are investigated by temperature, polarization as well as power dependent photoluminescence, and polarization dependent Raman spectroscopy. The correlation between the structural and optical properties will be discussed. [Preview Abstract] |
Monday, March 21, 2011 2:03PM - 2:15PM |
B11.00015: Phase diagram, structure, and electronic properties of (Ga$_{1-x}$Zn$_x$)(N$_{1-x}$O$_x$) solid solution Li Li, Philip B. Allen We studied (Ga$_{1-x}$Zn$_x$)(N$_{1-x}$O$_x$) solid solution by Density Functional Theory (DFT). To conduct thermodynamic simulations, we built a database of structures and constructed a Cluster Expansion(CE). The subsequent Monte Carlo simulation gives a calculated phase diagram with a wide miscibility gap and an ordered $x$=0.5 compound. The disordered phase displays strong short range ordering (SRO) at experimental temperatures. We then used snapshots from MC to investigate structural and electronic properties by DFT on large supercells. Consistent with previous theoretical and experimental findings, lattice parameters appear to deviate from Vegard's law with small upward bowing. Bond lengths depend strongly on local environment, with a variation much larger than the difference of bond length between ZnO and GaN. The downward band gap bowing deviates from parabolic by having more rapid onset of bowing at low and high concentrations. Our results show that SRO influences both the structural and electronic properties. [Preview Abstract] |
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