Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session W19: Dopants and Defects in Semiconductors IV |
Hide Abstracts |
Sponsoring Units: DMP Chair: Matthew McCluskey, Washington State University Room: Morial Convention Center 211 |
Thursday, March 13, 2008 2:30PM - 2:42PM |
W19.00001: The role of nitrogen vacancies and hydrogen in conductivity of InN Anderson Janotti, Chris G. Van de Walle Using first-principles methods we investigate the electronic properties and stability of the nitrogen vacancy and monatomic hydrogen in InN. We find that nitrogen vacancies act as shallow donors, but they have high formation energies in $n$-type InN. Therefore, N vacancies are unlikely to cause the observed unintentional $n$-type conductivity in as-grown InN. Hydrogen can occupy interstitial as well as substitutional sites in InN. Interstitial hydrogen has low formation energy, is stable in the bond-center configuration, and acts exclusively as a shallow donor (H$_i^+$). The calculated frequency of the H-N stretching mode is 3050 cm$^{-1}$. Hydrogen can also substitute for nitrogen in InN, bonding equally to the four In nearest neighbors in a multicenter-bond configuration [1]. Substitutional hydrogen also has low formation energy and, counterintuitively, forms a double-donor center. Our results suggest that monatomic hydrogen is a plausible cause of the unintentional $n$-type conductivity that is almost universally observed in as-grown InN.\newline [1] A. Janotti and C. G. Van de Walle, Nature Mater. {\bf 6}, 44 (2007). [Preview Abstract] |
Thursday, March 13, 2008 2:42PM - 2:54PM |
W19.00002: Thermopower measurements of n- and p-type InN J. W. Ager III, N. R. Miller, R. E. Jones, W. J. Schaff, W. Walukiewicz InN has the largest electron affinity, 5.8 eV, of any known semiconductor. At its surface, the Fermi level is pinned ca. 0.9 eV above the conduction band edge, leading to an electron accumulation layer in n-type material and an inversion layer in p-type material. Recently, we have used capacitance-voltage measurements with an electrolyte contact to deplete the surface inversion layer in Mg-doped InN and observe space charge due to ionized acceptors {[}1{]}. However, these measurements do not give information about the proportion of acceptors that are ionized, or about hole transport. Here, thermopower measurements are used to deduce the majority carrier type under the surface inversion layer in Mg-doped InN. Observation of a positive Seebeck coefficient provides direct and definitive evidence of mobile holes in InN:Mg. Temperature-dependent measurements from 200-300 K are consistent with degenerate conduction in the highly doped films. Modeling of the experimental data to determine the carrier effective masses and scattering mechanisms will be presented. {[}1{]} R. E. Jones \emph{et al.}, \emph{Phys. Rev. Lett.} \textbf{96}, 125505 (2006). [Preview Abstract] |
Thursday, March 13, 2008 2:54PM - 3:06PM |
W19.00003: Site Selective CEES and Nearfield Optical Spectroscopy on Nd:GaN N. Jha, P. Capek, V. Dierolf, E. Readinger, G. Metcalfe, H. Shen, M. Wraback We perform spatially resolved CEES on Nd ions that are in-situ-doped into GaN epitaxial films on c-plane sapphire substrate grown by plasma assisted molecular beam epitaxy. For a wide range of concentration (up to 8{\%}) we find in the emission a dominant incorporation site, which can be identified with good certainty as a substitutional `Ga' site. While resonant excitation yields strong emission signals even at high temperatures, indicating good intrinsic quantum efficiency, above bandgap excitation of the dominant incorporation site is rather inefficient. The conclusion is further supported by the observation of additional weak peaks in the spectra attributed to above band-gap excitation of minority sites (with presumably better excitation efficiencies). For the majority site, confocal and NSOM imaging under selective excitation show changes in emission intensity, excitation and emission wavelength on a submicron length scale. These observations are consistent with an interpretation that the changes are due to fluctuations in Nd-concentration that create fluctuation in the local strain fields that are caused by the substitution of the small Ga ion by a larger Nd ion (0.62A vs 0.99A). [Preview Abstract] |
Thursday, March 13, 2008 3:06PM - 3:18PM |
W19.00004: Excitation mechanisms of rare-earth ions in GaN Z. Fleischman, S. Penn, L. Maurer, Z. Dong, V. Dierolf Understanding the excitation mechanisms of rare earth ions in GaN is key to achieving more efficient EL emission from devices based on this material system. For that purpose, we performed site-selective photo- and cathodo-luminesence spectroscopy on Eu-doped GaN layers. We identified 8 different Eu environments, which are excited after the creation of electron-hole pairs through excitation channels with drastically different transfer efficiencies. In particular, we find one majority site and one minority site that is strongly coupled to an intrinsic GaN defect. For these most pronounced cases, resonant excitation shows that the majority site is 6 times more abundant than the defect-related site, while saturated CL data show only a factor of 3. This indicates that not all of the majority site ions are able to be excited electrically. We explain this and other observations with a model for the Eu excitation mechanism that involves two different intrinsic GaN defects acting as intermediate traps. We determined that the most efficiently excitable Eu are those near such a defect trap. Overall, this work shows that a higher population of defect traps in GaN is desirable for the most efficient rare earth luminescence. [Preview Abstract] |
Thursday, March 13, 2008 3:18PM - 3:30PM |
W19.00005: First principles calculations for Gd doped GaN Chandrima Mitra, Walter Lambrecht Gd doped GaN has been reported by Dhar et al. to have magnetic moments of order a few 1000 $\mu_B$ per Gd in the very dilute limit of $10^{15}$ Gd/cm$^3$ and to show above room temperature ferromagnetism. Here we present first principle electronic structure calculations to study the spin splitting of the conduction band with varying concentration of Gd in GaN. Our calculations show that the spin splitting varies linearly with the concentration of Gd which suggests an almost zero splitting if one were to extrapolate to the 1 ppm dilute concentration of Gd. Thus the large magnetic moments cannot be explained simply by assuming donor electrons (for example from oxygen) will fill the spin-split conduction band. The spin polarization of the Ga and N atoms around Gd atom in a supercell of 1.5\% Gd were found to be small and to become negligible beyond second nearest neighbors. In these, studies, we either added oxygen or Si as co-dopants or a background charge to fill the spin-split conduction band. This indicates that the proposed model of Dhar of polarization of the host is not supported by our calculations. The magnetic exchange interaction parameter, for nearest neighbour Gd atoms have also been calculated by mapping the energy differences between the ferromagnetic and antiferromagnetic arrangement onto the Heisenberg's model. Effects of strain, supercell size and shape, and other dopants on the exchange interactions were investigated. [Preview Abstract] |
Thursday, March 13, 2008 3:30PM - 3:42PM |
W19.00006: Inclined Dislocation Pairs in Green GaInN/GaN Light Emitting Diodes Grown on Bulk GaN Substrate Mingwei Zhu, Theeradetch Detchprohm, Shi You, Yong Xia, Wei Zhao, Yufeng Li, Jayantha Senawiratne, Christian Wetzel, Lianghong Liu, Edward Preble, Drew Hanser Inclined dislocation pairs (IDPs) were observed for the first time in the active region of ten-quantum-well green GaInN/GaN light emitting diodes grown on c-plane bulk GaN substrate. The two inclined dislocations (IDs) in one IDP usually start closely in the first three quantum wells and propagate to different sides of [0001] growth direction. By analyzing transmission electron microscopy images of IDs at different projection directions and reconstructing them in the three dimensional crystal, all IDs were found to tilt from the [0001] direction towards the $<$1-100$>$ directions by 18 - 23$^{\circ}$. The two IDs in one IDP tilt to equivalent $<$1-100$>$ directions separated by either 120$^{\circ}$ or 180$^{\circ}$. All of the IDs are edge-type with a Burger vector 1/3$<$11-20$>$. The creation of IDPs might help to release the strain accumulated in the active region. In spite of the existence of these IDPs in the active region, this green LED on GaN shows a 7-fold stronger photoluminescence than those on sapphire. [Preview Abstract] |
Thursday, March 13, 2008 3:42PM - 3:54PM |
W19.00007: Electrical activation studies of Al$_{0.4}$Ga$_{0.6}$N and Al$_{0.5}$Ga$_{0.5}$N implanted with silicon for n-type doping. Elizabeth Moore, Yung Kee Yeo, Mee-Yi Ryu, Robert Hengehold A systematic electrical activation study of Si-implanted Al$_{x}$Ga$_{1-x}$N with Al concentrations of 40 and 50{\%} grown on sapphire substrates by MEMOCVD has been made as a function of ion dose and anneal temperature. The silicon ions were implanted at 200 keV with doses from 1x10$^{14}$ to 1x10$^{15}$ cm$^{-2}$ at room temperature. The samples were proximity cap annealed from 1150 to 1350 $^{o}$C for 20 minutes in a nitrogen environment. Hall-effect measurements were made from 10 to 700 K and cathodoluminescence measurements were taken at 7 K. Electrical activations of nearly 100{\%} were obtained for the Al$_{0.4}$Ga$_{0.6}$N:Si after annealing at 1350 \r{ }C for 20 minutes for doses of 1x10$^{14}$ and 5x10$^{14}$ cm$^{-2}$ and after annealing at 1200 \r{ }C for 20 minutes for the dose of 1x10$^{15}$ cm$^{-2}$. The Al$_{0.5}$Ga$_{0.5}$N:Si also had high activations of nearly 100{\%} for the two lower doses after annealing at 1300 \r{ }C for 20 minutes, while for a dose of 1x10$^{15}$ cm$^{-2}$, an activation of 66{\%} was obtained after the same annealing treatment. The highest room temperature mobility for the Al$_{0.4}$Ga$_{0.6}$N and Al$_{0.5}$Ga$_{0.5}$N samples are 61 and 55 cm$^{2}$/V$\cdot $s, respectively for the samples annealed at 1350 \r{ }C for 20 minutes. CL spectra support the electrical results in determining the optimal annealing conditions. [Preview Abstract] |
Thursday, March 13, 2008 3:54PM - 4:06PM |
W19.00008: Effects of Dopants and Annealing on the Structure and Electronic properties of GaAsN Yu Jin, Matthew Reason, Hailing Chen, Cagliyan Kurdak, Rachel Goldman In this work, we investigate the effects of different n-type dopants and rapid thermal annealing (RTA) on the structure and electronic properties of GaAsN bulk-like films grown by molecular beam epitaxy. For as-grown GaAsN:Si and GaAsN:Te films, similar free carrier densities (n) and electron mobilities ($\mu )$ are observed. However, after post-growth RTA, a substantial increase in both n and $\mu $ is observed in the GaAsN:Te films, with negligible change in those of the GaAsN:Si films. Apparently, RTA reduces the concentration of N-related trapping and scattering centers in GaAsN:Te. On the other hand, the annealing process enhances the diffusion of Si, presumably leading to the formation of additional N$_{As}$-Si$_{Ga }$defect complexes. For both GaAsN:Te and GaAsN:Si films, x-ray rocking curves reveal reduced lattice parameters following annealing, suggesting a decrease in the interstitial [N], which leads to the improvement in electronic properties for the GaAsN:Te films. In the case of GaAsN:Si, the reduction in interstitial [N] is presumably balanced by an increase in the density of N$_{As}$--Si$_{Ga}$ defect complexes. The effect of dopants and annealing on the structure and electronic properties of InGaAsN will also be discussed. [Preview Abstract] |
Thursday, March 13, 2008 4:06PM - 4:18PM |
W19.00009: Bismuth related changes in the electronic properties of high quality dilute GaAs$_{1-x}$Bi$_{x}$. Lekhnath Bhusal, Denis Karaiskaj, Ryan France, Aaron Ptak, Angelo Mascarenhas, Tom Tiedje In this work we will present the electronic and optical properties of dilute GaAs$_{1-x}$Bi$_{x}$ epitaxial layers for the range of samples with concentration up to $\sim $3{\%}. Variation of fundamental band gap (E$_{0})$ and the transition from the spin-orbit split off valance band (E$_{0}+\Delta )$ using the contactless modulated electroreflectance will be presented as a function of temperature (77-300K) and Bi concentrations. We also will discuss the isoelectronic codoping of Bi and nitrogen, as the excellent quality of GaAsBi samples presented in the work opens the path for the codoping of Bi with N to improve the electronic properties of dilute nitride III-V alloys. [Preview Abstract] |
Thursday, March 13, 2008 4:18PM - 4:30PM |
W19.00010: A defect relaxation model for the carbon vacancy in SiC Jamiyanaa Dashdorj, Mary Ellen Zvanut Deep level intrinsic defects in high purity semi-insulating SiC play in important role in electrical compensation necessary to achieve high resistivity. We use a constant light intensity approach to steady-state photo-electron paramagnetic resonance (EPR) and time-dependent photo-EPR to study the ionization cross sections and relaxation energies of the well-studied defect, the positively charged carbon vacancy, V$_{c}^{+}$. As-grown 4H-SiC samples with room temperature resistivity of 10$^{10}$ Ohm-cm were studied at 4 K and 80 K. The shape of the absorption curve for V$_{c}^{+}$, as revealed by the steady state measurements, has a peak at 2.3 eV and photo-threshold at 1.8 eV. We interpret the difference between these two values as a structural relaxation upon release of an electron from the defect to conduction band. Consistently, preliminary time-dependent measurements reveal a Franck-Condon transition at 2.3 eV for release of an electron from the defect to the conduction band, and a second Franck-Condon transition at an energy greater than 1.3 eV for capture of electron at the defect from the valence band. The difference of no more than 1 eV may be interpreted as a relaxation energy, consistent with the interpretation of steady-state data. The details of the experimental approach and the formulation of the relaxation model will be presented. [Preview Abstract] |
Thursday, March 13, 2008 4:30PM - 4:42PM |
W19.00011: Direct Imaging of Point Defect Configurations for Au Atoms Inside Si Nanowires K. van Benthem, S.H. Oh, A.Y. Borisevich, W. Luo, P. Werner, N.D. Zakharov, S.T. Pantelides, S.J. Pennycook Aberration-corrected scanning transmission electron microscopy (STEM) was used to directly image individual Au atom configurations inside Si nanowires grown by Au-catalyzed vapor-liquid-solid molecular beam epitaxy. A three-dimensional analysis of the nanowire microstructure revealed Au atom concentrations five orders of magnitude higher than equilibrium values in bulk silicon. Three distinct interstitial Au atom configurations were identified in addition to the substitutional configuration. The stability of the observed point defect configurations was further investigated by density-functional theory. The observed configurations are in excellent agreement with theory. However, a comparison of the number densities of the various configurations with the calculated formation energies indicates an effective temperature of approximately 1000 degrees centigrade suggesting significant beam-induced atomic diffusion. [Preview Abstract] |
Thursday, March 13, 2008 4:42PM - 4:54PM |
W19.00012: Ni doping of semiconducting boron carbide S. Adenwalla, Jing Liu, Nina Hong Semiconducting boron carbide (BC) is intrinsically p-type. The addition of Ni has been shown to dope it n-type. I-V measurements on Ni doped BC on both p-and n-type Si (1*10$^{15}$ cm$^{-3}$ and 4.5*10$^{13}$ cm$^{-3})$ indicate changes in the doping level with increasing Ni concentration. At the highest dopant level, Ni doped BC on n-type Si showed n-n+ diode characteristics. The change of doping concentration was confirmed by the built-in potential increase from 0.1 V in the low Ni doped p-n diode to 1.2 V in the high Ni-doped p-n diode as well as by measurements of the reverse saturation current. The addition of Ni does not lead to significant structural changes in the BC as measured by x-ray diffraction. X-ray fluorescence data indicate an upper bound of 2 ppm for the Ni concentration. Using these results homojunction p-n diodes were fabricated from layers of undoped p-type BC and Ni doped n-type BC and characterized by I-V and capacitance-voltage (C-V) measurement. Homojunction devices are shown to be especially promising for thermal neutron detection. [Preview Abstract] |
Thursday, March 13, 2008 4:54PM - 5:06PM |
W19.00013: First principles investigations into alkali intercalation of hexagonal boron nitride Bahadir Altintas, Cihan Parlak, Resul Eryigit, Cetin Bozkurt Although hexagonal boron nitride(hBN) is quite similar to graphite structurally, it has been very difficult to obtain any intercalation compound of hBN while there are hundreds of graphite intercalation compounds. We have investigated the possible intercalation of hBN by alkali atoms in the density functional theory framework by using pseudopotentials and plane-wave basis. The structural, electronic and lattice dynamical properties of hypothetical hBN analogues of LiC$_{3}$, LiC$_{6}$, KC$_{8}$, CsC$_{8}$, CaC$_{6}$ are calculated.We have found that although the electronic structure, band structure and fermi surface of alkali intercalated hBN is very similar to that of alkali intercalated graphite, the lattice dynamics show a set of negative frequency modes which indicate that alkali-intercalated hBN is not stable. [Preview Abstract] |
Thursday, March 13, 2008 5:06PM - 5:18PM |
W19.00014: Effects of point defects on the electrical properties of aluminum antimonide: a first principles investigation Vincenzo Lordi, Daniel {\AA}berg, Paul Erhart A first principles study is conducted of the effects of point defects on the electrical properties of bulk AlSb, a material of interest for room temperature gamma radiation detection. Detailed calculations were performed for all native defects, including vacancies, antisites, interstitials, and split interstitials, and also for a variety of impurities (H, C, Si, Ge, Sn, P, O, S, Se, Te). Formation energies of each defect in different charge states were calculated to determine the equilibrium defect density and net carrier density. Carrier scattering rates for each defect were calculated using perturbation theory to determine the effects on electron and hole transport. The most detrimental, as well as innocuous, defects were identified. Relative solubilities of the impurities were examined along with their scattering rates to find efficient dopants that minimize mobility degradation. Finally, carrier trapping cross sections and energy levels were calculated to study the role of each defect in deep level trapping. [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. |
© 2024 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