Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session J21: Focus Sessions: Dopants and Defects in Semiconductors II |
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Sponsoring Units: DMP Chair: Matthew McCluskey, Washington State University Room: 323 |
Tuesday, March 17, 2009 11:15AM - 11:51AM |
J21.00001: Defects in Mg doped (Al,In)GaN thin films and nanostructures Invited Speaker: Development of p-type (Al,In)GaN revolutionized the field of solid state lighting in the way that it was hard to imagine, development and introduction to market of light emitters in short period of time and tremendous amount of progress in other areas that was enabled by such development. Although many studies have been done to understand the defects related to Mg incorporation in epitaxially grown AlInGaN films, there are still many open questions. These include the relationship between the defects (type and density) and Mg incorporated and the electrical property of the film. An interesting open question is how optical characteristics of Mg doped (Al, In) GaN can predict its electrical property. In this presentation, we try to address this question. Recent advances in development of nanostructures based on III-nitrides include growth of high quality GaN nanowires. Although large body of work exists in growth and characterization of Si doped GaN nanowires the report work on Mg doped GaN is scarce. In the present work, we will discuss our recent progress in studying optical and electrical characteristics of Mg doped GaN nanowires and defect stabilization in nanostructure and thin films.\\[4pt] In collaboration with M. Reshchikov, Department of Physics, Virginia Commonwealth University, Richmond, VA 23284; N. Tripathi, B. J. Messer, and M. Tungare, College of Nanoscale Science and Engineering, UAlbany-State University of New York, Albany, NY 12203 [Preview Abstract] |
Tuesday, March 17, 2009 11:51AM - 12:03PM |
J21.00002: Interaction of hydrogen with defects in GaN Yevgeniy Puzyrev, Matthew Beck, Blair Tuttle, Ron Schrimpf, Dan Fleetwood, Sokrates Pantelides Hydrogen has long been known to have a dual role in Si electronics. It can passivate interfacial dangling bonds and other defects, but it can also be an agent of degradation and aging because it can be released under a variety of conditions. When released, it can depassivate other defects by forming H$_{2}$. In GaN, H has been known to play a key role in p-type doping (it helps Mg enter substitutionally, with an H attached to it; H is then removed to activate the Mg as a dopant). Here we present results of first-principles density-functional calculations exploring the role of H as a degradation agent in GaN devices, e.g., degradation by hot electrons. We find that H binds strongly to N antisite defects and is not removed during the process of dopant activation. Under normal operating conditions, hydrogenated N antisite defects are benign. However, hot electrons can release the H atoms from these defects, making them active electron traps. The results provide an explanation of pertinent data on hot-electron device degradation. This work was supported in part by an AFOSR MURI grant. [Preview Abstract] |
Tuesday, March 17, 2009 12:03PM - 12:15PM |
J21.00003: Intrinsic spin polarization of cation vacancies in group-III nitrides Yoshihiro Gohda, Atsushi Oshiyama Group-III nitrides are of significant importance not only in optoelectronic devices but also in potential applications to spintronics. Recently, we have clarified by means of total-energy DFT+U calculations that spins of Ga vacancies in Gd-doped GaN interact ferromagnetically [1]. We have also found that the magnetic moment increases monotonically with the increasing number of Ga vacancies, which explains experimental observations of colossal magnetic moments in Gd-doped GaN [2]. In this contribution, we report newly performed first-principles calculations that clarify spin polarization and lattice relaxation of cation vacancies with various charge states in a few group-III nitrides. Spin-polarized electronic configurations obtained in the present study are indicative of intrinsic ferromagnetism due to cation vacancies in nitride semiconductors. \\[0pt] [1] Y. Gohda and A. Oshiyama, Phys. Rev. B 78, 161201 (R) (2008). \\[0pt] [2] S. Dhar et al., Phys. Rev. Lett. 94, 037205 (2005). [Preview Abstract] |
Tuesday, March 17, 2009 12:15PM - 12:27PM |
J21.00004: N-H$_{n}$ complexes in GaAsN:H containing more than two H atoms Lanlin Wen, Michael Stavola, W. Beall Fowler, Antonio Polimeni, Mario Capizzi, Gabriele Bisognin, Marina Berti The III-N-V alloys have attracted much attention because of a large reduction of the band gap that occurs for N concentrations of a few percent. The hydrogenation of these alloys eliminates the effect of N.[1] IR experiments and theory revealed the properties of an NH$_{2}$ complex that can cause these novel effects.[2] Further studies by theory [3] and experiment [4] suggest the formation of defect complexes that contain more than two H atoms per N atom. In the present talk, new IR data provide experimental clues about the structures of NH$_{n}$ defect complexes with n$>$2 that have been found in GaAsN samples that were hydrogenated at reduced temperature. [1] A. Polimeni et al., Phys. Rev. B \textbf{63}, 201204 (2001). [2] S. Kleekajai et al., Phys. Rev. B \textbf{77}, 085213 (2008) and the references contained therein. [3] A.A. Bonapasta et al., Phys. Rev. Lett. \textbf{98}, 206403 (2007). [4] M. Berti et al., Phys. Rev. B \textbf{76}, 205323 (2007). [Preview Abstract] |
Tuesday, March 17, 2009 12:27PM - 12:39PM |
J21.00005: N-H vibrational frequencies in GaAs:N:H$_{n}$ W. Beall Fowler, M. Stavola, Lanlin Wen, A. Polimeni, M. Capizzi While the fundamental H-related defect in GaAs:N and GaP:N appears to have an NH$_{2}$ character,[1] considerable recent evidence suggests that an additional one or two hydrogen atoms may in some cases be involved.[2,3] We have used the CRYSTAL06 \textit{ab} \textit{initio} quantum code[4] with density functional theory to investigate these possibilities, obtaining theoretical equilibrium positions, ground-state energies, and vibrational frequencies with all combinations of H and D. In all cases investigated, the NH$_{2}$ configuration is preserved, but observable shifts in the N-H or N-D vibrational frequencies are predicted. Supported by NSF Grant 541744. [1] S. Kleekajai \textit{et al.,} Phys. Rev. B \textbf{77}, 085213 (2008) and references contained therein. [2] A. A. Bonapasta \textit{et al.}, Phys. Rev. Lett. \textbf{98}, 206403 (2007). [3] M. Berti \textit{et al.}, Phys. Rev. B \textbf{76}, 205323 (2007). [4] R. Dovesi \textit{et al.}, \textit{Crystal06 User's Manual} (University of Torino, Torino, 2006). [Preview Abstract] |
Tuesday, March 17, 2009 12:39PM - 12:51PM |
J21.00006: Effects of Si-N complexes on the electronic properties of GaAsN Yu Jin, Ryan Jock, Hailing Cheng, Cagliyan Kurdak, Rachel Goldman Silicon is the most common n-type dopant in GaAs-based materials and devices; however, in dilute nitride alloys, it has been suggested that Si and N atoms form Si-N complexes which act as deep electron traps. Here, we report the first quantitiative evidence of Si-N complex formation by comparing the properties of GaAsN films doped with Si and Te, with a variety of N-dopant spatial separations. First, we compare bulk-like GaAsN:Si films, where Si and N reside in the same layer, with modulation doped heterostructures, where N and Si atoms are spatially separated. A decrease in free carrier concentration, [n], with increasing N composition is observed in bulk-like films but not heterostructures, suggesting N-Si defect complexes in the bulk GaAsN layers are likely acting as trapping centers. In addition, we compared GaAsN films doped with Si and Te. For GaAsN:Te films, [n] increases substantially with increasing annealing temperature, but little change is observed in GaAsN:Si films. In GaAsN:Si, the annealing-induced increase in [n] is balanced by the formation of additional Si-N complexes. [Preview Abstract] |
Tuesday, March 17, 2009 12:51PM - 1:03PM |
J21.00007: Influence of N Interstitials on the electronic properties of GaAsN Alloys Ryan Jock, Yu Jin, Hailing Cheng, Cagliyan Kurdak, Rachel Goldman GaAsN alloys contain a significant fraction of interstitial N, which is often reported to act as a scattering and/or trapping center. In some cases, annealing has been reported to reduce the interstitial N fraction, presumably due to N diffusion to As vacancies. However, the influence of interstitial N on the electronic properties of GaAsN alloys remains unknown. In this work, we used annealing to probe the influence of N interstitials on the electronic properties of GaAsN. In as-grown GaAsN films, temperature-dependent Hall measurements reveal a thermally activated increase in free carrier concentration for temperatures above 150 K, suggesting the presence of a defect level below the conduction band edge, presumably due to interstitial N. Upon annealing, the free carrier concentration increases and becomes nearly temperature-independent, indicating a decrease in the concentration of trapping centers, presumably due to a reduced concentration of interstitial N. [Preview Abstract] |
Tuesday, March 17, 2009 1:03PM - 1:15PM |
J21.00008: Quaternary Ga$_{1-x}$In$_{x}$P$_{1-y}$N$_{y}$ alloys described by clustering of In and N in GaP Koushik Biswas, Alberto Franceschetti, Stephan Lany The interactions between the different atomic constituents in an alloy affect the microstructure, and ultimately, the electronic properties of the alloy. Specifically, in group III-V alloys the energy of formation of single defects and the binding energy of defect complexes play an important role in determining the microstructure.~ We present a model that starts from the dilute defect picture and extends to alloys of low to moderate concentrations. Using a valence-force-field (VFF) method we calculate the energy of formation of isolated N and In defects and that of small defect clusters formed by N and In in a GaP host. Considering a 1:2.12 N to In ratio that conserves lattice matching to GaP, we show that in a N concentration range up to $\sim $ 15{\%}, the formation energy of the random alloy can be described by the random probability to form such defect clusters. This approach allows the thermodynamic modeling of the microstructure of quaternary alloys, such as GaInNP, without intricate lattice-energy expansions and Monte-Carlo simulation techniques. In GaInNP, we find that short range ordering due to large atom to small atom preferential binding (i.e. InN+GaP) strongly reduces the energy compared to the random distribution. [Preview Abstract] |
Tuesday, March 17, 2009 1:15PM - 1:27PM |
J21.00009: Mechanism of Interaction between Hydrogen and the Two-dimensional Electron Gas in AlGaN/GaN High Electron Mobility Transistors Jason Gu, Mahak Khandelwal, Jacob Melby, Michael Steeves, Yuh-Renn Wu, Robert Lad, Robert F. Davis The large polarization difference between AlGaN and GaN causes a two-dimensional electron gas (2DEG) to form at the interface between the two semiconductors. Capacitance-voltage (CV) measurements revealed a charge density of 4.71x10$^{12}$ electrons/cm$^{2}$ in our 60 nm Al0.2Ga0.8N on 1.5 microns of GaN heterostructure. Exposure to hydrogen in the presence of a catalyst (Pt) resulted in a marked increase in the conductivity through the 2DEG. An interface state passivation mechanism is proposed as the most probable cause of this phenomenon. This mechanism was modeled using a self-consistent Schr\"{o}dinger-Poisson solver, which showed that the passivation of interface states causes the shift of the Fermi level towards the conduction band, thereby increasing the carrier density of the 2DEG by 9{\%}. In-situ CV measurements showed a 16{\%} increase in the carrier density and a non-parallel shift in the CV curve when hydrogen was introduced, indicating in a change in the number of available states. This supports interface state passivation as a cause of the increase in the conductivity through the 2DEG. [Preview Abstract] |
Tuesday, March 17, 2009 1:27PM - 1:39PM |
J21.00010: Magnetodielectric coupling in Au/GaAs:Si Schottky barriers S. Tongay, A.F. Hebard, Y. Hikita, H. Hwang A surprisingly large ($>$20{\%}) negative magnetocapacitance in non-magnetic Au/GaAs:Si Schottky barriers is attributed to a magnetic field ($H)$ induced increase in the binding energy of the shallow donor Si impurity atoms. Capacitance ($C)$ dispersion is used to identify the impurity ionization and capture processes that give rise to an $H$-dependent density of ionized impurities $N_d (H)$in the depletion region. Internal photoemission experiments confirm that the large $H$-induced shifts in the built-in potential $V_{bi} $, inferred from Mott-Schottky (1/$C^{2}$ versus voltage) measurements, are not due to an $H$-dependent Schottky barrier height (SBH), thus requiring a modification of the abrupt junction approximation which identifies the dependence of $V_{bi} $ on $N_d (H)$rather than the SBH. The linearity of the Mott-Schottky plots is preserved, as experimentally observed. The underlying magnetodielectric coupling not only allows a new opportunity for the tuning of the dopant carrier density by an external means (magnetic field) but should be important for understanding the behavior of related interfacial structures incorporating dilute magnetic semiconductors and/or complex oxides. [Preview Abstract] |
Tuesday, March 17, 2009 1:39PM - 1:51PM |
J21.00011: Point Defects and Dielectric Loss at MM Wavelengths in Wide-Gap Semiconductors Jyotsna Dutta, Charles Jones, V.V. Parshin, B. Garin, V.I. Polyakov, A. Rukovishnikov Data are presented on wide-gap semiconductors of various grades for their dielectric loss values at millimeter wavelengths to explore their potential for various RF technology related applications. In order to identify the impurities or electrically active defects that give rise to the excess loss, temperature-dependent conductivity and DLTS measurements have been undertaken. Dielectric loss measurements over a wide range of temperatures are in progress to verify the results obtained from electrical methods and help to determine the primary loss mechanisms for these materials in the millimeter wave length range. Experimental results and their implications to loss properties will be discussed. [Preview Abstract] |
Tuesday, March 17, 2009 1:51PM - 2:03PM |
J21.00012: Dual-Surfactant effect on enhancing different p-type doping in GaP. Junyi Zhu, Gerald Stringfellow, Feng Liu We report first principles calculations demonstrating a dual-surfactant effect of Sb and H on enhancing Zn, Mg, Be and Cd in vapor phase epitaxially grown GaP thin films. The combined effects of Sb and H lower significantly the doping energy all the p-type dopants in GaP, while neither Sb nor H can work alone as effectively. The role of H is to satisfy the electron counting rule. The role of Sb is to serve as an electron reservoir to help electron redistribution. The enhancement is the lowest for Mg which is probably due to the lowest electronegativity of Mg among these four elements. [Preview Abstract] |
Tuesday, March 17, 2009 2:03PM - 2:15PM |
J21.00013: InSb epilayers and quantum wells grown on Ge(001) substrates by MBE Mukul Debnath, Tetsuya Mishima, Mike Santos, Khalid Hossain, Wayne Holland For digital logic applications, transistors with both electron and hole channels are required. InSb:Ge heterostructure is an ideal material since the highest carrier mobilities for n and p-type quantum wells (QWs) are observed in InSb and Ge channels, respectively. We report on the MBE growth of InSb-based materials on Ge(001) substrates. A temperature variation two-step growth procedure (TSGP) is more effective than direct growth of InSb on Ge(001). In the TSGP, an initial 100-nm InSb layer was grown at a temperature of 340$^{o}$C before increasing the substrate temperature to 420$^{o}$C for the rest of the growth. The initial growth forms a wetting layer that minimizes defects at the InSb/Ge interface. The X-ray rocking curve width of a 5.0-$\mu $m-thick InSb epilayer is 173 arc sec. Electron mobilities of a 5.0-$\mu $m-thick InSb epilayer and an InSb/Al$_{0.20}$In$_{0.80}$Sb QW at room temperature are 34,500 and 8,600 cm$^{2}$/V-s, respectively. These are the highest mobilities for an InSb epilayer and QW on Ge(001) substrates reported so far. This work was supported by NSF Grant DMR-0520550 and OCAST contract AR071-025. [Preview Abstract] |
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