Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session L15: Focus Session: Dilute Nitride Semiconductors: From Atoms to Devices II |
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Sponsoring Units: FIAP DCMP DMP Chair: Eicke Weber, University of California-Berkeley Room: LACC 405 |
Tuesday, March 22, 2005 2:30PM - 3:06PM |
L15.00001: Band Anticrossing Effects in Dilute Nitrides Invited Speaker: Recent advances in nonequilibrium epitaxial growth techniques have led to successful synthesis of alloys of distinctly different semiconductors. An important class of such materials are Highly Mismatched Alloys (HMAs). These are compound semiconductors formed when metallic (electronegative) anions are partially replaced by isoelectronic, more electronegative (metallic) atoms. Dilute nitrides in which highly electronegative N atoms partially replace standard group V elements are the most prominent and extensively studied class of HMAs. Using Ga$_{1-y}$In$_{y}$N$_{x}$As$_{1-x}$ as a prototypical HMA, experimental and theoretical studies will be presented that show how all the unusual properties of these alloys can be explained by considering the interaction between highly localized states of substitutional N atoms and the extended states of Ga$_{1-y}$In$_{y}$As matrix in the Band Anticrossing (BAC) model. The interaction splits the conduction band into two nonparabolic bands resulting in large changes in the electrical and optical properties of these materials. The BAC model provides a consistent and quantitative description of experimentally observed data including the large band gap bowing, splitting of the conduction band, and increase enhancement of the electron effective mass. Also, it explains the mutual passivation effect in which group IV donors form nearest neighbor pairs with substitutional N atoms, which eliminates the activity of both species. Most recently we have found that the electronic properties of N-rich GaN$_{1-x}$As$_{x}$ (x$<$0.06) HMAs are determined by an anticrossing interaction between localized donor-like As states and the valence band states of the GaN matrix. The finding provides a basis for a description of the electronic structure of these alloys in the whole composition range. [Preview Abstract] |
Tuesday, March 22, 2005 3:06PM - 3:42PM |
L15.00002: Penetration of dilute nitrogen states deep into the GaPN conduction band$^{\ast}$ Invited Speaker: Sergey Dudiy We study the electronic structure consequences of perturbations caused by dilute N impurities in GaP by means of large supercell ($\sim$1700 atoms) calculations, using a fully atomistic empirical pseudopotential method. We find that numerous localized states are introduced by a single N atom and N clusters, not only close to the band edge but also throughout the GaP conduction band[1], up to $\sim 1$ eV above the conduction band edge. Many of these ensuing states have no counterpart in any of the previous simplified models, such as impurity band or band anticrossing models. These high energy N-localized states are essential for understanding of a previously puzzling observation of splitting of PLE intensity at the GaP $\Gamma_{1c}$ energy into two features, one blue shifting and the other staying pinned in energy with increasing N concentration. Our calculations also explain the observed build up of the featureless spectral intensity between the GaP $X_{1c} $ and $\Gamma_{1c}$ energies with increasing $x$, as being due to the $L-L$ like optical transitions from the states {\it below the VBM}. This work is done in collaboration with Paul Kent and Alex Zunger. \newline [1] S.V. Dudiy, P.R.C. Kent, and A. Zunger, PRB {\bf 70}, 161304 (2004). \newline $^{\ast}$ Supported by DOE-SC-BES-DMS. [Preview Abstract] |
Tuesday, March 22, 2005 3:42PM - 3:54PM |
L15.00003: Effects of N incorporation on the electronic structure of GaNP: Origin of the 2.87 eV optical transition Irina Buyanova, M. Izadifard, Weimin M. Chen, H.P. Xin, C.W. Tu, S.J. Pearton Temperature dependent photoluminescence excitation (PLE) spectroscopy is employed to evaluate basic physical properties of the 2.87 eV absorption peak, recently discovered (I. A. Buyanova et al, PRB 69, 201303 (2004)) in the GaN$_{x}$P$_{1-x}$ alloys. Whereas appearance of this transition is found to be facilitated by incorporation of N and also H atoms, its intensity does not scale with N content. This questions a possible association of this feature with a N-related localized state. Based on the results of temperature dependent measurements, the involved state is concluded to have a non-$\Gamma $ character. Excitation of the known N-related localized states via this state is found to be non-selective, opposed to that between the N-related centers. The observed properties are shown to be hardly consistent with those predicted for the higher lying localized state of the isolated N atom derived from the $\Gamma $ conduction band minimum (CBM). Alternative explanations for the ``2.87 eV'' state as being due to either a t$_{2}$ component of the X$_{3}^{c}$ (or L$_{1}^{c})$ CBM or a level arising from a complex of N and H (in some form) are also discussed. [Preview Abstract] |
Tuesday, March 22, 2005 3:54PM - 4:06PM |
L15.00004: Vibrational spectroscopy of N-H2 complexes in GaPN S. Kleekajai, M. Stavola, W.B. Fowler, M. Capizzi, A. Polimeni, C.W. Tu, K. Martin The dilute III-N-V alloys have attracted much recent attention because of a large reduction of the band-gap energy that occurs for N concentrations of a few percent. The hydrogenation of these alloys gives rise to an increase of the band-gap energy, eliminating the effect of N [1]. Vibrational spectroscopy provides a powerful probe of the structures of the important N- and H- containing complexes in these materials. A previous study of the vibrational properties of GaAsN:H showed that the dominant N- and H-containing defect contains two weakly coupled N-H oscillators, a result that is inconsistent with an H$_{2}$* configuration that several theoretical groups have suggested to explain the properties of H in GaAsN and GaPN [2]. New results from an IR study of the N- and H-containing defects that are produced in GaPN by hydrogenation have led to a better understanding of the vibrational properties of N-H$_{2}$ complexes in the III-N-V alloys. This work is supported by NSF Grant DMR 0403641. 1. A. Polimeni \textit{et al.}, Phys. Rev. B \textbf{63}, 201204 (R) (2001). 2. F. Jiang \textit{et al.}, Phys. Rev. B \textbf{69}, 041309 (R) (2004). [Preview Abstract] |
Tuesday, March 22, 2005 4:06PM - 4:18PM |
L15.00005: Effects of heavy nitrogen doping on the host band structure of GaP B. Fluegel, Yong Zhang, J.F. Geisz, A. Mascarenhas A recently observed excitation peak in photoluminescence excitation (PLE) spectra of GaP$_{1-x}$N$_{x}$ epilayers, that remains pinned \textbf{\textit{below}} the \textit{$\Gamma $} point of the GaP$_{1-x}$N$_{x}$ with N concentration, is attributed to a transition from the valence band edge to either the $t_{2}$(X$_{3})$ or $t_{2}(L)$ conduction bands by Buyanova et al. [PRB 69, 201303(R), 2004]. A theoretical study based on an empirical pseudopotential band structure calculation offers an alternative explanation for the pinned peak claiming that it is produced by high energy N-cluster states, despite the fact that the calculated pinned peak is \textbf{\textit{above}} the \textit{$\Gamma $} point [Duidy et al., PRB 70, 161304(R), 2004]. Using absorption and PLE studies on free-standing samples, we show that this pinned peak is merely an artifact that arises from the GaP buffer layer and is not associated with the GaP:N epilayers. Also, we directly probe the host conduction band minimum (CBM) near $X_{1C}$ using absorption, which shows that a weak CBM absorption peak remains stationary up to nitrogen composition x = 0.1 {\%} before it is smeared out by the inhomogeneous broadening. This result further supports the conclusion that the absorption below the host CBM in heavily N doped GaP is primarily due to the formation of an impurity band consisting of broadened states of N pairs and clusters (Zhang et al, PRB 62, 4493, 2000). [Preview Abstract] |
Tuesday, March 22, 2005 4:18PM - 4:30PM |
L15.00006: Investigations of the energy-fine structure related to different nitrogen nearest-neighbor environments in GaInNAs layers and GaInNAs/GaAs quantum wells Robert Kudrawiec, Jan Misiewicz A formation of In-N bonds instead Ga-N ones in GaInNAs compound after annealing is one of the most interesting features of this compound. The aim of this paper is to investigate this issue for sets of different GaInNAs layers and GaInNAs/GaAs quantum wells by photoreflectance (PR) and contactless electroreflectance (CER). Five possible nitrogen nearest-neighbour environments, i.e. short-range-clusters, lead to five discrete band gap energies. In this work the temperature dependence of the band gap energy E(T) related to the individual clusters has been investigated. In addition, we show a first CER evidence of the energy-fine structure of the band gap for GaInNAs system. Besides GaInNAs samples series of GaNAs and GaNAsSb samples have been investigated in PR and CER. It has been shown that after annealing a blueshift of the band gap energy appear also for these samples. However, no energy-fine structure of the band gap energy has been observed for these compounds. [Preview Abstract] |
Tuesday, March 22, 2005 4:30PM - 4:42PM |
L15.00007: Structure and local vibrational frequencies of the 2H complex in H-irradiated GaAs:N Mao-Hua Du, Sukit Limpijumnong, Shengbai Zhang Hydrogen irradiation of GaAs:N samples leads to a giant blue shift of the band-gap [1]. Insight on the H complex has recently been available through infrared studies [2], showing three distinct H-modes (3195, 2967, and 1447 cm$^{-1})$, all correspond to N-H bonds. The absence of the Ga-H bond, however, contradicts previously proposed low-energy H$_{2}$* model where one H is on Ga whereas the other is on N [3]. Analysis of the measured isotope shifts shows that the H complex in the H-irradiated GaAs:N samples should involve two coupled H atoms. Based on density functional calculations, we propose a new nitrogen-2H complex. Not only the model accounts for the observed giant blue shift due to H-irradiation, but the calculated H-vibrational frequencies (3207, 3052, and 1417 cm$^{-1})$ and isotope shifts are also in good agreement with experiment. Supported by the U. S. DOE/ BES and EERE under contract No. DE-AC36-99GO10337. [1] G. Baldassarri H. v. H., et al., Appl. Phys. Lett.\textbf{78}, 3472 (2001) [2] F. Jiang, et al., Phys. Rev. B \textbf{66}, 073313 (2002) [3] A. Janotti, et al. Phys. Rev. Lett. \textbf{89}, 086403 (2002) [Preview Abstract] |
Tuesday, March 22, 2005 4:42PM - 4:54PM |
L15.00008: Ion Beam Synthesis of InAsN Nanostructures X. Weng, P.T. Wang, R.S. Goldman, Y.Q. Wang We recently demonstrated the utility of ion-beam-synthesis for producing light-emitting GaAsN nanostructures [1]. Here, we report the ion-beam-synthesis of InAsN nanostructures, using low temperature N implantation into epitaxial InAs. 100keV N ion implantation, with a dose of 5x10$^{17}$cm$^{-2}$, leads to complete amorphization of a $\sim $300nm thick surface layer. Following annealing, this layer transformed into three layers: a nanostructure layer containing $\sim $5nm zincblende InN-rich InAsN crystallites within an amorphous matrix, a polycrystalline layer consisting of $\sim $100nm InAs-rich InAs:N crystals and amorphous domains, and layer of solid-phase epitaxially grown InAs. These results suggest that ion-beam synthesis is promising for producing InN-rich nanostructures or/and InAs-rich alloys. We will also discuss the effects of implantation and annealing conditions on the structure and properties of ion beam synthesized InAsN nanostructures. [1] X. Weng. R.S. Goldman, et al, J. Appl. Phys. 92, 4012 (2002); Appl. Phys. Lett. 85, 2774 (2004). [Preview Abstract] |
Tuesday, March 22, 2005 4:54PM - 5:06PM |
L15.00009: The influence of growth temperature on the nitrogen incorporation into MBE-grown GaInNAs-on-GaAs epilayers E.-M. Pavelescu, M. Pessa, J. Konttinen, M. Dumitrescu, J. Wagner, R. Kudrawiec, J. Misiewicz We have studied the influence of growth temperature (within the 410-470 $^{o}$C range) on the nitrogen incorporation into lattice-matched GaInNAs-on-GaAs epilayers grown by molecular-beam epitaxy under constant fluxes. It was found that, over the whole temperature range, nitrogen is incorporated both on substitutional sites and as dimers on Ga and As sites. On substitutional sites nitrogen is present in the form of N-Ga$_{4}$ clusters and, to a lesser extent, in the form of N-Ga$_{3}$In ones. Increasing the growth temperature reduces the amount of substitutional nitrogen and increases the ratio between the N-Ga$_{3}$In and N-Ga$_{4}$ clusters. At the same time, the band gap increases. The amount of nitrogen dimers also decreases with increased growth temperature but the ratio between nitrogen dimers and nitrogen substitutionals appears not to be affected by the growth temperature. The effects of annealing on the incorporated nitrogen are discussed in the paper. [Preview Abstract] |
Tuesday, March 22, 2005 5:06PM - 5:18PM |
L15.00010: GaAs-based InGaAsN Lasers Changsi Peng, Tomi Jouhti, Janne Konttinen, Markus Pessa We demonstrated 1262 nm high performance single mode InGaAsN lasers. 4 $\mu $m stripe ridge waveguide InGaAsN lasers were processed. For as-cleaved case, pulsed threshold current was only 15 mA (313 A/cm$^{2})$ for 1200-$\mu $m-long chips at room temperature (RT). The laser can work beyond 120 $^{\circ}$C. After AR/HR coating, pulsed emission was up to 250 mW at RT. For cw operation, the lasers show a very low threshold of 25 mA and maximum output was up to 40 mW for 1200 $\mu $m length chip at RT. All the emission above was kink-free and single mode. New InGaAsN quantum well (QW) structures were designed. Comparing with the conventional InGaAsN QW structures, photoluminescence (PL) investigations show a significant improvement. After 3000 sec of annealing at 700 $^{o}$C, the PL peak area is about 20 times higher while the wavelength keeps 25 nm longer. After 800 sec of annealing, the PL quenched slowly for the conventional structures because of the strain relaxation, while the PL of the new structures increased rapidly and show no saturation after 3000 sec of annealing. [Preview Abstract] |
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