Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session Z21: Solid State Lighting and Other Semiconductors |
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Sponsoring Units: FIAP Chair: Angelo Mascarenhas, National Renewable Energy Laboratory Room: 323 |
Friday, March 22, 2013 11:15AM - 11:27AM |
Z21.00001: Interplay of polarization fields and Auger recombination in the efficiency droop of nitride light-emitting diodes Emmanouil Kioupakis, Qimin Yan, Chris G. Van de Walle The wider adoption of solid-state lighting is hampered by the significant efficiency reduction of nitride light-emitting diodes (LEDs) at high power. Although Auger recombination has been shown to contribute to this efficiency loss, many of the supporting studies focused on bulk materials. In contrast, LEDs consist of quantum wells that exhibit polarization fields, which strongly influence the recombination rates. We use Schrodinger-Poisson calculations in order to investigate the effect of polarization fields in nitride quantum wells on the carrier recombination rates and the efficiency of nitride LEDs. Our results demonstrate that both the efficiency-droop and green-gap problems can be attributed to the combined effect of Auger recombination and the spatial separation of electrons and holes induced by the polarization fields. Our results show that the suppression of polarization fields is a promising solution to improve the high-power efficiency of nitride LEDs. [Preview Abstract] |
Friday, March 22, 2013 11:27AM - 11:39AM |
Z21.00002: CuPt atomic ordering and band gap reduction in AlInP for green LED applications Daniel Beaton, Kunal Mukherjee, Kirstin Alberi, Theresa Christian, Angelo Mascarenhas, Eugene Fitzgerald Efficient light emission in the wavelength range of 575-595nm (green/amber) is necessary for high colour rendering index (CRI) colour-mixed white LED light sources. The present lack of efficient light emitters in this range is known as the 'green gap'. However, it is possible to achieve efficient green/amber light emission with III-V semiconductor alloys, specifically by using direct band gap AlInP alloys, where carrier confinement for device application can result from the band off-set between ordered and disordered material of the same composition. The greater size discrepancy between Al and In results in higher degrees of CuPt atomic ordering and larger band gap reductions than typically reported for other order materials, such as GaInP. Samples are grown lattice matched to InGaAs graded buffer layers grown on GaAs substrates and atomic ordering is observed by TEM. Photoluminescence and modulated reflectance characterization are used to quantify the band gap shift as a function of order parameter. [Preview Abstract] |
Friday, March 22, 2013 11:39AM - 11:51AM |
Z21.00003: Demonstration of amber-green light emitting diodes with lattice-mismatched AlInP active region Theresa Christian, Daniel Beaton, Kunal Mukherjee, Kirstin Alberi, Angelo Mascarenhas, Eugene Fitzgerald Future solid-state lamps based on all-LED white light emission will require four emitter colors (red, amber, green, and blue) to achieve good color rendering while maintaining high efficiency. Traditional LED material systems are well-suited to the red and blue ends of the spectrum but there is not yet a clear front-runner material for efficient light emission in the amber-green wavelength range (570 -- 595 nm). The compound semiconductor alloy Al$_x$In$_{1-x}$P has the potential to achieve this target due to its high direct bandgap. This talk will present results from our recent fabrication of amber-green LEDs featuring an AlInP double-heterostructure device structure. Cladding layers for carrier confinement are achieved through control of atomic ordering in the AlInP material. To fully exploit the high direct bandgap that occurs at lattice constants below that of GaAs, these devices are grown on InGaAs/GaAs virtual substrates. Devices are characterized in terms of current-voltage behavior, electroluminescence emission spectra and drive current dependence. [Preview Abstract] |
Friday, March 22, 2013 11:51AM - 12:03PM |
Z21.00004: Theoretical Analysis of the Band Offsets and Band Bending in (0001) In$_{x}$Ga$_{\mathrm{1-x}}$N/GaN Heterostructures and Quantum Wells Liang Dong, S. Pamir Alpay Valence band offsets ($\Delta E_{V})$ and built-in electric fields of (0001) In$_{x}$Ga$_{\mathrm{1-x}}$N/GaN heterostructures and quantum wells are studied as a function of In composition $x$ using first principles calculations based on density functional theory (DFT). These properties determine the degree of quantum confinements and wave function overlapping of electrons and holes, and thus the overall efficiencies of electronic/optoelectronic devices based on these structures. We show that with increasing $x$, $\Delta E_{V}$ of (0001) In$_{x}$Ga$_{\mathrm{1-x}}$N/GaN displays a parabolic bowing in both strain-free (fully relaxed) heterostructures and pseudomorphic quantum wells on $c$-plane GaN substrates. $\Delta E_{V}$ of (0001) InN/GaN in these two cases (0.98 eV and 0.64 eV, respectively) can be used to explain the deviations in experimental results that vary from 1.1 eV to 0.58 eV. We also show that the DFT calculated built-in electric fields in these constructs agree with continuum-level electrostatic analysis based on Maxwell and Poisson's relations, taking into account the first and second order of piezoelectric couplings. [Preview Abstract] |
Friday, March 22, 2013 12:03PM - 12:15PM |
Z21.00005: Effects of quantum-well shape and polarization on simulations of InGaN/GaN multi-quantum-well light-emitting diodes Patrick McBride, Qimin Yan, Chris Van de Walle We investigate the effects of different InGaN quantum well (QW) profiles in $c$-plane InGaN/GaN 3-QW blue light-emitting diodes (LEDs) by employing a semi-empirical drift-diffusion model. Our results show that changing the typically assumed square indium profile to one with a smoother interfacial transition leads to a significant modification of the band diagram, carrier overlap, and current-voltage characteristics. In previous works, an \emph{ad hoc} reduction of the polarization field has often been used to generate simulated results that match experiment while the realistic indium profile is not taken into account. However, our results indicate that the indium profile plays an important role in determining the current vs. voltage characteristics of InGaN/GaN heterostructure LEDs. [Preview Abstract] |
Friday, March 22, 2013 12:15PM - 12:27PM |
Z21.00006: Plasma assisted molecular beam epitaxy of strain-balanced a-plane InGaN/AlGaN periodic structures Ryan Enck, Nathaniel Woodward, C.S. Gallinat, G.D. Metcalfe, Hongen Shen, Michael Wraback A-plane nitride semiconductors have a tunable anisotropic absorption edge that can be exploited to create a compact, broad spectrum THz radiation detector which leverages fiber lasers operating at telecommunication wavelengths. Incident THz radiation is detected by observing the anisotropic change in the anisotropic absorption in the semiconductor of a femtosecond probe pulse by monitoring the polarization rotation of the probe. The sensitivity of this detection method requires a high quality a-plane wurtzite semiconductor with sufficient thickness to provide a large enough polarization rotation as required by the detection scheme. We report on the growth and characterization of strain balanced InGaN/AlGaN periodic structures on various substrates and buffer layers to obtain thick epilayers while maintaining a large absorption anisotropy. We use x-ray diffraction to determine the strain, composition, degree of relaxation, and thickness of our samples and polarization dependent transmission spectroscopy to measure the anisotropic absorption and polarization rotation in these materials [Preview Abstract] |
Friday, March 22, 2013 12:27PM - 12:39PM |
Z21.00007: Blue and Green light InGaN/GaN Multiquantum-Well grown by plasma-assisted molecular beam epitaxy Chia-Hsuan Hu, Ikai Lo, Cheng-Hung Shih, Wen-Yuan Pang, Cheng-Da Tsai, Yu-Chiao Lin High-efficiency red, green and blue light-emitting diodes (LEDs) can be used in the construction of full color display. We have grown green and blue light InGaN/GaN multiquantum-well (MQW) thin film on sapphire substrate with GaN buffer by using plasma-assisted molecular beam epitaxy. The optical properties of the samples were analyzed by photoluminescence measurement in room temperature. Under constant nitrogen flux condition, we obtained the blue and green emitting bands from different samples by modified the Indium and Gallium flux ratio in MQW. In high nitrogen flux condition, the wavelength shifts to 560nm, which provides an effective way to reach high Indium incorporation LED. In order to improve the quality, we can control the growth temperature and InGaN/GaN thickness. There are more than five order satellite peaks in Double Crystal X-ray Diffraction data. Smooth surface morphology has been verified in our samples by scanning electron microscope. [Preview Abstract] |
Friday, March 22, 2013 12:39PM - 12:51PM |
Z21.00008: The epitaxial relationship between M-Plane and c-plane GaN grown on gamma-LiAlO$_{2}$ Ying-Chieh Wang, Ikai Lo, Cheng-Hong Shih, Chia-Hsueng Hu, Cheng-Da Tsai, Shou-Ting You The M-plane and c-plane oriented GaN have been found co-existed in the $\gamma $-LiAlO$_{2}$ substrate grown by molecular beam epitaxy (MBE). Two-step growth with different N/Ga ratios has been used in the experiment at growth temperature 670$^{\circ}$C. By the SEM images, the smooth M-plane surface was observed and the c-plane GaN 3-D structures homogenously spread on it. From the scanning of $\omega $-2$\theta $ X-ray diffraction pattern, the peaks at 32.295$^{\circ}$ and 34.505$^{\circ}$ were attributed to the M-plane and c-plane GaN. The microstructure of the samples was investigated by transmission electron microscopic (TEM) study. It was found that the c-plane and M-plane GaN both were oriented from the substrate with the same growth direction and arranged vertically to the substrate with a periodical pattern. The interfaces between the c-plane and M-plane GaN can be confirmed clearly by one or two monolayer in high resolution TEM images. The stacking faults were found at the edge of c-plane side at the interface that released the dislocation between the M- and c-plane GaN. In summary, we found that the M-plane and c-plane GaN can be assembled on $\gamma $-LiAlO$_{2}$ substrate with a clear phase-transition interface. [Preview Abstract] |
Friday, March 22, 2013 12:51PM - 1:03PM |
Z21.00009: Gallium-monochalcogenides mechanically exfoliated at temperatures above room temperature Jose Fonseca Vega, Hui Fang, Ali Javey, Oscar Dubon In recent years, there has been an increased interest toward layered 2D materials beyond graphene. Among these III-VI metal-chalcogenide layered semiconductors are interesting materials for 2D applications as the digitally controlled crystal thickness (by the number of layers) opens a new degree of freedom to tailor electronic properties. In this work, thin layers of GaSe and GaTe were obtained via micromechanical exfoliation and transferred onto SiO2/Si substrates at temperatures ranging from room temperature to 75 C. Exfoliation above room temperature showed a dramatic increase in yield and mean surface area for the exfoliated single-crystalline flakes, 75 C and 50 C being the optimum conditions for GaSe and GaTe, respectively. Few-layer flakes were observed through optical microscopy. It was found that GaTe offered an additional challenge for exfoliation; this was attributed to its monoclinic crystal structure, contrasting GaSe's hexagonal structure. Atomic force microscopy thickness measurements determined the amount of layers in the exfoliated flakes. Micro-Raman and photoluminescence spectroscopy reveal an evolution in properties in these materials as a function of thickness. Results from measurements of field-effect transistors will be presented. [Preview Abstract] |
Friday, March 22, 2013 1:03PM - 1:15PM |
Z21.00010: Structural and Electronic Properties in multilayer (BiSe)$_n$(TiSe$_2$)$_m$ Misfit compounds Benjamin Trump, Maxime Siegler, Ken Livi, Tyrel McQueen The nature of the charge density wave (CDW) transition in 1T-TiSe$_2$ has been hotly debated, and variously described as a simple CDW to the formation of an excitonic insulator. Here we report the synthesis and basic physical properties of the incommensurate layered chalcogenides (BiSe)$_n$(TiSe$_2$)$_m$. Their structure consists of a rock-salt type BiSe layer separated by one or more edge-sharing TiSe$_2$ octahedral layer. These octahedral layers are isomorphic to the layers found in 1T-TiSe$_2$, and thus provide a mechanism to study the electronically driven structural transition in TiSe$_2$ as a function of the number of layers. Structural determinations from electron and x-ray diffraction, using 4/5-D superspace approach, will be presented, and the implications of our results on the understanding of CDW formation in TiSe$_2$ will be discussed. The effects of doping with Cu to observe possible superconducting behavior is also explored. [Preview Abstract] |
Friday, March 22, 2013 1:15PM - 1:27PM |
Z21.00011: Optically lossless semiconductors reached by means of bichromatic irradiation Adil-Gerai Kussow, Alkim Akyurtlu Non-omhic semiconductors are theoretically studied in the fields of two parametrically coupled electromagnetic waves. A second-order non-linearity due to the non-omhicity couples waves and causes exchange energy between the modes. Based on Maxwell's equations and coherence requirements, it is demonstrated that the optical losses in the probe mode are compensated due to the flow of energy from the support mode. Estimates are made to show that the total loss suppression can be realized in semiconductors with low optical dispersion, e.g. zinc telluride (ZnTe), within the mid-IR to Long Wavelength --IR regime, and the appropriate design for the experimental validation is suggested. [Preview Abstract] |
Friday, March 22, 2013 1:27PM - 1:39PM |
Z21.00012: Growth morphology of boron doped single crystal diamond Sunil Karna, Yogesh Vohra The growing demand of wide band semiconductors entice researcher to investigate electronic properties in diamond. The chemical vapor deposition (CVD) method has shown that various level of doping can be possible in diamond films. The purpose of this study was to investigate the growth morphology and quality of boron doped diamond film with deposition parameters. Various level of boron doped diamond films were synthesized epitaxially on synthetic (100) ib type diamond substrate using microwave plasma assisted CVD. The structural, optical and electrical characterizations were made to study effect of deposition parameters and pretreatment of substrates on surface morphology and growth quality. Raman spectra showed shape modification of the zone center optical phonon line and its downshift with the increasing boron content in the film. Additional bands were also observed in lower wavelength region below optical phonon line. Surface modification of films with increasing boron content has been observed in atomic force microscopy. High growth rate and high quality films were obtained with the addition of a few ppm of nitrogen in feed gas during deposition with little compromise on conductivity. Electrical measurement showed carriers have been transported via two different conduction mechanisms. [Preview Abstract] |
Friday, March 22, 2013 1:39PM - 1:51PM |
Z21.00013: Growth and Contrast of Hexagonal Boron Nitride: From Submonolayer Islands to Multilayer Films Justin Koepke, Joshua Wood, Eric Pop, Joseph Lyding Strong interest in hexagon boron nitride (h-BN) as a substrate for graphene devices [1] or as a template for growth of other layered compounds [2] has motivated recent attempts to synthesize large scale h-BN by chemical vapor deposition (CVD). We synthesize h-BN by low pressure CVD on polycrystalline Cu foil in a hot wall tube furnace with a heated ammonia borane precursor carried downstream by Ar and H$_{\mathrm{2}}$ gas. Transmission electron microscopy (TEM) diffraction patterns show that the resulting growths are highly crystalline, with several layers obtained for longer growth times. Short growth times show that the h-BN nucleates in triangular islands at a higher precursor temperature than previously reported in [3] and a lower temperature than reported in [4]. In-air calcination of the Cu foils after partial h-BN growth allows optical contrast of the previously transparent h-BN islands on the Cu foil. This observed resistance to oxidation suggests that grown h-BN films can serve as an insulating anti-corrosion layer. \\[4pt] [1] J. Xue, et al., Nat. Mater. 10, 282 (2011).\\[0pt] [2] P. Gehring, et al., Nano Lett. 12, 5137 (2012).\\[0pt] [3] K.K. Kim, et al., \textit{Nano Lett.} 12, 161 (2012).\\[0pt] [4] N. Guo, et al., Nanotechnology. 23, 415605 (2012). [Preview Abstract] |
Friday, March 22, 2013 1:51PM - 2:03PM |
Z21.00014: MOCVD grown hexagonal BN epilayers for DUV photonics Sashikanth Majety, Jing Li, Jingyu Lin, Hongxing Jiang Hexagonal boron nitride (hBN) has attracted a lot of interest recently owing to its excellent physical properties and its potential use as a template in graphene electronics. We report on the successful growth of hBN epilayers using metal organic chemical vapor deposition (MOCVD) on sapphire and n-AlGaN substrates. P-type conductivity control was also achieved by in-situ Mg doping. This provides us with an opportunity to solve the problem of low quantum efficiency of DUV devices using Al-rich AlGaN alloys due to their extremely low p-type conductivity. Mg doped hBN epilayers grown on insulating templates were p-type with an in-plane resistivity of 2.3 $\Omega $ cm. Diode behavior in the p-n structures of p-hBN/n-Al$_{0.62}$Ga$_{0.38}$N has been demonstrated. Our results indicate that hBN epilayers have potential for DUV optoelectronic devices and also demonstrate the feasibility of using highly conductive p-type hBN as electron blocking and p-contact layers for AlGaN based deep UV emitters. This work is supported by DOE. [Preview Abstract] |
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