Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session A40: Semiconductors: Growth of Nitrides |
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Sponsoring Units: FIAP Chair: Nelson Tansu, Lehigh University Room: Colorado Convention Center 503 |
Monday, March 5, 2007 8:00AM - 8:12AM |
A40.00001: Optimized growth of lattice-matched InAlN/GaN heterostructures by molecular beam epitaxy Stefan Schmult, Theo Siegrist, Mike Sergent, Mike Manfra, Rich Molnar A fundamental problem in the epitaxial growth of hexagonal group III/Nitride heterostructures along their c-axis is the in-plane lattice-mismatch between the binary compounds GaN, AlN and InN. This mismatch is responsible for stress and strain formation and leads in its extreme to cracking, deteriorating the optical and electrical properties of the samples. The ternary compound In$_ {x}$Al$_{1-x}$N with x$\sim$0.17 is expected to have an identical in-plane lattice constant as GaN. Here we report on the MBE growth of lattice-matched In$_{x}$Al$_ {1-x}$N on thick GaN templates. Optimizing the growth conditions and systematically investigating the influence of the flux ratio between Aluminum, Indium and Nitrogen leads to high quality layers, as assessed by x-ray diffraction. The extracted full widths at half maximum of the InAlN peak in $\omega$-2$\theta$ and rocking curve scans are 190arcsec and 300arcsec respectively and the lattice-match is confirmed by reciprocal lattice mapping. Sharp, intense high-order satellite peaks as well as the occurrence of interface interferences in the x-ray diffraction spectra confirm the high crystalline quality and abrupt interfaces of short period GaN/InAlN superlattices. These simple heterostructures are preludes to more complex structures like distributed Bragg reflectors and micro cavities. [Preview Abstract] |
Monday, March 5, 2007 8:12AM - 8:24AM |
A40.00002: AlN, InN, and their alloys' growth issues in Plasma Source MBE. Yuriy Danylyuk, Gregory Auner A systematic investigation of the growth of AlN, InN,and InAlN by Plasma Source MBE (PSMBE) was performed. The growth conditions were optimized based on RHEED analysis during growth and dissociation RGA experiments. For the PSMBE technique, the most important growth parameters are the flux levels (as determined by RF power and Ar/N ratio), and growth temperature. We present experimental work on AlN, InN, and InAlN grown on an AlN buffer layer deposited on sapphire (c), (r), and (a) plane substrates. The films are epitaxial with no phase segregation as shown by x-ray diffraction analysis. In-situ RHEED analysis was used to determine RHEED intensity oscillations, strain profiles, and coherence length profiles simultaneously. The results indicate a 2D-3D type's growth mode. Characterization of the (Al, In)-Nitrides film were performed by post growth techniques such as XRD, XPS, AFM, Optical (micro-Raman, photoluminescence, and UV-VIS- NIR-IR spectroscopy), and Electrical (Hall measurements). The results of the in-situ end ex-situ characterization of (Al, In)-Nitrides films by are presented in this work and confirmed high structural and optical qualities of (Al, In) - Nitride films. [Preview Abstract] |
Monday, March 5, 2007 8:24AM - 8:36AM |
A40.00003: Preferential growth of zinc-blende and wurtzite GaN as effected by the conditions of MBE Benjamin Shi, M.-H. Xie Homoepitaxial growth of GaN on its (0001) or (111) may result in both wurtzite and zinc-blende phases. We have conducted a detailed study to identify the dependence on various conditions. The experiments show that at low substrate temperatures but high gallium fluxes, the meta-stable zinc-blende phase will be strongly favored, while at high temperatures and/or low gallium fluxes, thermal equilibrium wurtzite phase will dominate. There is no significant dependence of crystallographic structure on deposition rate observed. In the STM study of initial stage nucleation on wurtzite film, 2D islands of both phases have been identified and statistical relative stabilities of the two phases are obtained at different temperatures. The relative stabilities show a significant asymmetry at low versus high temperature, which indicates that preferential nucleation at the initial stage would determine the film's crystallographic structure. [Preview Abstract] |
Monday, March 5, 2007 8:36AM - 8:48AM |
A40.00004: Non-polar GaN structures on $\gamma $-LiAlO$_{2}$ grown by plasma-assisted molecular beam epitaxy Li-Wei Tu, H.M. Huang, M.Z. Hsu, L.K. Wang, Y.L. Cheng, M.C. Chou, C.L. Hsiao, Q.Y. Chen, H.W. Seo, W.K. Chu A-plane lithium aluminate (LAO) in $\gamma $-phase crystal structure, $\gamma $-LiAlO$_{2}$ (100), was used as the substrate which was grown by Czochralski pulling method. With a lattice mismatch of [0001]GaN$\vert \vert $[010]LAO $\sim $ 0.3{\%} and [11\underline {2}0]GaN$\vert \vert $[001]LAO $\sim $1.7{\%}, $\gamma $-LiAlO$_{2}$ (100) has a much smaller lattice mismatch with the GaN (1\underline {1}00) than the conventional substrates. M-plane GaN epilayer was successfully grown by plasma-assisted molecular beam epitaxy. X-ray diffraction theta/two-theta scan shows a diffraction peak due to m-plane GaN. Raman scattering confirms Raman modes from the GaN (1\underline {1}00) structure. Cathodoluminescence yields a peak at 363 nm at room temperature. Nanostructures were explored also. Comparisons to structures grown on the c-plane will be presented. [Preview Abstract] |
Monday, March 5, 2007 8:48AM - 9:00AM |
A40.00005: Effect of nitridation on the molecular beam epitaxy growth of GaN on ZrB$_{2}$(0001)/Si(111) Yukiko Yamada-Takamura, Z.T. Wang, Y. Fujikawa, T. Sakurai, Q.K. Xue, J. Tolle, J. Kouvetakis, I.S.T. Tsong ZrB$_{2}$ is a conductive, reflective, and lattice-matched buffer layer for GaN growth on Si. Here we report the effect of nitridation on the epitaxial growth of GaN on ZrB$_{2}$(0001) films prepared \textit{ex situ} and \textit{in situ}, which was studied using an ultrahigh vacuum molecular beam epitaxy - scanning probe microscopy (MBE-SPM) system. The growth of GaN was carried out by rf-plasma assisted MBE, and epitaxy of wurtzite GaN with N-polarity was observed on both \textit{ex-situ} and \textit{in-situ} prepared ZrB$_{2}$ films. The nitridation of ZrB$_{2}$ films were conducted by exposing them to active nitrogen, and well-ordered hexagonal boron nitride (h-BN) formation was observed when the annealing temperature was above 900$^{o}$C. The partially formed BN layer affected neither the epitaxy nor the polarity of GaN, but when the surface was fully covered with well-ordered h-BN, GaN growth did not occur. The high GaN nucleation selectivity observed between clean and h-BN covered ZrB$_{2}$ suggests the possibility of applying epitaxial lateral overgrowth method, which is known to be difficult in elemental source GaN MBE growth. Ref. Z. T. Wang \textit{et al.,} J. Appl. Phys. 100, 033506 (2006). [Preview Abstract] |
Monday, March 5, 2007 9:00AM - 9:12AM |
A40.00006: Critical parameters for growth of optimized GaN and InGaN/GaN MQW structures on freestanding HVPE GaN substrates by MOCVD James Grandusky, Vibhu Jindal, Neeraj Tripathi, Fatemeh Shahedipour-Sandvik, Alexei Vertiatchikh, Greg Dunne, Hai Lu, Edmund Kaminsky, Rajesh Melkote With the continued improvement and availability of freestanding Nitride substrates, such as those grown by HVPE, these substrates are becoming more commonly used for growth and device applications. However, even with a reduced dislocation density as compared to heteroepitaxially grown GaN layers on sapphire or SiC, devices fabricated on these substrates are often less efficient. One reason for this is that generally growth is carried out using optimized conditions for growth on non-native substrates. In this work optimization of the growth conditions was carried out for GaN layers and InGaN/GaN MQW structures on freestanding HVPE GaN substrates. It was found that the optimized conditions for growth on these substrates are different as compared to growth on GaN on sapphire templates. The results of the optimization and the differences in the growth will be presented along with insight into the differences seen experimentally. [Preview Abstract] |
Monday, March 5, 2007 9:12AM - 9:24AM |
A40.00007: Electroluminescence from Er doped III-nitride light emitters synthesized by metal organic chemical vapor deposition C. Ugolini, J. Y. Lin, H. X. Jiang, J. M. Zavada It has been well recognized that GaN is a very attractive host for Er due to the low degree of thermal quenching of radiative intra-4f Er$^{3+}$ transitions and the large Er doping concentrations that can be achieved. These properties, in conjunction with the 1.54 $\mu $m transition of Er$^{3+}$, make Er doped GaN structures promising for light emitters and amplifiers operating at the telecommunication wavelength. Recently, our group has reported on the optical properties of Er doped GaN epilayers synthesized by metal organic chemical vapor deposition (MOCVD) using photoluminescence (PL). We now report on the electroluminescence (EL) of Er doped III-nitride light emitters synthesized by MOCVD. These structures were characterized with x-ray diffraction, atomic force microscopy, scanning electron microscopy, PL, EL, and Hall measurements. EL spectra of these emitters exhibit emission at 537 and 558 nm (intra-4f Er$^{3+ }$transitions from the $^{2}$H$_{11/2 }$and $^{4}$S$_{3/2}$ to the $^{4}$I$_{15/2}$, respectively), and at 1.0 and 1.54 $\mu $m (transitions from the $^{4}$I$_{11/2}$ and $^{4}$I$_{13/2}$ to the $^{4}$I$_{15/2}$, respectively). The effects of growth conditions such as temperature, V/III ratio, and growth rate will be discussed. EL from emitters of different Er concentrations as well as potential applications of these Er doped III-nitride light emitters will also be discussed. [Preview Abstract] |
Monday, March 5, 2007 9:24AM - 9:36AM |
A40.00008: Effects of polarity on material's quality of Al-rich AlGaN alloys T.M. Al tahtamouni, N. Nepal, J.Y. Lin, H.X. Jiang AlGaN alloys have the capability of tuning the direct band gap in a large energy range, from about 3.4 to 6.1 eV, which makes them very useful for ultraviolet (UV) and deep UV (DUV) optoelectronic device applications. Although recent progresses have led to the realization of several operational DUV devices such as light emitting diodes operating at wavelengths $<$ 300 nm, high performance DUV optoelectronic devices working at $\lambda \quad \le $ 280 nm still suffer from many serious problems such as stability and reliability. One of the important growth parameters that affects the properties of III-nitrides is the growth polarity. In this work, Al-rich Al$_{x}$Ga$_{1-x}$N alloys (x$\sim $0.8) with different polarities were grown on sapphire substrates by metal organic chemical vapor deposition (MOCVD). Various characterizations techniques were used to study the structural, electrical, and optical properties of these alloys. It was found that the material quality is significantly influenced by the growth polarity. Samples with Al-polarity have a much higher crystalline quality and better surface morphology than those of N-polarity. Additionally, photoluminescence spectra of Al-polarity samples exhibit only the band edge transition, while those of N-polarity also comprise a deep level impurity transition. [Preview Abstract] |
Monday, March 5, 2007 9:36AM - 9:48AM |
A40.00009: Growth of Mg-doped InN by Metal Organic Chemical Vapor Deposition N. Khan, N. Nepal, J.Y. Lin, H.X. Jiang InN with an energy gap of $\sim $ 0.7 eV, has recently attracted extensive attention due to its potential applications in semiconductor devices such as light emitting diodes, lasers, and high efficiency solar cells. However the ability to grow both p-type and n-type InN is essential to realize these devices. All as grown unintentionally doped InN are n-type. The tendency of native defects in InN to form donors manifests itself severely at surfaces where high levels of electron accumulation are observed. The highly n-type conductive layer at the surface of InN films creates difficulties in the demonstration of p-type InN. Nevertheless it is important to investigate the optical and structural properties of Mg-doped InN. We report here on the growth of Mg-doped InN epilayers by metal organic chemical vapor deposition. Photoluminescence (PL) was employed to study the effects of different growth conditions of Mg-doped InN. PL studies revealed that in addition to emission peak at $\sim $ 0.82 eV in undoped InN layers, Mg-doped InN layers exhibit an emission peak at $\sim $ 0.75 eV. The peak at $\sim $ 0.75eV for Mg-doped InN could be related to defects generated by Mg doping in InN. Various other measurements such as Hall effect measurement, X-ray diffraction and atomic force microscopy were carried out to provide further understanding. [Preview Abstract] |
Monday, March 5, 2007 9:48AM - 10:00AM |
A40.00010: Cantilever Epitaxy of AlN using Hydride Vapor Phase Epitaxy Scott A. Newman, Derrick S. Kamber, Yuan Wu, Edward Letts, Steven P. DenBaars, James S. Speck, Shuji Nakamura AlN is an important material for AlGaN-based electronic and optoelectronic devices such as UV Light Emitting Diodes and High Electron Mobility Transistors. We have grown AlN films with reduced Threading Dislocation (TD) densities using Cantilever Epitaxy with the Hydride Vapor Phase Epitaxy growth method. Prior to growth, 6H-SiC substrates were processed using standard lithography and ICP etching to form periodic ridge/trench patterns. Ridges were oriented in the $\left\langle {1\bar {1}00} \right\rangle _{SiC} $ direction, and trenches were etched up to 12.6 $\mu $m deep. AlN was grown laterally from 2-4 $\mu $m wide ridges over 3-6 $\mu $m wide trenches and coalesced. Plan-view TEM analysis showed that TD densities in the wing regions were less than 8.3 x 10$^{6}$ cm$^{-2}$ as compared to 3.9 x 10$^{9}$ in the seed regions. The TDs are predominantly edge-type with \textbf{b} =$\frac{1}{3}\left\langle {11\overline 2 0} \right\rangle $. Most of these TDs originate from the AlN-SiC interfaces on the tops of the ridges and propagate vertically. A small number of inclined dislocations propagate into the wing region. [Preview Abstract] |
Monday, March 5, 2007 10:00AM - 10:12AM |
A40.00011: Growth and structural properties of hexagonal BN thin films on graphitized 6H-SiC substrates Y. Kobayashi, H. Hibino, T. Akasaka, T. Makimoto, T. Nakamura, N. Matsumoto Hexagonal boron nitride (h-BN) is a promising material system for optical device applications in the ultraviolet spectral region because of its wide bandgap and large exciton binding energies of 5.97 eV and 149 meV, respectively. An exploration of a suitable substrate is a central challenge for high-quality h-BN thin film growth. We report here the successful growth of h-BN thin films by metalorganic vapor phase epitaxy (MOVPE) on graphitized 6H-SiC substrates. Annealing 6H-SiC substrates in ultrahigh vacuum prior to MOVPE growth provides graphitized 6H-SiC substrates whose surfaces are covered with graphite having several monolayers thickness. X-ray diffraction reveals that the BN thin films are pure single-phase (0001) h-BN with the c-axis normal to the 6H-SiC (0001) surface and that the c-axis lattice constant of the h-BN thin films is identical to that of bulk h-BN samples. This work is partly supported by a Grant-in-Aid for Scientific Research (A) {\#}18206004 from the Japan Society for the Promotion of Science. [Preview Abstract] |
Monday, March 5, 2007 10:12AM - 10:24AM |
A40.00012: Photoluminescence studies of impurity transitions involving nitrogen vacancies in Mg-doped AlGaN alloys M. L. Nakarmi, N. Nepal, J. Y. Lin, H. X. Jiang Although tremendous progress has been made in the development of AlGaN alloys and their applications in deep UV devices, achieving p-type conductivity in Al-rich AlGaN alloys is still highly challenging because of the large activation energy of the magnesium (Mg) acceptors and strong compensation effects due to the presence of intrinsic defects. We report on the growth by metalorganic chemical vapor deposition and photoluminescence studies of Mg-doped Al$_{x}$Ga$_{1-x}$N alloys. A group of deep level impurity transitions was observed in Mg-doped Al$_{x}$Ga$_{1-x}$N alloys which was identified to have the same origin as the previously reported blue line at 2.8 eV in Mg-doped GaN and was assigned to the recombination of electrons bound to the nitrogen vacancy with three positive charges (V$_{N}^{3+})$ and neutral Mg acceptors. Based on the measured activation energies of the Mg acceptors in AlGaN and the observed impurity emission peaks, the V$_{N}^{3+}$ energy levels in Al$_{x}$Ga$_{1-x}$N have been deduced for the entire alloy range. The presence of high density of V$_{N}^{3+}$ deep donors translates to the reduced p-type conductivity in AlGaN alloys due to their ability for capturing free holes. With the identification of the emission peaks associated with V$_{N}^{3+}$ hole compensating centers, we were able to improve the p-type conductivity of Al-rich AlGaN by monitoring and suppressing the intensity of the V$_{N}^{3+}$ related emissions. [Preview Abstract] |
Monday, March 5, 2007 10:24AM - 10:36AM |
A40.00013: Defect Ordering in InN Rebecca E. Jones, H. C. M. van Genuchten, K. M. Yu, W. Walukiewicz, J. W. Ager, III, Z. Liliental-Weber, J. Wu, E. E. Haller, H. Lu, W. J. Schaff Energetic particle irradiation followed by thermal annealing has been used to create InN films with both high electron concentration and high mobility. The mobility values are larger than have been reported for as-grown, undoped InN films with comparable electron concentrations ($>$ 10$^{19}$ cm$^{-3})$. The high mobility can be explained by a thermally-induced ordering of the native point defects produced by the irradiation. An analysis of the concentration dependence of the electron mobility shows that the defects are triply charged, and therefore the strong Coulomb interaction energy between them is minimized by the formation of a donor superlattice. Here we present evidence for this ordering, including experimental results and theoretical modeling. [Preview Abstract] |
Monday, March 5, 2007 10:36AM - 10:48AM |
A40.00014: Redirecting of misfit dislocations from AlN/Si interface into the substrate Z. Liliental-Weber, R.L. Maltez, X. Ni, H. Morkoc In order to increase lifetime of CW lasers based on the III-nitrides, a low defect density in GaN/AlN based materials is required. For the first time it was shown that misfit dislocations formed at the AlN/Si interface can interact with dislocation loops formed around He bubbles created by He implantation into Si, and dislocations can move into the Si substrate instead of into the epi-layer. The optimal implantation dose and the distance of the He bubbles from the surface were determined. The growth temperature of AlN was used as the annealing temperature. Understanding of physical basis of strain relaxation at the AlN/Si interface can lead to the development of techniques leading to annihilation of threading dislocations in the GaN/AlN layers grown on foreign substrates. [Preview Abstract] |
Monday, March 5, 2007 10:48AM - 11:00AM |
A40.00015: Rare-earth nitride films; Ion assisted growth. Joe Trodahl, Simon Granville, Ben Ruck, Andrew Preston, Tony Bittar, Grant Williams We have recently reported a study of Gd nitride films grown by evaporating Gd in the presence of low-pressure N$_{2}$ gas. That work demonstrated that the material is a semiconductor in both the ambient-temperature paramagnetic and low-temperature ferromagnetic phases, with a conductivity determined by nitrogen vacancies. The present paper will report growth in a reactive environment that reduces the density of those vacancies. Films were grown by evaporating a number of rare earths by ion-assisted deposition (IAD), exploring films grown in ions with energies from 0 to 1000 eV. All of these IAD films show reduced crystallite size, expanded lattice constant, depressed magnetic ordering temperature and increased resistivity as compared to N$_{2}$-grown films. The optical band gap is largely unchanged by IAD. [Preview Abstract] |
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