UCLA ELENGR 114 - Epitaxial Growth and Formation of Interfacial Misfit Array

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Epitaxial growth and formation of interfacial misfit array for tensileGaAs on GaSbS. H. Huang,a兲G. Balakrishnan, M. Mehta, A. Khoshakhlagh,L. R. Dawson, and D. L. Huffakerb兲Center for High Technology Materials, University of New Mexico, 1313 Goddard SE, Albuquerque,New Mexico 87106P. L iDepartment of Earth and Planetary Science, University of New Mexico, Albuquerque, New Mexico 87131共Received 27 February 2007; accepted 14 March 2007; published online 16 April 2007兲The authors report the formation of an interfacial misfit 共IMF兲 array in the growth of relaxed GaAsbulk layers on a 共001兲 GaSb surface. Under specific conditions, the high quality IMF array has aperiod of 5.6 nm and can accommodate the 7.78% tensile GaAs/GaSb lattice mismatch. The misfitsite is identified as a 90° edge dislocation using Burger’s circuit theory and confirmed byhigh-resolution cross-section transmission electron microscopy 共TEM兲 images. The resulting GaAsbulk material is both strain-free and highly crystalline. Plan-view TEM images show threadingdislocation density of ⬃3 ⫻106/cm2. This material demonstration will enable novel devicestructures including an embedded GaSb active region in GaAs device matrix. © 2007 AmericanInstitute of Physics. 关DOI: 10.1063/1.2723649兴Exploiting lattice-mismatched GaSb/GaAs andGaAs/GaSb heterojunctions are of considerable interest forIII-Sb electronic and optoelectronic devices on a GaAs sub-strate such as midwave infrared lasers, detectors, andtransistors.1–3At the compressive GaSb/GaAs interface,popular growth techniques such as metamorphic buffers共MBs兲 have enabled sufficiently low dislocation densities torealize some of these devices.4,5In previous demonstrations,the MB is typically ⬎1␮m in thickness and produces adefect density ⬍107/cm2. To circumvent the MB thickness, anew and novel growth technique involving 90° interfacialmisfit 共IMF兲 dislocations has recently been demonstrated byour group at the compressive interface to enable room tem-perature 共RT兲 lasing at 1.65␮m from a GaSb active regionon GaAs.6The IMF relieves strain immediately at the com-pressive heterointerface. The experimental results indicatethat the IMF dislocations relieve 98.5% of the strain energyand yields defect density ⬍105/cm2to enable high qualityGaSb materials on a GaAs substrate.7However, there are device applications such as midwaveinfrared 共MWIR兲 vertical cavity surface emitting lasers thatmight benefit from the III-Sb active region to be fully em-bedded in the GaAs matrix. Such a structure exploits thenarrow band gap III-Sb materials to access MWIR alongwith the mature GaAs processing technology, superior elec-trical contacts, thermal conductivity, and access to a nativeoxide 共AlxOy兲. Such a device requires simultaneous controlof the compressive 共GaSb on GaAs兲 and tensile 共GaAs onGaSb兲 interfaces. To date, epitaxy at the tensile GaAs onGaSb interface has not been addressed in the literature. Inthis letter, we describe the formation of an IMF for strain-relieved, low defect growth of GaAs on GaSb 共001兲 thatparallels the IMF formation at the compressive GaSb/ GaAsinterface.At the compressive GaSb on GaAs interface, the IMFformation is initiated with an Sb soak during which time, theSb atoms self-assemble such that each Sb atom forms asingle bond with an underlying Ga 共001兲 atom.7,8The Sbatoms, however, do not react with the GaAs substrate todisplace the As atoms.9Strain relief is achieved by a skippedSb–Ga bond every 13 atomic sites which form the IMFarray.10The tensile IMF has a similar atomic structure initiatedby a single layer of As 共001兲 atoms bonded to the underlyingGa 共001兲 atomic layer. Strain relief is achieved by a skippedAs–Ga bond every 13 lattice sites. However, in contrast tothe nonreactive nature of the Sb atom at the GaAs surface,the IMF formation at the tensile GaAs on GaSb interface ismore complex since the As2specie reacts aggressively withthe GaSb surface during an As2soak. This reactivity willform nanoscale highly crystallographic pits11and makes areconstructed As layer on the GaSb surface difficult toestablish. The surface chemistry is driven by a negative en-thalpy of reaction for both the anion exchange reaction andthe isoelectronic AsSb compound formation reaction共GaSb+As2→ 2GaAs+Sb2, ⌬Hⴰ=−47.6 kJ/ mol; GaSb+As2→ GaAs+AsSb, ⌬Hⴰ=−33.9 kJ/ mol兲.9,12The purposeof this study is to understand the effect of this reaction on theGaAs/GaSb interface.The samples used in this interfacial analysis are grownon a V80H reactor with valved crackers for both the As andthe Sb source. The crackers are operated at 900 and 950 °C,respectively, so that the atomic species from the sources areAs2and Sb2. The growth is initiated on a GaSb substratewith a thermal oxide desorption process followed by a GaSbsmoothing layer characterized by a 1 ⫻3 reconstruction. Thesmooth GaSb surface is then subjected to an As2overpres-sure with an approximate beam equivalent pressure of1⫻ 10−6mTorr. This overpressure is maintained for 0, 10, or60 s, respectively. Before the As growth is initiated, the Sbvalve is closed allowing Sb atoms to desorb leaving a Ga-rich surface. This process, which is confirmed by reflectiona兲Electronic mail: [email protected]兲Electronic mail: [email protected] PHYSICS LETTERS 90, 161902 共2007兲0003-6951/2007/90共16兲/161902/3/$23.00 © 2007 American Institute of Physics90, 161902-1Downloaded 21 Nov 2007 to 64.106.37.204. Redistribution subject to AIP license or copyright; see http://apl.aip.org/apl/copyright.jsphigh electron energy diffraction indicating Ga-rich 共4 ⫻2兲pattern, reduces Sb/ As intermixing. Following the As2soak,the GaAs growth is initiated without any changes in thegrowth temperature resulting in a smooth GaAs surface withcontinued growth.The resulting misfit array and bulk material have beenanalyzed carefully using low-resolution and high-resolutiontransmission electron microscopy 共TEM兲 images.Figures 1共a兲–1共c兲 show the cross-sectional TEM images of abulk GaAs layers 共100 nm兲 grown on the GaSb surfaces un-der different As2soak times 共60, 10, and 0 s, respectively兲.At 60 s , the As2etches nanoscale pits at the GaAs/GaSbinterface shown in Fig. 1共a兲. These pits vary in both size andshape with average dimensions of ⬃25 nm wide and10–40 nm high. Subsequent GaAs bulk overgrowth coales-cences over


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UCLA ELENGR 114 - Epitaxial Growth and Formation of Interfacial Misfit Array

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