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Mar 2012

Volume 30, Issue 2 (partial)

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Low resistance and thermally stable Ti/Al-based Ohmic contacts to N-face n-GaN for vertical light-emitting diodes by using Ti(Ga) solid solution and TiN layers

Joon-Woo Jeon, Woong-Sun Yum, Tae-Yeon Seong, Sang Youl Lee, and June-O Song

J. Vac. Sci. Technol. B 30, 020601 (2012); doi:10.1116/1.3678490 (4 pages)

Online Publication Date: 24 January 2012

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The authors report on the formation of highly reliable Ti/Al-based ohmic contacts to N-face n-GaN for high-performance vertical light-emitting diodes by using Ti(Ga) solid solution and TiN layers. The Ti(Ga) solid solution layer is used to minimize the outdiffusion of Ga atoms from the n-GaN surface region. Unlike the Ti/Al contacts, the Ti(Ga)/Ti/Al and Ti(Ga)/TiN/Al samples exhibit ohmic behavior with contact resistivities of 3.9 – 4.8 × 10−4 Ωcm2 after annealing at 250 °C. It was further shown that unlike the Ti(Ga)/TiN/Al samples, the Ti/Al and the Ti(Ga)/Ti/Al samples are largely electrically degraded when annealed at 300 °C in an oven. Based on x-ray photoemission spectroscopy and secondary ion mass spectrometry results, ohmic formation and degradation mechanisms are briefly described and discussed.
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85.60.Jb Light-emitting devices
84.32.Dd Connectors, relays, and switches
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Characteristic comparison of AlGaN/GaN enhancement-mode HEMTs with CHF3 and CF4 surface treatment

C. H. Chen, C. W. Yang, H. C. Chiu, and Jeffrey. S. Fu

J. Vac. Sci. Technol. B 30, 021201 (2012); doi:10.1116/1.3680115 (6 pages)

Online Publication Date: 1 February 2012

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In this study, enhancement-mode (E-mode) AlGaN/GaN HEMTs that underwent CHF3 and CF4 plasma treatment beneath the gate metal were fabricated. These treatments were applied because, although previous studies have formed AlF3 compound layers after fluorine-based plasma treatment to suppress the polarization-induced charge density, the surface negative charges still influenced the device gate leakage current and trap density. In the device in this study, unlike in previous CF4 plasma-treated GaN E-mode devices, the hydrogen atoms of the CHF3 plasma were introduced to compensate for vacancies by donating an electron to a vacancy acceptor level, thereby reducing the number of vacancy induced traps. Based on the measured subthreshold slope (SS) and the effective interface state density (Dit) results, the SS value of a CHF3-treated HEMT was 80 mV/decade and the Dit was 1.23 × 1012 cm−2. Moreover, the CHF3-treated HEMT exhibited a current gain cut-off frequency, a maximum oscillation frequency, and an output power of 6.7, 26, and 14.8 dBm (302 mW/mm), respectively. The 1/f noise measurement results of the CHF3-treated HEMT indicated that the flicker noise-induced generation-recombination noise and gate leakage-induced generation-recombination noise were also improved. Therefore, the CHF3-treated HEMT has great potential for use in low-distortion power amplifiers and logic control circuits.
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85.30.Tv Field effect devices
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Probing temporal evolution of extreme ultraviolet assisted contamination on Ru mirror by x-ray photoelectron spectroscopy

A. Al-Ajlony, A. Kanjilal, M. Catalfano, M. Fields, S. S. Harilal, A. Hassanein, and B. Rice

J. Vac. Sci. Technol. B 30, 021601 (2012); doi:10.1116/1.3680122 (6 pages)

Online Publication Date: 1 February 2012

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Extreme ultraviolet (EUV) radiation mediated carbon contamination and oxidation of the Ru mirror surface, and the corresponding impact on reflectivity were studied. In particular, time-dependent systematic decrease in EUV reflectivity with a 13.5 nm wavelength of light in high vacuum atmosphere was recorded and correlated with the change in chemical composition on the Ru surface as derived from in situ x-ray photoelectron spectroscopy (XPS). The contamination on Ru surface is caused by residual impurities of the test chamber. The recorded XPS spectra show a sudden increase in carbon concentration in the first 1 h followed by a slow but linear growth in the presence of EUV radiation. Further analyses show a slight increase in Ru oxide, whereas the concentration of water molecules decreases continuously. Moreover, the carbon monoxide level at the surface was stabilized after initial increase in concentration for an hour. The impact of water molecules and the accumulation of carbon atoms on the Ru surface are discussed in details.
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81.65.Mq Oxidation
68.35.Dv Composition, segregation; defects and impurities
79.60.-i Photoemission and photoelectron spectra
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
61.05.js X-ray photoelectron diffraction
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
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Emission properties of carbon nanowalls on porous silicon

Stanislav A. Evlashin, Yuri A. Mankelevich, Vladimir V. Borisov, Andrey A. Pilevskii, Anton S. Stepanov, Victor A. Krivchenko, Nikolai V. Suetin, and Alexander T. Rakhimov

J. Vac. Sci. Technol. B 30, 021801 (2012); doi:10.1116/1.3681287 (6 pages)

Online Publication Date: 1 February 2012

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For the past two decades various methods of carbon nanostructures growth have been proposed. Special substrate pretreatment methods are generally used to grow carbon nanowalls on silicon substrates and among them are mechanical and catalytic methods and ion bombardment in an rf discharge with bias. This work describes the possibility of growing carbon structures on porous silicon in a dc discharge without any additional pretreatment of the substrate surface. Carbon structures were grown on n- and p-type (100) porous silicon substrates produced by using standard photoelectrochemical etching. The analysis of these carbon structures revealed nanocrystalline carbon with multilayer carbon nanotubes and fibers. All samples demonstrated low field emission thresholds (Etr < 3 V/μm) and high current densities, showing an achieved current density of more than 6 A/cm2 for an electric field of E ∼ 15 V/μm. The authors investigated various modifications of porous silicon samples and carbon structures and demonstrated a practicable technique to create a reproducible uniform spot that varies in size from several millimeters to tens of millimeters. The authors propose a simplified and less expensive alternative to existing methods.
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81.07.De Nanotubes
81.65.Cf Surface cleaning, etching, patterning
82.50.-m Photochemistry
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
73.63.Fg Nanotubes
79.70.+q Field emission, ionization, evaporation, and desorption
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Monolithic integration of silicon CMOS and GaN transistors in a current mirror circuit

W. E. Hoke, R. V. Chelakara, J. P. Bettencourt, T. E. Kazior, J. R. LaRoche, T. D. Kennedy, J. J. Mosca, A. Torabi, A. J. Kerr, H.-S. Lee, and T. Palacios

J. Vac. Sci. Technol. B 30, 02B101 (2012); doi:10.1116/1.3665220 (6 pages)

Online Publication Date: 6 December 2011

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GaN high electron mobility transistors (HEMTs) were monolithically integrated with silicon CMOS to create a functional current mirror circuit. The integrated circuit was fabricated on 100 mm diameter modified silicon-on-insulator (SOI) wafers incorporating a resistive (111) silicon handle substrate and a lightly doped (100) silicon device layer. In a CMOS-first process, the CMOS was fabricated using the (100) device layer. Subsequently GaN was grown by plasma molecular beam epitaxy in windows on the (111) handle substrate surface without wire growth despite using gallium-rich growth conditions. Transmission lines fabricated on the GaN buffer/SOI wafer exhibited a microwave loss of less than 0.2 dB/mm up to 35 GHz. Direct current measurements on GaN HEMTs yielded a current density of 1.0 A/mm and transconductance of 270 mS/mm. At 10 GHz and a drain bias of 28 V, 1.25 mm long transistors demonstrated a small signal gain of 10.7 dB and a maximum power added efficiency of 53% with a concomitant power of 5.6 W. The silicon and GaN transistors were interconnected to form high yield test interconnect daisy chains and a monolithic current mirror circuit. The CMOS output drain current controlled the GaN transistor quiescent current and consequently the microwave gain.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.30.Tv Field effect devices
84.30.Le Amplifiers

InGaN laser diodes operating at 450–460 nm grown by rf-plasma MBE

C. Skierbiszewski, M. Siekacz, H. Turski, G. Muzioł, M. Sawicka, A. Feduniewicz-Żmuda, J. Smalc-Koziorowska, P. Perlin, S. Grzanka, Z. R. Wasilewski, R. Kucharski, and S. Porowski

J. Vac. Sci. Technol. B 30, 02B102 (2012); doi:10.1116/1.3665223 (5 pages)

Online Publication Date: 6 December 2011

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This work demonstrates the first true blue laser diodes (LDs) grown by plasma assisted molecular beam epitaxy that operate at the region of 450–460 nm. The single quantum well LDs were grown on several types of c-plane bulk GaN substrates, with threading dislocation densities varying from 104 to 108cm−2. The key factors that allowed the authors to achieve lasing in true-blue wavelengths are improvements in the growth technology of the InGaN quantum wells attributed to the high nitrogen flux used and the design of the LD structure, which reduced the light losses in the cavity. The authors discuss the influence of the diodes’ design on the parameters of LDs.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Characterization of Bi2Te3 and Bi2Se3 topological insulators grown by MBE on (001) GaAs substrates

Xinyu Liu, David J. Smith, Helin Cao, Yong P. Chen, Jin Fan, Yong-Hang Zhang, Richard E. Pimpinella, Malgorzata Dobrowolska, and Jacek K. Furdyna

J. Vac. Sci. Technol. B 30, 02B103 (2012); doi:10.1116/1.3668082 (4 pages)

Online Publication Date: 9 December 2011

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Films of pseudohexagonal Bi2Te3, Bi2Se3 and their alloys were successfully grown by molecular beam epitaxy on GaAs (001) substrates. The growth mechanism and structural properties of these films were investigated by reflection high-energy electron diffraction, atomic force microscopy, x-ray diffraction (XRD), high-resolution transmission electron microscopy, and Raman spectroscopy and mapping. The results indicate that the epitaxial films are highly uniform and are of high crystalline quality.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Nk Insulators
78.30.Hv Other nonmetallic inorganics
68.55.aj Insulators

Suppressed phase separation in thick GaInAsSb layers across the compositional range grown by molecular beam epitaxy for 1.7–4.9 μm infrared materials

Asli Yildirim and John P. Prineas

J. Vac. Sci. Technol. B 30, 02B104 (2012); doi:10.1116/1.3668088 (7 pages)

Online Publication Date: 13 December 2011

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Thick 2 um Ga1-xInxAsySb1-y layers lattice-matched to (100)-GaSb were grown by molecular beam epitaxy across the compositional range x = 0 to 1. By lowering the growth temperature to the 410 – 450 C range, phase separation was suppressed throughout the miscibility gap, as evidenced in measurements such as photoluminescence, high-resolution x-ray diffraction, atomic force microscopy, and cross-sectional transmission electron microscopy. Bright photoluminescence was recorded in the sample series ranging from 1.7 to 4.9 ums.
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81.05.Ea III-V semiconductors
64.75.Qr Phase separation and segregation in semiconductors
78.55.Cr III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Structural and luminescent properties of bulk InAsSb

W. L. Sarney, S. P. Svensson, H. Hier, G. Kipshidze, D. Donetsky, D. Wang, L. Shterengas, and G. Belenky

J. Vac. Sci. Technol. B 30, 02B105 (2012); doi:10.1116/1.3670749 (4 pages)

Online Publication Date: 21 December 2011

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The strong bandgap bowing in the InAsxSb1−x alloy system allows it to potentially be used for infrared photodetection in the middle and long wavelength range. The authors have used compositionally graded metamorphic buffer layers to accommodate the misfit strain between InAsxSb1−x alloys and GaSb and InSb substrates in order to reach the long wave infrared range. In this work, we present the characterization of metamorphically grown InAsxSb1−x films that demonstrate strong photoluminescence in the spectral range from 5 to 9 μm.
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81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
71.20.Nr Semiconductor compounds

Structural properties of InAs/InAs1–xSbx type-II superlattices grown by molecular beam epitaxy

Lu Ouyang, Elizabeth H. Steenbergen, Yong-Hang Zhang, Kalyan Nunna, Diana L. Huffaker, and David J. Smith

J. Vac. Sci. Technol. B 30, 02B106 (2012); doi:10.1116/1.3672026 (5 pages)

Online Publication Date: 21 December 2011

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Strain-balanced InAs/InAs1−xSbx type-II superlattices (SLs) have been proposed for possible long-wavelength infrared applications. This paper reports a detailed structural characterization study of InAs/InAs1−xSbx SLs with varied Sb composition grown on GaSb (001) substrates by modulated and conventional molecular beam epitaxy (MBE). X-ray diffraction was used to determine the SL periods and the average composition of the InAs1−xSbx alloy layers. Cross-section transmission electron micrographs revealed the separate In(As)Sb/InAs(Sb) ordered-alloy layers within individual InAs1−xSbx layers for SLs grown by modulated MBE. For the SLs grown by conventional MBE, examination by high-resolution electron microscopy revealed that interfaces for InAs1−xSbx deposited on InAs were more abrupt, relative to InAs deposited on InAs1−xSbx: this feature was attributed to Sb surfactant segregation occurring during the SL growth. Overall, these results establish that strain-balanced SL structures with excellent crystallinity can be achieved with proper design (well thickness versus Sb composition) and suitably optimized growth conditions.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
82.70.Uv Surfactants, micellar solutions, vesicles, lamellae, amphiphilic systems, (hydrophilic and hydrophobic interactions)

Strain-balanced InAs/InAs1−xSbx type-II superlattices grown by molecular beam epitaxy on GaSb substrates

Elizabeth H. Steenbergen, Kalyan Nunna, Lu Ouyang, Bruno Ullrich, Diana L. Huffaker, David J. Smith, and Yong-Hang Zhang

J. Vac. Sci. Technol. B 30, 02B107 (2012); doi:10.1116/1.3672028 (5 pages)

Online Publication Date: 21 December 2011

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Strain-balanced InAs/InAs1−xSbx type-II superlattices (SLs) on GaSb substrates with 0.27 ≤ x ≤0.33 were grown by molecular beam epitaxy and demonstrated photoluminescence (PL) up to 11.1 μm. The calculated SL bandgap energies agree with the PL peaks to within 5 meV for long-wavelength infrared samples (9.5, 9.9, and 11.1 μm) and to within 9 meV for a mid-wavelength infrared sample (5.9 μm). X-ray diffraction measurements reveal average SL mismatches of less than 0.2%, and the PL full-width-at-half-maximums increase with the mismatch, confirming the importance of strain-balancing for material quality.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.Cd Superlattices
71.20.Nr Semiconductor compounds
78.55.Cr III-V semiconductors

Interface properties of (In,Ga)As/GaAs quantum wells grown by solid-phase epitaxy

E. Luna, R. Hey, and A. Trampert

J. Vac. Sci. Technol. B 30, 02B108 (2012); doi:10.1116/1.3672022 (5 pages)

Online Publication Date: 27 December 2011

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(In,Ga)As/GaAs quantum wells (QWs) are successfully fabricated via a thermally induced structural transition from deposited amorphous material to epitaxial films, also known as solid-phase epitaxy (SPE). Although exact processes occurring during the epilayer formation are unknown, it is shown that the method allows the fabrication of high quality QWs with abrupt and symmetric composition profiles. As discussed here, the analysis of the chemical interface (composition profile) of the SPE-grown QWs, and its comparison with the element profiles of similar heterostructures grown by conventional molecular beam epitaxy (C-MBE) provides further insight into the SPE processes. In particular, we find that regardless of the fabrication method (SPE vs C-MBE), the smooth variation of the element concentration with the position across the interface is remarkably well described by a sigmoidal function. Such functional dependence is determined by fundamental processes occurring during the growth; thus suggesting that the basic mechanisms of interface formation are similar in SPE and C-MBE. Finally, the effect of self- and post-growth thermal annealing on SPE QWs is also discussed.
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81.15.Np Solid phase epitaxy; growth from solid phases
68.55.ag Semiconductors
68.65.Fg Quantum wells
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors

Molecular beam epitaxy control and photoluminescence properties of InAsBi

S. P. Svensson, H. Hier, W. L. Sarney, D. Donetsky, D. Wang, and G. Belenky

J. Vac. Sci. Technol. B 30, 02B109 (2012); doi:10.1116/1.3672023 (5 pages)

Online Publication Date: 27 December 2011

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Thick InAsBi layers were grown for photoluminescence (PL) characterization. The As to In overpressure ratio was carefully characterized and adjusted to achieve Bi-droplet-free surfaces. A closed loop feedback system was used to maintain the As overpressure during a 5-h deposition sequence. Despite a high degree of control of the growth parameters, evidence for local phase separation was observed in the PL spectra.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Rare-earth-metal oxide buffer for epitaxial growth of single crystal GeSi and Ge on Si(111)

Rytis Dargis, Erdem Arkun, Andrew Clark, Radek Roucka, Robin Smith, David Williams, Michael Lebby, and Alexander A. Demkov

J. Vac. Sci. Technol. B 30, 02B110 (2012); doi:10.1116/1.3673799 (6 pages)

Online Publication Date: 28 December 2011

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Ternary and binary rare-earth oxides that are used as a template buffer, which accommodates the crystal lattice mismatch between substrate and a semiconductor layer, are discussed here. The oxides were grown on Si(111) substrates and exhibit the cubic bixbyite crystal structure. Stabilization of the cubic bixbyite structure of ternary erbium-neodymium oxide and lanthanum oxide was analyzed using structural investigation of the epitaxially grown oxides and ab initio density functional theory calculations. The authors demonstrate that despite the more energetically favorable hexagonal structure of bulk lanthanum oxide a pseudomorphic single crystal cubic lanthanum oxide layer grows under nonequilibrium conditions of a molecular beam epitaxy process on gadolinium oxide. Growth of hexagonal lanthanum oxide begins when the critical thickness of the layer is reached. Germanium was epitaxially grown on the cubic bixbyite lanthanum sesquioxide. Due to a higher surface energy, germanium starts to grow in the form of twinned islands on the oxide layer that later merge, forming a closed layer. X ray diffraction reveals mostly single crystal structure of the germanium layer with stacking twins located only at the interface with the lanthanum oxide layer.
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68.55.ag Semiconductors
61.72.Mm Grain and twin boundaries
65.40.gp Surface energy
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Photoluminescence study of self-assembled GaAs quantum wires on (631)A-oriented GaAs substrates

E. Cruz-Hernández, D. Vázquez-Cortés, A. Cisneros-de-la-Rosa, E. López-Luna, V. H. Méndez-García, and S. Shimomura

J. Vac. Sci. Technol. B 30, 02B111 (2012); doi:10.1116/1.3673798 (4 pages)

Online Publication Date: 9 January 2012

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The authors report a low-temperature photoluminescence (PL) study of multiple GaAs layers grown between AlAs(0.6 nm)/GaAs(0.6 nm) short-period superlattice barriers (SLBs) simultaneously grown on both GaAs(631)A and (100) substrates. Five GaAs-layers of different nominal thicknesses (LW, ranging from 12 to 2.4 nm) were grown by molecular beam epitaxy. By using (631)A-oriented substrates a self-organized and highly ordered corrugation is obtained in the growth of the GaAs layers, and at the end of the SLB growth, flat surfaces are found. Whereas, for the (100)-oriented sample, flat interfaces are confirmed after the growth of GaAs and SLB layers. By reducing LW below ∼3.6 nm in the (631) sample, strong quantum wire (QWR)-like confinement is achieved as deduced from polarized PL spectroscopy where polarization degrees as large as 0.43 are obtained. The PL emission energy of the (631)-QWRs is redshifted, as compared with the transitions of the (100)-oriented quantum wells, when LW is reduced. The authors explain this energy shift by the widening of the effective thickness of the confinement regions in the GaAs layers.
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78.55.Cr III-V semiconductors
81.16.Dn Self-assembly
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.La Quantum wires (patterned in quantum wells)
81.07.Vb Quantum wires

Analysis of defect-free GaSb/GaAs(001) quantum dots grown on the Sb-terminated (2 × 8) surface

Andrew J. Martin, Timothy W. Saucer, Kai Sun, Sung Joo Kim, Guang Ran, Garrett V. Rodriguez, Xiaoqing Pan, Vanessa Sih, and Joanna Millunchick

J. Vac. Sci. Technol. B 30, 02B112 (2012); doi:10.1116/1.3675455 (5 pages)

Online Publication Date: 9 January 2012

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Multilayer and single layer GaSb/GaAs(001) quantum dot structures were grown on an Sb-terminated (2 × 8) surface reconstruction and compared to those grown on an As-terminated (2 × 4) surface reconstruction. Uncapped quantum dots grown on the (2 × 8) surface were approximately 25% smaller in diameter and had a larger width/height aspect ratio. Quantum dots grown on both surfaces were defect free at the quantum dot/spacer layer interface. The dots did not appear to be fully compact when imaged by transmission electron microscopy, which may be due to dissolution and/or quantum ring formation. The quantum dot photoluminescence peak for dots grown on the (2 × 8) surface was brighter but at the same energy as that of dots grown on the (2 × 4) surface. This was likely the result of a higher areal density of dots on the (2 × 8) surface and a lower tendency for them to intermix during capping, resulting in dots of similar size for both samples after capping. Quantum dots grown on the (2 × 8) surface also displayed greater morphological stability when quenched in the absence of Sb.
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68.65.Hb Quantum dots (patterned in quantum wells)
68.47.Fg Semiconductor surfaces
78.67.Hc Quantum dots
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
81.40.Gh Other heat and thermomechanical treatments
68.35.bg Semiconductors

Homoepitaxial N-polar GaN layers and HEMT structures grown by rf-plasma assisted molecular beam epitaxy

D. F. Storm, D. J. Meyer, D. S. Katzer, S. C. Binari, Tanya Paskova, E. A. Preble, K. R. Evans, Lin Zhou, and David J. Smith

J. Vac. Sci. Technol. B 30, 02B113 (2012); doi:10.1116/1.3676175 (7 pages)

Online Publication Date: 12 January 2012

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The authors have investigated the growth and structural and electrical properties of homoepitaxial GaN layers and GaN/AlGaN heterostructures grown on free-standing, hydride vapor phase epitaxy grown, N-polar GaN:Fe substrates by rf-plasma molecular beam epitaxy. Secondary-ion mass spectroscopic analysis of unintentionally doped and Be-doped N-polar GaN layers indicate that oxygen is the dominant impurity in all layers and is largely insensitive to growth temperature in the range investigated (675 °C < TS < 760 °C). Transmission electron microscopy (TEM) indicates that threading dislocations are generated at the regrowth interface in these samples; in contrast to homoepitaxial growth on Ga-polar GaN, and that the density of threading dislocations diminishes as the growth temperature increases. However, examination by TEM indicates that threading dislocations are not generated at the regrowth interface of samples subjected to pregrowth substrate surface cleaning by gallium deposition and desorption and subsequent growth of ultrathin (15 Å) initial AlN layers. N-polar GaN/AlGaN heterostructures grown on Be-doped homoepitaxial N-polar GaN buffers exhibit low buffer leakage and Hall mobilities up to 1680 cm2/Vs at sheet densities of 1.3 × 1013 cm−2. High electron mobility transistors have been fabricated on these structures; drain current densities over 700 mA/mm and breakdown voltages as high as 70 V have been measured.
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85.30.Tv Field effect devices
85.75.Hh Spin polarized field effect transistors
68.55.A- Nucleation and growth

Growth of GaSb1−xBix by molecular beam epitaxy

Yuxin Song (宋禹忻), Shumin Wang, Ivy Saha Roy, Peixiong Shi, and Anders Hallen

J. Vac. Sci. Technol. B 30, 02B114 (2012); doi:10.1116/1.3672025 (7 pages)

Online Publication Date: 18 January 2012

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Molecular beam epitaxy for GaSb1−xBix is investigated in this article. The growth window for incorporation of Bi in GaSb was found. Strategies of avoiding formation of Bi droplets and enhancing Bi incorporation were studied. The Bi incorporation was confirmed by SIMS and RBS measurements. The Bi concentration in the samples was found to increase with increasing growth temperature and Bi flux. The position of GaSb1−xBix layer peak in XRD rocking curves is found to be correlated to Bi composition. Surface and structural properties of the samples were also investigated. Samples grown on GaSb and GaAs substrates were compared and no apparent difference for Bi incorporation was found.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.05.Np Atom, molecule, and ion scattering (for structure determination only)
68.55.J- Morphology of films
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Magnetic anisotropy of GaAs/Fe/Au core-shell nanowires grown by MBE

K. Tivakornsasithorn, R. E. Pimpinella, V. Nguyen, X. Liu, M. Dobrowolska, and J. K. Furdyna

J. Vac. Sci. Technol. B 30, 02B115 (2012); doi:10.1116/1.3678203 (4 pages)

Online Publication Date: 24 January 2012

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GaAs/Fe/Au core-shell nanowires were grown on GaAs(111)B substrates by molecular beam epitaxy. Scanning electron microscopy images show that the Fe shell has successfully coated the sidewalls of GaAs nanowires. Magnetic anisotropy of GaAs/Fe core-shell nanowires was studied by ferromagnetic resonance and by superconducting quantum interference device magnetometer. The authors’ results show that the magnetic anisotropy of this novel core-shell nanowire system cannot be simply described by any known theory, as revealed by attempts to use micromagnetic simulation using the Object Oriented MicroMagnetic Framework. The observed features thus suggest the existence of a domain structure that is specific to this new system
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75.30.Gw Magnetic anisotropy
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.07.Gf Nanowires
75.75.Cd Fabrication of magnetic nanostructures
75.75.Fk Domain structures in nanoparticles

Electrical properties of C60 and Si codoped GaAs layers

Jiro Nishinaga and Yoshiji Horikoshi

J. Vac. Sci. Technol. B 30, 02B116 (2012); doi:10.1116/1.3678205 (4 pages)

Online Publication Date: 24 January 2012

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C60 uniformly doped GaAs and C60, Si codoped GaAs layers are grown by a migration enhanced epitaxy method. C60 doped GaAs layers show a single and sharp diffraction peak in x-ray diffraction and only an LO phonon peak is confirmed, indicating that the crystalline quality is fairly good. All of the C60 doped GaAs layers have highly resistive characteristics, and C60, Si codoped GaAs layers show n-type conductivity only when the Si concentration is of the same order or greater than the total carbon concentrations. At low temperatures the conductivity of the C60, Si codoped GaAs layers increases with exposure to light whose energy is below the GaAs bandgap energy. The electron concentrations and mobilities of the layers are confirmed to be increased under illumination by wavelengths between 900 and 1100 nm. These results imply that the electron transitions from the valence band to the trap levels and from the trap levels to the conduction band occur simultaneously as if the traps act as intralevels. As a result, the carrier concentrations are enhanced in the same way they would be if the excitation was above the GaAs bandgap energy.
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73.61.Ey III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
72.60.+g Mixed conductivity and conductivity transitions

Molecular beam epitaxial growth and characterization of nitrogen δ-doped AlGaAs/GaAs quantum wells

Shin-ichiro Furuse, Kengo Sumiya, Masato Morifuji, and Fumitaro Ishikawa

J. Vac. Sci. Technol. B 30, 02B117 (2012); doi:10.1116/1.3678204 (5 pages)

Online Publication Date: 1 February 2012

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The authors carry out δ-doping at the middle of AlGaAs/GaAs quantum wells employing molecular beam epitaxy and varying the nitrogen coverage up to 0.5 monolayers. Transmission electron micrography and x ray diffraction indicate the introduction of a nitrogen δ-doped layer with precisely controlled position and nitrogen coverage. Photoluminescence spectra obtained for the samples show clear redshift of spectral peak positions depending on the amount of nitrogen, suggesting the band structure is modified by the δ-doping. The growth can be carried out at a substrate temperature of 560 °C. The growth temperature, which is high compared with that of standard dilute nitride compounds, could suppress the formation of growth-induced defects, resulting in the weak effect of post-growth thermal annealing on the characteristics of room-temperature photoluminescence.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.67.De Quantum wells

InAs MOS devices passivated with molecular beam epitaxy-grown Gd2O3 dielectrics

C. A. Lin, M. L. Huang, P.-C. Chiu, H.-K. Lin, J.-I. Chyi, T. H. Chiang, W. C. Lee, Y. C. Chang, Y. H. Chang, G. J. Brown, J. Kwo, and M. Hong

J. Vac. Sci. Technol. B 30, 02B118 (2012); doi:10.1116/1.3678206 (4 pages)

Online Publication Date: 1 February 2012

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InAs MOS devices passivated with molecular beam epitaxy (MBE)-grown Gd2O3 2–3 monolayers thick followed by an Al2O3 cap have demonstrated excellent electrical performances and interfacial properties. Band offset energies of in situ atomic-layer-deposited (ALD)-Al2O3/MBE-Gd2O3/InAs and ALD-Al2O3/InAs were determined by in situ x-ray photoelectron spectroscopy in conjunction with Fowler–Nordheim tunneling current analysis. A conduction-band offset energy (ΔEc) and a valence-band offset energy of 2.3 and 3.92 eV for ALD-Al2O3/InAs were determined, respectively. The insertion of a Gd2O3 layer increases the value of ΔEc by nearly 0.1 eV as compared to the case for Al2O3 directly deposited on InAs. The distribution of interfacial density of states (Dit) within the InAs bandgap, deduced by the conductance method at 77 K, gives a low Dit value of 1012 cm−2 eV−1 near the conduction-band edge. Moreover, with energy band engineering in the heterostructure, gate-first depletion channel InAs MOSFETs have produced drain current density of 46 μA/μm and transconductance of 17 μS/μm for 12-μm-gate-length devices at 300 K.
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85.30.Tv Field effect devices

Molecular beam epitaxy growth of AlGaN quantum wells on 6H-SiC substrates with high internal quantum efficiency

Wei Zhang, A. Yu. Nikiforov, C. Thomidis, J. Woodward, H. Sun, Chen-Kai Kao, D. Bhattarai, A. Moldawer, L. Zhou, D. J. Smith, and T. D. Moustakas

J. Vac. Sci. Technol. B 30, 02B119 (2012); doi:10.1116/1.3678208 (5 pages)

Online Publication Date: 1 February 2012

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The authors report the development of high internal quantum efficiency AlN/AlGaN/AlN double heterostructures and AlGaN/AlN multiple quantum wells (MQWs) grown on 6H-SiC and 4H-SiC substrates of various miscuts by plasma-assisted molecular-beam epitaxy. The authors find that the luminescence spectra for identical MQWs show a single peak across the gap, with a wavelength that is redshifted by ∼20 nm as the excess Ga during growth of the wells increases. The internal quantum efficiency of the double heterostructures emitting at 250 nm is found to be 43%, and that of the multiple quantum wells emitting at 245 nm is 68%. These results suggest that AlGaN alloys on SiC substrates are capable of producing deep-ultraviolet emitters with high efficiency. The authors propose that these results can be accounted for by the introduction of lateral band structure potential fluctuations due to the changing of the growth mode from physical vapor phase epitaxy to liquid phase epitaxy (LPE) as the excess gallium increases. In this LPE mode the arriving active nitrogen species from the plasma source and aluminum atoms from the aluminum effusion cells dissolve in the excess liquid gallium and incorporate into the film from the liquid phase.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.65.Fg Quantum wells
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
81.07.St Quantum wells

Shallow defect states in GaAs responsible for GaAs bandgap upconversion induced by electron beam during MBE growth

David M. Tex and Itaru Kamiya

J. Vac. Sci. Technol. B 30, 02B120 (2012); doi:10.1116/1.3679547 (4 pages)

Online Publication Date: 1 February 2012

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Upconversion through excitation of bulk GaAs is investigated by change in crystal growth conditions with electron beam (e-beam). The upconverted photoluminescence intensity is enhanced several times by striking the source fluxes with e-beam during molecular beam epitaxy (MBE) growth. Experimental evidence for a shallow intermediate state being responsible for this upconversion is presented. It is suggested that the intermediate state may be formed by shallow exciton trap states induced by As anti-site defects, which can be increased with e-beam during MBE growth.
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71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.80.Fe Electron and positron radiation effects
71.20.Ps Other inorganic compounds
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