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4 Feb 2013

Volume 102, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 102, 053102 (2013); http://dx.doi.org/10.1063/1.4789442 (5 pages)

P. H. Kim, C. Doolin, B. D. Hauer, A. J. R. MacDonald, M. R. Freeman, P. E. Barclay, and J. P. Davis
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Identification of the native defect doping mechanism in amorphous indium zinc oxide thin films studied using ultra high pressure oxidation

Sunghwan Lee and David C. Paine

Appl. Phys. Lett. 102, 052101 (2013); http://dx.doi.org/10.1063/1.4790187 (5 pages) | Cited 2 times

Online Publication Date: 4 February 2013

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The mechanism of native defect doping in amorphous In-Zn-O (a-IZO) has not previously been established but is likely associated with native oxygen defect doping. We have used high pressure oxidation and defect equilibrium analysis to show a −1/6 power dependence of carrier density on oxygen fugacity in a-IZO. This dependency is predicted for oxygen vacancy-like donor defects. Extrapolation of equilibrium constants established at high pressures to atmospheric pressure reveals that the equilibrium carrier density in a-IZO at 200 °C is higher (>1020/cm3) than typical as-deposited channel carrier densities (<1017/cm3). This is consistent with observed increases in channel carrier density and negative threshold voltage shift in annealed a-IZO thin film transistor devices.
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61.72.uj III-V and II-VI semiconductors
68.35.bj Amorphous semiconductors, glasses
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.40.Gh Other heat and thermomechanical treatments
81.65.Mq Oxidation
82.60.Hc Chemical equilibria and equilibrium constants

The source of the threading dislocation in GaSb/GaAs hetero-structures and their propagation mechanism

Yi Wang, P. Ruterana, S. Kret, S. El Kazzi, L. Desplanque, and X. Wallart

Appl. Phys. Lett. 102, 052102 (2013); http://dx.doi.org/10.1063/1.4790296 (5 pages)

Online Publication Date: 4 February 2013

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The misfit and threading dislocations during GaSb epitaxy on GaAs substrate were investigated by weak beam dark field and high angle dark field scanning transmission electron microscopy. The geometric phase analysis and dislocation density tensor analysis were next used to analyze the strain around the threading dislocations and quantify the corresponding Burgers vectors. It is shown that there are three types of threading dislocations (mixed, edge, and pair of mixed types) close to the interface, which originate from the 60°, Lomer, and 60° pair misfit dislocations, respectively. During the growth of the epitaxial layer, the edge type as well as the pair of mixed threading dislocations split into two mixed type dislocations for the glide in {111} planes. Eventually, only mixed type dislocations have been observed at the surface of thick GaSb layers.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors

Correlation between Ti source/drain contact and performance of InGaZnO-based thin film transistors

Kwang-Hyuk Choi and Han-Ki Kim

Appl. Phys. Lett. 102, 052103 (2013); http://dx.doi.org/10.1063/1.4790357 (5 pages) | Cited 1 time

Online Publication Date: 4 February 2013

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Ti contact properties and their electrical contribution to an amorphous InGaZnO (a-IGZO) semiconductor-based thin film transistor (TFT) were investigated in terms of chemical, structural, and electrical considerations. TFT device parameters were quantitatively studied by a transmission line method. By comparing various a-IGZO TFT parameters with those of different Ag and Ti source/drain electrodes, Ti S/D contact with an a-IGZO channel was found to lead to a negative shift in VT (−Δ 0.52 V). This resulted in higher saturation mobility (8.48 cm2/Vs) of a-IGZO TFTs due to effective interfacial reaction between Ti and an a-IGZO semiconducting layer. Based on transmission electron microcopy, x-ray photoelectron depth profile analyses, and numerical calculation of TFT parameters, we suggest a possible Ti contact mechanism on semiconducting a-IGZO channel layers for TFTs.
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73.40.Ns Metal-nonmetal contacts
85.30.Tv Field effect devices

Phosphorus doping of 4H SiC by liquid immersion excimer laser irradiation

Akihiro Ikeda, Koji Nishi, Hiroshi Ikenoue, and Tanemasa Asano

Appl. Phys. Lett. 102, 052104 (2013); http://dx.doi.org/10.1063/1.4790621 (4 pages)

Online Publication Date: 4 February 2013

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Phosphorus doping of 4H SiC is performed by KrF excimer laser irradiation of 4H SiC immersed in phosphoric acid. Phosphorus is incorporated to a depth of a few tens of nanometers at a concentration of over 1020/cm3 without generating significant crystal defects. Formation of a pn junction diode with an ideality factor of 1.06 is demonstrated.
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61.72.up Other materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects

Scattering due to large cluster embedded in quantum wells

Changbo Liu, Guijuan Zhao, Guipeng Liu, Yafeng Song, Heng Zhang, Dongdong Jin, Zhiwei Li, Xianglin Liu, Shaoyan Yang, Qinsheng Zhu, and Zhanguo Wang

Appl. Phys. Lett. 102, 052105 (2013); http://dx.doi.org/10.1063/1.4782218 (4 pages)

Online Publication Date: 5 February 2013

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Two dimensional electron gas mobility limited by the scattering of large cluster is studied. From this study, we find that the scattering caused by conduction band offset between host well and multiple mini-quantum well (mini-QW) series aligned along the QW channel, i.e., quantum pits, can be treated as a variable in our calculation. The results show that the mobility increases with increasing barrier height, which is opposite to the well-known interface roughness scattering mobility. To make the calculation simple, the InxGa1−xN/InyGa1−yN QW double-heterostructure is selected to along (11math0) non-polarized direction, along which the barrier and well are both flat.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.35.Ct Interface structure and roughness

Tensile strained GeSn on Si by solid phase epitaxy

R. R. Lieten, J. W. Seo, S. Decoster, A. Vantomme, S. Peters, K. C. Bustillo, E. E. Haller, M. Menghini, and J.-P. Locquet

Appl. Phys. Lett. 102, 052106 (2013); http://dx.doi.org/10.1063/1.4790302 (5 pages)

Online Publication Date: 5 February 2013

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We demonstrate single crystalline GeSn with tensile strain on silicon substrates. Amorphous GeSn layers are obtained by limiting the adatom surface mobility during deposition. Subsequent annealing transforms the amorphous layer into single crystalline GeSn by solid phase epitaxy. Excellent structural quality is demonstrated for layers with up to 6.1% of Sn. The GeSn layers show tensile strain (up to +0.34%), which lowers the difference between direct and indirect band transition and makes this method promising for obtaining direct band gap group IV layers. GeSn with 4.5% Sn shows increased optical absorption compared to Ge and an optical band gap of 0.52 eV.
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81.15.Np Solid phase epitaxy; growth from solid phases
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
68.55.at Other materials
73.61.At Metal and metallic alloys
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Bz Metals and metallic alloys

Carrier transport mechanism of low resistance Ti/Al/Au ohmic contacts to AlInN/GaN heterostructures

Seongjun Kim, Jae-Hyun Ryou, Russell D. Dupuis, and Hyunsoo Kim

Appl. Phys. Lett. 102, 052107 (2013); http://dx.doi.org/10.1063/1.4790384 (4 pages)

Online Publication Date: 5 February 2013

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The carrier transport mechanism of a low resistance Ti/Al/Au Ohmic contact to AlInN/GaN heterostructures was investigated. The Ohmic contact produced upon thermal annealing was due to the generation of TiN contact inclusions with a density of 2.8 × 108 cm−2, i.e., spike mechanism. The sheet resistance of channel layer was found to follow power law, yielding the power index of −1.57. Temperature dependent contact resistance could be understood based on the parallel network model consisting of distributed resistance components of TiN contact inclusion (predominant) and the rest sound region (negligible), giving the barrier height of 0.65 eV and the carrier density of 2.3 × 1019 cm−3 at the TiN/GaN interfaces.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential

Diameter-dependent boron diffusion in silicon nanowire-based transistors

Andreas Schulze, Antonios Florakis, Thomas Hantschel, Pierre Eyben, Anne S. Verhulst, Rita Rooyackers, Anne Vandooren, and W. Vandervorst

Appl. Phys. Lett. 102, 052108 (2013); http://dx.doi.org/10.1063/1.4790438 (4 pages)

Online Publication Date: 5 February 2013

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We analyzed the carrier profile in silicon nanowire-based tunnel-FETs as a function of nanowire diameter using scanning spreading resistance microscopy. The nanowires were etched into an epitaxially grown stack, of which the top layer was in situ boron doped and the top contact was implanted. We revealed a significantly reduced boron diffusion inside narrower nanowires and a nonuniform diffusion depth in wider nanowires. Using process simulations, we attribute the latter to a reduced transient enhanced diffusion close to the nanowire sidewall caused by the recombination of excess interstitials. The shallower profile in narrower nanowires is related to an enhanced interstitial annihilation.
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85.30.Tv Field effect devices
66.30.J- Diffusion of impurities

Spatially resolved investigation of strain and composition variations in (In,Ga)N/GaN epilayers

Benjamin Wilsch, Uwe Jahn, Bernd Jenichen, Jonas Lähnemann, Holger T. Grahn, Hui Wang, and Hui Yang

Appl. Phys. Lett. 102, 052109 (2013); http://dx.doi.org/10.1063/1.4790591 (4 pages)

Online Publication Date: 5 February 2013

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The strain state and composition of a 400 nm thick (In,Ga)N layer grown by metal-organic chemical vapor deposition on a GaN template are investigated by spatially integrated x-ray diffraction and cathodoluminescence (CL) spectroscopy as well as by spatially resolved CL and energy dispersive x-ray analysis. The CL investigations confirm a process of strain relaxation accompanied by an increasing indium content toward the surface of the (In,Ga)N layer, which is known as the compositional pulling effect. Moreover, we identify the strained bottom, unstrained top, and gradually relaxed intermediate region of the (In,Ga)N layer. In addition to an increase of the indium content along the growth direction, the strain relaxation leads to an enhancement of the lateral variations of the indium distribution toward the surface.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.ag Semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence

Infrared reflectivity spectra of gas-source molecular beam epitaxy grown dilute InNxAs1−x/InP (001)

Devki N. Talwar, Tzuen-Rong Yang, Hao Hsiung Lin, and Zhe Chuan Feng

Appl. Phys. Lett. 102, 052110 (2013); http://dx.doi.org/10.1063/1.4790605 (4 pages)

Online Publication Date: 5 February 2013

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Vibrational spectra of gas-source molecular beam epitaxy grown dilute InNxAs1−x/InP (001) alloys are obtained using a Fourier-transform infrared (IR) spectroscopy. A triply degenerate NAs local vibrational mode of Td-symmetry is observed near 438 cm−1 corresponding to the In-N bond energy. The analysis of composition dependent infrared reflectivity spectra in InNAs has predicted a two-phonon-mode behavior. In In(Ga)-rich GaInNAs alloys the observed splitting of the NAs local mode into a doublet for the NAs–Ga1(In1)In3(Ga3) pair-defect of C3v-symmetry is consistent with our simulated results based on a sophisticated Green's function theory.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
63.20.kg Phonon-phonon interactions
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors

Photocurrent induced by two-photon excitation in ZnTeO intermediate band solar cells

Tooru Tanaka, Masaki Miyabara, Yasuhiro Nagao, Katsuhiko Saito, Qixin Guo, Mitsuhiro Nishio, Kin M. Yu, and Wladek Walukiewicz

Appl. Phys. Lett. 102, 052111 (2013); http://dx.doi.org/10.1063/1.4790643 (4 pages)

Online Publication Date: 5 February 2013

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Intermediate band (IB) solar cell structures based on ZnTeO highly mismatched alloy were examined to demonstrate a photocurrent induced by a two-photon excitation (TPE) process. Two types of the devices, with and without a blocking layer for the IB, are prepared. The device with a blocked IB exhibits small external quantum efficiency (EQE) in photon energy range in which electron transitions from valence band (VB) to IB take place, implying the electron accumulation in IB. The enhancement of EQE is observed in TPE experiments as a result of electron transition from VB to conduction band via IB.
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88.40.J- Types of solar cells

Negative spin-exchange splitting in the exciton fine structure of AlN

Martin Feneberg, María Fátima Romero, Benjamin Neuschl, Klaus Thonke, Marcus Röppischer, Christoph Cobet, Norbert Esser, Matthias Bickermann, and Rüdiger Goldhahn

Appl. Phys. Lett. 102, 052112 (2013); http://dx.doi.org/10.1063/1.4790645 (4 pages)

Online Publication Date: 5 February 2013

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The exact energy position of the free exciton transition and thus the lowest band gap in bulk wurtzite AlN are still under discussion. By combined high resolution optical emission and absorption experiments on a sample with (1math00) surface, we resolve the fine structure of the lowest energy free exciton and determine an electron-hole spin-exchange interaction constant of j = −4 meV. This results in a low energy Γ1 exciton at 6.032 eV and a high energy Γ5 component at 6.040 eV. Only the latter one is observable for (0001) oriented AlN films due to selection rules.
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71.35.Cc Intrinsic properties of excitons; optical absorption spectra
71.70.Gm Exchange interactions
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
71.20.Nr Semiconductor compounds

Energy-loss rate of a fast particle in two-dimensional semiconductors with Rashba spin-orbit coupling

W. Feng, Asya Tawfiq, J. C. Cao, and C. Zhang

Appl. Phys. Lett. 102, 052113 (2013); http://dx.doi.org/10.1063/1.4790847 (3 pages)

Online Publication Date: 6 February 2013

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The energy-loss rate (ELR) of a charged particle in a two-dimensional semiconductor with Rashba spin-orbit coupling is studied. Our model takes into account of the temperature and density dependence of the electronic properties of the Rashba system. The energy and temperature dependence of the ELR are presented. It is found that a finite Rashba spin-orbit coupling offers a mechanism of tuning the mean scattering time in narrow-gap semiconductors. With a change of Rashba parameter of around 3 times, the mean scattering time can change by one to two orders of magnitude.
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71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
73.21.Fg Quantum wells
73.22.-f Electronic structure of nanoscale materials and related systems
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
71.20.Nr Semiconductor compounds

High beta lasing in micropillar cavities with adiabatic layer design

M. Lermer, N. Gregersen, M. Lorke, E. Schild, P. Gold, J. Mørk, C. Schneider, A. Forchel, S. Reitzenstein, S. Höfling, and M. Kamp

Appl. Phys. Lett. 102, 052114 (2013); http://dx.doi.org/10.1063/1.4791563 (4 pages)

Online Publication Date: 7 February 2013

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We report on lasing in optically pumped adiabatic micropillar cavities, based on the AlAs/GaAs material system. A detailed study of the threshold pump power and the spontaneous emission β factor in the lasing regime for different diameters dc is presented. We demonstrate a reduction of the threshold pump power by over 2 orders of magnitude from dc = 2.25 μm down to 0.95 μm. Lasing with β factors exceeding 0.5 shows that adiabatic micropillars are operating deeply in the cavity quantum electrodynamics regime.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Sa Microcavity and microdisk lasers
42.60.By Design of specific laser systems

800 meV localization energy in GaSb/GaAs/Al0.3Ga0.7As quantum dots

T. Nowozin, L. Bonato, A. Högner, A. Wiengarten, D. Bimberg, Wei-Hsun Lin, Shih-Yen Lin, C. J. Reyner, Baolai L. Liang, and D. L. Huffaker

Appl. Phys. Lett. 102, 052115 (2013); http://dx.doi.org/10.1063/1.4791678 (4 pages)

Online Publication Date: 7 February 2013

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The localization energies, capture cross sections, and storage times of holes in GaSb quantum dots (QDs) are measured for three GaSb/GaAs QD ensembles with different QD sizes. The structural properties, such as height and diameter, are determined by atomic force microscopy, while the electronic properties are measured using deep-level transient spectroscopy. The various QDs exhibit varying hole localization energies corresponding to their size. The maximum localization energy of 800 (±50) meV is achieved by using additional Al0.3Ga0.7As barriers. Based on an extrapolation, alternative material systems are proposed to further increase the localization energy and carrier storage time of QDs.
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73.21.La Quantum dots
81.07.Ta Quantum dots
79.10.Ca Deep-level photothermal spectroscopy
68.37.Ps Atomic force microscopy (AFM)
68.65.Hb Quantum dots (patterned in quantum wells)
71.55.Eq III-V semiconductors
73.20.Qt Electron solids
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