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9 May 2005

Volume 86, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 86, 191102 (2005); http://dx.doi.org/10.1063/1.1922084 (3 pages)

Nir Dahan, Avi Niv, Gabriel Biener, Vladimir Kleiner, and Erez Hasman
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Band structure and alignment of the AlN/SiC heterostructure

Jongwoo Choi, Ragesh Puthenkovilakam, and Jane P. Chang

Appl. Phys. Lett. 86, 192101 (2005); http://dx.doi.org/10.1063/1.1923187 (3 pages) | Cited 10 times

Online Publication Date: 2 May 2005

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Valence-band structures and band alignments at the AlN/SiC interface are studied by x-ray photoelectron spectroscopy (XPS) combined with first-principle calculations. Theoretical valence-band structures of SiC and AlN, and band offsets at their interface, were obtained by plane-wave pseudopotential method within the framework of density functional theory. The conduction- and valence-band offsets determined by XPS are 1.3 and 1.7 eV, respectively, in excellent agreement with the theoretical values. These relatively large band offsets indicate that AlN is suitable as a gate dielectric or a lattice-matched interfacial layer on SiC.
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73.50.-h Electronic transport phenomena in thin films
73.20.At Surface states, band structure, electron density of states
73.61.Ey III-V semiconductors
73.61.Le Other inorganic semiconductors
79.60.Jv Interfaces; heterostructures; nanostructures

Activation characteristics of ion-implanted Si+ in AlGaN

Y. Irokawa, O. Fujishima, T. Kachi, S. J. Pearton, and F. Ren

Appl. Phys. Lett. 86, 192102 (2005); http://dx.doi.org/10.1063/1.1926422 (3 pages) | Cited 11 times

Online Publication Date: 2 May 2005

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Multiple-energy Si+ implantation in the range 30–360 keV into Al0.13Ga0.87N for n-type doping was carried out at room temperature, followed by annealing at 1150–1375 °C for 5 min. Activation efficiencies close to 100% were obtained for ion doses of 1.0×1015 cm−2 after annealing at 1375 °C, with a resulting sheet resistance of 74 Ω/square. By sharp contrast, the activation efficiency at 1150 °C was only 4% for this dose, with a sheet resistance of 1.63×104 Ω/square. The activation efficiency was also a function of dose, with a maximum activation percentage of only 55% for lower doses of 1.0×1014 cm−2 annealed at 1375 °C. This is due to the comparatively larger effect of compensating acceptors at the lower dose and is also lower than the corresponding activation of Si in pure GaN under these conditions (78%). The measurement temperature dependence of sheet carrier density showed an activation energy of 23 meV, consistent with the ionization energy of Si in AlGaN.
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61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.80.Jh Ion radiation effects
61.72.S- Impurities in crystals

Low-resistance ohmic contacts to p-ZnMgO grown by pulsed-laser deposition

Hyuck Soo Yang, Y. Li, D. P. Norton, K. Ip, S. J. Pearton, Soohwan Jang, and F. Ren

Appl. Phys. Lett. 86, 192103 (2005); http://dx.doi.org/10.1063/1.1925309 (3 pages) | Cited 10 times

Online Publication Date: 3 May 2005

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Electron-beam deposited Ni/Au is found to produce ohmic contacts to p-type ZnMgO (p ∼ 1016 cm−3) after annealing in the range 300–450 °C. A minimum specific contact resistance of ∼ 10−2 Ω cm2 at room temperature and of 4×10−5 Ω cm2 at 473 K from circular transmission line measurements was obtained after annealing at 350 °C for 1 min in air. Higher anneal temperatures produced higher contact resistances and reaction of the contact metallurgy with diffusion of Ni to the surface of the Au layer where it became oxidized. The effective barrier height obtained from the measurement temperature dependence of the specific contact resistance, assuming thermionic emission, showed a value of 0.39±0.01 eV, much lower than the theoretical value of ∼ 2.4 eV. The difference in theoretical and experimental values is a clear indication of the strong role played by surface states, as reported earlier for Au Schottky contacts on ZnO.
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73.40.Cg Contact resistance, contact potential
73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
61.72.Cc Kinetics of defect formation and annealing
79.40.+z Thermionic emission

Improved hole mobilities and thermal stability in a strained‐Si/strained‐Si1−yGey/strained‐Si heterostructure grown on a relaxed Si1−xGex buffer

Saurabh Gupta, Minjoo L. Lee, and Eugene A. Fitzgerald

Appl. Phys. Lett. 86, 192104 (2005); http://dx.doi.org/10.1063/1.1923195 (3 pages) | Cited 4 times

Online Publication Date: 3 May 2005

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A dual channel heterostructure consisting of strained‐Si/strained‐Si1−yGey on a relaxed Si1−xGex buffer (y>x), provides a platform for fabricating metal–oxide–semiconductor field-effect transistors with high hole mobilities. Ge outdiffusion during high temperature processing steps from the strained‐Si1−yGey layer into the relaxed Si1−xGex buffer reduces the hole mobilities in these heterostructures. We present a strained‐Si/strained‐Si1−yGey/strained‐Si heterostructure on relaxed Si1−xGex, in which the strained-Si layer between the strained‐Si1−yGey and relaxed Si1−xGex reduces Ge outdiffusion. Improved hole mobilities in this heterostructure are also observed over similar dual channel heterostructures which could be a result of better hole confinement in the strained‐Si1−yGey layer of the proposed heterostructure.
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81.05.Cy Elemental semiconductors
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.35.Fx Diffusion; interface formation
73.61.Cw Elemental semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance

Room temperature near-ultraviolet emission from In-rich InGaN/GaN multiple quantum wells

Soon-Yong Kwon, Sung-Il Baik, Young-Woon Kim, Hee Jin Kim, Dong-Su Ko, Euijoon Yoon, Jung-Won Yoon, Hyeonsik Cheong, and Yoon-Soo Park

Appl. Phys. Lett. 86, 192105 (2005); http://dx.doi.org/10.1063/1.1923177 (3 pages) | Cited 18 times

Online Publication Date: 3 May 2005

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We grew In-rich InGaN/GaN multiple quantum wells (MQWs) using growth interruption (GI) by metalorganic chemical vapor deposition. The quality of overgrown InGaN/GaN QW layers in MQWs was largely affected by the crystalline quality and interfacial abruptness of the underlying QW layer. Introduction of 10 s GI was very effective in improving the crystalline quality and interfacial abruptness of InGaN QW layers, and we grew a ten periods of 1-nm-thick In-rich InGaN/GaN MQW with 10 s GI and obtained a strong near-ultraviolet (UV) emission ( ∼ 390 nm) at room temperature. We believe that use of less than 1-nm-thick In-rich InGaN MQW can be a candidate for near-UV source, which might replace the conventional low-indium content (<10%), thicker InGaN QW layer.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
68.65.Fg Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Modulating the growth conditions: Si as an acceptor in (110) GaAs for high mobility p-type heterostructures

F. Fischer, D. Schuh, M. Bichler, G. Abstreiter, M. Grayson, and K. Neumaier

Appl. Phys. Lett. 86, 192106 (2005); http://dx.doi.org/10.1063/1.1923761 (3 pages) | Cited 8 times

Online Publication Date: 4 May 2005

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We implement metallic layers of Si-doped (110) GaAs as modulation doping in high mobility p-type heterostructures, changing to p-growth conditions for the doping layer alone. The strongly autocompensated doping is characterized in bulk samples first, identifying the metal-insulator transition density and confirming classic hopping conduction in the insulating regime. To overcome the poor morphology inherent to Si p-type (110) growth, heterostructures are then fabricated with only the modulation-doping layer grown under p-type conditions. Such heterostructures show a hole mobility of μ = 1.75×105 cm2/V s at density p = 2.4×1011 cm−2. We identify the zero-field spin-splitting characteristic of p-type heterostructures, but observe a remarkably isotropic mobility and a persistent photoconductivity unusual for p heterojunctions grown on other facets. This modulated growth technique is particularly relevant for p-type cleaved-edge overgrowth and for III-V growth chambers, where Si is the only dopant.
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81.05.Dz II-VI semiconductors
81.05.Cy Elemental semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.55.-a Thin film structure and morphology
61.72.uj III-V and II-VI semiconductors
72.20.Ee Mobility edges; hopping transport
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance
71.30.+h Metal-insulator transitions and other electronic transitions
72.60.+g Mixed conductivity and conductivity transitions
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects

Spin-polarized transport of two-dimensional electron gas embedded in a diluted magnetic semiconductor

W. Yang, Kai Chang, and F. M. Peeters

Appl. Phys. Lett. 86, 192107 (2005); http://dx.doi.org/10.1063/1.1927693 (3 pages) | Cited 3 times

Online Publication Date: 4 May 2005

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The spin-polarized transport property of a diluted magnetic semiconductor two-dimensional electron gas is investigated theoretically at low temperature. A large current polarization can be found in this system even at small magnetic fields and oscillates with increasing magnetic field while the carrier polarization is vanishingly small. The magnitude as well as the sign of the current polarization can be tuned by varying magnetic field, the electron density and the Mn concentration.
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72.25.Dc Spin polarized transport in semiconductors
75.50.Pp Magnetic semiconductors
73.21.Fg Quantum wells

Highly Si-doped AlN grown by plasma-assisted molecular-beam epitaxy

M. Hermann, F. Furtmayr, A. Bergmaier, G. Dollinger, M. Stutzmann, and M. Eickhoff

Appl. Phys. Lett. 86, 192108 (2005); http://dx.doi.org/10.1063/1.1923180 (3 pages) | Cited 15 times

Online Publication Date: 5 May 2005

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We have studied the influence of the growth conditions on the Si incorporation in AlN films grown by plasma-assisted molecular-beam epitaxy. Nitrogen-rich growth conditions allow controlled incorporation of Si up to a concentration of 5.2×1021 cm−3, determined by elastic recoil detection analysis, whereas Si incorporation is supressed under Al-rich growth conditions. The structural and morphological properties determined by x-ray diffraction and atomic force microscopy were not affected up to Si concentrations of 1.2×1021 cm−3. The electrical conductivity for the N-rich growth regime first increases with Si concentration followed by a decrease due to an increase of the activation energy up to 570 meV for a Si content of 1.2×1021 cm−3. For higher silicon concentrations, we have observed a sharp decrease in activation energy and an increase in conductivity by four orders of magnitude, attributed to the onset of impurity band conduction.
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81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
52.77.Dq Plasma-based ion implantation and deposition
73.61.Ey III-V semiconductors
68.37.Ps Atomic force microscopy (AFM)
61.72.uj III-V and II-VI semiconductors

Large negative persistent photoconductivity in InAs/AlSb quantum wells

Yu. G. Sadofyev, A. Ramamoorthy, J. P. Bird, S. R. Johnson, and Y.-H. Zhang

Appl. Phys. Lett. 86, 192109 (2005); http://dx.doi.org/10.1063/1.1926407 (3 pages) | Cited 3 times

Online Publication Date: 5 May 2005

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Negative persistent photoconductivity in backgated InAs/AlSb quantum wells under red and blue light emitting diode illumination is observed to depend on both illumination energy and intensity. During these experiments the electron sheet density is varied by one order of magnitude from 5.6×1011 to 5.8×1010 cm−2. This behavior is attributed to the role of optically excited holes in the AlSb barrier layers near the InAs quantum well. Furthermore, a long relaxation time in the electron sheet density is observed and attributed to the slow movement of electrons from the InAs quantum well to ionized deep levels in the AlSb barriers.
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81.07.St Quantum wells
81.05.Ea III-V semiconductors
72.40.+w Photoconduction and photovoltaic effects
73.21.Fg Quantum wells
71.55.Eq III-V semiconductors
73.63.Hs Quantum wells
78.67.De Quantum wells
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.20.Nr Semiconductor compounds
73.20.At Surface states, band structure, electron density of states

Atomic layer deposition of high-κ dielectrics on nitrided silicon surfaces

Ye Xu and Charles B. Musgrave

Appl. Phys. Lett. 86, 192110 (2005); http://dx.doi.org/10.1063/1.1922080 (3 pages) | Cited 6 times

Online Publication Date: 6 May 2005

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An atomistic mechanism for the initiation of atomic layer deposition (ALD) of hafnium oxide (HfO2) on nitrided silicon surfaces was investigated using density functional theory. Reactions involving two different metal precursors are studied. Hf[N(CH3)2]4 does not form an adsorbed molecular complex, while HfCl4 has an adsorption energy of 0.30 eV. The ALD ligand exchange reaction is direct and 0.19 eV exothermic for Hf[N(CH3)2]4 with a barrier of 0.63 eV, while it is mediated by a complex intermediate and 0.40 eV endothermic for HfCl4 with a barrier of 0.97 eV. These results indicate that Hf[N(CH3)2]4 is both thermodynamically and kinetically superior to HfCl4 for the initial ALD of HfO2 on nitrided silicon surfaces.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
68.43.Mn Adsorption kinetics
65.90.+i Other topics in thermal properties of condensed matter (restricted to new topics in section 65)

Fermi-level band filling and band-gap renormalization in Ga-doped ZnO

J. D. Ye, S. L. Gu, S. M. Zhu, S. M. Liu, Y. D. Zheng, R. Zhang, and Y. Shi

Appl. Phys. Lett. 86, 192111 (2005); http://dx.doi.org/10.1063/1.1928322 (3 pages) | Cited 27 times

Online Publication Date: 6 May 2005

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The fundamental optical properties of Ga-doped ZnO films grown by metalorganic chemical vapor deposition were investigated by room-temperature transmittance and photoluminescence (PL) spectroscopy. The Burstein–Moss (BM) shift of the absorption edge energy is observed at the carrier concentration up to 2.47×1019 cm−3. The absorption edges are fitted to a comprehensive model based on the electronic energy-band structure near critical points plus relevant discrete and continuum excitonic effects, taking account of the Fermi-level filling factor. The theoretical calculation for BM effect is in good agreement with the experimental facts, considering the nonparabolic nature of conduction-band and band-gap renormalization (BGR) effects. Meanwhile, the monotonic redshift of the near-band-gap emission detected by PL measurements has also been observed with increasing free-carrier concentration, which is attributed to the BGR effects, and can be fitted by an n1/3 power law with a BGR coefficient of 1.3×10−5 meV cm.
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81.05.Dz II-VI semiconductors
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
71.55.Gs II-VI semiconductors
71.20.Nr Semiconductor compounds
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uj III-V and II-VI semiconductors
71.35.-y Excitons and related phenomena

Purification and crystallization of tungsten wires fabricated by focused-ion-beam-induced deposition

M. Prestigiacomo, F. Bedu, F. Jandard, D. Tonneau, H. Dallaporta, L. Roussel, and P. Sudraud

Appl. Phys. Lett. 86, 192112 (2005); http://dx.doi.org/10.1063/1.1927714 (3 pages) | Cited 11 times

Online Publication Date: 6 May 2005

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We studied the behavior of tungsten wires, fabricated by focused-ion-beam-induced deposition and subjected to high current density. We present a simple electrical treatment, which allows an improved wire resistivity of more than 80%. We have distinguished two steps in the treatment. When the current density reaches 1.4×107 A/cm2, Ga atoms segregate and form droplets on the wire. As the current density increases, new droplets appear and merge into a single droplet. At 5.8×107 A/cm2, the droplet evaporates, the resistance is lost and the wire crystallizes. The final resistivity is close to 55 μΩ cm. The same treatment applied to as-deposited platinum wires does not lead to the same observations: neither segregation nor crystallization was found.
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81.05.Bx Metals, semimetals, and alloys
81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.20.Ym Purification
64.70.D- Solid-liquid transitions
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
64.75.-g Phase equilibria

Electron tunneling spectroscopy study of traps in high-k gate dielectrics: Determination of physical locations and energy levels of traps

Miaomiao Wang, Wei He, and T. P. Ma

Appl. Phys. Lett. 86, 192113 (2005); http://dx.doi.org/10.1063/1.1924893 (2 pages) | Cited 10 times

Online Publication Date: 6 May 2005

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It will be demonstrated that the electron tunneling spectroscopy (ETS), obtained by taking the second derivative of the current-voltage (I–V) characteristic of a tunnel barrier, is an effective technique to probe traps in ultra-thin gate dielectrics where significant tunneling currents flow. By taking the electron tunneling spectra in both polarities, one can determine the locations and energy levels of traps that appear in the ETS spectra. The procedure for the above and the associated derivation will be presented. Examples are shown to demonstrate the use of ETS to track the evolution of traps in high-k gate dielectrics under electrical stress.
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73.40.Gk Tunneling
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
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