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18 Apr 2005

Volume 86, Issue 16, Articles (16xxxx)

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On the band structure lineup of ZnO heterostructures

Winfried Mönch

Appl. Phys. Lett. 86, 162101 (2005); http://dx.doi.org/10.1063/1.1897436 (2 pages) | Cited 14 times

Online Publication Date: 11 April 2005

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The interface-induced gap states (IFIGS) are the fundamental mechanism which determines the band structure lineup at semiconductor interfaces. The valence-band offsets of semiconductor heterostructures are given by the difference of the respective IFIGS branch-point energies and electric-dipole terms which may be omitted for elemental group-IV semiconductors, SiC, as well as the III–V, II–VI, and I–III–VI2 compounds and alloys. The branch-point energy of ZnO is determined as 3.04±0.21 eV from an analysis of experimental valence-band offsets reported for various ZnO heterostructures.
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73.20.At Surface states, band structure, electron density of states
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Inhomogeneous distribution of dislocations in a SiGe graded layer and its influence on surface morphology and misfit dislocations at the interface of strained Si/Si0.8Ge0.2

X. L. Yuan, T. Sekiguchi, J. Niitsuma, Y. Sakuma, S. Ito, and S. G. Ri

Appl. Phys. Lett. 86, 162102 (2005); http://dx.doi.org/10.1063/1.1905802 (3 pages) | Cited 5 times

Online Publication Date: 12 April 2005

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To improve the quality of a strained Si layer on a SiGe virtual substrate, the distribution of dislocations in a graded SiGe layer is characterized using electron beam induced current (EBIC). A crosshatch pattern of dark and bright bands running along the two 〈110〉 directions is observed in an EBIC image taken with a 25-keV-electron beam at 80 K. These dark and bright EBIC bands are attributed, respectively, to high- and low-density dislocation regions in the graded SiGe layer, as is confirmed by transmission electron microscopy. The effects of such an inhomogeneous dislocation distribution on the surface morphology and the generation of misfit dislocations (MDs) at the interface of strained Si/SiGe are investigated. Comparison between the EBIC image and an atomic force microscope image shows that the high-density dislocation regions are correlated with ridges on the surface topography. A chemical etching image shows that most of the MDs lie along the edges of surface ridges. Possible mechanisms of MD generation at the interface of the strained Si/SiGe are proposed.
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81.05.Cy Elemental semiconductors
81.05.Hd Other semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.65.Cf Surface cleaning, etching, patterning
68.35.Ct Interface structure and roughness
68.55.-a Thin film structure and morphology
68.37.Lp Transmission electron microscopy (TEM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Spectral and temporal resolution of recombination from multiple excitation states in modulation-doped AlGaN/GaN multiple quantum well heterostructures

M. Furis, A. N. Cartwright, E. L. Waldron, and E. F. Schubert

Appl. Phys. Lett. 86, 162103 (2005); http://dx.doi.org/10.1063/1.1905785 (3 pages)

Online Publication Date: 12 April 2005

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Time-resolved photoluminescence measurements of carrier lifetimes in modulation-doped (100 Å) AlxGa1−xN/(100 Å) GaN multiple quantum well heterostructures are reported. The photoluminescence (PL) spectrum exhibits several lines associated with recombination of carriers from multiple excited electron states to the hole ground state. The PL decay times associated with ground state recombination, e0h0, are found to be much longer than the inverse repetition rate of our system (20 μs) and estimated to be 9 ms. The experimental lifetimes associated with carrier recombination from excited states vary between 4 μs for the first excited state, e1h0, and 4.5 ns for the fourth excited state, e4h0. These lifetimes are in very good agreement with a self-consistent calculation of radiative recombination lifetimes which takes into account piezoelectric and spontaneous polarization. The significant differences in recombination lifetimes are the result of the large built-in electric field in the wells (0.5 MV/cm).
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78.67.De Quantum wells
73.63.Hs Quantum wells
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Spin control in heteromagnetic nanostructures

A. V. Scherbakov, A. V. Akimov, D. R. Yakovlev, W. Ossau, L. Hansen, A. Waag, and L. W. Molenkamp

Appl. Phys. Lett. 86, 162104 (2005); http://dx.doi.org/10.1063/1.1906322 (3 pages) | Cited 8 times

Online Publication Date: 12 April 2005

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We suggest and verify experimentally a concept of heteromagnetic semiconductor structures. It is based on spin diffusion between layers of the nanostructure with different magnetic properties and allows to control the spin-switching rate for magnetic ions. A ten times increase of spin-lattice relaxation rate of magnetic Mn ions is achieved in Zn1−xMnxSe/Be1−yMnyTe heteromagnetic structures with an inhomogeneous distribution of Mn ions.
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75.50.Pp Magnetic semiconductors
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.50.Tt Fine-particle systems; nanocrystalline materials
76.60.Es Relaxation effects
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Direct observation of copper depletion and potential changes at copper indium gallium diselenide grain boundaries

M. J. Hetzer, Y. M. Strzhemechny, M. Gao, M. A. Contreras, A. Zunger, and L. J. Brillson

Appl. Phys. Lett. 86, 162105 (2005); http://dx.doi.org/10.1063/1.1906331 (3 pages) | Cited 36 times

Online Publication Date: 12 April 2005

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We have used micro-Auger electron spectroscopy, cathodoluminescence spectroscopy, and work function measurements in copper indium gallium diselenide polycrystalline solar cell films cleaved in ultrahigh vacuum. We establish that, relative to the grain interior, the grain boundary shows (1) a Cu composition decrease, as large as a factor of two, (2) a work function decrease of up to 480 meV, and (3) no additional radiative recombination centers despite a high concentration of grain boundary (GB) defects. These results confirm theoretical predictions that (i) polar GB interfaces are stabilized by massive ( ∼ 50%) removal of Cu atoms, leading to (ii) a valence band offset between GB and grain interiors that (iii) repels holes from the GB, thus likely reducing GB electron-hole recombination and improving photovoltaic (and other photonic) device operation.
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81.05.Hd Other semiconductors
79.20.Fv Electron impact: Auger emission
78.66.Li Other semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
61.72.Mm Grain and twin boundaries
73.30.+y Surface double layers, Schottky barriers, and work functions
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.61.Le Other inorganic semiconductors

High mobility two-dimensional hole system in GaAs/AlGaAs quantum wells grown on (100) GaAs substrates

M. J. Manfra, L. N. Pfeiffer, K. W. West, R. de Picciotto, and K. W. Baldwin

Appl. Phys. Lett. 86, 162106 (2005); http://dx.doi.org/10.1063/1.1900949 (3 pages) | Cited 21 times

Online Publication Date: 13 April 2005

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We report on the transport properties of a high mobility two-dimensional hole system (2DHS) confined in GaAs/AlGaAs quantum wells grown by molecular-beam epitaxy on the (100) surface of GaAs. The quantum wells are modulation doped with carbon utilizing a resistive filament source. At T = 0.3 K and carrier density p = 1×1011 cm−2, a mobility of 106 cm2/Vs is achieved. At fixed carrier density p = 1011 cm−2, the mobility is found to be a nonmonotonic function of the quantum well width. The mobility peaks at 106 cm2/Vs for a 15-nm well and is reduced for both smaller and larger well widths for these (100) samples. The mobility anisotropy is found to be small. Mobility along [0math1] is approximately 20% higher than along the [011] direction. In addition, the low-temperature carrier density is found to have low sensitivity to light. The hole density increases by only ∼ 10% after exposure to red light at T = 4.2 K. In structures designed for a lower carrier density of 3.6×1010 cm−2, a mobility of 800 000 cm2/Vs is achieved at T = 15 mK.
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81.07.St Quantum wells
81.05.Ea III-V semiconductors
73.63.Hs Quantum wells
73.50.Fq High-field and nonlinear effects
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.43.Qt Magnetoresistance

Electron spin interferometry using a semiconductor ring structure

Y. K. Kato, R. C. Myers, A. C. Gossard, and D. D. Awschalom

Appl. Phys. Lett. 86, 162107 (2005); http://dx.doi.org/10.1063/1.1906301 (3 pages) | Cited 17 times

Online Publication Date: 13 April 2005

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A ring structure fabricated from GaAs is used to achieve interference of the net spin polarization of conduction band electrons. Optically polarized spins are split into two packets by passing through two arms of the ring in the diffusive transport regime. Optical pumping with circularly polarized light on one arm establishes dynamic nuclear polarization which acts as a local effective magnetic field on electron spins due to the hyperfine interaction. This local field causes one spin packet to precess faster than the other, thereby controlling the spin interference when the two packets are combined.
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85.75.−d
78.47.-p Spectroscopy of solid state dynamics

Sulfur-induced exciton localization in Te-rich ZnSTe alloy

X. D. Yang, Z. Y. Xu, Z. Sun, Y. Ji, B. Q. Sun, I. K. Sou, and W. K. Ge

Appl. Phys. Lett. 86, 162108 (2005); http://dx.doi.org/10.1063/1.1906303 (3 pages) | Cited 1 time

Online Publication Date: 13 April 2005

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Exciton localization in Te-rich ZnSTe epilayers has been studied by photoluminescence (PL) and time-resolved PL. The sulfur-related exciton emission is found to dominate the radiative recombination at low temperature and is shifted to the low energy with the increase of S concentration. By measuring the PL dependence on temperature and by analyzing the PL decay process, we have clarified the localization nature of the sulfur-related exciton emission. Furthermore, the difference of the localization effect in Te- and S-rich ZnSTe is also compared and discussed.
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71.35.-y Excitons and related phenomena
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
78.47.-p Spectroscopy of solid state dynamics

Electronic transitions at defect states in Cz p-type silicon

A. Castaldini, D. Cavalcoli, A. Cavallini, S. Binetti, and S. Pizzini

Appl. Phys. Lett. 86, 162109 (2005); http://dx.doi.org/10.1063/1.1881788 (3 pages) | Cited 8 times

Online Publication Date: 14 April 2005

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Point and extended defects introduced in p-type Cz Si by oxygen precipitation and plastic deformation have been investigated with electrical and optical methods. Different materials (oxygen precipitated and/or deformed Cz Si and Fz Si) were examined in order to separate the role of oxygen precipitation, plastic deformation, and metallic contamination on the radiative and nonradiative electronic transitions at defect centers. A deep hole trap, named T1, has been associated with dislocation-related impurity centers; additional deep traps have been related to contamination by grown-in transition metals and to clusters involving oxygen atoms.
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81.05.Cy Elemental semiconductors
71.55.Cn Elemental semiconductors
61.72.Nn Stacking faults and other planar or extended defects
61.72.J- Point defects and defect clusters
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.55.Ap Elemental semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Depletion characteristics of two-dimensional lateral p‐n-junctions

D. Reuter, C. Werner, A. D. Wieck, and S. Petrosyan

Appl. Phys. Lett. 86, 162110 (2005); http://dx.doi.org/10.1063/1.1897829 (3 pages) | Cited 9 times

Online Publication Date: 14 April 2005

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We have fabricated two-dimensional in-plane p‐n junctions from a p-doped pseudomorphic GaAs/In0.1Ga0.9As/Al0.35Ga0.65As heterostructure employing Si compensation doping by focused ion beam implantation. The current–voltage characteristics at room temperature showed good rectifying behavior, and the current in the reverse direction was below 1 nA for voltages up to 10 V. The depletion width was measured by optical beam-induced current, and a linear dependence on the reverse bias was found which is in contrast to the square root dependence observed in three-dimensional junctions. The results agree well with theoretical predictions.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.uj III-V and II-VI semiconductors
73.40.Ei Rectification
72.40.+w Photoconduction and photovoltaic effects

Charging efficiency and lifetime of image-bound electrons on a dielectric surface

M. Biasini, R. D. Gann, J. A. Yarmoff, A. P. Mills, L. N. Pfeiffer, K. W. West, X. P. A. Gao, and B. C. D. Williams

Appl. Phys. Lett. 86, 162111 (2005); http://dx.doi.org/10.1063/1.1906314 (3 pages) | Cited 3 times

Online Publication Date: 14 April 2005

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The surface charge generated on an Al0.24Ga0.76As/GaAs quantum well sample by electron bombardment was monitored by measuring the change in the conductivity of the channel. Upon turning off the electron bombardment the surface charge on adsorbed layers of xenon and water at 8 K decays in room temperature darkness with a lifetime τ = 0.30±0.02 s. The average charging efficiency, μ0, defined as the ratio of the charge collected by the surface to the beam current times the charging time, is μ0 ≃ 0.001. Surface charging proves to be an effective method for contactless gating of field effect devices.
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73.63.Hs Quantum wells
73.21.Fg Quantum wells
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
73.40.-c Electronic transport in interface structures

Free and bound excitons in GaN/AlGaN homoepitaxial quantum wells grown on bulk GaN substrate along the nonpolar (11math0) direction

H. Teisseyre, C. Skierbiszewski, B. Łucznik, G. Kamler, A. Feduniewicz, M. Siekacz, T. Suski, P. Perlin, I. Grzegory, and S. Porowski

Appl. Phys. Lett. 86, 162112 (2005); http://dx.doi.org/10.1063/1.1899258 (3 pages) | Cited 15 times

Online Publication Date: 15 April 2005

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Nonpolar multiple quantum wells (MQWs) have been grown by plasma assisted molecular beam epitaxy on bulk GaN crystals oriented along the (11math0) direction. The photoluminescence intensity of the nonpolar MQWs was significantly higher than that found for the polar samples, both at low (10 K) and room temperature. This is a consequence of the lack of built-in electric field in samples grown along the (11math0) direction. Clearly resolved spectra of the excitons have been observed in the studied MQWs. Studies of these excitonic structures, by means of polarization and temperature measurements enabled us to assign the observed lines to free and bound excitons in GaN quantum wells.
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81.07.St Quantum wells
81.05.Ea III-V semiconductors
78.67.De Quantum wells
73.21.Fg Quantum wells
78.55.Cr III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.Fg Quantum wells
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