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24 Apr 2000

Volume 76, Issue 17, pp. 2325-2474

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Effect of GaAsyP1−y(0 ⩽ y<1) interlayers on the structural, optical, and electrical characteristics of GaAs/InGaP heterojunction

Yong-Hwan Kwon, Weon G. Jeong, Yong-Hoon Cho, and Byung-Doo Choe

Appl. Phys. Lett. 76, 2379 (2000); http://dx.doi.org/10.1063/1.126352 (3 pages) | Cited 11 times

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The effect of GaAsyP1−y(0 ⩽ y<1) interlayers on the characteristics of GaAs/InGaP heterojunction has been investigated. For samples having GaAsyP1−y interlayers in the range of 0<y ⩽ 0.75 inserted in the GaAs-on-InGaP interface, sharp GaAs band-edge emissions are recovered. These results are attributed to smoothly grown InGaAs(P) interfacial layers with the band-gap energy higher than that of GaAs through transmission electron microscopy measurements. In addition, the amount of carrier depletion at the GaAs-on-InGaP interface is smaller with the use of GaAsyP1−y interlayers than that for no interlayer in capacitance–voltage measurements. © 2000 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
68.35.Ct Interface structure and roughness
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
71.20.Nr Semiconductor compounds
73.20.At Surface states, band structure, electron density of states

Cooperative nucleation leading to ripple formation in InGaAs/GaAs films

Nehal S. Chokshi and Joanna Mirecki Millunchick

Appl. Phys. Lett. 76, 2382 (2000); http://dx.doi.org/10.1063/1.126353 (3 pages) | Cited 18 times

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In0.25Ga0.75As epilayers were grown on GaAs (001) substrates (1.8% misfit strain) by molecular beam epitaxy to investigate the two-dimensional to three-dimensional transition as a function of thickness (t ⩽ 30 MLs). Tapping-mode atomic force micrographs show the evolution of the morphology as a function of thickness. As the film is deposited, the nucleation of 3D islands followed by cooperative nucleation of pits is observed. As the thickness increases, both islands and pits continue to nucleate and grow until they coalesce, resulting in a fully formed ripple morphology running along the [1math0]. The ripples also exhibit a secondary alignment roughly along the 〈310〉 which is attributed to the nucleation of islands with {136} faces. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
64.60.Q- Nucleation
68.35.B- Structure of clean surfaces (and surface reconstruction)

Thermoelectric properties of Bi2Sr2Co2Ox polycrystalline materials

Ryoji Funahashi, Ichiro Matsubara, and Satoshi Sodeoka

Appl. Phys. Lett. 76, 2385 (2000); http://dx.doi.org/10.1063/1.126354 (3 pages) | Cited 88 times

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Bi2Sr2Co2O9 (BC-2202) polycrystalline materials with a layered structure have been prepared by partial melting. The chemical compositions of the samples are Bi2Sr2Co2Ox (2202), Bi1.8Sr2Co2Ox (Bi-1.8), and Bi2Sr1.8Co2Ox (Sr-1.8). All three samples are p-type conductors. The electric properties, namely, the Seebeck coefficient (S) and electric resistivity (ρ), of the samples are dependent on chemical composition. The S values increase with temperature at T>673 K and, at 973 K, reach 100, 110, and 150 μV K−1 for the 2202, the Bi-1.8, and the Sr-1.8 samples, respectively. Thermal conductivity (κ) for all samples is lower than for ordinary conducting oxides. The figure of merit (Z) increases with temperature for all samples. Z values at 973 K are 0.77×10−4, 0.61×10−4, and 2.0×10−4 K−1 for the 2202, Bi-1.8, and Sr-1.8 samples, respectively. The thermoelectric properties depend on the chemical composition of the BC-2202 phase. The BC-2202 material thus appears to be a promising thermoelectric material due to its high performance at high temperature (∼1000 K). © 2000 American Institute of Physics.
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72.15.Jf Thermoelectric and thermomagnetic effects
72.20.Pa Thermoelectric and thermomagnetic effects
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys

Dynamic behavior of hot-electron–hole plasma in highly excited GaN epilayers

S. Juršėnas, G. Kurilčik, G. Tamulaitis, A. Žukauskas, R. Gaska, M. S. Shur, M. A. Khan, and J. W. Yang

Appl. Phys. Lett. 76, 2388 (2000); http://dx.doi.org/10.1063/1.126355 (3 pages) | Cited 11 times

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The room-temperature spontaneous luminescence of electron–hole plasma was investigated in GaN epilayers under extremely high quasi-steady-state photoexcitation. The photoluminescence spectra were measured for excitation power densities up to 200 MW/cm2 both under quasiresonant and off-resonant excitation conditions. High carrier temperatures up to 1000 K were observed under off-resonant excitation. A nonmonotonous dependence of the luminescence band peak position Ep on the excitation power density was observed. We attribute this nonmonotonous behavior of Ep to two competing mechanisms: (i) band-gap shrinkage due to carrier screening effects (redshift); and (ii) nonequilibrium carrier heating (blueshift). The obtained results are in a good agreement with finite-temperature theory of the band-gap renormalization. © 2000 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.50.Mx High-frequency effects; plasma effects
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.Ey III-V semiconductors
73.20.At Surface states, band structure, electron density of states

Individual and collective effects of oxygen and ethanol on the conductance of SnO2 thin films

Vladimir V. Kissine, Victor V. Sysoev, and Sergey A. Voroshilov

Appl. Phys. Lett. 76, 2391 (2000); http://dx.doi.org/10.1063/1.126381 (3 pages) | Cited 4 times

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We study the changes in the conductance of the fully depleted SnO2 films exposed both to oxygen or ethanol vapors in vacuum and to their mixture in the air. The dependence of free carrier concentration on the acceptor-like and/or donor-like gas pressure is discussed assuming the flat-band condition. We show that the gas sensitivity of the depleted semiconductor layer can be explained taking into account the compensation of the sample conductivity by the surface adsorbed species. The results of calculations are in good agreement with our experimental data. © 2000 American Institute of Physics.
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73.61.Le Other inorganic semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Evidence of interdot electronic tunneling in vertically coupled In0.4Ga0.6As self-organized quantum dots

J. Urayama, T. B. Norris, B. Kochman, J. Singh, and P. Bhattacharya

Appl. Phys. Lett. 76, 2394 (2000); http://dx.doi.org/10.1063/1.126356 (3 pages) | Cited 12 times

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Ultrafast differential transmission spectroscopy with a resonant pump reveals evidence of electronic tunneling among the excited levels of vertically aligned In0.4Ga0.6As self-organized quantum dots. This evidence of tunneling is observed as a rapid spectral redistribution of electrons within a few hundred femtoseconds of optical excitation. Measurements show that this spectral spread is independent of carrier density and, therefore, indicate that carrier–carrier scattering is not the main mechanism for carrier redistribution. Instead, electronic tunneling is responsible for the interdot coupling; tunneling rate calculations agree reasonably with the experiment, supporting this conclusion. © 2000 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Gk Tunneling
78.47.-p Spectroscopy of solid state dynamics
78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
78.30.Fs III-V and II-VI semiconductors

Evidence of an oxygen recombination center in p+–n GaInNAs solar cells

A. Balcioglu, R. K. Ahrenkiel, and D. J. Friedman

Appl. Phys. Lett. 76, 2397 (2000); http://dx.doi.org/10.1063/1.126383 (3 pages) | Cited 22 times

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We have studied deep-level impurities in p+–n GaInNAs solar cells using deep-level transient spectroscopy (DLTS). These films were grown by atmospheric- and low-pressure metalorganic vapor-phase epitaxy. The base layer is doped with silicon, and the emitter layer is zinc doped. Two types of samples have been studied: samples were grown with and without the addition of oxygen impurity. Two electron traps were found in all samples. These are designated as: E1, at EC−0.23–EC−0.27eV, E2 at EC−0.45eV, and E2∗ at 0.77 eV. With the addition of oxygen impurity, DLTS showed additional traps designated as E3 (electron) at EC−0.59eV and H3 (hole) at EV+0.59 eV. Using secondary ion mass spectroscopy, the oxygen concentration was found to be about 2–3×1019 and 1×1017 cm−3 in two sets of samples. However, only samples containing oxygen contained the two near-midgap levels (E3 and H3). We present evidence that these levels are associated with the oxygen defect. As we change the dc bias voltage, the E3 trap disappears in unison with the appearance of the H3 trap. Furthermore, E3 and H3 trap levels have comparable capture cross sections. This oxygen-related trap is an effective recombination center. The measured Shockley–Hall–Read lifetime for this center is about 0.6 μs. © 2000 American Institute of Physics.
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84.60.Jt Photoelectric conversion
71.55.Eq III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.Ey III-V semiconductors

Self-organized formation and photoluminescence of Cd1−xMnxTe quantum dots grown on ZnTe by atomic layer epitaxy

Yoshikazu Terai, Shinji Kuroda, and Kôki Takita

Appl. Phys. Lett. 76, 2400 (2000); http://dx.doi.org/10.1063/1.126357 (3 pages) | Cited 14 times

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Self-organized quantum dots (QDs) of Cd1−xMnxTe were grown on the ZnTe(100) surface by atomic layer epitaxy. Atomic force microscope measurement on the surface of a 3.5-ML-thick Cd1−xMnxTe layer revealed dot formation in a high density of the order of 1010–1011 cm−2 when the Mn composition x was less than 10%. The typical dot size was given approximately by 20 nm in diameter and 2 nm in height. In photoluminescence (PL) measurements on the capped QDs, the excitonic emissions from the QDs were observed at 2.16–2.27 eV in the range of Mn composition x = 0%–10%. The PL spectra from Cd1−xMnxTe QDs with x = 0.6%–10.2% consisted of two lines separated by about 20 meV. The dependence of the PL energies on the Mn composition and the Zeeman shift were compared with the calculation. © 2000 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
75.50.Pp Magnetic semiconductors
81.05.Dz II-VI semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
78.20.Ls Magneto-optical effects

Selective enhancement of 1540 nm Er3+ emission centers in Er-implanted GaN by Mg codoping

S. Kim, S. J. Rhee, X. Li, J. J. Coleman, and S. G. Bishop

Appl. Phys. Lett. 76, 2403 (2000); http://dx.doi.org/10.1063/1.126358 (3 pages) | Cited 36 times

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The ∼1540 nm 4I13/2 to 4I15/2 Er3+ photoluminescence (PL) and photoluminescence excitation (PLE) spectra of Er-implanted Mg-doped GaN reveal a selective enhancement of one of the nine different Er3+ centers observed previously in PL and PLE studies of Er-implanted undoped GaN. These Er3+ PL spectra are excited selectively by pump wavelengths that correspond to broadband, below-gap absorption bands associated with different Er3+ centers. In the Er-implanted, Mg-doped GaN, both the 1540 nm PL spectrum characteristic of the so-called violet-pumped Er3+ center and the ∼2.8–3.4 eV (violet) PLE band that enables its selective excitation are significantly enhanced by Mg doping. In addition, the violet-pumped PL center dominates the above-gap-excited Er3+ PL spectrum of Er-implanted Mg-doped GaN, whereas it was nearly unobserveable under above-gap excitation in Er-implanted undoped GaN. These results confirm our hypothesis that appropriate codopants can increase the efficiency of trap-mediated above-gap excitation of Er3+ emission in Er-implanted GaN. © 2000 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
71.55.Eq III-V semiconductors
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Photoexcited carrier transfer in InGaAs quantum dot structures: Dependence on the dot density

Saulius Marcinkevicius and Rosa Leon

Appl. Phys. Lett. 76, 2406 (2000); http://dx.doi.org/10.1063/1.126359 (3 pages) | Cited 23 times

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Carrier dynamics has been measured by time-resolved photoluminescence in self-assembled InGaAs/GaAs quantum-dot structures with dot density of the order of 108–1010 cm−2. The time of carrier transfer into a dot, which ranges from 2 to 20 ps, has been found to decrease with increasing quantum dot density. The temperature and photoexcited carrier density dependencies of the carrier transfer times suggest that potential barriers at wetting layer and quantum-dot interfaces hinder carrier capture in low-density quantum-dot structures. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.50.Dn Low-field transport and mobility; piezoresistance
78.47.-p Spectroscopy of solid state dynamics
73.50.Pz Photoconduction and photovoltaic effects

Large, nitrogen-induced increase of the electron effective mass in InyGa1−yNxAs1−x

C. Skierbiszewski, P. Perlin, P. Wisniewski, W. Knap, T. Suski, W. Walukiewicz, W. Shan, K. M. Yu, J. W. Ager, E. E. Haller, J. F. Geisz, and J. M. Olson

Appl. Phys. Lett. 76, 2409 (2000); http://dx.doi.org/10.1063/1.126360 (3 pages) | Cited 147 times

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A dramatic increase of the conduction band electron mass in a nitrogen-containing III–V alloy is reported. The mass is found to be strongly dependent on the nitrogen content and the electron concentration with a value as large as 0.4m0 in In0.08Ga0.92As0.967N0.033 with 6×1019 cm−3 free electrons. This mass is more than five times larger than the electron effective mass in GaAs and comparable to typical heavy hole masses in III–V compounds. The results provide a critical test and fully confirm the predictions of the recently proposed band anticrossing model of the electronic structure of the III–N–V alloys. © 2000 American Institute of Physics.
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71.20.Nr Semiconductor compounds
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Gating individual nanotubes and crosses with scanning probes

Thomas W. Tombler, Chongwu Zhou, Jing Kong, and Hongjie Dai

Appl. Phys. Lett. 76, 2412 (2000); http://dx.doi.org/10.1063/1.125611 (3 pages) | Cited 21 times

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Atomic force microscopy tips are used to apply point-like local gates to manipulate the electrical properties of individual single-walled carbon nanotubes (SWNT) contacted by Ti electrodes. Depleting a semiconducting SWNT at a local point along its length leads to orders of magnitude decrease of the nanotube conductance, whereas local gating to metallic SWNTs causes no change in the conductance of the system. These results shed light into gating effects on metal-tube contacts. Electrical properties of SWNT crosses are also investigated. Scanning-probe gating is used to identify the metallic or semiconducting nature of the nanotube components in the crosses. © 2000 American Institute of Physics.
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73.61.Wp Fullerenes and related materials
85.40.Ls Metallization, contacts, interconnects; device isolation
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