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22 Mar 1999

Volume 74, Issue 12, pp. 1645-1775

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The adsorption of oxygen at GaN surfaces

Tosja K. Zywietz, Jörg Neugebauer, and Matthias Scheffler

Appl. Phys. Lett. 74, 1695 (1999); http://dx.doi.org/10.1063/1.123658 (3 pages) | Cited 73 times

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A critical point in device fabrication based on GaN is the controlled doping and the incorporation of impurities like, e.g., oxygen. We have explored the adsorption of oxygen at the wurtzite (0001) and (000math) GaN surfaces employing density-functional theory. Our results show that both surface orientations are very active towards oxygen adsorption, explaining the high oxygen concentrations typically observed in GaN. However, the (0001) and (000math) surfaces behave differently and oxygen incorporation is expected to be higher at the (000math) surface. The different reactivity is explained in terms of the specific structural configurations. © 1999 American Institute of Physics.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
68.35.Dv Composition, segregation; defects and impurities
81.05.Ea III-V semiconductors
81.65.Mq Oxidation

Charge transfer in photovoltaics consisting of interpenetrating networks of conjugated polymer and TiO2 nanoparticles

A. C. Arango, S. A. Carter, and P. J. Brock

Appl. Phys. Lett. 74, 1698 (1999); http://dx.doi.org/10.1063/1.123659 (3 pages) | Cited 94 times

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We study the effect of blended and layered titanium dioxide (TiO2) nanoparticles on charge transfer processes in conjugated polymer photovoltaics. A two order of magnitude increase in photoconductivity and sharp saturation is observed for layered versus blended structures, independent of the cathode work function. Using electrodes with similar work functions, we observe low dark currents and open circuit voltages of 0.7 V when a TiO2 nanoparticle layer is self-assembled onto the indium–tin–oxide electrode. Our results for the layered morphologies are consistent with charge collection by exciton diffusion and dissociation at the TiO2 interface. © 1999 American Institute of Physics.
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73.50.Pz Photoconduction and photovoltaic effects
73.30.+y Surface double layers, Schottky barriers, and work functions
71.35.-y Excitons and related phenomena
71.20.Rv Polymers and organic compounds
72.15.Nj Collective modes (e.g., in one-dimensional conductors)
73.61.Ph Polymers; organic compounds

Optical properties of InAs quantum dots in a Si matrix

R. Heitz, N. N. Ledentsov, D. Bimberg, A. Yu. Egorov, M. V. Maximov, V. M. Ustinov, A. E. Zhukov, Zh. I. Alferov, G. E. Cirlin, I. P. Soshnikov, N. D. Zakharov, P. Werner, and U. Gösele

Appl. Phys. Lett. 74, 1701 (1999); http://dx.doi.org/10.1063/1.123660 (3 pages) | Cited 32 times

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We investigate the optical properties of nanoscale InAs quantum dots (QDs) in a Si matrix. At a growth temperature of 400 °C, the deposition of 7 ML InAs leads to the formation of coherent islands with dimensions in the 2–4 nm range. A luminescence band in the 1.3 μm region found exclusively for samples with such InAs QDs exhibits a pronounced excitation density dependence of the peak position and a decay time of 440 ns. The optical properties suggest an indirect type II transition for InAs/Si QDs. The electronic structure of InAs/Si QDs is discussed in view of available band offset information. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Effects of surface reconstruction on III–V semiconductor interface formation: The role of III/V composition

B. Z. Nosho, W. H. Weinberg, W. Barvosa-Carter, B. R. Bennett, B. V. Shanabrook, and L. J. Whitman

Appl. Phys. Lett. 74, 1704 (1999); http://dx.doi.org/10.1063/1.123661 (3 pages) | Cited 24 times

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Using molecular-beam epitaxy and in situ scanning tunneling microscopy, we demonstrate how different reconstructions associated with different III–V growth surfaces can create interfacial roughness, and that an understanding of this phenomenon can be used to control the roughness on the atomic scale. Specifically, the different compositions of a clean InAs(001)-(2×4) surface (V/III=0.5 ML/0.75 ML) and an Sb-terminated one (∼1.7 ML/1 ML) cause the InSb-like interfacial surface to have a bilevel morphology. This surface roughness can be eliminated by depositing additional In to exactly compensate for the difference. It is likely that similar types of roughness occur in all heterostructures where the growth surface reconstruction changes at the interfaces, and that a similar procedure will be equally effective at reducing that roughness. © 1999 American Institute of Physics.
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68.35.Ct Interface structure and roughness
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.55.-a Thin film structure and morphology

Effects of embedded crystallites in amorphous silicon on light-induced defect creation

Toshihiro Kamei, Paul Stradins, and Akihisa Matsuda

Appl. Phys. Lett. 74, 1707 (1999); http://dx.doi.org/10.1063/1.123662 (3 pages) | Cited 39 times

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We investigate effects of embedded crystallites in hydrogenated amorphous silicon on light-induced metastable dangling-bond defect creation in a systematic manner. Inclusion of a small volume fraction of crystallites into the amorphous matrix significantly suppresses defect creation against moderate light illumination. Excess carriers generated in the amorphous matrix tend to recombine in the embedded crystallites, which suppresses nonradiative recombination within the amorphous matrix and the subsequent defect creation. The presence of a small volume fraction of crystallites, however, is no longer effective to improve the stability against strong light exposure such as pulsed laser irradiation. In this case, the higher carrier concentration favors bimolecular direct carrier recombination within the amorphous matrix. © 1999 American Institute of Physics.
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61.43.Dq Amorphous semiconductors, metals, and alloys
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
72.40.+w Photoconduction and photovoltaic effects
71.55.Jv Disordered structures; amorphous and glassy solids
72.80.Cw Elemental semiconductors
72.80.Ng Disordered solids

Trapping of minority carriers in multicrystalline silicon

D. Macdonald and A. Cuevas

Appl. Phys. Lett. 74, 1710 (1999); http://dx.doi.org/10.1063/1.123663 (3 pages) | Cited 87 times

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Abnormally high effective carrier lifetimes have been observed in multicrystalline silicon wafers using both transient and steady-state photoconductance techniques. A simple model based on the presence of trapping centers explains this phenomenon both qualitatively and quantitatively. By fitting this model to experimental data acquired with a quasi-steady-state photoconductance technique, it is possible to determine the trap density, trap energy, and the ratio between the mean-trapping time and mean-escape time. A correlation between trap density and dislocation density in the material has been found. © 1999 American Institute of Physics.
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72.80.Cw Elemental semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.40.+w Photoconduction and photovoltaic effects

Structural characterization of amorphized InP: Evidence for chemical disorder

C. J. Glover, M. C. Ridgway, K. M. Yu, G. J. Foran, T. W. Lee, Y. Moon, and E. Yoon

Appl. Phys. Lett. 74, 1713 (1999); http://dx.doi.org/10.1063/1.123664 (3 pages) | Cited 9 times

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Extended x-ray absorption fine-structure measurements at the In K edge of amorphous InP are presented. The presence of chemical disorder in the form of like-atom bonding has been unambiguously demonstrated in stoichiometric InP amorphized by ion implantation. In–In bonding comprised 14%±4% of the In–atom constituent bonds. Also, relative to the crystalline value of four P atoms, an increase in the total In coordination number to 4.16±0.32 atoms was observed for the amorphous phase, as composed of 3.56±0.19 P and 0.60±0.13 In atoms. Experimental results were consistent with recent ab initio structural calculations and, furthermore, demonstrated that amorphous InP is best described by a Polk-like continuous random network, containing both even- and odd-membered rings. © 1999 American Institute of Physics.
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61.43.Dq Amorphous semiconductors, metals, and alloys
78.70.Dm X-ray absorption spectra

Spatially resolved observation of Coulomb blockade and negative differential conductance on a Ag cluster on the clean GaAs(110) surface

C.-S. Jiang, T. Nakayama, and M. Aono

Appl. Phys. Lett. 74, 1716 (1999); http://dx.doi.org/10.1063/1.123665 (3 pages) | Cited 10 times

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By performing current-image tunneling spectroscopy at room temperature, we have observed the staircase current–voltage (I–V) characteristic and negative differential conductance on a single Ag cluster on a clean GaAs(110) surface. The I–V characteristics have changed spatially with the position of the tip on the cluster. The characteristics are understood in terms of Coulomb blockade and resonance of electron standing-wave states in the cluster with the states of the underlying substrate. © 1999 American Institute of Physics.
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73.23.Hk Coulomb blockade; single-electron tunneling
73.40.Ns Metal-nonmetal contacts
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

An ion-beam technique for measuring surface diffusion coefficients

P. M. DeLuca, J. G. C. Labanda, and S. A. Barnett

Appl. Phys. Lett. 74, 1719 (1999); http://dx.doi.org/10.1063/1.123666 (3 pages) | Cited 6 times

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The effective surface diffusion coefficient of Ga along the [110] direction on vicinal GaAs(001)2×4 surfaces during molecular-beam epitaxy was measured using specular ion current measurements. In this technique, 3 keV Ar ions were impinged upon the surface at a glancing angle (typically 3°), and the specularly scattered ion current was measured. Since specular reflections require a locally flat surface, adatoms cause a decrease in the measured current, allowing an average adatom density measurement. The time dependence of the Ga adatom population was measured during and after Ga deposition. Diffusion coefficients, obtained from the adatom lifetimes using a simple model of diffusion to the step edges, were fit well by the expression D = 2×10−9 exp(−0.73 eV/kT)cm2/s from 400 to 600 °C. © 1999 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Stability of ultrathin semiconductor layers

Massimiliano Di Ventra

Appl. Phys. Lett. 74, 1722 (1999); http://dx.doi.org/10.1063/1.123667 (3 pages) | Cited 2 times

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The thermodynamical stability of ultrathin semiconductor layers embedded in isovalent bulk materials has been investigated by ab initio pseudopotential techniques. The AlAs/GaAs and GaAs/GaP structures have been chosen as prototypical examples for this study. We show that independently of the thin layers thickness: (i) At 0 K, the lattice-matched structures are thermodynamically more stable in the ideal configuration than in the case in which some Al and Ga atoms are allowed to diffuse forming a mixed plane; it is the finite-temperature entropy which finally favors the mixed configuration. Conversely, (ii) the lattice-mismatched structures are thermodynamically more stable in the mixed configuration than in the ideal one. In the latter case, it is mainly the chemical mixing and not the relaxation effects which favors diffusion. © 1999 American Institute of Physics.
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68.60.Dv Thermal stability; thermal effects
71.15.Nc Total energy and cohesive energy calculations
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
65.20.-w Thermal properties of liquids
65.40.gd Entropy

Thermal effect on current gains of an AlGaAs/GaAs heterostructure-emitter bipolar transistor

H. B. Lo, E. S. Yang, and Y. F. Yang

Appl. Phys. Lett. 74, 1725 (1999); http://dx.doi.org/10.1063/1.123668 (3 pages) | Cited 1 time

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The temperature effect on current gains is presented for an AlGaAs/GaAs heterostructure-emitter bipolar transistor (HEBT). Experimental results show that the HEBT has much less temperature sensitivity in current gain than a heterojunction bipolar transistor. The current gains for the HEBT are almost constant with the substrate temperature at a high current regime. This indicates that the HEBT could be a good candidate for power applications. © 1999 American Institute of Physics.  
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79.40.+z Thermionic emission
85.30.Pq Bipolar transistors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ey III-V semiconductors

Cathodoluminescence enhancement in porous silicon cracked in vacuum

J. Rams, B. Mendez, G. Craciun, R. Plugaru, and J. Piqueras

Appl. Phys. Lett. 74, 1728 (1999); http://dx.doi.org/10.1063/1.123669 (3 pages) | Cited 12 times

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An increase of the cathodoluminescence (CL) signal of porous silicon (PS) cracked in vacuum of up to three orders of magnitude has been achieved. Under high electron-beam currents, the samples cracked in interconnected pieces of tens of microns, exposing new surfaces to the electron beam. This treatment enhances the radiative intensity in PS associated with a broadband peaked at 720 nm, which is highly stable while the sample is kept in vacuum. Cross-sectional CL observations show that most of the light is generated in the top surface of the porous layer. The spectral depth dependence of the emitted light reveals a relatively weak blue emission in the region closer to the substrate. © 1999 American Institute of Physics.
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78.60.Hk Cathodoluminescence, ionoluminescence
62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure

Time-resolved microwave technique for ultrafast charge-carrier recombination time measurements in diamonds and GaAs

S. V. Garnov, A. I. Ritus, S. M. Klimentov, S. M. Pimenov, V. I. Konov, S. Gloor, W. Lüthy, and H. P. Weber

Appl. Phys. Lett. 74, 1731 (1999); http://dx.doi.org/10.1063/1.123670 (3 pages) | Cited 11 times

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Recombination times of laser-excited charge carriers in natural diamond crystals, polycrystalline chemical vapor deposited (CVD) diamond films, and GaAs wafers were measured with 1 ns time resolution by a microwave-radiation technique. A waveguide scheme was applied to record time-dependent reflection and transmission of 140 GHz cw radiation. The measured recombination carrier lifetimes in the bulk of natural and CVD diamond samples were found to be of 1–3 ns. In GaAs, a distinguishing difference between the bulk (15 ns) and surface (3.5 ns) recombination times was observed. To validate the applicability of the developed technique, a computer simulation of the microwave-radiation interaction with excited plane–parallel specimens has been performed applying the Fabry–Perot resonator theory and the classical Drude model. © 1999 American Institute of Physics.
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72.80.Cw Elemental semiconductors
73.61.Ey III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.66.Fd III-V semiconductors
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects
78.47.-p Spectroscopy of solid state dynamics
78.70.Gq Microwave and radio-frequency interactions

Femtosecond midinfrared-induced luminescence study of the ultrafast dynamics of split-off holes in GaAs

Kent C. Burr and C. L. Tang

Appl. Phys. Lett. 74, 1734 (1999); http://dx.doi.org/10.1063/1.123671 (3 pages) | Cited 7 times

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The ultrafast relaxation dynamics of split-off holes in GaAs are studied using a time-resolved two-wavelength excitation luminescence technique. Following valence-to-conduction-band transitions that are excited by near-infrared femtosecond pulses, delayed midinfrared femtosecond pulses are used to promote holes from the heavy-hole band to the split-off-hole band. The subsequent conduction-to-split-off-hole luminescence indicates that the room-temperature lifetime of split-off holes in GaAs is approximately 50 fs. The accompanying changes in conduction-to-heavy-hole-and-light-hole luminescence when holes are transferred to the split-off band are also observed. © 1999 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
71.20.Nr Semiconductor compounds
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
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