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9 Aug 1999

Volume 75, Issue 6, pp. 745-878

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High-temperature light emission from InAs quantum dots

A. Patanè, A. Polimeni, P. C. Main, M. Henini, and L. Eaves

Appl. Phys. Lett. 75, 814 (1999); http://dx.doi.org/10.1063/1.124522 (3 pages) | Cited 23 times

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We study the photoluminescence (PL) properties of InAs/GaAs self-assembled quantum dots in a temperature range (T = 300–500 K) above that reported to date. Various power excitation densities were used, allowing us to identify the important contribution of nonradiative channels in quenching the dot PL as the temperature is increased. The role played by the wetting layer on the dot PL intensity has been investigated in samples in which the separation of the dot and wetting layer levels is tuned by post-growth annealing. This experiment reveals that, at a high temperature (>300 K), the relative population of the dot and wetting layer levels is given by a Boltzmann distribution. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
81.40.Gh Other heat and thermomechanical treatments

Modeling of Ge surface segregation in vapor-phase deposited Si1−xGex thin films

Y.-J. Zheng, A. M. Lam, and J. R. Engstrom

Appl. Phys. Lett. 75, 817 (1999); http://dx.doi.org/10.1063/1.124523 (3 pages) | Cited 12 times

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Recent experimental results concerning Ge segregation in Si1−xGex epitaxial thin films deposited on Si(100) substrates using Si2H6 and GeH4 cannot be accounted for by a simple two-site model involving surface and bulk states. This is due to Ge enrichment in the subsurface layers. Here, we demonstrate that a simple model based on the regular solution theory, which invokes both nearest, and next-nearest neighbor interactions, can explain the Ge enrichment in the subsurface. A computer simulation using the Monte Carlo method verifies the assumptions made in the model, and both methods show excellent agreement with the experimental data. © 1999 American Institute of Physics.
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68.55.Nq Composition and phase identification
64.75.-g Phase equilibria
68.35.Fx Diffusion; interface formation

Matrix effects in particle induced x-ray emission channeling measurements of ZnSe/GaAs heterostuctures

A. Seppälä and J. Räisänen

Appl. Phys. Lett. 75, 820 (1999); http://dx.doi.org/10.1063/1.124524 (3 pages) | Cited 1 time

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The significance of the matrix effects, i.e., of self-absorption and secondary fluorescence, in particle induced x-ray emission (PIXE) channeling measurements was studied in epitaxial ZnSe layers on a GaAs substrate. The effect of self-absorption on Zn and Se channeling minimum yields was found to be significant only with thick ZnSe layers. The importance of secondary fluorescence was estimated by applying an introduced correction formula to the measured Zn minimum yields for ZnSe/GaAs heterostructures. The corrections in Zn minimum yields were significant at high proton energies (>2 MeV). Thus, errors for instance in impurity atom lattice location determinations by PIXE channeling occur unless these effects are correctly taken into account. © 1999 American Institute of Physics.
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61.85.+p Channeling phenomena (blocking, energy loss, etc.)
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
68.55.Nq Composition and phase identification
68.35.Ct Interface structure and roughness

Observation of valence band electron emission from n-type silicon field emitter arrays

Meng Ding, Han Kim, and Akintunde I. Akinwande

Appl. Phys. Lett. 75, 823 (1999); http://dx.doi.org/10.1063/1.124525 (3 pages) | Cited 17 times

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Electron emission from the valence band of n-type Si field emitter arrays is reported. High electrostatic field at the surface of Si was achieved by reducing the radius of the emitter tip. Using oxidation sharpening, 1 μm aperture polycrystalline Si gate, n-type Si field emitter arrays with small tip radius (∼10 nm) were fabricated. Three distinct emission regions were observed: conduction band emission at low gate voltages, saturated current emission from the conduction band at intermediate voltages, and valence band plus conduction band emission at high gate voltages. Emission currents at low and high voltages obey the Fowler–Nordheim theory. The ratio of the slopes of the corresponding Fowler–Nordheim fits for these two regions is 1.495 which is in close agreement with the theoretical value of 1.445. © 1999 American Institute of Physics.
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85.45.Db Field emitters and arrays, cold electron emitters
79.70.+q Field emission, ionization, evaporation, and desorption
71.20.Mq Elemental semiconductors
73.40.Gk Tunneling

A role of illumination during etching to porous silicon oxidation

J. Salonen, V-P. Lehto, M. Björkqvist, and E. Laine

Appl. Phys. Lett. 75, 826 (1999); http://dx.doi.org/10.1063/1.124526 (3 pages) | Cited 6 times

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The oxidation behavior of porous silicon (PS) has been found to be related to illumination during etching. The autocatalytic oxidation behavior at room temperature arises from the unrelaxed surface induced by the preparation under illumination and can be removed using thermal treatment in a nitrogen atmosphere. The effect is absent in the case of degenerate PS and smaller in p type than in n-type PS. The correlation between the oxidation behavior and the microstructural dimensions is also discussed. © 1999 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.05.Rm Porous materials; granular materials
81.65.Mq Oxidation
81.65.Cf Surface cleaning, etching, patterning
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
81.40.Gh Other heat and thermomechanical treatments

Surface morphology in InAs/GaAs(111)A heteroepitaxy: Experimental measurements and computer simulations

Brett Z. Nosho, Luis A. Zepeda-Ruiz, Rodney I. Pelzel, W. Henry Weinberg, and Dimitrios Maroudas

Appl. Phys. Lett. 75, 829 (1999); http://dx.doi.org/10.1063/1.124527 (3 pages) | Cited 8 times

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The surface morphology of InAs films grown on GaAs(111)A has been studied by scanning tunneling microscopy. The vertical surface displacement on the InAs films has been found to depend on the underlying GaAs buffer layer thickness: specifically, thin GaAs layers are observed to behave mechanically similar to compliant substrates. Atomistic simulations within a valence force field model have been used to compare quantitatively how the InAs surface morphology depends on film thickness and the underlying GaAs layer thickness. The experimental and theoretical results are in excellent agreement over a range of film thicknesses where the misfit dislocation network at the semicoherent InAs/GaAs interface is fully developed. © 1999 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.Bb Theories and models of crystal defects
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.72.Lk Linear defects: dislocations, disclinations
68.35.Ct Interface structure and roughness

Evidence for a dominant midgap trap in n-ZnSe grown by molecular beam epitaxy

A. Hierro, D. Kwon, S. H. Goss, L. J. Brillson, S. A. Ringel, S. Rubini, E. Pelucchi, and A. Franciosi

Appl. Phys. Lett. 75, 832 (1999); http://dx.doi.org/10.1063/1.124528 (3 pages) | Cited 10 times

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A midgap deep level in n-type ZnSe grown by molecular beam epitaxy (MBE) on In0.04Ga0.96As/GaAs is detected and investigated by deep level optical spectroscopy and cathodoluminescence spectroscopy. The deep level has an optical threshold energy of 1.46 eV below the conduction band edge, and its concentration strongly depends on the Zn:Se beam pressure ratio during initial nucleation of the ZnSe layer. The concentration of this level decreases by a factor of ∼8 for Se rich vs Zn rich nucleation conditions, correlating with a decrease in the Se vacancy concentration for Se-rich nucleation. The investigation of photocapacitance transients revealed a strong interaction of the 1.46 eV level with both the conduction and the valence bands. Moreover, this level showed the largest optical cross section (emission rate of ∼ 103 s−1) of all of the levels found in the ZnSe layer. Taken together, these observations suggest this level may be an important recombination-generation center in MBE-grown ZnSe devices on GaAs substrates. © 1999 American Institute of Physics.
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71.55.Gs II-VI semiconductors
72.40.+w Photoconduction and photovoltaic effects
78.60.Hk Cathodoluminescence, ionoluminescence
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors

Midinfrared second-harmonic generation in p-type InAs/GaAs self-assembled quantum dots

T. Brunhes, P. Boucaud, S. Sauvage, F. Glotin, R. Prazeres, J.-M. Ortega, A. Lemaître, and J.-M. Gérard

Appl. Phys. Lett. 75, 835 (1999); http://dx.doi.org/10.1063/1.124529 (3 pages) | Cited 6 times

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Resonant second-harmonic generation is reported in InAs/GaAs self-assembled quantum dots. Frequency doubling is observed between confined states in the valence band of the quantum dots. The second-order nonlinear susceptibility is maximum at 168 meV (7.4 μm wavelength) and is observed for an in-plane polarized excitation. A value of χzxx(2) as large as 2×10−7 (m/V) is measured for one dot plane. A three-dimensional numerical calculation of the valence band states shows that the second-harmonic generation involves a resonant excitation between the h000 and h101 states and a state close to the continuum wetting layer states. © 1999 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
42.65.An Optical susceptibility, hyperpolarizability

Time-resolved photoluminescence studies of free and donor-bound exciton in GaN grown by hydride vapor phase epitaxy

G. E. Bunea, W. D. Herzog, M. S. Ünlü, B. B. Goldberg, and R. J. Molnar

Appl. Phys. Lett. 75, 838 (1999); http://dx.doi.org/10.1063/1.124530 (3 pages) | Cited 29 times

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Time-resolved photoluminescence (PL) spectroscopy was used to study the radiative recombination of free and donor-bound excitons in unintentionally doped GaN grown by hydride vapor phase epitaxy. Low temperature (4 K), time-integrated PL spectra identified the free exciton (A), the donor-bound exciton peak ∼6 meV below, and the acceptor-bound exciton ∼20 meV below the free exciton peak. A radiative recombination lifetime of 295 ps for the free exciton and 530 ps for donor-bound exciton were found at 4 K. The decay of the free exciton remained single exponential to room temperature, with an increase in lifetime to 530 ps, consistent with the thermal excitation of exciton states. © 1999 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
71.35.-y Excitons and related phenomena
71.55.Eq III-V semiconductors

Charge transport in polymer light-emitting diodes at high current density

I. H. Campbell, D. L. Smith, C. J. Neef, and J. P. Ferraris

Appl. Phys. Lett. 75, 841 (1999); http://dx.doi.org/10.1063/1.124531 (3 pages) | Cited 23 times

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We present measured and calculated current–voltage (I–V) characteristics of diodes fabricated using a soluble poly(p-phenylene vinylene) derivative. Steady-state and pulsed electrical excitation were used to acquire the I–V characteristics for current densities from 1×10−3 to 1.3×103 A/cm2. Hole current is predominant in the diode. The I–V characteristics were fit using a device model that assumes an electric field-dependent hole mobility of the Poole–Frenkel form that is independent of the charge carrier density. The measured and calculated I–V characteristics are in good agreement over the full range of current density. The maximum electric field and carrier density is about 4×106 V/cm and 1×1018 cm−3, respectively. These results demonstrate that an electric field-dependent mobility, without carrier density dependence, provides an accurate description of hole transport in this polymer over this range of field and carrier density. © 1999 American Institute of Physics.
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85.60.Jb Light-emitting devices
73.61.Ph Polymers; organic compounds
73.50.Fq High-field and nonlinear effects
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