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23 Apr 2001

Volume 78, Issue 17, pp. 2417-2603

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What determines the emission peak energy of the blue luminescence in highly Mg-doped p-GaN?

J. S. Colton and P. Y. Yu

Appl. Phys. Lett. 78, 2500 (2001); http://dx.doi.org/10.1063/1.1367904 (3 pages) | Cited 8 times

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We report a study of the 2.8 eV blue luminescence (BL) in heavily Mg-doped p-GaN via resonant excitation with a tunable blue dye laser. The dependence of the BL on the excitation photon energy (Eex) is unlike that of the yellow luminescence found in n-type GaN. An Urbach-type band tail, with Urbach parameter of 33 meV is observed in the vicinity of the BL energy. We propose that the peak energy of the BL marks the transition from localized states to delocalized states within this band tail. © 2001 American Institute of Physics.
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71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
71.20.Nr Semiconductor compounds

Electron affinity of AlxGa1−xN(0001) surfaces

S. P. Grabowski, M. Schneider, H. Nienhaus, W. Mönch, R. Dimitrov, O. Ambacher, and M. Stutzmann

Appl. Phys. Lett. 78, 2503 (2001); http://dx.doi.org/10.1063/1.1367275 (3 pages) | Cited 46 times

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The electronic properties and the electron affinities of AlxGa1−xN(0001) surfaces were investigated by ultraviolet photoemission spectroscopy (UPS) over the whole composition range. The samples were prepared by N-ion sputtering and annealing. Surface cleanliness and stoichiometry were monitored with x-ray photoemission spectroscopy. Samples with high aluminum content showed traces of oxygen which could not be removed by further cleaning cycles. However, we have evidence that the oxygen is located in the bulk and not at the surface. From the UP spectra the ionization energies and electron affinities as a function of composition x were determined. A decrease in electron affinity with increasing aluminum content was found, but the electron affinity remains positive for all x. Thus, earlier predictions of negative electron affinity for high aluminum content were not confirmed. © 2001 American Institute of Physics.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
81.05.Ea III-V semiconductors
68.35.Dv Composition, segregation; defects and impurities
79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.40.Gh Other heat and thermomechanical treatments
81.65.Cf Surface cleaning, etching, patterning

Metastability of defects in p-GaAs grown from a Ga-rich melt

Z.-Q. Fang, J. W. Kim, and P. W. Yu

Appl. Phys. Lett. 78, 2506 (2001); http://dx.doi.org/10.1063/1.1365100 (3 pages) | Cited 1 time

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We report the observation of metastability for defects in Si-doped p-GaAs grown from a Ga-rich melt. A configuration change occurs suddenly at a critical temperature (near 120 K) during cooldown scans, giving rise to discontinuous deep-level transient spectra. A similar phenomenon was observed on electron-irradiated float-zone-refined Si and explained in terms of entropy variations in the configurational space. We believe that the metastability found in the p-GaAs sample is also due to a barrierless transformation of defect configuration, driven by variations in both entropy and the charge state of GaAs. © 2001 American Institute of Physics.
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71.55.Eq III-V semiconductors
81.05.Ea III-V semiconductors
81.10.Fq Growth from melts; zone melting and refining

Gap states of hydrogenated amorphous silicon near and above the threshold of microcrystallinity with subtle boron compensation

Shuran Sheng, Xianbo Liao, and Guanglin Kong

Appl. Phys. Lett. 78, 2509 (2001); http://dx.doi.org/10.1063/1.1368185 (3 pages) | Cited 11 times

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The effects of hydrogen dilution, subtle boron compensation, and light-soaking on the gap states of hydrogenated amorphous silicon films (a-Si:H) near and above the threshold of microcrystallinity have been investigated in detail by the constant photocurrent method and the improved phase-shift analysis of modulated photocurrent technique. It is shown that high hydrogen dilution near the threshold of microcrystallinity leads to a more ordered network structure and to the redistribution of gap states; it gives rise to a small peak at about 0.55 eV and a shoulder at about 1.2 eV below the conduction band edge, which are associated with the formation of microcrystallites embedded in the amorphous silicon host matrix. A concurrent subtle boron compensation is demonstrated to prevent excessive formation of microcrystallinity, and to help promote the growth of the ordered regions and reduce the density of gap defect states, particularly those associated with microcrystallites. Hydrogen-diluted and appropriately boron-compensated a-Si:H films deposited near the threshold of microcrystallinity show the lowest density of the defects in both the annealed and light-soaked states, and hence, the highest performance and stability. © 2001 American Institute of Physics.
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71.55.Cn Elemental semiconductors
72.80.Cw Elemental semiconductors
81.05.Cy Elemental semiconductors
72.80.Ng Disordered solids
73.61.Jc Amorphous semiconductors; glasses
81.05.Gc Amorphous semiconductors
68.55.-a Thin film structure and morphology
73.50.Pz Photoconduction and photovoltaic effects
72.40.+w Photoconduction and photovoltaic effects
71.55.Jv Disordered structures; amorphous and glassy solids
73.61.Cw Elemental semiconductors
71.23.Cq Amorphous semiconductors, metallic glasses, glasses

On the nature of the D1-defect center in SiC: A photoluminescence study of layers grown by solid-source molecular-beam epitaxy

A. Fissel, W. Richter, J. Furthmüller, and F. Bechstedt

Appl. Phys. Lett. 78, 2512 (2001); http://dx.doi.org/10.1063/1.1367883 (3 pages) | Cited 15 times

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Undoped and boron-doped SiC layers are grown on hexagonal SiC(0001) substrates by means of solid-source molecular-beam epitaxy. Hexagonal 4H– and 6H–SiC layers are grown homoepitaxially via step-controlled epitaxy, whereas the cubic 3C–SiC is grown pseudomorphically via nucleation and subsequent step flow. The low-temperature photoluminescence spectra only show the well-known emission lines of the so-called D1 center. The line positions are compared with results of first-principles calculations. The growth conditions, the line shape, and the line shift with the polytype support an interpretation as bound-exciton recombination at a native-defect complex that contains a Si vacancy. © 2001 American Institute of Physics.
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71.55.Ht Other nonmetals
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Hd Other semiconductors
78.66.Li Other semiconductors
68.55.A- Nucleation and growth
78.55.Hx Other solid inorganic materials
61.72.J- Point defects and defect clusters

Thermal-annealing dependence of C-related atomic configuration in Si1−x−yGexCy crystals grown by ultra-high-vacuum chemical-vapor deposition

Y. Kanzawa, T. Saitoh, and M. Kubo

Appl. Phys. Lett. 78, 2515 (2001); http://dx.doi.org/10.1063/1.1367294 (3 pages) | Cited 5 times

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Si1−x−yGexCy crystals were grown by ultra-high-vacuum chemical-vapor deposition and their thermal-annealing behaviors were studied by infrared (IR) absorption measurements. The present samples exhibited absorption peaks originating from local vibrational modes of substitutional C atoms with two different atomic configurations; one is a C atom with four Si neighbors (Si4 configuration) and the other is with one Ge and three Si neighbors (Si3Ge1 configuration). As the annealing temperature was increased from 700 to 950 °C, the absorption peak of the C atoms with Si3Ge1 configuration increased in intensity. This clearly demonstrated that thermal annealing leads to the formation of Ge–C bonds. Moreover, the composition dependence of the IR spectra suggested that Ge–C bonds are formed to reduce the strain energy of the Si1−x−yGexCy crystals. © 2001 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.40.Gh Other heat and thermomechanical treatments
78.66.Li Other semiconductors
78.30.Hv Other nonmetallic inorganics
63.20.Pw Localized modes
61.50.Lt Crystal binding; cohesive energy

Low-frequency photocurrent noise in semiconductors: Effect of nonlinear current–voltage characteristics

Anna Carbone, Piero Mazzetti, and Fausto Rossi

Appl. Phys. Lett. 78, 2518 (2001); http://dx.doi.org/10.1063/1.1368188 (3 pages) | Cited 3 times

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A current noise model for planar metal–semiconductor–metal photodetectors is proposed, which allows one to account for the low-frequency excess-noise behavior measured in several semiconductor devices. According to the proposed model—based on a multiplicative noise mechanism—the photocurrent noise power can be directly related to the carrier density and to the photogeneration level. Moreover, in the absence of potential-barrier fluctuations, the standard 1/n behavior of the simple g–r noise model is recovered. © 2001 American Institute of Physics.
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73.50.Pz Photoconduction and photovoltaic effects
85.60.Gz Photodetectors (including infrared and CCD detectors)
73.40.Sx Metal-semiconductor-metal structures
73.50.Td Noise processes and phenomena

Switching behavior of semiconducting carbon nanotubes under an external electric field

Alain Rochefort, Massimiliano Di Ventra, and Phaedon Avouris

Appl. Phys. Lett. 78, 2521 (2001); http://dx.doi.org/10.1063/1.1367295 (3 pages) | Cited 23 times

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We investigate theoretically the switching characteristics of semiconducting carbon nanotubes connected to gold electrodes under an external (gate) electric field. We find that the external introduction of holes is necessary to account for the experimental observations. We identify metal-induced gap states (MIGS) at the contacts and find that the MIGS of an undoped tube would not significantly affect the switching behavior, even for very short tube lengths. We also explore the miniaturization limits of nanotube transistors, and, on the basis of their switching ratio, we conclude that transistors with channels as short as 50 Å would have adequate switching characteristics. © 2001 American Institute of Physics.
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73.63.Fg Nanotubes

Spectrum dynamics of negative-effective-mass oscillators under terahertz radiation

J. C. Cao, X. L. Lei, A. Z. Li, and H. C. Liu

Appl. Phys. Lett. 78, 2524 (2001); http://dx.doi.org/10.1063/1.1364661 (3 pages) | Cited 13 times

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We report on a theoretical investigation of power spectrum dynamics in negative-effective-mass (NEM) p+pp+ oscillators under the influence of terahertz (THz) electromagnetic radiation. Possible types of transport states (periodic or chaotic) and transitions between them are examined with the intensity and frequency of the radiation as controlling parameters. When the driving frequency is fixed to the self-oscillating frequency times the inverse Golden ratio, the resulting power spectrum pattern displays a very complex mosaic scenario with a self-similar emergence of high-order mixing frequencies. © 2001 American Institute of Physics.
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84.30.Ng Oscillators, pulse generators, and function generators
05.45.Xt Synchronization; coupled oscillators
85.30.Kk Junction diodes
07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources
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