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18 Feb 2002

Volume 80, Issue 7, pp. 1111-1310

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Normal-incidence Ge quantum-dot photodetectors at 1.5 μm based on Si substrate

S. Tong, J. L. Liu, J. Wan, and Kang L. Wang

Appl. Phys. Lett. 80, 1189 (2002); http://dx.doi.org/10.1063/1.1449525 (3 pages) | Cited 30 times

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Coherent Ge quantum dots embedded in Si spacing layers were grown on Si substrate by molecular-beam epitaxy in the Stranski–Krastanov mode. Photoluminescence measurement showed a Ge-dot-related peak at 1.46 μm. p-i-n photodiodes with the intrinsic layer containing Ge dots were fabricated, and current–voltage (I–V) measurement showed a low dark current density of 3×10−5 A/cm2 at −1 V. A strong photoresponse at 1.3–1.52 μm originating from Ge dots was observed, and at normal incidence, an external quantum efficiency of 8% was achieved at −2.5 V. © 2002 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
72.40.+w Photoconduction and photovoltaic effects
78.67.Hc Quantum dots
73.63.Kv Quantum dots
78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators

Improved extraction of carrier concentration and depletion width from capacitance–voltage characteristics of silicon n+–p-well junction diodes

A. Poyai, C. Claeys, and E. Simôen

Appl. Phys. Lett. 80, 1192 (2002); http://dx.doi.org/10.1063/1.1435809 (3 pages) | Cited 6 times

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An accurate method is proposed for the extraction of the carrier concentration profile (pp well) and the depletion width (Wp well) in a p-well region from high-frequency capacitance measurements by accounting for the series resistance and the capacitance of the n+ region. Wp well was calculated from the capacitance in the p-well region (Cp well), while pp well was derived from the slope of the plot 1/Cp well2 versus reverse bias. The pp well extracted was compared with profiles obtained from spreading resistance probe results. The differences between the two techniques are within 15% in the accessible depletion width, which will be discussed in view of the depth resolution anticipated. © 2002 American Institute of Physics.
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85.30.Kk Junction diodes
73.61.Cw Elemental semiconductors
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Control of p- and n-type conductivity in sputter deposition of undoped ZnO

Gang Xiong, John Wilkinson, Brian Mischuck, S. Tüzemen, K. B. Ucer, and R. T. Williams

Appl. Phys. Lett. 80, 1195 (2002); http://dx.doi.org/10.1063/1.1449528 (3 pages) | Cited 96 times

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Recent theoretical studies have concluded that the low formation enthalpies of intrinsic donor defects should preclude achievement of p-type conductivity in undoped ZnO grown in thermal equilibrium with a molecular oxygen reservoir. This letter demonstrates that reactive sputtering can produce intrinsic p-type ZnO, controlled by adjusting the oxygen partial pressure in the sputtering plasma. We report the properties of p–n homojunctions fabricated in this way, and characterize transport in the films by Hall measurements. Our finding of p-type conductivity in undoped ZnO grown with dissociated oxygen is qualitatively consistent with the effect of higher chemical potential of atomic oxygen reactant on defect formation enthalpies. This parallels to some degree the recent attention to nitrogen acceptor incorporation by means of dissociating nitrogen source gases. © 2002 American Institute of Physics.
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73.61.Ga II-VI semiconductors
81.05.Dz II-VI semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
81.15.Cd Deposition by sputtering
71.55.Gs II-VI semiconductors
72.80.Ey III-V and II-VI semiconductors
68.55.-a Thin film structure and morphology
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Observation of the Mott–Gurney law in tris (8-hydroxyquinoline) aluminum films

M. Kiy, P. Losio, I. Biaggio, M. Koehler, A. Tapponnier, and P. Günter

Appl. Phys. Lett. 80, 1198 (2002); http://dx.doi.org/10.1063/1.1449527 (3 pages) | Cited 23 times

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We show that tris (8-hydroxyquinoline) aluminum (Alq3) thin films produced and characterized under ultrahigh vacuum conditions present a well-defined squared-law dependence of the injected current on the applied voltage at applied electric fields of the order of 0.25–1 MV/cm. From this, one derives an electric-field-independent electron mobility of the order of 10−7 cm2/(V s), with a variation between different samples of about one order of magnitude. Observations of current–voltage characteristics with clear indications of trap-filling and space-charge-limited conduction at high fields in Alq3 excludes the existence of traps with an exponential distribution of trap energies, as is commonly assumed in amorphous materials. © 2002 American Institute of Physics.
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73.61.Ng Insulators
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
73.50.Fq High-field and nonlinear effects
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

A nanofabrication scheme for InAs/AlSb heterostructures

M. J. Yang, K. A. Cheng, C. H. Yang, and J. C. Culbertson

Appl. Phys. Lett. 80, 1201 (2002); http://dx.doi.org/10.1063/1.1449526 (3 pages) | Cited 12 times

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We report a technique for nanofabrication in the InAs/GaSb/AlSb 6.1 Å material system that utilizes the large difference in the surface Fermi level pinning position for InAs [Efs(InAs)] compared with that for AlSb. An InAs/AlSb single quantum well is capped with a 3 nm, intentionally p-doped InAs layer. As a result of its construction and a relatively low Efs(InAs) there are no free carriers in the InAs/AlSb single quantum well making the quantum well insulating as-grown. Simply by selectively removing the thin p-doped InAs cap layer with a wet etch, the surface Fermi level becomes pinned on AlSb and shifted upward by half an electron volt. This results in a drastic change in band bending and creates a conducting electron channel in the buried InAs quantum well. We demonstrate with experiment and the support of a self-consistent band bending calculation that this scheme is highly effective for nanofabrication. © 2002 American Institute of Physics.
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81.16.-c Methods of micro- and nanofabrication and processing
81.07.St Quantum wells
81.05.Ea III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning
73.21.Fg Quantum wells
73.63.Hs Quantum wells
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Evidence for nonlinear macroscopic polarization in III–V nitride alloy heterostructures

Vincenzo Fiorentini, Fabio Bernardini, and Oliver Ambacher

Appl. Phys. Lett. 80, 1204 (2002); http://dx.doi.org/10.1063/1.1448668 (3 pages) | Cited 119 times

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We provide explicit rules to calculate the nonlinear polarization for nitride alloys of arbitrary composition, and hence, the bound sheet charge induced by polarization discontinuity at the interfaces between different alloy and binary (epi)layers. We then present experimental results and simulations of polarization-related quantities in selected nitride-alloy-based heterostructure systems. The agreement of experiment and simulation, also in comparison to previous approaches, strongly suggests that the macroscopic polarization of nitride alloys is indeed nonlinear as a function of composition. © 2002 American Institute of Physics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.65.-j Piezoelectricity and electromechanical effects
77.22.Ej Polarization and depolarization
68.65.Fg Quantum wells

ZnRh2O4: A p-type semiconducting oxide with a valence band composed of a low spin state of Rh3+ in a 4d6 configuration

Hiroshi Mizoguchi, Masahiro Hirano, Satoru Fujitsu, Tomonari Takeuchi, Kazushige Ueda, and Hideo Hosono

Appl. Phys. Lett. 80, 1207 (2002); http://dx.doi.org/10.1063/1.1450252 (3 pages) | Cited 33 times

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It is demonstrated that a ZnRh2O4 normal spinel with a band gap of ∼2.1 eV is a unique material as a p type wide-gap semiconductor. The electrical conductivity of the sputtered film was 0.7 S cm−1 at 300 K with no intentional doping. The electronic structure was investigated by photoemission and inverse photoemission measurements and indicated that the band gap is composed mainly of ligand field splitting of an octahedrally coordinated Rh3+ octahedron between fully occupied t2g6 and empty eg0 sets. © 2002 American Institute of Physics.
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73.61.Le Other inorganic semiconductors
71.20.Nr Semiconductor compounds
79.60.Bm Clean metal, semiconductor, and insulator surfaces
78.70.-g Interactions of particles and radiation with matter
72.80.Jc Other crystalline inorganic semiconductors
71.70.Ch Crystal and ligand fields

Optical and electrical properties of Mg-doped p-type AlxGa1−xN

J. Li, T. N. Oder, M. L. Nakarmi, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 80, 1210 (2002); http://dx.doi.org/10.1063/1.1450038 (3 pages) | Cited 50 times

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Mg-doped AlxGa1−xN epilayers with Al content up to 0.27 were grown on sapphire substrates by metalorganic chemical vapor deposition (MOCVD). p-type conduction in these alloys has been achieved, as confirmed by variable temperature Hall-effect measurements. Emission lines of band-to-impurity transitions of free electrons with neutral Mg acceptors as well as localized excitons have been observed in the p-type AlxGa1−xN alloys. The Mg acceptor activation energies EA were deduced from photoluminescence spectra and were found to increase with Al content and agreed very well with those obtained by Hall measurements. From the measured activation energy as a function of the Al content, EA versus x the resistivity of AlxGa1−xN alloys with high Al contents can be deduced. Our results thus indicated that alternative methods for acceptor activation in AlGaN alloys with high Al contents must be developed. Our results have also shown that PL measurements provide direct means of obtaining EA, especially where this cannot be obtained accurately by electrical methods due to high resistance of Mg-doped AlxGa1−xN alloys with high Al content. © 2002 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
71.55.Eq III-V semiconductors

Photocurrent studies of an active polymer layer in a resonant microcavity

Th. B. Singh, U. V. Waghmare, and K. S. Narayan

Appl. Phys. Lett. 80, 1213 (2002); http://dx.doi.org/10.1063/1.1448171 (3 pages) | Cited 7 times

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A microcavity enhanced photodiode, consisting of an active semiconducting-polymer layer is studied in detail. The photodiode spectral response indicates features which specifically arise from the cavity geometry factors, as expected from the simulation of the optical-field pattern within the cavity. The results indicate the tuning of photodetection energy range far below the band gap of semiconducting polymer along with sizable gain and speed. © 2002 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.60.Gz Photodetectors (including infrared and CCD detectors)
78.66.Qn Polymers; organic compounds

PbTe based superlattice structures with high thermoelectric efficiency

H. Beyer, J. Nurnus, H. Böttner, A. Lambrecht, T. Roch, and G. Bauer

Appl. Phys. Lett. 80, 1216 (2002); http://dx.doi.org/10.1063/1.1448388 (3 pages) | Cited 38 times

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We report on an enhanced thermoelectric figure of merit ZT = σS2T/λ (where σ is electrical conductivity, S is thermopower, T is absolute temperature, and λ is thermal conductivity) for PbTe/PbSe0.20Te0.80 superlattices (SLs) and PbTe doping SLs due to a reduction of the thermal conductivity λ parallel to the layer planes. Despite a small decrease of the power factors σS2 due to a reduction of σ in these superlattices, the figure of merit is higher as compared to the corresponding bulk materials and reaches maximum values in the temperature range between 400 and 570 K.© 2002 American Institute of Physics.
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73.61.Le Other inorganic semiconductors
73.50.Lw Thermoelectric effects
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Logarithmically perturbed two dimensional oscillator model of a quantum-dot nanostructure

Mark W. Coffey

Appl. Phys. Lett. 80, 1219 (2002); http://dx.doi.org/10.1063/1.1448663 (3 pages) | Cited 2 times

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We present a logarithmically perturbed two-dimensional isotropic oscillator model of a quantum-dot nanostructure. The logarithmic potential has an ionic line charge physical origin. We estimate the magnitude of this line charge and we obtain the matrix elements required by perturbation theory. The measured ground-state energy depression for a GaAs/AlGaAs/InGaAs heterostructure can be quantitatively accounted for by the model (although not uniquely). We include the effects of nonzero angular momentum states, which play a significant role in determining the dot current–voltage curves. We mention the immediate selection rule imposed by a perturbing potential of rotational symmetry, together with further analytic results. © 2002 American Institute of Physics.
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73.21.La Quantum dots

Hydrogen response mechanism of Pt–GaN Schottky diodes

J. Schalwig, G. Müller, U. Karrer, M. Eickhoff, O. Ambacher, M. Stutzmann, L. Görgens, and G. Dollinger

Appl. Phys. Lett. 80, 1222 (2002); http://dx.doi.org/10.1063/1.1450044 (3 pages) | Cited 80 times

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Besides silicon carbide, group-III nitrides are also suitable large-band-gap semiconductor materials for high-temperature gas sensor devices. Exposing GaN-based Schottky diodes with catalytically active platinum electrodes to hydrogen, we observed a decrease of the rectifying characteristics which we attribute to a decrease in Schottky barrier height. Current–voltage and elastic recoil detection measurements were used to investigate the H-sensing behavior of such devices. Our results indicate an interfacial effect as the origin of the sensor response to hydrogen. © 2002 American Institute of Physics.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.30.Kk Junction diodes
85.30.Hi Surface barrier, boundary, and point contact devices
82.45.Jn Surface structure, reactivity and catalysis
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
73.40.Ei Rectification

Common-emitter current–voltage characteristics of a pnp GaN bipolar junction transistor

Kazuhide Kumakura, Toshiki Makimoto, and Naoki Kobayashi

Appl. Phys. Lett. 80, 1225 (2002); http://dx.doi.org/10.1063/1.1447593 (3 pages) | Cited 7 times

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We fabricated a pnp GaN bipolar junction transistor and investigated its common-emitter current–voltage characteristics. The device structures were grown by metalorganic vapor phase epitaxy on a sapphire substrate. The base thickness was 0.12 μm and its doping concentration was estimated to be lower than mid-1017 cm−3. We have obtained a maximum common-emitter current gain of 50 at room temperature for collector current ranging from −10−5 to −10−4 A. © 2002 American Institute of Physics.
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85.30.Pq Bipolar transistors

Acoustic phonon scattering of two-dimensional electrons in GaN/AlGaN heterostructures

W. Knap, E. Borovitskaya, M. S. Shur, L. Hsu, W. Walukiewicz, E. Frayssinet, P. Lorenzini, N. Grandjean, C. Skierbiszewski, P. Prystawko, M. Leszczynski, and I. Grzegory

Appl. Phys. Lett. 80, 1228 (2002); http://dx.doi.org/10.1063/1.1448401 (3 pages) | Cited 19 times

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We have measured the temperature dependence of the mobility of the two-dimensional electron gas in AlGaN/GaN heterostructures grown on bulk GaN substrates. The linear dependence of the inverse mobility on temperature at temperatures below 50 K indicates the importance of acoustic phonon scattering in these high mobility heterostructures. Using the temperature dependence of the mobility at a range of carrier densities, we determined the GaN conduction band deformation potential to be ac = 9.1±0.7 eV. This result provides a crucial parameter for accurate calculations of intrinsic mobility limits in AlGaN/GaN heterostructures. © 2002 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Negative differential resistance in scanning-tunneling spectroscopy of diamond films

D. D. D. Ma, Y. G. Wang, Li Lu, C. S. Lee, and S. T. Lee

Appl. Phys. Lett. 80, 1231 (2002); http://dx.doi.org/10.1063/1.1448168 (3 pages) | Cited 4 times

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Heavily boron-doped diamond film surfaces were investigated using ultra high-vacuum scanning tunneling microscopy. Negative differential resistance (NDR) was observed in the I–V curves measured from the diamond facets using scanning tunneling spectroscopy. NDR peaks with a peak-to-valley ratio as high as 90 were observed in about half of the I–V curves measured at room temperature. The NDR phenomenon is attributed to the existence of localized electron states on the diamond film surfaces. The I–V curves obtained at the diamond grain boundaries showed the characteristics of the graphite phase, while those acquired from the grain facets manifested obvious rectification in accordance with the wide band gap of diamond. © 2002 American Institute of Physics.
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73.61.Cw Elemental semiconductors
73.50.Fq High-field and nonlinear effects
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
73.20.At Surface states, band structure, electron density of states
61.72.Mm Grain and twin boundaries
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