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17 Apr 2000

Volume 76, Issue 16, pp. 2149-2312

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Temperature dependent polarization switching and band-gap anomalies in strained GaxIn1−xAs quantum wire heterostructures

D. E. Wohlert and K. Y. Cheng

Appl. Phys. Lett. 76, 2247 (2000); http://dx.doi.org/10.1063/1.126310 (3 pages) | Cited 7 times

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We report on the polarized photoluminescence (PPL) properties of strained GaxIn1−xAs quantum wire (QWR) heterostructures formed in situ by the strain-induced lateral-layer ordering process. It is found that the PPL spectra of these QWRs have unique properties that depend on temperature and orientation of the pump polarization with respect to the QWR direction. In particular, the dominant polarization switches when the sample is warmed from 77 to 300 K provided the pump polarization is parallel to the QWRs. This indicates that the light-hole (LH) and heavy-hole (HH) bands cross with increasing temperature, which implies that the multiaxial strain in this material is a function of temperature. Furthermore, this effect is only observed in GaxIn1−xAs QWR heterostructures that display anomalous band-gap stability with respect to temperature. It is believed that the strain induced temperature dependent LH–HH crossing as evidenced by the polarization switching switching effect is responsible for this anomaly. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Interface trap profile near the band edges at the 4H-SiC/SiO2 interface

N. S. Saks, S. S. Mani, and A. K. Agarwal

Appl. Phys. Lett. 76, 2250 (2000); http://dx.doi.org/10.1063/1.126311 (3 pages) | Cited 54 times

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The transconductance of SiC metal–oxide–semiconductor field-effect transistors (MOSFETs) is typically much lower in devices fabricated on the 4H-SiC polytype compared to 6H. It is believed that this behavior is caused by extreme trapping of inversion electrons due to a higher density of traps Dit at the SiC/SiO2 interface in 4H-SiC. Here we present an approach for profiling Dit versus energy in the band gap using a modified capacitance–voltage technique on large-area MOSFETs. We find that Dit increases towards the conduction band edge Ec in both polytypes, and that Dit is much higher in 4H- compared to 6H-SiC for devices fabricated in the same process lot. © 2000 American Institute of Physics.
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85.30.Tv Field effect devices
73.20.At Surface states, band structure, electron density of states
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
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

Energy level alignment at the conjugated phenylenevinylene oligomer/metal interface

S. C. Veenstra, U. Stalmach, V. V. Krasnikov, G. Hadziioannou, H. T. Jonkman, A. Heeres, and G. A. Sawatzky

Appl. Phys. Lett. 76, 2253 (2000); http://dx.doi.org/10.1063/1.126312 (3 pages) | Cited 17 times

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In this letter we report an investigation of the interfacial electronic structure formed by metals and conjugated oligomers using ultraviolet photoelectron spectroscopy. Au and Ag were used as metal substrates for two five-ring phenylenevinylene oligomers: unsubstituted p-bis[(p-styryl)styryl]benzene (P5V4) and the analogous oligomer with 2-methoxy-5-(2’-ethyl-hexyloxy) substitution on the central ring (MEH-P5V4). We found for all interfaces a lowering of the energy levels of the organic overlayer by 0.4–1.2 eV. Remarkably, this energy lowering, presumably due to interface dipole layers, was always such as to keep the hole injection barrier nearly constant and therefore at most weakly sensitive to the work function of the metal or the ionization potential of the oligomer. © 2000 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
79.60.Jv Interfaces; heterostructures; nanostructures
73.61.Ph Polymers; organic compounds

Room-temperature Al single-electron transistor made by electron-beam lithography

Yu. A. Pashkin, Y. Nakamura, and J. S. Tsai

Appl. Phys. Lett. 76, 2256 (2000); http://dx.doi.org/10.1063/1.126313 (3 pages) | Cited 34 times

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We present a lithographically made Al single-electron transistor that shows gate modulation at room temperature. The temperature dependence of the modulation agrees with the orthodox theory, however, energy-level quantization in a tiny metallic island affects the device characteristics below 30 K. The charge-equivalent noise of the device at 300 K was measured to be ∼ 4×10−2 e/Hz1/2 at 1 Hz and is expected to be 1000 times lower in the white-noise regime at higher frequencies. © 2000 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer
85.35.Gv Single electron devices

Elimination of carrier-density nonuniformities by surface acoustic waves

Y. Takagaki, E. Wiebicke, K.-J. Friedland, H. Kostial, and K. H. Ploog

Appl. Phys. Lett. 76, 2259 (2000); http://dx.doi.org/10.1063/1.126314 (3 pages) | Cited 2 times

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The action on a two-dimensional electron gas (2DEG) by electric fields that accompany surface acoustics waves (SAWs) propagating in GaAs-AlxGa1−xAs heterostructures is typically negligible because of screening. In the quantum Hall regime, the longitudinal conductivity of the 2DEG is nearly zero when the Fermi level lies in the Landau gap. Consequently, the SAWs can build up electric fields that are strong enough to rake off mobile electrons. We demonstrate that inhomogeneous carrier distributions produced in the course of photoionization of DX centers can be flattened out by applying the SAWs in high magnetic fields. © 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
73.61.Ey III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
71.55.Eq III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.35.Gy Mechanical properties; surface strains
71.20.Nr Semiconductor compounds
73.43.-f Quantum Hall effects
73.20.Hb Impurity and defect levels; energy states of adsorbed species

InGaP/InGaAsN/GaAs NpN double-heterojunction bipolar transistor

P. C. Chang, A. G. Baca, N. Y. Li, X. M. Xie, H. Q. Hou, and E. Armour

Appl. Phys. Lett. 76, 2262 (2000); http://dx.doi.org/10.1063/1.126315 (3 pages) | Cited 26 times

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We have demonstrated a functional NpN double-heterojunction bipolar transistor (DHBT) using InGaAsN for the base layer. The InGaP/In0.03Ga0.97As0.99N0.01/GaAs DHBT has a low VON of 0.81 V, which is 0.13 V lower than in a InGaP/GaAs heterojunction bipolar transistor (HBT). The lower turn-on voltage is attributed to the smaller band gap (1.20 eV) of metalorganic chemical vapor deposition-grown In0.03Ga0.97As0.99N0.01 base layer. GaAs is used for the collector; thus the breakdown voltage (BVCEO) is 10 V, consistent with the BVCEO of InGaP/GaAs HBTs of comparable collector thickness and doping level. To alleviate the current blocking phenomenon caused by the larger conduction band discontinuity between InGaAsN and GaAs, a graded InGaAs layer with δ doping is inserted at the base–collector junction. The improved device has a peak current gain of seven with ideal current–voltage characteristics. © 2000 American Institute of Physics.
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85.30.Pq Bipolar transistors
81.05.Ea III-V semiconductors

Microscopic theory of hot-carrier relaxation in semiconductor-based quantum-cascade lasers

Rita C. Iotti and Fausto Rossi

Appl. Phys. Lett. 76, 2265 (2000); http://dx.doi.org/10.1063/1.126316 (3 pages) | Cited 21 times

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A microscopic analysis of basic nonequilibrium phenomena in unipolar quantum devices is presented. In particular, energy-relaxation processes governing the hot-carrier dynamics in the active region of GaAs-based quantum-cascade lasers are investigated by means of a generalized ensemble Monte Carlo simulation. Such analysis is essential in determining the validity range and limitations of purely macroscopic models with respect to basic device parameters, like injection current and temperature. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.30.De Semiconductor-device characterization, design, and modeling
81.05.Ea III-V semiconductors
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
72.20.Ht High-field and nonlinear effects
73.50.Fq High-field and nonlinear effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
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

Coupled InAs/GaAs quantum dots with well-defined electronic shells

S. Fafard, M. Spanner, J. P. McCaffrey, and Z. R. Wasilewski

Appl. Phys. Lett. 76, 2268 (2000); http://dx.doi.org/10.1063/1.126317 (3 pages) | Cited 49 times

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Artificial molecules are studied using coupled quantum-dot (QD) ensembles with well-defined electronic shells. The coupling strength between the zero-dimensional states is varied by changing the distance between two layers of stacked self-assembled InAs/GaAs QDs. For strongly coupled QDs grown with a 4 nm spacer, state-filling spectroscopy reveals a shift of the QD symmetric state to lower energies by ∼23 meV. The wetting layer states are also strongly coupled because of the shallow confinement, resulting in a redshift of its symmetric state by ∼26 meV. © 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
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors

Influence of oxygen on the activation of p-type GaN

B. A. Hull, S. E. Mohney, H. S. Venugopalan, and J. C. Ramer

Appl. Phys. Lett. 76, 2271 (2000); http://dx.doi.org/10.1063/1.126318 (3 pages) | Cited 40 times

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The presence of oxygen in the annealing environment can exhibit a strong influence on the activation of p-GaN, as demonstrated by experiments described in this letter. We activated p-GaN at 600–900 °C in four environments: ultrahigh purity (UHP) N2 gettered to remove residual O2, UHP N2 without gettering, 99.5% UHP N2/0.5% UHP O2, and 90% UHP N2/10% UHP O2. The resistivity of the p-GaN was lowest when O2 was intentionally introduced during activation and was highest when extra care was taken to getter residual O2 from the annealing gas. The experiments also demonstrate that unintentionally incorporated O2 can be at high enough levels to influence the activation process. © 2000 American Institute of Physics.
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61.72.Cc Kinetics of defect formation and annealing
61.72.Yx Interaction between different crystal defects; gettering effect
81.65.Tx Gettering
72.80.Ey III-V and II-VI semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance

Conductance oscillations induced by longitudinal resonant states in heteroepitaxially defined Ga0.25In0.75As/InP electron waveguides

Qin Wang, N. Carlsson, I. Maximov, P. Omling, L. Samuelson, W. Seifert, Weidong Sheng, I. Shorubalko, and H. Q. Xu

Appl. Phys. Lett. 76, 2274 (2000); http://dx.doi.org/10.1063/1.126319 (3 pages) | Cited 12 times

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We have measured at low temperatures the conductance of electron waveguides fabricated from modulation-doped quantum wells by wet etching and regrowth. We have found that, for a waveguide with abruptly changed geometry at the entrance and exit, the conductance shows oscillations, which are superimposed on a conventional conductance plateau structure. The periods and amplitudes of conductance oscillations depend on the length to width aspect ratio of the waveguide. In addition, the amplitudes of conductance oscillations decrease with increasing temperature. We propose that the observed oscillations are caused by the formation of longitudinal resonant electron states in the waveguide, in analogy with optical Fabry–Perot effects. © 2000 American Institute of Physics.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.61.Ey III-V semiconductors
85.35.Ds Quantum interference devices

Performance degradation of small silicon devices caused by long-range Coulomb interactions

M. V. Fischetti and S. E. Laux

Appl. Phys. Lett. 76, 2277 (2000); http://dx.doi.org/10.1063/1.126320 (3 pages) | Cited 11 times

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In small silicon devices, conduction electrons in the channel are subject to long-range Coulomb interactions with electrons in the heavily doped drain, source, and gate regions. We show that, for devices with channel lengths shorter than about 40 nm and oxides thinner than 2.5 nm, these interactions cause a reduction of the electron velocity. We present results obtained using both semiclassical two-dimensional self-consistent Monte Carlo/Poisson simulations and a quantum-mechanical model based on electron scattering from gate–oxide interface plasmons. © 2000 American Institute of Physics.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.50.Bk General theory, scattering mechanisms
73.50.Dn Low-field transport and mobility; piezoresistance

Defects in planar Si pn junctions studied with electrically detected magnetic resonance

T. Wimbauer, K. Ito, Y. Mochizuki, M. Horikawa, T. Kitano, M. S. Brandt, and M. Stutzmann

Appl. Phys. Lett. 76, 2280 (2000); http://dx.doi.org/10.1063/1.126321 (3 pages) | Cited 2 times

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We report electrically detected magnetic resonance (EDMR) measurements on planar Si pn junctions which were isolated via local oxidation of silicon (LOCOS). The investigations of the as-fabricated diodes show the presence of various defects. We observe Pb centers at the boundary to the LOCOS isolation and an isotropic Si dangling bond related signal which is assumed to be a consequence of ion implantation. The E′H center—a hydrogen-complexed oxygen vacancy in the SiO2 device isolation—is also detected via EDMR. The EDMR detection mechanism, which is based on resonant changes of the device current, restricts the detected oxide defects to those which are close to the interface. © 2000 American Institute of Physics.
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76.30.Mi Color centers and other defects
61.72.J- Point defects and defect clusters
71.55.Cn Elemental semiconductors
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.Hb Impurity and defect levels; energy states of adsorbed species
81.65.Mq Oxidation

Annealing dynamics of nitrogen-implanted GaAs films investigated by current–voltage and deep-level transient spectroscopy

J. F. Chen, J. S. Wang, M. M. Huang, and N. C. Chen

Appl. Phys. Lett. 76, 2283 (2000); http://dx.doi.org/10.1063/1.126322 (3 pages) | Cited 8 times

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We present electrical data to show that, after nitrogen implantation, GaAs films become resistive after high-temperature annealing. The activation energies of the resistance are determined to be 0.34, 0.59, and 0.71 eV after annealing at 500, 700, and 950 °C, respectively. The increase in the activation energy with increasing annealing temperature can be explained by the results of traps detected in deep-level transient spectroscopy, where two traps at 0.32 and 0.70 eV are observed in the samples after annealing. The intensity of the trap at 0.32 eV is found to reduce by annealing. By comparing to the result of the x-ray diffraction, we suspect that this trap is related to the lattice-expansion defects. The trap at 0.70 eV is observed only in samples annealed at high temperatures. Since this trap contributes to the high-resistive effect, we believe that it is associated with the nitrogen ions. © 2000 American Institute of Physics.
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71.55.Eq III-V semiconductors
73.61.Ey III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.uj III-V and II-VI semiconductors
61.80.Jh Ion radiation effects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.82.Fk Semiconductors
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