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20 Mar 2000

Volume 76, Issue 12, pp. 1489-1630

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Matrix dependence of strain-induced wavelength shift in self-assembled InAs quantum-dot heterostructures

N.-T. Yeh, T.-E. Nee, J.-I. Chyi, T. M. Hsu, and C. C. Huang

Appl. Phys. Lett. 76, 1567 (2000); http://dx.doi.org/10.1063/1.126097 (3 pages) | Cited 43 times

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We report on the matrix-dependent strain effect in self-assembled InAs quantum-dot heterostructures using photoluminescence measurements. A series of samples were prepared to examine the effect of quantum dot position with respect to the so-called strain-reducing layer (SRL). Since the SRL reduces the residual hydrostatic strain in the quantum dots, long emission wavelength of 1.34 μm is observed for the InAs quantum dots with an In0.16Ga0.84As SRL. The dependence of the emission wavelength on the thickness of the cap layer on SRL also indicates the importance of the role of matrix in the strain relaxation process of the dots. Using In0.16Al0.84As instead of In0.16Ga0.84As as the SRL, a blueshift in wavelength is observed because the elastic stiffness of In0.16Al0.84As is higher than that of In0.16Ga0.84As and less strain is removed from the dots with In0.16Al0.84As SRL. © 2000 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
73.61.Ey III-V semiconductors

Self-assembled InGaN quantum dots grown by molecular-beam epitaxy

C. Adelmann, J. Simon, G. Feuillet, N. T. Pelekanos, B. Daudin, and G. Fishman

Appl. Phys. Lett. 76, 1570 (2000); http://dx.doi.org/10.1063/1.126098 (3 pages) | Cited 69 times

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Self-assembled InGaN islands were grown by molecular-beam epitaxy on GaN, following a Stranski–Krastanow growth mode. Atomic force microscopy revealed that their dimensions were small enough to expect zero-dimensional quantum effects: the islands were typically 27 nm wide and 2.9 nm high. Strong blue-violet photoluminescence of the dots is observed, persisting up to room temperature. The temperature dependence of the photoluminescence is analyzed and compared to that of InGaN quantum well and bulk samples. © 2000 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Hole and electron emission from InAs quantum dots

C. M. A. Kapteyn, M. Lion, R. Heitz, D. Bimberg, P. N. Brunkov, B. V. Volovik, S. G. Konnikov, A. R. Kovsh, and V. M. Ustinov

Appl. Phys. Lett. 76, 1573 (2000); http://dx.doi.org/10.1063/1.126099 (3 pages) | Cited 61 times

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Carrier escape processes from self-organized InAs quantum dots QDs embedded in GaAs are investigated by time-resolved capacitance spectroscopy. Electron emission is found to be dominated by tunneling processes. In addition to tunneling from the ground state, we find thermally activated tunneling involving excited QD states with an activation energy of 82 meV. For holes, the tunnel contribution is negligible and thermal activation from the QD ground state to the GaAs valence band with an activation energy of 164 meV dominates. Extrapolation to room temperature yields an emission time constant of 5 ps for holes, which is an order of magnitude larger than for electrons. The measured activation energies agree well with theoretically predicted QD levels. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.47.-p Spectroscopy of solid state dynamics
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Photoreflectance spectra of excitonic polaritons in GaN substrate prepared by lateral epitaxial overgrowth

S. F. Chichibu, K. Torii, T. Deguchi, T. Sota, A. Setoguchi, H. Nakanishi, T. Azuhata, and S. Nakamura

Appl. Phys. Lett. 76, 1576 (2000); http://dx.doi.org/10.1063/1.126100 (3 pages) | Cited 32 times

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Photoreflectance (PR) spectra of high-purity, nearly free-standing GaN substrate were compared with emission and reflectance spectra, which were analyzed based on a model exciton-polariton picture in which A, B, and C free excitons couple simultaneously to an electromagnetic wave. The GaN substrate with reduced dislocation density was prepared by lateral epitaxial overgrowth technique and it exhibited predominant excitonic emissions with the decay time nearly 1 ns even at room temperature. The transition energies obtained from the PR spectrum agree with the energies of bottlenecks of the excitonic polariton branches. The result means that perturbation-induced change in the dielectric function is mainly due to polaritons. Temperature dependence of the A-exciton energy was well described using a model which assumes Einstein phonons. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.20.-e Optical properties of bulk materials and thin films
78.20.Jq Electro-optical effects
73.20.At Surface states, band structure, electron density of states
71.35.Lk Collective effects (Bose effects, phase space filling, and excitonic phase transitions)

Intersubband transitions in GaAs coupled-quantum-wells for use as a tunable detector at THz frequencies

A. M. Tomlinson, C. C. Chang, R. J. Stone, R. J. Nicholas, A. M. Fox, M. A. Pate, and C. T. Foxon

Appl. Phys. Lett. 76, 1579 (2000); http://dx.doi.org/10.1063/1.126101 (3 pages) | Cited 5 times

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We demonstrate a detection mechanism for 2–5 THz radiation using intersubband transitions between anticrossing electron levels in a GaAs/AlGaAs coupled-quantum-well photodiode. The THz radiation is detected as a modulation in the photocurrent generated by a visible laser. This modulation is caused by carrier heating effects due to absorption of energy by intersubband transitions. Since the frequency of the intersubband transitions varies with the electric-field strength, the device can function as a voltage-tunable THz detector. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors

Control of the band-gap shift in quantum-well intermixing using a germanium interlayer

J. H. Teng, S. J. Chua, G. Li, A. Saher Helmy, and J. H. Marsh

Appl. Phys. Lett. 76, 1582 (2000); http://dx.doi.org/10.1063/1.126102 (3 pages) | Cited 5 times

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A simple technique for controlling the shift in band gap in AlGaAs/GaAs and InGaAs/GaAs quantum-well (QW) structures is reported. It involves the evaporation of a thin Ge layer and then covering it with spin-on silica followed by rapid thermal annealing. The quantum-well intermixing was suppressed in the presence of this Ge layer between the sample surface and the spin-on silica. The interdiffusion rate was reduced by more than one order of magnitude compared to that without the Ge interlayer. The blueshift of the band gap can be controlled by varying the thickness of the Ge interlayer. A differential band-gap shift of more than 100 meV can be achieved with a 500 Å Ge interlayer for both the AlGaAs/GaAs and InGaAs/GaAs QW structures. The optical quality of the material was not deteriorated by the Ge cover compared to the SiO2 cover as seen from the photoluminescence intensity and spectral linewidth. Using an appropriate mask, this technique has the potential to tune the band gap in selected areas across a single wafer. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.20.Hb Impurity and defect levels; energy states of adsorbed species
68.35.Fx Diffusion; interface formation
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.Ct Interface structure and roughness
61.72.Cc Kinetics of defect formation and annealing

Reduction of interface-state density in 4H–SiC n-type metal–oxide–semiconductor structures using high-temperature hydrogen annealing

K. Fukuda, S. Suzuki, T. Tanaka, and K. Arai

Appl. Phys. Lett. 76, 1585 (2000); http://dx.doi.org/10.1063/1.126103 (3 pages) | Cited 27 times

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The effects of hydrogen annealing on capacitance–voltage (C–V) characteristics and interface-state density (Dit) of 4H–SiC metal–oxide–semiconductor (MOS) structures have been investigated. The Dit was reduced to as low as 1×1011 eV−1 cm−2 at Ec−E = 0.6 eV using hydrogen annealing above 800 °C, where Ec−E is the energy level from the conduction-band edge. Secondary ion mass spectroscopy and Dit analysis revealed that Dit decreased with the increase of hydrogen concentration accumulated at the SiO2/4H–SiC interface. The interface states at SiO2/4H–SiC are thought to be originated from the dangling bonds of C atoms as well as Si atoms, because Dit decreases as the hydrogen annealing temperature increases and saturates around 800 °C. This high-temperature hydrogen annealing is useful for accumulation-type SiC metal–oxide–semiconductor field-effect transistors, which have n-type MOS structures to reduce the Dit. © 2000 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.72.Cc Kinetics of defect formation and annealing

Impurity reduction in In0.53Ga0.47As layers grown by liquid phase epitaxy using Er-treated melts

S. Dhar, Shampa Paul, and V. N. Kulkarni

Appl. Phys. Lett. 76, 1588 (2000); http://dx.doi.org/10.1063/1.126104 (3 pages) | Cited 5 times

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Hall mobility and carrier concentration measurements are done on In0.53Ga0.47As layers grown by liquid phase epitaxy from melts containing 0.1–0.18 wt % Er. The carrier concentration in the layer decreased to 2×1014 cm−3 upon the addition of 0.16 wt % Er to the growth melt but the corresponding mobility of the layer increased only marginally. A detailed analysis of the temperature-dependent Hall mobility data for the samples using a theoretical curve fitting technique revealed that the donor impurities in the material are reduced to a greater extent compared to the acceptors, making the layers compensated. The experimental mobilities are further compared with the published values of theoretically calculated mobilities for InGaAs with similar compensations. It is shown that the space charge scattering effects are to be considered in order to get a good agreement between the experimental and the theoretical values. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
81.05.Ea III-V semiconductors

Double-dot charge transport in Si single-electron/hole transistors

L. P. Rokhinson, L. J. Guo, S. Y. Chou, and D. C. Tsui

Appl. Phys. Lett. 76, 1591 (2000); http://dx.doi.org/10.1063/1.126105 (3 pages) | Cited 11 times

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We studied transport through ultrasmall Si quantum-dot transistors fabricated from siliconon-insulator wafers. At high temperatures, 4<T<100 K, the devices show single-electron or single-hole transport through the lithographically defined dot. At T<4 K, current through the devices is characterized by multidot transport. From the analysis of the transport in samples with double-dot characteristics, we conclude that extra dots are formed inside the thermally grown gate oxide which surrounds the lithographically defined dot. © 2000 American Institute of Physics.
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85.35.Gv Single electron devices
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.23.Hk Coulomb blockade; single-electron tunneling
73.61.Cw Elemental semiconductors

Nitrogen vacancy scattering in n-GaN grown by metal-organic vapor phase epitaxy

Qin-Sheng Zhu and Nobuhiko Sawaki

Appl. Phys. Lett. 76, 1594 (2000); http://dx.doi.org/10.1063/1.126106 (3 pages) | Cited 7 times

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Electron mobility limited by nitrogen vacancy scattering was taken into account to evaluate the quality of n-type GaN grown by metal-organic vapor phase epitaxy. The nitrogen vacancy scattering potential used for our mobility calculation has to satisfy two requirements: such potential is (1) spatially short range, and (2) finite and not divergent at the vacancy core. A square-well potential was adopted to calculate the mobility, because it satisfies not only these two requirements, but also simplifies the calculation. As a result, the estimated mobility shows a T−1/2 temperature dependence, and is very sensitive to the potential well width. After introducing the nitrogen vacancy scattering, we obtained the best fitting between the calculated and experimental results for our high quality sample, and it was found that the measured mobility is dominated by ion impurity and dislocation scatterings at the low temperatures, but dominated by optical phonon and nitrogen vacancy scatterings at the high temperatures. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.J- Point defects and defect clusters
73.50.Dn Low-field transport and mobility; piezoresistance
72.20.Fr Low-field transport and mobility; piezoresistance

Electrical measurements of individual semiconducting single-walled carbon nanotubes of various diameters

Chongwu Zhou, Jing Kong, and Hongjie Dai

Appl. Phys. Lett. 76, 1597 (2000); http://dx.doi.org/10.1063/1.126107 (3 pages) | Cited 105 times

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Individual semiconducting single-walled carbon nanotubes (SWNTs) of various diameters are studied by electrical measurements. Transport through a semiconducting SWNT involves thermal activation at high temperatures, and tunneling through a reverse biased metal–tube junction at low temperatures. Under high bias voltages, current–voltage (I–V) characteristics of semiconducting SWNTs exhibit pronounced asymmetry with respect to the bias polarity, as a result of local gating. SWNT transistors that mimic conventional p-metal-oxide-semiconductor field-effect transistor with similar I–V characteristics and high transconductance are enabled. © 2000 American Institute of Physics.
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73.61.Wp Fullerenes and related materials
73.40.Gk Tunneling

Indium segregation in InGaN quantum-well structures

N. Duxbury, U. Bangert, P. Dawson, E. J. Thrush, W. Van der Stricht, K. Jacobs, and I. Moerman

Appl. Phys. Lett. 76, 1600 (2000); http://dx.doi.org/10.1063/1.126108 (3 pages) | Cited 36 times

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Direct evidence for In-segregation in InGaN/GaN quantum-well structures is given via highly spatially resolved energy dispersive x-ray analysis performed in a dedicated scanning transmission electron microscope. The In fluctuations become increasingly pronounced in the vicinity of dislocations. The latter assist In diffusion and cause severe Ga/In intermixing. © 2000 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Highly conductive diamond probes for scanning spreading resistance microscopy

T. Hantschel, P. Niedermann, T. Trenkler, and W. Vandervorst

Appl. Phys. Lett. 76, 1603 (2000); http://dx.doi.org/10.1063/1.126109 (3 pages) | Cited 40 times

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Scanning spreading resistance microscopy (SSRM) is a powerful method for the characterization of Si semiconductor devices based on atomic force microscopy (AFM). It requires conductive probe tips made of doped diamond. Although various solid diamond probes have been fabricated, they could not satisfy the requirements for SSRM. Therefore, we have developed a SSRM probe composed of a pyramidal diamond tip attached to a Si cantilever. This letter describes the probe fabrication process briefly and presents excellent SSRM measurements obtained on Si calibration samples. Solid diamond tips integrated in Si cantilevers were used for SSRM showing a significantly higher dynamic range than the conductive probes known to date. © 2000 American Institute of Physics.
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85.30.De Semiconductor-device characterization, design, and modeling
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
07.79.Lh Atomic force microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
72.20.Fr Low-field transport and mobility; piezoresistance
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