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19 Apr 1999

Volume 74, Issue 16, pp. 2253-2392

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Reduced thermal conductivity in low-temperature-grown GaAs

A. W. Jackson, J. P. Ibbetson, A. C. Gossard, and U. K. Mishra

Appl. Phys. Lett. 74, 2325 (1999); http://dx.doi.org/10.1063/1.123839 (3 pages) | Cited 10 times

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Thermal conductivity of low-temperature-grown GaAs(LT GaAs) was measured at room temperature using a self-heated photolithographically patterned platinum wire on the surface of the sample. Finite element calculations were performed to extract the thermal conductivity from the nonlinear I–V characteristic of the wires. For LT GaAs grown at a substrate temperature of 240 °C, the thermal conductivity was found to be only 23% of the value for stoichiometric GaAs. Rapid thermal annealing of the sample at 650 °C for 30 s increased the thermal conductivity to 46% of the GaAs value. Strong phonon scattering by point defects could account for reduced thermal conductivity in the as-grown material. The reduced thermal conductivity in the annealed material, however, is not consistent with our current understanding of the defects in annealed LT GaAs. © 1999 American Institute of Physics.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
61.72.Cc Kinetics of defect formation and annealing
63.20.kp Phonon-defect interactions
02.70.Dh Finite-element and Galerkin methods

Fabrication of high-quality one- and two-dimensional electron gases in undoped GaAs/AlGaAs heterostructures

R. H. Harrell, K. S. Pyshkin, M. Y. Simmons, D. A. Ritchie, C. J. B. Ford, G. A. C. Jones, and M. Pepper

Appl. Phys. Lett. 74, 2328 (1999); http://dx.doi.org/10.1063/1.123840 (3 pages) | Cited 14 times

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We have developed a technique for the fabrication of high-mobility electron gases formed in undoped GaAs/AlGaAs heterostructures. The use of an insulated gate allows independent control over the carrier density in the Hall bar and ohmic contact regions of the device. This unique design eliminates difficulties in obtaining reliable ohmic contacts, particularly in the low carrier density regime. In the absence of remote ionized impurity scattering, extremely high transport mobilities are obtained at low carrier densities (1×106 cm2 V−1 s−1 at 1×1010 cm−2). This design has been adapted to the formation of undoped one-dimensional electron gases that show clean and reproducible conductance plateau at 1.5 K. © 1999 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

Boron-enhanced diffusion of boron: Physical mechanisms

Aditya Agarwal, H.-J. Gossmann, and D. J. Eaglesham

Appl. Phys. Lett. 74, 2331 (1999); http://dx.doi.org/10.1063/1.123841 (3 pages) | Cited 34 times

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Silicon layers containing B in excess of a few atomic percent create a supersaturation of Si self-interstitials in the underlying Si, resulting in enhanced diffusion of B in the substrate [boron-enhanced diffusion (BED)]. The temperature and time dependence of BED is investigated here. Evaporated boron as well as ultralow energy 0.5 keV B-implanted layers were annealed at temperatures from 1100 to 800 °C for times ranging from 3 to 3000 s. Isochronal 10 s anneals reveal that the BED effect increases with increasing temperature up to 1050 °C and then decreases. In contrast, simulations based on interstitial generation via the kick-out mechanism predict a decreasing dependence leading to the conclusion that the kick-out mechanism is not the dominant source of excess interstitials responsible for BED. The diffusivity enhancements from the combined effects of BED and transient-enhanced diffusion, measured in 2×1015 cm−2, 0.5 keV B-implanted samples, show a similar temperature dependence as seen for evaporated B, except that the maximum enhancement occurs at 1000 °C. The temperature-dependent behavior of BED supports the hypothesis that the source of excess interstitials is the formation of a silicon boride phase in the high-boron-concentration silicon layer. © 1999 American Institute of Physics.
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66.30.J- Diffusion of impurities
81.05.Cy Elemental semiconductors
85.40.Ry Impurity doping, diffusion and ion implantation technology
61.72.J- Point defects and defect clusters
61.72.uf Ge and Si
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Cc Kinetics of defect formation and annealing

Two-dimensional quantum-confined Stark effect in V-groove quantum wires: Excited state spectroscopy and theory

H. Weman, E. Martinet, M.-A. Dupertuis, A. Rudra, K. Leifer, and E. Kapon

Appl. Phys. Lett. 74, 2334 (1999); http://dx.doi.org/10.1063/1.123842 (3 pages) | Cited 8 times

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We report on the electric field effects in photoluminescence (PL) and PL excitation (PLE) measurements of reverse-biased GaAs V-groove quantum wires. We observe large redshifts (9 meV at −65 kV/cm) of PL and PLE peaks as well as field dependent intensity and polarization anisotropy variations, which are analyzed by a two-dimensional quantum confined Stark effect model. © 1999 American Institute of Physics.
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78.20.Jq Electro-optical effects
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Observation of quantum dot-like behavior of GaInNAs in GaInNAs/GaAs quantum wells

H. P. Xin, K. L. Kavanagh, Z. Q. Zhu, and C. W. Tu

Appl. Phys. Lett. 74, 2337 (1999); http://dx.doi.org/10.1063/1.123843 (3 pages) | Cited 77 times

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We report a quantum dot-like behavior of GaInNAs due to composition nonuniformity of N and In in GaInNAs/GaAs quantum wells (QWs). Images of cross-sectional transmission electron microscopy show that the wells of both Ga0.7In0.3As/GaAs and Ga0.7In0.3N0.02As0.98/GaAs are undulated due to lateral variations in strain. This effect is more pronounced in the N-containing QWs due to nonuniform In and N concentrations. Rapid thermal annealing causes a blueshift of the photoluminescence (PL) peak, and results in a splitting of the as-grown broad PL emission into two peaks. The In and N composition fluctuation after annealing becomes predominantly bimodal. The low-energy PL peak is attributed to excitons localized at deep levels, which are originated from In- and N-rich regions in the wells acting as quantum dots (QD). The high-energy peak PH is likely due to the excitons of the 2D QWs. To reduce the local strain, N atoms are preferentially localized in the In-rich regions, so the separation between these two peaks increases with increasing N concentration. Increasing excitation intensity results in a significant blueshift for PL and little blueshift for PH, due to the easier band filling of the localized QD states than QW states. © 1999 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.05.Ea III-V semiconductors
71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.72.Cc Kinetics of defect formation and annealing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
71.35.-y Excitons and related phenomena
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.20.Fz Weak or Anderson localization

High-transparency Ni/Au ohmic contact to p-type GaN

J. K. Sheu, Y. K. Su, G. C. Chi, P. L. Koh, M. J. Jou, C. M. Chang, C. C. Liu, and W. C. Hung

Appl. Phys. Lett. 74, 2340 (1999); http://dx.doi.org/10.1063/1.123844 (3 pages) | Cited 102 times

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In this study, a very thin Ni/Au bilayer metal film was prepared by electron beam evaporation and thermal alloying to form ohmic contact on p-type GaN film. After thermal alloying, the current–voltage (I–V) characteristic of Ni/Au contact on p-type GaN film exhibited ohmic behavior. The Ni/Au contacts showed a specific contact resistance of 1.7×10−2 Ω cm2 at an alloying temperature of 450 °C. In addition, the light transmittance of the Ni/Au (2 nm/6 nm) bilayer on p-type GaN was measured to be around 85% at 470 nm. These results suggest that a suitable metallization technology for the fabrication of light emitting devices can be achieved. © 1999 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
81.05.Ea III-V semiconductors
73.40.Cg Contact resistance, contact potential
78.66.Bz Metals and metallic alloys
85.40.Ls Metallization, contacts, interconnects; device isolation
78.66.Fd III-V semiconductors

Mesoscopic composition fluctuations in semiconductor alloys: Effect on infrared devices

M. W. Muller and A. Sher

Appl. Phys. Lett. 74, 2343 (1999); http://dx.doi.org/10.1063/1.123845 (3 pages) | Cited 4 times

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Semiconductor alloys like Hg1−xCdxTe and Al1−xGaxAs, where there is a close lattice constant match between the constituents, are nearly random. Consider mesoscopic size scales of radius r that are large compared with a lattice constant ( ∼ 25 A<r< ∼ 250 A), but small compared with typical device dimensions. In such regions the number of substitutional sites is small enough so the root-mean-square concentration fluctuation 〈(Δx)2〉1/2 is sufficiently large to produce random arrays of mesoscopic “quantum dots” that adversely affect many device properties. The influence of the adverse effects differ among various properties—for example, electron and hole mobilities, lifetimes, and so on—but, in general, are worse the smaller the fundamental gap becomes. These kinds of fluctuations are suppressed in lattice-mismatched alloys like Hg1−xZnxTe and Ga1−xInxAs because there is a long-range strain energy penalty associated with them. Thus, lattice-mismatched alloys are more spatially uniform than lattice-matched alloys. © 1999 American Institute of Physics.
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61.66.Bi Elemental solids
61.66.Dk Alloys
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.60.Gz Photodetectors (including infrared and CCD detectors)

CdTe(111)B grown on Si(111) by molecular beam epitaxy

S. Rujirawat, Y. Xin, N. D. Browning, S. Sivananthan, David J. Smith, S.-C. Y. Tsen, Y. P. Chen, and V. Nathan

Appl. Phys. Lett. 74, 2346 (1999); http://dx.doi.org/10.1063/1.123846 (3 pages) | Cited 14 times

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We demonstrate the growth of large-area, domain-free CdTe(111)B single crystals on As-passivated Si(111) substrates by molecular beam epitaxy using ZnTe buffer layers. The crystal quality of the CdTe(111)B/ZnTe(111)B/Si(111) films was examined by x-ray diffraction (56 arcs), etch-pit-density (2×105 cm−2) analysis, and transmission electron microscopy, and was found to be comparable to or better than the best CdTe(111)B films grown directly on vicinal Si(001). Surface reconstructions were observed by reflection high-energy electron diffraction at different stages. Diffraction intensity oscillations demonstrated the layer-by-layer growth mode of the CdTe surface. An interface model for these films is proposed. © 1999 American Institute of Physics.
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81.05.Dz II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology

Near-field scanning optical microscopy of indium gallium nitride multiple-quantum-well laser diodes

D. K. Young, M. P. Mack, A. C. Abare, M. Hansen, L. A. Coldren, S. P. Denbaars, E. L. Hu, and D. D. Awschalom

Appl. Phys. Lett. 74, 2349 (1999); http://dx.doi.org/10.1063/1.123847 (3 pages) | Cited 12 times

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Near-field scanning optical microscopy is used to image electroluminescence from three and ten quantum-well (QW) indium gallium nitride based laser diodes. Facet cross sections are imaged with a spatial resolution of <100 nm, below and above the lasing threshold. Observation of spatially resolved spectra near the active region reveals compositional fluctuations as well as absorption and reemission of the lasing mode. Single-mode emission is observed for narrow (3 and 5 μm wide) 3 QW laser bars. Near-field measurements show a relationship between modal emission, waveguide structure, and lateral device size. © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.60.Fi Electroluminescence
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Deformation field in single-crystal fields semiconductor substrates caused by metallization features

I. C. Noyan, P.-C. Wang, S. K. Kaldor, and J. L. Jordan-Sweet

Appl. Phys. Lett. 74, 2352 (1999); http://dx.doi.org/10.1063/1.123848 (3 pages) | Cited 26 times

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The results of an x-ray microdiffraction study of the deformation field surrounding Ni thin film pads on a 111-type Si wafer are reported. The strain fields were mapped by measuring the Si 333 reflection intensities over an area containing several pads. The positions of the pads were simultaneously determined by recording the Ni Kα fluorescence as a function of position. The results indicate that, contrary to the results from analytical solutions and finite-element models, the position of maximum strain contrast is slightly outside the pad edge. © 1999 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
68.35.Gy Mechanical properties; surface strains
78.70.En X-ray emission spectra and fluorescence
62.20.F- Deformation and plasticity

Lattice location of Ca in GaN using ion channeling

H. Kobayashi and W. M. Gibson

Appl. Phys. Lett. 74, 2355 (1999); http://dx.doi.org/10.1063/1.123849 (3 pages) | Cited 10 times

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The Ca dopant site in the GaN lattice has been investigated using ion channeling. Metal organic chemical vapor deposition grown GaN on c-plane sapphire substrates implanted with 40Ca at a dose of 1×1015 cm−2 with postimplant annealing were studied. Our results indicate that more than 80% of Ca are near Ga sites even in as-implanted samples, however, they are displaced by ∼0.2 Å from the Ga sites and that the Ca goes to the exact Ga sites after annealing at 1100 °C while the annealing did not change the apparent fraction of substitutional Ca. We suggest that the displaced Ca in the as-implanted sample are electrically compensated due to formation of complex defects with donor-like point defects and that CaGa becomes electrically active when these complex defects are broken and the point defects diffuse away with annealing at 1100 °C. © 1999 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.S- Impurities in crystals
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
81.40.Gh Other heat and thermomechanical treatments
61.72.J- Point defects and defect clusters
66.30.J- Diffusion of impurities

Low-temperature luminescence of exciton and defect states in heteroepitaxial GaN grown by hydride vapor phase epitaxy

B. J. Skromme, J. Jayapalan, R. P. Vaudo, and V. M. Phanse

Appl. Phys. Lett. 74, 2358 (1999); http://dx.doi.org/10.1063/1.123850 (3 pages) | Cited 35 times

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Low-temperature (1.7–20 K) photoluminescence and reflectance are used to investigate the free and bound exciton and shallow impurity states in GaN. A 300-μm-thick GaN layer grown by hydride vapor phase epitaxy on sapphire(0001), with an exceptionally low dislocation density (3×106 cm−2) is used to obtain very high quality spectra. Both free and bound n = 2 excitons are identified, leading to a confirmation of the A free exciton binding energy as about 26.4 meV, independent of strain. Principal neutral donor-bound exciton (D0,X) peaks involving two to three different donors are resolved, as are two-electron satellites involving up to five different residual donors with binding energies ranging from 22 to 34.5 meV. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
71.55.Eq III-V semiconductors
71.35.-y Excitons and related phenomena
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors

Self-limitation of AlGaN/GaN quantum well energy by built-in polarization field

N. Grandjean, J. Massies, and M. Leroux

Appl. Phys. Lett. 74, 2361 (1999); http://dx.doi.org/10.1063/1.123851 (3 pages) | Cited 55 times

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Wurtzite AlGaN/GaN quantum well (QW) structures were grown by molecular beam epitaxy on c-plane sapphire substrates and the QW transition energies were measured by low temperature photoluminescence. Both the well widths and the Al mole fraction in the AlxGa1−xN(0<x<0.3) 100-Å-thick barriers have been varied in order to assess the built-in electric field present in the quantum heterostructures. It is found that the electric field increases linearly with the Al composition. The magnitude of this electric field is as high as 1 MV/cm for an Al mole fraction of 0.27. The main consequence is that whatever the investigated Al composition range, the well thickness must be lower than 30 Å in order to get a transition energy greater than the band gap of GaN. © 1999 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Room-temperature visible and infrared photoluminescence from Pr-implanted GaN films by focused-ion-beam direct write

L. C. Chao and A. J. Steckl

Appl. Phys. Lett. 74, 2364 (1999); http://dx.doi.org/10.1063/1.123852 (3 pages) | Cited 19 times

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Visible and infrared photoluminescence (PL) have been obtained from Pr-implanted GaN films using focused-ion-beam (FIB) direct write utilizing a Pr–Pt liquid alloy ion source. FIB implantation was performed on GaN films grown by molecular-beam epitaxy (MBE), hydride vapor-phase epitaxy, and metalorganic chemical-vapor deposition. After annealing, strong room-temperature emission was observed in the red (at 650 nm) and in the infrared (at several wavelengths including 0.96, 1.3, and 1.9 μm). Essentially identical PL spectra were obtained in the implanted GaN films as in the in situ Pr-doped GaN films grown by MBE. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
61.72.uj III-V and II-VI semiconductors
61.82.Fk Semiconductors
85.40.Ry Impurity doping, diffusion and ion implantation technology
78.55.Cr III-V semiconductors
61.80.Jh Ion radiation effects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Cc Kinetics of defect formation and annealing

Direct observation of localized high current densities in GaN films

E. G. Brazel, M. A. Chin, and V. Narayanamurti

Appl. Phys. Lett. 74, 2367 (1999); http://dx.doi.org/10.1063/1.123853 (3 pages) | Cited 69 times

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Local high current densities in areas around dislocations with a screw component might be responsible for the observed high leakage currents in GaN-based electronic devices. Using ballistic electron emission microscopy, threading dislocations with a screw component are found to be accompanied by high current densities and low effective Schottky barrier heights. The electronic states responsible for this extremely nonuniform behavior of GaN films are metastable trap states. The experimental results show that acceptor- and donor-like charge traps coexist in the vicinity of dislocations with a screw component. © 1999 American Institute of Physics.
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73.61.Ey III-V semiconductors
71.55.Eq III-V semiconductors
81.05.Ea III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Lk Linear defects: dislocations, disclinations
68.37.Vj Field emission and field-ion microscopy
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.30.+y Surface double layers, Schottky barriers, and work functions

Ta2O5 thin films with exceptionally high dielectric constant

Jun Lin, Nakabayasi Masaaki, Atsuhiro Tsukune, and Masao Yamada

Appl. Phys. Lett. 74, 2370 (1999); http://dx.doi.org/10.1063/1.123854 (3 pages) | Cited 47 times

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We have achieved tantalum pentoxide (Ta2O5) thin films with extremely highly predominant 〈001〉 orientation. The Ta2O5 thin films have an exceptionally high dielectric constant of 90–110, and capacitors using these Ta2O5 films as a dielectric layer show the high capacitance and low leakage current meeting the requirements for the new generation of memory devices. © 1999 American Institute of Physics.
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77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.61.Ng Insulators

Growth of high mobility GaN by ammonia-molecular beam epitaxy

H. Tang and James B. Webb

Appl. Phys. Lett. 74, 2373 (1999); http://dx.doi.org/10.1063/1.123855 (2 pages) | Cited 41 times

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The growth of high electron mobility GaN on (0001) sapphire by ammonia molecular beam epitaxy is reported. A buffer layer of AlN <300 Å is initially deposited by magnetron sputter epitaxy, a technique where the aluminum source is a planar dc magnetron sputter cathode and ammonia is used for the nitrogen source. The GaN epilayer is deposited using a conventional K cell for the gallium source and ammonia for the nitrogen source. The layers were doped using silane. Measured room temperature electron mobilities of 560 cm2/V s were observed for layers with carrier densities of ∼ 1.5×1017 cm−3. The 4 K photoluminescence spectrum showed a very strong donor bound exciton at 3.48 eV with a full width at half maximum (FWHM) of 4.9 meV. X-ray diffraction studies showed the layers to have good crystallinity with FWHM of the ω–2θ and ω scans as low as 13.7 and 210 arcsec, respectively. © 1999 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
81.05.Ea III-V semiconductors
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
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