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10 Jun 1996

Volume 68, Issue 24, pp. 3371-3508

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ZnCdSe/ZnCdMgSe quantum wells on InP substrates for visible emitters

A. Cavus, L. Zeng, M. C. Tamargo, N. Bambha, F. Semendy, and A. Gray

Appl. Phys. Lett. 68, 3446 (1996); http://dx.doi.org/10.1063/1.115788 (3 pages) | Cited 21 times

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We have grown ZnCdSe/ZnCdMgSe quantum well (QW) structures nearly lattice matched to InP substrates. Emission energies from 2.307 to 2.960 eV were measured by low‐temperature photoluminescence at 10 K for samples with QW thicknesses between 5 and 80 Å. By using exactly lattice‐matched QWs, the lower limit of the energy range can be lowered to about 2.2 eV (at 10 K). We propose that these structures could be used in entirely lattice‐matched semiconductor lasers operating at room temperature in the blue, green, and yellow regions. Because of the absence of strain, these materials are expected to be less prone to degradation than the current blue‐green lasers grown on GaAs. © 1996 American Institute of Physics.
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78.55.Et II-VI semiconductors
42.55.Px Semiconductor lasers; laser diodes
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Nonresonant electron tunneling in cluster superlattice of tellurium in zeolite

Zi Kang Tang and Xiang‐Rong Wang

Appl. Phys. Lett. 68, 3449 (1996); http://dx.doi.org/10.1063/1.115789 (3 pages) | Cited 19 times

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We study the current‐voltage (I–V) characteristics of tellurium (Te) cluster superlattice in Linde type‐A (LTA) zeolite. We observed both the hysteresis current loop and the current peak. The current loop and the current peak, however, are history dependent. Under the same experimental conditions, we find that the current peak position moves to the higher voltage when the sample temperature is increased. We clarify that both the current loop and peak are transient phenomena. The observed current peak is a phenomenon of the pseudonegative differential resistance. We explain the observed I–V characteristics as the results of the structure change of Te clusters inside zeolite cages under an external electric field. The current peak can be understood as the effect of the finite transient time during which Te clusters change from one structure into another under an applied voltage. © 1996 American Institute of Physics.
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73.40.Gk Tunneling
72.20.-i Conductivity phenomena in semiconductors and insulators

Unambiguous photoreflectance determination of electric fields using phase suppression

S. L. Tyan, Y. C. Wang, J. S. Hwang, and H. Shen

Appl. Phys. Lett. 68, 3452 (1996); http://dx.doi.org/10.1063/1.115790 (3 pages) | Cited 4 times

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Photoreflectance measurements have been performed on a δ‐doped GaAs homojunction. Two Franz–Keldysh oscillation features originating from two different regions (a buffer layer and a top layer) of the structure superimpose with each other in the photoreflectance spectrum. By properly selecting the reference phase, one of the features can be suppressed, thus enabling us to determine the electric fields from the two regions unambiguously. The electric field in the top layer is 3.5±0.2×105 V/cm, which is in good agreement with theoretical calculation. The electric field in the buffer layer is 1.2±0.1×104 V/cm. © 1996 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states

Free‐standing versus AlAs‐embedded GaAs quantum dots, wires, and films: The emergence of a zero‐confinement state

Alberto Franceschetti and Alex Zunger

Appl. Phys. Lett. 68, 3455 (1996); http://dx.doi.org/10.1063/1.115791 (3 pages) | Cited 25 times

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Using a plane‐wave pseudopotential method we investigate the electronic structure of free‐standing and of AlAs‐embedded GaAs quantum dots, wires, and films. We predict that (i) the confinement energy of the valence‐band maximum (VBM) is larger in AlAs‐embedded than in free‐standing quantum structures, because of the zero‐confinement character of the VBM wave function in the latter case; (ii) small GaAs quantum structures have an indirect band gap, whereas large GaAs quantum structures have a direct band gap; (iii) the conduction‐band minimum of small free‐standing quantum structures originates from the GaAs X1c valley, while it derives from the AlAs X1c state in AlAs‐embedded quantum structures; (iv) the critical size for the direct/indirect crossover is larger in embedded quantum structures than in free‐standing quantum structures. © 1996 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

The bistability of the thermal donors in silicon

T. Hallberg and J. L. Lindström

Appl. Phys. Lett. 68, 3458 (1996); http://dx.doi.org/10.1063/1.115792 (3 pages) | Cited 9 times

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The bistability of the two first thermal donors (TDs) in silicon has been studied by means of infrared (IR) spectroscopy. The two IR vibrational bands positioned at about 975 and 988 cm−1 which are due to TD1 and TD2, respectively, have been found to show bistable properties. It is shown that the low energy configurations of both TD1 and TD2 give rise to IR absorption, with a common vibrational band at about 1020 cm−1. © 1996 American Institute of Physics.
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71.55.Cn Elemental semiconductors

Oxide mediated epitaxy of CoSi2 on silicon

R. T. Tung

Appl. Phys. Lett. 68, 3461 (1996); http://dx.doi.org/10.1063/1.115793 (3 pages) | Cited 104 times

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Uniform, single‐crystal CoSi2 layers have been grown on Si by the technique of oxide mediated epitaxy (OME). Deposition of a thin layer of cobalt (1–3 nm) onto surfaces covered with a thin silicon oxide layer and annealing at 500–700 °C led to the growth of epitaxial, essentially uniform, CoSi2 layers on the (100), (110), and (111) surfaces of Si. The nucleation and growth of silicide apparently occurred subsurface, leaving the silicon oxide layer largely on the surface of the silicide after the growth. On all surfaces, thicker (10–30 nm), excellent quality, CoSi2 single‐crystal thin films have been grown by repeated growth sequences. Experimental results are presented along with a discussion on the possible roles played by the thin oxide layer in promoting the epitaxial growth of silicide. © 1996 American Institute of Physics.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

The ordered–disordered transition in Si delta‐doped GaAs

A. V. Buyanov, P. O. Holtz, W. M. Chen, B. Monemar, T. G. Anderson, and J. Thordson

Appl. Phys. Lett. 68, 3464 (1996); http://dx.doi.org/10.1063/1.115794 (3 pages) | Cited 3 times

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We report results for Si layers embedded in GaAs, extending from the delta‐doped (δ‐doped) range up to 6 monolayers (MLs) derived by means of variable temperature resistivity and Hall effect measurements, secondary ion mass spectrometry (SIMS), and high resolution x‐ray diffractometry (HRXRD) techniques. The conductivity transition from free carrier transport in ordered δ‐layers (<1 ML) to strongly localized two‐dimensional variable range hopping (2D‐VRH) transport under potential fluctuation disordered conditions (≳4 ML) is clearly observed. This observation is in good agreement with the SIMS and HRXRD data. Results from the intermediate case with 2–3 MLs are also discussed. © 1996 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Quantitative investigation of localized ion irradiation effects in n‐channel metal‐oxide‐semiconductor field‐effect transistors using single ion microprobe

Meishoku Koh, Katsuyuki Horita, Bungo Shigeta, Kai Igarashi, Takashi Matsukawa, Takashi Tanii, Shigetaka Mori, and Iwao Ohdomari

Appl. Phys. Lett. 68, 3467 (1996); http://dx.doi.org/10.1063/1.116076 (3 pages) | Cited 4 times

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Localized ion irradiation effects in n‐channel metal‐oxide‐semiconductor field‐effect transistor (n‐ch MOSFET) have been investigated quantitatively by means of both the single ion microprobe (SIMP) and single ion beam induced charge (SIBIC) imaging. An extremely large leakage current in the subthreshold gate voltage Vg–drain current Id characteristics (Vg< threshold voltage Vth) have been induced by exposing a small fraction of the MOSFET gate area to MeV He single ions, while the turn‐on Vg–Id characteristics (Vg≳Vth) have scarcely been affected. The causes of the large leakage current in the subthreshold region induced by the localized ion irradiation have been discussed. © 1996 American Institute of Physics.
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85.30.Tv Field effect devices
61.80.Jh Ion radiation effects

Deep level defects in Mg‐doped, p‐type GaN grown by metalorganic chemical vapor deposition

W. Götz, N. M. Johnson, and D. P. Bour

Appl. Phys. Lett. 68, 3470 (1996); http://dx.doi.org/10.1063/1.116075 (3 pages) | Cited 49 times

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Deep level defects in Mg‐doped, p‐type GaN were characterized by deep level transient spectroscopy (DLTS) and photoemission capacitance transient spectroscopy (ODLTS). The measurements were conducted on n+‐p junction diodes grown by metalorganic chemical vapor deposition. DLTS revealed discrete deep levels in the lower half of the band gap with activation energies for hole emission of 0.21, 0.39, and 0.41 eV. While DLTS is able to detect deep levels only in the proximity of the valance band edge in p‐type, wide band‐gap semiconductors, ODLTS enables detection of deep levels throughout the band gap of GaN. The ODLTS spectrum of Mg‐doped, p‐type GaN is dominated by a deep level with an optical threshold energy for photoionization of ∼1.8 eV. This deep level, which appears to be energetically located near midgap is present in the highest concentration (∼2.4×1015 cm−3) among the deep levels detected in our GaN material. None of the detected deep levels is present in sufficient concentration to significantly compensate the shallow acceptor dopant in our Mg‐doped, p‐type GaN. © 1996 American Institute of Physics.
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71.55.Eq III-V semiconductors

Si and Si/P implants in In0.5Ga0.5P and In0.5Al0.5P

J. C. Zolper and H. C. Chui

Appl. Phys. Lett. 68, 3473 (1996); http://dx.doi.org/10.1063/1.115763 (3 pages) | Cited 4 times

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Si and Si/P ion implantation doping of In0.5Ga0.5P and In0.5Al0.5P has been studied for several Si and P doses at energies of 90 and 100 keV, respectively. For single Si implants in InGaP a maximum Hall sheet electron concentration of 1.33×1013 cm−2 is achieved for a Si dose of 5×1013 cm−2. When an optimum dose (2.5×1013 cm−2) P coimplant is performed this electron concentration is increased by 65%. The same dose Si implants in InAlP show a maximum effective activation of 3.9% with no P coimplantation and 5.2% with a P‐implant dose 1.5 times the silicon dose. The apparent donor ionization energies are estimated from variable temperature Hall measurements to be 2–5 meV for InGaP and ∼80 meV for InAlP. The deeper level in InAlP is attributed to the DX level found in the Al‐containing material. The reduction in sheet resistance associated with the use of Si/P coimplantation in InGaP containing heterostructures should contribute to significant performance enhancements in HFETs and lasers. © 1996 American Institute of Physics.
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71.55.Eq III-V semiconductors
61.72.uj III-V and II-VI semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Vibrational spectroscopy of arsenic‐hydrogen complexes in ZnSe

M. D. McCluskey, E. E. Haller, F. X. Zach, and E. D. Bourret‐Courchesne

Appl. Phys. Lett. 68, 3476 (1996); http://dx.doi.org/10.1063/1.116799 (3 pages) | Cited 6 times

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Using infrared absorption spectroscopy, we have observed hydrogen local vibrational modes (LVMs) in arsenic‐doped ZnSe grown by metalorganic chemical vapor deposition (MOCVD). When hydrogen is used as a carrier gas, we find an absorption peak at 2165.6 cm−1, which we attribute to a bond‐stretching mode of a hydrogen attached to an arsenic acceptor in a bond‐centered orientation. With deuterium substituting the hydrogen carrier gas, we find an additional peak at 1557.1 cm−1 with 1/3 the intensity of the hydrogen peak. The isotopic frequency ratio is r=vH/vD=1.3908, similar to values found in many hydrogen/deuterium‐related complexes. The larger area of the hydrogen peak indicates that most of the hydrogen comes from decomposition reactions involving the metalorganic molecules. The temperature dependent shift of the ZnSe:As,H mode is proportional to the lattice thermal energy U(T), a consequence of the anharmonic coupling between the LVMs and the lattice phonons.
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78.30.Fs III-V and II-VI semiconductors
63.20.Pw Localized modes
63.20.kp Phonon-defect interactions

Laser irradiation effects on tunneling properties of n‐type GaAs and InAs by scanning tunneling microscopy

Takuji Takahashi and Masahiro Yoshita

Appl. Phys. Lett. 68, 3479 (1996); http://dx.doi.org/10.1063/1.115764 (3 pages) | Cited 5 times

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We have studied the effect of laser irradiation on the tunneling properties of n‐type GaAs and InAs by scanning tunneling microscopy. We measured the changes of tip height between on and off cycles of the laser light at different wavelengths and laser power. The laser‐induced tip‐sample separation is observed to be very large in GaAs compared with InAs when above‐band‐gap laser light is used. This result can be explained in terms of the shrinkage of the surface depletion layers by generated photocarriers. © 1996 American Institute of Physics.
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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
73.20.At Surface states, band structure, electron density of states
73.40.Gk Tunneling

Layer‐by‐layer atomic manipulation on Si(111)‐7×7 surface

T. Komeda, R. Hasunuma, H. Mukaida, and H. Tokumoto

Appl. Phys. Lett. 68, 3482 (1996); http://dx.doi.org/10.1063/1.115765 (3 pages) | Cited 5 times

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Layer‐by‐layer removal of Si atoms from the Si(111)‐7×7 surface was executed at room temperature by making a point contact of a biased W tip of scanning tunneling microscope (STM) to the sample surface. The adatom layer and the three layers were controllably removed by tuning the sample bias voltage. In the created holes, clear atomic images were obtained. The current between the STM tip and substrate exhibited characteristic structures during the tip excursion, which are closely related with the atom removal process and the nature of the Si nanoscale wire, respectively. © 1996 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
68.35.B- Structure of clean surfaces (and surface reconstruction)
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

Nonalloyed ohmic contacts to heavily Be‐doped GaP and InxGa1−xP

M. V. Tagare, T. P. Chin, and J. M. Woodall

Appl. Phys. Lett. 68, 3485 (1996); http://dx.doi.org/10.1063/1.115766 (3 pages) | Cited 5 times

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Nonalloyed ohmic contacts, with contact resistances as low as 9 μΩ  cm2, are obtained to p++ GaP using Ni and Ti–Au. Very high p‐type doping (5×1019 cm−3) is achieved in GaP using a growth temperature of 400 °C followed by an ex situ high‐temperature rapid thermal anneal. The p‐type dopant is beryllium and the films are grown by solid source molecular beam epitaxy equipped with a valved phosphorus cracker. A record high hole concentration (2×1019 cm−3) is reported in In0.49Ga0.51P by using a growth temperature of 350 °C. © 1996 American Institute of Physics.
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73.40.Cg Contact resistance, contact potential
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Band line‐up transition in AlxGa1−xAs/In0.5Ga0.5P from capacitance‐voltage analysis

Il‐Jong Kim, Yong‐Hoon Cho, Kwan‐Shik Kim, Byung‐Doo Choe, and H. Lim

Appl. Phys. Lett. 68, 3488 (1996); http://dx.doi.org/10.1063/1.115767 (3 pages) | Cited 16 times

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The conduction‐band discontinuity ΔEc of AlxGa1−xAs/In0.5Ga0.5P heterojunctions grown by liquid phase epitaxy on GaAs substrate was studied using the capacitance–voltage (C–V) characterization technique. The C–V measurements were made on a series of samples with x ranging from zero to about 0.3. The carrier profiles for the samples with x=0 and x=0.06 give ΔEc values of 90 and 40 meV, respectively, showing the type I (straddling) band line‐up. For x=0.18 and 0.29, the values of ΔEc were 45 and 110 meV, respectively, with the carrier profile characteristic of the type II (staggered) band line‐up. From these results, ΔEc of the heterojunction is found to vanish at about x = 0.12. This agrees well with our previous result determined from the photoluminescence measurements. © 1996 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Synthesis of single domain strontium ferrite powder by pulsed laser ablation

Rashmi Nawathey‐Dikshit, S. R. Shinde, S. B. Ogale, S. D. Kulkarni, S. R. Sainkar, and S. K. Date

Appl. Phys. Lett. 68, 3491 (1996); http://dx.doi.org/10.1063/1.115768 (3 pages) | Cited 16 times

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Strontium hexaferrite nanoparticles have been successfully prepared from a sintered SrFe12O19 target, using pulsed excimer laser ablation and cold condensation technique. The as‐condensed powders do not exhibit the same magnetic properties as the target material. However, annealing at a high temperature of 850 °C for 3 h in air followed by fast cooling yields very high coercivity of 6665 Oe, exhibiting presence of single domain particles. Vibrating sample magnetometry (VSM), scanning electron microscopy (SEM), and x‐ray diffraction (XRD) techniques are used to study the magnetism, microstructure, and phase formation in the powders, respectively. © 1996 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
81.15.Fg Pulsed laser ablation deposition
61.43.Gt Powders, porous materials

Enhancing the low field magnetoresistive response in perovskite manganites

H. Y. Hwang, S.‐W. Cheong, and B. Batlogg

Appl. Phys. Lett. 68, 3494 (1996); http://dx.doi.org/10.1063/1.115769 (3 pages) | Cited 30 times

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We report significant improvement in the magnetoresistive (MR) response of perovskite manganites for small applied fields by the use of heterostructures with soft ferromagnets. At room temperature, a 5900‐fold enhancement of the MR response at 10 Oe in La2/3Ca1/3MnO3 has been achieved using (Mn,Zn)Fe2O4 as the soft ferromagnet. By utilizing soft ferromagnets with various magnetic properties, this technique allows for enormous flexibility in ‘‘designing’’ a desired MR response for the manganites, particularly in low fields. © 1996 American Institute of Physics.
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75.47.De Giant magnetoresistance

A distance regulation scheme for scanning near‐field optical microscopy

A. Dräbenstedt, J. Wrachtrup, and C. von Borczyskowski

Appl. Phys. Lett. 68, 3497 (1996); http://dx.doi.org/10.1063/1.115770 (3 pages) | Cited 15 times

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In this letter we present a detection scheme for shear force distance regulation in scanning near‐field optical microscopy. Instead of an optical detection of the amplitude of tip vibrations and damping due to shear forces, a piezoelectric pickup has been developed. It is shown that the signal obtained with this pick up is of comparable or even superior sensitivity than the conventional optical scheme and can be easily incorporated into every near‐field microscope. Because of its easy implementation and adjust free performance, the method has the potential to considerably simplify the usage of near‐field microscopes. © 1996 American Institute of Physics.
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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
07.79.Fc Near-field scanning optical microscopes

Computed laminography for materials testing

J. Zhou, M. Maisl, H. Reiter, and W. Arnold

Appl. Phys. Lett. 68, 3500 (1996); http://dx.doi.org/10.1063/1.115771 (3 pages) | Cited 8 times

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We have developed a computed laminography system for the inspection of large or flat objects using x rays. By this new laminographic method only a translation of the object is necessary. Both the x‐ray source and the detector remain stationary. Object cross sections are reconstructed from digital projections taken during the object motions and for the reconstruction well‐known algorithms are used. By use of a microfocus x‐ray tube and a line detector, objects can be inspected with a slice resolution of about 50 μm independent of the object size. © 1996 American Institute of Physics.
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07.85.-m X- and γ-ray instruments
81.70.Ex Nondestructive testing: electromagnetic testing, eddy-current testing

Detection of single macromolecules using a cryogenic particle detector coupled to a biopolymer mass spectrometer

Damian Twerenbold, Jean‐Luc Vuilleumier, Daniel Gerber, Almut Tadsen, Ben van den Brandt, and Patrick M. Gillevet

Appl. Phys. Lett. 68, 3503 (1996); http://dx.doi.org/10.1063/1.115772 (3 pages) | Cited 36 times

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Macromolecules with masses up to 50 kDa have been detected with a cryogenic particle detector in a MALDI time‐of‐flight biopolymer mass spectrometer. The cryogenic particle detector was a Sn/Sn‐ox/Sn tunnel junction operated at a temperature of 0.4 K. A calibration with 6 keV single photons inferred that the delayed detector pulses corresponded to the absorption of the kinetic energy of a single macromolecule. Time‐of‐flight spectra of lysozyme proteins are presented. The mass resolution is 100 Da at 14 300 Da. The energy sensitive detection mechanism suggests that cryogenic particle detectors have a high and mass independent detection efficiency for macromolecules. © 1996 American Institute of Physics.
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87.80.-y Biophysical techniques (research methods)
07.75.+h Mass spectrometers

Scanning tip microwave near‐field microscope

T. Wei, X.‐D. Xiang, W. G. Wallace‐Freedman, and P. G. Schultz

Appl. Phys. Lett. 68, 3506 (1996); http://dx.doi.org/10.1063/1.115773 (3 pages) | Cited 72 times

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A near‐field microscope which operates in the rf/microwave frequency range is described. In this microscope, a scanning tunneling microscope (STM)‐like tip rather than an aperture is used as a point‐like evanescent field emitter. A spatial resolution of ∼5 μm (∼λ/100 000) is achieved in the current version. The design of the microscope as well as the principal factors which affect its performance are discussed. © 1996 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
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