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23 Sep 1996

Volume 69, Issue 13, pp. 1823-1980

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Exciton diffusion length in microcrystalline chlorophyll a

Chouhaid Nasr, Toufik Taleb, Roger M. Leblanc, and Surat Hotchandani

Appl. Phys. Lett. 69, 1823 (1996); http://dx.doi.org/10.1063/1.117445 (3 pages) | Cited 2 times

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The measurements of photocurrent as a function of depletion layer or Schottky barrier width have been performed to determine the exciton diffusion length (L) in microcrystalline chlorophyll a (Chl a). This method of determining L is particularly advantageous in that it does not require a prior knowledge of the absorption coefficient of the material as is usually the case with other, e.g., constant surface photovoltage or constant photocurrent techniques. A value of 180 Å has been obtained for L in Chl a. While this value is comparable to those for many organic semiconductors, it is much inferior to that for the minority carriers in inorganic photoconductors. The smaller diffusion length may, in part, explain the feeble power conversion efficiency of Chl a and other organic photovoltaic cells. © 1996 American Institute of Physics.
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72.40.+w Photoconduction and photovoltaic effects
72.80.Le Polymers; organic compounds (including organic semiconductors)
71.35.-y Excitons and related phenomena

Phase‐contrast microtomography with coherent high‐energy synchrotron x rays

C. Raven, A. Snigirev, I. Snigireva, P. Spanne, A. Souvorov, and V. Kohn

Appl. Phys. Lett. 69, 1826 (1996); http://dx.doi.org/10.1063/1.117446 (3 pages) | Cited 52 times

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Cross‐sectional information on low electron density materials can be obtained by probing a sample with a 60 keV coherent synchrotron x‐ray beam in an in‐line holography setup. Such objects are practically transparent to high energy x rays and create a phase shift of the wave front only. Images of a 100 μm diameter boron fiber were recorded in the extreme near field region, where contrast occurs only at interfaces between regions with different decrements of refractive index. Theoretical simulations are in good agreement with the measured intensities. In a tomographic reconstruction the 15 μm diameter core of the fiber is clearly visible, demonstrating the possibility of reconstructing three dimensional interfaces between low density materials. © 1996 American Institute of Physics.
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42.30.Wb Image reconstruction; tomography
07.85.Qe Synchrotron radiation instrumentation
78.70.Ck X-ray scattering
42.40.Ht Hologram recording and readout methods

Far‐field and beam characteristics of vertical‐cavity surface‐emitting lasers

Y.‐G. Zhao, Y.‐S. Zhang, X.‐L. Huang, L.‐T. Zhang, W.‐X. Chen, L.‐F. Cong, C.‐Z. Jin, X.‐W. Hu, and W. Wang

Appl. Phys. Lett. 69, 1829 (1996); http://dx.doi.org/10.1063/1.117447 (3 pages) | Cited 2 times

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We have determined the far‐field patterns and beam parameters of vertical‐cavity surface‐emitting lasers (VCSELs) with different structures. The results show that the window diameter and the active‐layer aperture of VCSELs strongly influence laser far‐field distributions and beam characteristics; for VCSELs with small window ω=5 μm, only one dominant lobe has been observed in the far‐field profiles, even though injected current was increased up to 2 Ith; and the smaller the ratio of the window diameter to the active‐layer aperture, the larger is the far‐field divergence. The laser structure dependence of the K factor has also been studied. © 1996 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Dynamic studies of charge‐separated‐state enhancement of the optical nonlinearity of a porphyrin heterodimer

Jinhai Si, Yougui Wang, Qiguang Yang, Peixian Ye, Hongjian Tian, Qingfu Zhou, and Huijun Xu

Appl. Phys. Lett. 69, 1832 (1996); http://dx.doi.org/10.1063/1.117448 (3 pages) | Cited 1 time

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Light‐induced enhancement of the third‐order nonlinear optical susceptibility of a heterodimer consisting of two different porphyrin monomers, a zinctetra(4‐sulfonatophenyl)porphyrin and a zinctetra(4‐N‐methyl‐pyridyl)porphyrin, was observed when the sample was optically pumped by a 30 ps, 532 nm pump pulse. The temporal behavior of the enhancement was studied. It was found that the enhancement was due predominantly to the population of the charge‐separated state with a large electronic third‐order nonlinear optical susceptibility © 1996 American Institute of Physics.
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42.65.An Optical susceptibility, hyperpolarizability
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.47.-p Spectroscopy of solid state dynamics

All‐optical switching in a dye‐doped polymer fiber Fabry–Perot waveguide

D. J. Welker and M. G. Kuzyk

Appl. Phys. Lett. 69, 1835 (1996); http://dx.doi.org/10.1063/1.117449 (2 pages) | Cited 11 times

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We report on the demonstration of all‐optical switching in a 110 μm diam, 1 cm long Fabry–Perot cavity defined in a dye‐doped polymer optical fiber waveguide. Such a device is a basic building block of optical logic. © 1996 American Institute of Physics.
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42.81.Qb Fiber waveguides, couplers, and arrays
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.70.Jk Polymers and organics
07.60.Vg Fiber-optic instruments

Holographic storage and high background imaging using photorefractive multiple quantum wells

R. Jones, S. C. W. Hyde, M. J. Lynn, N. P. Barry, J. C. Dainty, P. M. W. French, K. M. Kwolek, D. D. Nolte, and M. R. Melloch

Appl. Phys. Lett. 69, 1837 (1996); http://dx.doi.org/10.1063/1.117450 (3 pages) | Cited 23 times

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We report holographic, real time, depth‐resolved image acquisition, storage, and reconstruction in photorefractive GaAs/AlGaAs multiple quantum wells under high background radiation conditions. Reconstructed images of 50 μm transverse and depth resolution have been achieved using this device as a coherence gate to image through 9 mean free paths of turbid scattering medial © 1996 American Institute of Physics.
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42.70.Ln Holographic recording materials; optical storage media
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.40.Ht Hologram recording and readout methods
78.66.Fd III-V semiconductors

Transverse modes and lasing characteristics of selectively grown vertical cavity semiconductor lasers

M. Orenstein, Y. Satuby, U. Ben‐Ami, and J. P. Harbison

Appl. Phys. Lett. 69, 1840 (1996); http://dx.doi.org/10.1063/1.117451 (3 pages) | Cited 2 times

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Vertical‐cavity surface emitting lasers (VCSELs) were grown by molecular beam epitaxy over openings in a SiN4 mask, deposited on a GaAs wafer. We obtained ready to use lasers and laser arrays, laterally defined by the polycrystalline, highly resistive material grown over the SiN4 laser. The performance of the lasers (e.g., 20×20 μm2 by size) were similar to that of VCSELs defined by post growth processing methods. Special transverse modes characteristics and a well defined polarization were observed in square shaped lasers and it was attributed to selective growth induced anisotropy. © 1996 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

A fiber‐mounted, micromachined photoconductive probe with 15 nV/Hz1/2 sensitivity

Richard K. Lai, Jiunn‐Ren Hwang, John Nees, Theodore B. Norris, and John F. Whitaker

Appl. Phys. Lett. 69, 1843 (1996); http://dx.doi.org/10.1063/1.117452 (3 pages) | Cited 11 times

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We report the performance of a micromachined, photoconductive‐sampling probe that is fabricated on low‐temperature‐grown GaAs and mounted on a single‐mode optical fiber. The epitaxial probe has a temporal resolution of 3.5 ps, a spatial resolution of 7 μm, and a sensitivity of 15 nV/(Hz)1/2 when integrated with a high impedance, junction field‐effect transistor source follower. The fiber, which couples short laser pulses to the interdigitated detector pattern on the probe, also provides flexible support and mobility. The probe’s compact cross section makes it ideal for applications as an internal‐node, picosecond‐response, photoconductive sampling probe or wave form launcher for test and characterization of integrated circuits. © 1996 American Institute of Physics.
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73.40.Sx Metal-semiconductor-metal structures
73.50.Pz Photoconduction and photovoltaic effects
85.40.Qx Microcircuit quality, noise, performance, and failure analysis
07.60.Vg Fiber-optic instruments

A widely tunable (0.54–1.01 μm) double‐pass fiber Raman laser

Ilko K. Ilev, Hiroshi Kumagai, and Koichi Toyoda

Appl. Phys. Lett. 69, 1846 (1996); http://dx.doi.org/10.1063/1.117453 (3 pages) | Cited 4 times

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We present a novel and simple double‐pass fiber Raman laser in the visible and near‐IR regions, based on the use of a fiberoptic autocollimation technique with Littrow‐prism‐tuned emission. When the Raman medium is a 40‐m‐long 68‐μm‐core‐diam graded‐index multimode fiber with powerful (above 100 kW pulse power coupled into the fiber) nanosecond pumping using the second harmonic of a Nd:YAG laser (λp=532 nm), we obtain widely tunable generation in both the visible and near‐ IR. By using the double‐pass fiber Raman laser with various lengths of the multimode fiber, continuously tunable generation over a wide spectral range (0.54–1.01 μm) is obtained. © 1996 American Institute of Physics.
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42.55.Wd Fiber lasers
42.60.By Design of specific laser systems

Design and operation of a two‐cavity third harmonic Ka‐band gyroklystron

W. Lawson, B. Hogan, M. K. E. Flaherty, and H. Metz

Appl. Phys. Lett. 69, 1849 (1996); http://dx.doi.org/10.1063/1.117454 (3 pages) | Cited 3 times

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We present the operating characteristics of a two‐cavity third harmonic gyroklystron experiment. The input cavity utilizes a 9.854 GHz TE011 mode which is driven by a 100 kW magnetron. The TE031 output cavity has a resonant frequency of 29.57 GHz. The nominal beam voltage and current are 435 kV and 210 A, respectively. The pulse length is about 1 μs and the average ratio of parallel to perpendicular velocity is near one. Peak powers above 1.8 MW are achieved with an efficiency of about 2% and a gain of 14 dB. The theoretical simulations are in good agreement with the experimental results. © 1996 American Institute of Physics.
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84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)
41.75.Ht Relativistic electron and positron beams

Planar anchoring of nematic 4‐n‐pentyl‐4′‐cyanobiphenyl on self‐assembled monolayers formed from alkanethiols on gold

William J. Miller, Nicholas L. Abbott, Jonathan D. Paul, and Mara G. Prentiss

Appl. Phys. Lett. 69, 1852 (1996); http://dx.doi.org/10.1063/1.117455 (3 pages) | Cited 8 times

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We report measurements of planar anchoring of nematic 4‐n‐pentyl‐4′‐cyanobiphenyl (5CB) on self‐assembled monolayers (SAMs) formed from CH3(CH2)mSH (7⩽m⩽17) on films of gold (prepared without oblique deposition) by using reflection interferometry. The anchoring observed contrasts with past reports of homeotropic anchoring of 5CB by surfaces, such as monolayers formed from octadecyltrichlorosilane on silica, with energies as low as alkanethiols on gold (19 mN/m). The anisotropic dispersion force acting between 5CB and gold was calculated to favor planar anchoring of 5CB on SAMs formed from CH3(CH2)15SH by ∼0.1 mN/m, and can, therefore, override self‐interactions of 5CB that lead to homeotropic anchoring. Electric field‐induced Freederiksz transitions of 5CB supported on bare gold, and on SAMs formed from CH3(CH2)15SH on gold, confirm weaker (planar) anchoring of 5CB on SAMs on gold as compared to bare gold. © 1996 American Institute of Physics.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
68.08.-p Liquid-solid interfaces
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
42.70.Df Liquid crystals

Observation of folded acoustic phonons in nanocrystalline silicon/amorphous silicon multilayers

X. L. Wu, G. G. Siu, M. J. Stokes, S. Tong, F. Yan, X. N. Liu, X. M. Bao, S. S. Jiang, X. K. Zhang, and D. Feng

Appl. Phys. Lett. 69, 1855 (1996); http://dx.doi.org/10.1063/1.117456 (3 pages) | Cited 3 times

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We report in this letter the observation of folded acoustic phonons in hydrogenated nanocrystalline silicon/amorphous silicon multilayers with visible emission, which are prepared in a plasma enhanced chemical vapor deposition system. In the low‐frequency range of 10–100 cm−1, the obtained Raman spectra clearly show some folded doublets from longitudinal acoustic phonons. Using the elastic continuum model, we calculated their frequencies and the obtained results were in agreement with the experimental ones. In addition, some broad folded doublets and additional peaks were clearly observed in the sample with thin nancorystalline sublayers. We attributed them to the mixing of longitudinal and transverse acoustic phonons due to the layered structure. A confined acoustic mode was also proposed to be responsible for the strongly folded longitudinal acoustic phonon peak at 61 cm−1. © 1996 American Institute of Physics.
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78.30.Fs III-V and II-VI semiconductors
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Accuracy of the single‐electron pump using an optimized step‐like rf drive waveform

L. R. C. Fonseca, A. N. Korotkov, and K. K. Likharev

Appl. Phys. Lett. 69, 1858 (1996); http://dx.doi.org/10.1063/1.117457 (3 pages) | Cited 8 times

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We have performed an optimization of those parameters of a single‐electron pump that may influence the accuracy of this device as a standard of dc current. Two types of rf drive were considered: the traditional triangular waveform and a step‐like waveform. We have shown that, after optimization, the accuracy of the pump may be improved considerably in a wide range of drive frequencies, especially at low temperatures, using the step‐like waveform. For example, the error of a five‐junction pump with junction capacitances C=0.1 fF at 100 mK and 10 MHz may be as small as 10−13. © 1996 American Institute of Physics.
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73.23.Hk Coulomb blockade; single-electron tunneling
85.35.Gv Single electron devices
06.20.F- Units and standards

Bulk glass formation in the Pd–Ni–P system

Y. He, R. B. Schwarz, and J. I. Archuleta

Appl. Phys. Lett. 69, 1861 (1996); http://dx.doi.org/10.1063/1.117458 (3 pages) | Cited 91 times

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Bulk amorphous Pd–Ni–P rods with diameters ranging from 10 to 25 mm were prepared by a fluxing technique over a wide composition range. For most bulk glassy alloys studied, the difference between the glass transition temperature and the crystallization temperature, Tx−Tg, is larger than 90 K. Of all the alloy compositions examined, Pd40Ni40P20 has the highest glass formability, and 300‐g bulk amorphous cylinders, 25 mm in diameter and 50 mm in length, were easily and repeatedly formed. This size, however, is not an upper limit. The elastic properties of these bulk amorphous alloys were determined by a resonant ultrasound spectroscopy technique.
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81.05.Bx Metals, semimetals, and alloys
81.05.Kf Glasses (including metallic glasses)
62.20.D- Elasticity
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition

Monitoring HgCdTe layer uniformity by the differential absorption technique

V. Ariel, V. Garber, G. Bahir, S. Krishnamurthy, and A. Sher

Appl. Phys. Lett. 69, 1864 (1996); http://dx.doi.org/10.1063/1.117459 (3 pages) | Cited 12 times

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In this letter, we demonstrate how the differential absorption technique can be applied to study band gap uniformity in HgCdTe samples. The transmission of HgCdTe wafers is measured at room temperature and data filtering is used to remove both the interference fringes and high‐frequency noise. This data treatment approach produces reliable transmission data for HgCdTe layers as thin as 8 μm. In addition, the spectrum of the interference fringes is used to estimate the HgCdTe layer thickness with an accuracy of ±0.1 μm. The absorption coefficient is differentiated twice with respect to the photon energy and an approximate value of the band gap is estimated from extrema of the derivatives. By applying this procedure to different points on the same HgCdTe wafer, we can determine both lateral and transverse fluctuations of the semiconductor band gap. The initial results indicate that the accuracy of the differential absorption technique is around ±0.5 meV for HgCdTe wafers. The differential absorption technique appears suitable for routine characterization of HgCdTe wafers because it is simple, nondestructive, and applicable at room temperature. © 1996 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors

Vacancy‐type defects in molecular beam epitaxy low temperature grown GaAs, a positron beam lifetime study

J. Störmer, W. Triftshäuser, N. Hozhabri, and K. Alavi

Appl. Phys. Lett. 69, 1867 (1996); http://dx.doi.org/10.1063/1.117460 (3 pages) | Cited 15 times

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Positron beam lifetime spectroscopy has been utilized to study the depth distribution of vacancy‐type defects in molecular beam epitaxy GaAs grown at low temperature. Lifetime spectra were measured as a function of positron energy. From the analysis of the positron lifetime in as‐grown and annealed low temperature grown GaAs, the concentrations of Ga monovacancies and voids are estimated. Our results show that in an as‐grown sample the Ga monovacancy concentration is >3×1018 cm−3. It is also known that vacancy‐cluster concentration in an annealed sample exceeds 1018 cm−3 with a nonuniform spatial distribution. © 1996 American Institute of Physics.
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61.72.J- Point defects and defect clusters
61.72.Qq Microscopic defects (voids, inclusions, etc.)
78.70.Bj Positron annihilation

Effect of Al‐rich surface on Se δ‐doped GaAs grown by low‐pressure metalorganic chemical vapor deposition

J.‐H. Kim, D. H. Lim, G. M. Yang, Y. G. Shin, K. Y. Lim, and H. J. Lee

Appl. Phys. Lett. 69, 1870 (1996); http://dx.doi.org/10.1063/1.117461 (3 pages) | Cited 1 time

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We study Se δ‐doped GaAs grown by low‐pressure metalorganic chemical vapor deposition using hydrogen selenide as a doping precursor. The results of capacitance–voltage measurements show that the very sharp doping profile can be obtained by Se δ‐doping on an Al‐rich surface and Se segregation is also reduced by making an Al‐rich surface after δ‐doping. It is essential to utilize the δ‐doping sequence which does not have a post‐δ‐doping purge step to minimize the Se evaporation. © 1996 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Rapid solid phase crystallization of nanocrystalline silicon deposited by electron cyclotron plasma chemical vapor deposition

S. Holgado, J. Martínez, J. Garrido, C. Morant, and J. Piqueras

Appl. Phys. Lett. 69, 1873 (1996); http://dx.doi.org/10.1063/1.117462 (3 pages) | Cited 8 times

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Nanocrystalline silicon films were deposited in an electron cyclotron resonance plasma of Ar+H2+SiH4 on (100) and (111) oriented Si substrates without external heating. Before deposition, the substrates were cleaned in situ in an Ar+H2 plasma. This cleaning process caused surface roughness particularly on (100) substrates. Apparently, the excessive roughness of the interface with (100) Si surface prevented complete crystallization of the subsequently deposited films. In contrast, rapid solid phase crystallization of the films deposited on (111) surfaces occurred at around 1000 °C. © 1996 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder

High quality fluorinated silicon oxide films prepared by plasma enhanced chemical vapor deposition at 120 °C

Juho Song, P. K. Ajmera, and G. S. Lee

Appl. Phys. Lett. 69, 1876 (1996); http://dx.doi.org/10.1063/1.117463 (3 pages) | Cited 9 times

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Electrical characteristics of the fluorinated silicon oxide films prepared by plasma enhanced chemical vapor deposition at 120 °C using Si2H6 as silicon precursor and CF4 as fluorine precursor were studied. The addition of fluorine into Si–O network results in a decrease in the effective oxide charges as low as 1/6 of the value for the fluorine‐free silicon oxide films. It also improves the film breakdown property by significantly reducing early failures, resulting in the measured average dielectric breakdown field strength of 8.91 MV/cm. © 1996 American Institute of Physics.
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77.55.-g Dielectric thin films
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Reactivation of acceptors and trapping of hydrogen in GaN/InGaN double heterostructures

S. J. Pearton, S. Bendi, K. S. Jones, V. Krishnamoorthy, R. G. Wilson, F. Ren, R. F. Karlicek, and R. A. Stall

Appl. Phys. Lett. 69, 1879 (1996); http://dx.doi.org/10.1063/1.117464 (3 pages) | Cited 9 times

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The apparent thermal stability of hydrogen passivated Mg acceptors in GaN is a function of the annealing ambient employed, with H2 leading to a reactivation temperature approximately 150 °C higher than N2. The dissociation of Mg–H complexes and the loss of hydrogen from GaN are sequential processes, with reactivation occurring at ⩽700 °C for annealing under N2, while significant concentrations of hydrogen remain in the crystal even at 900 °C in implanted samples. The hydrogen is gettered to regions of highest defect density such as the InGaN layer in GaN/InGaN double heterostructure. © 1996 American Institute of Physics.
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68.60.Dv Thermal stability; thermal effects
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.72.Yx Interaction between different crystal defects; gettering effect

Nanostructuring on WSe2 with the atomic force microscope by a potential controlled electrochemical reaction

M. Böhmisch, F. Burmeister, J. Boneberg, and P. Leiderer

Appl. Phys. Lett. 69, 1882 (1996); http://dx.doi.org/10.1063/1.117465 (3 pages) | Cited 5 times

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We present a method for the controlled fabrication of stable nanostructures under ambient conditions. The surfaces under consideration, WSe2, are imaged by an atomic force microscope. By applying a voltage between the tip and the sample, we can control an etching process at the surface: different voltage thresholds for the creation and the growth of structures of one monolayer (Se–W–Se) depth are observed. Our measurements on p‐doped WSe2 strongly support an electrochemical corrosion reaction in a physisorbed water film. This method allows the in situ preparation and characterization of individual nanometer‐sized structures on WSe2 and other metal dichalcogenides. © 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
81.65.Cf Surface cleaning, etching, patterning
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

The compensation and depletion behavior of iron doped GaAs grown by molecular beam epitaxy

D. T. McInturff, E. S. Harmon, J. C. P. Chang, T. M. Pekarek, and J. M. Woodall

Appl. Phys. Lett. 69, 1885 (1996); http://dx.doi.org/10.1063/1.117466 (3 pages) | Cited 5 times

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We describe the growth and characterization of GaAs films in which a high concentration (1 at. %) of elemental iron is introduced during growth in a conventional molecular beam epitaxy system. For films grown at 600 °C, the iron incorporates as Fe3GaAs precipitates. Unlike the formation of As precipitates in low temperature grown (LTG) GaAs, iron precipitate formation does not require a postgrowth anneal. Hall measurements of the as‐grown GaAs/Fe3GaAs composite intentionally doped with silicon indicate that Fe3GaAs precipitates will deplete carriers in the same manner as As precipitates deplete carriers in annealed LTG GaAs. The degree of depletion depends on the initial growth temperature and the intentional doping level. Electrical behavior of samples subjected to a postgrowth rapid thermal anneal indicate that the material is deep level compensated by iron acceptor doping via dissolution of the Fe3GaAs precipitates. © 1996 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Qq Microscopic defects (voids, inclusions, etc.)
73.61.Ey III-V semiconductors

Effects of interdiffusion on the luminescence of InGaAs/GaAs quantum dots

R. Leon, Yong Kim, C. Jagadish, M. Gal, J. Zou, and D. J. H. Cockayne

Appl. Phys. Lett. 69, 1888 (1996); http://dx.doi.org/10.1063/1.117467 (3 pages) | Cited 138 times

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Large energy shifts in the luminescence emission from strained InGaAs quantum dots are observed as a result of postgrowth annealing and also when raising the upper cladding layer growth temperatures. These blueshifts occur concurrently with narrowing (from 61 to 24 meV) of the full width at half‐maxima for the emission from the quantum dot ensemble. These energy shifts can be explained by interdiffusion or intermixing of the interfaces rather than strain effects due to variations in capping layer thickness. Temperature behavior of the luminescence in annealed and nonannealed samples indicates a change in the shape and depth of the quantum dot confining potential. Quenching of the wetting layer luminescence after interdiffusion is also observed. © 1996 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
66.30.Ny Chemical interdiffusion; diffusion barriers

Characterizations of deep levels in SnTe‐doped GaSb by admittance spectroscopy

J. F. Chen, N. C. Chen, and H. S. Liu

Appl. Phys. Lett. 69, 1891 (1996); http://dx.doi.org/10.1063/1.117468 (3 pages) | Cited 4 times

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A dominant deep level with an activation energy of 0.23–0.26 eV was observed by admittance spectroscopy for SnTe‐doped GaSb layers grown directly on GaAs substrates by molecular beam epitaxy (MBE). The activation energy and capture cross section of the deep level are similar to the levels detected in S‐doped and Te‐doped GaSb grown by MBE, indicating that this deep level originates either from a native defect or a common impurity in n‐type GaSb. The Sb4/Ga flux ratio was found to affect the Hall mobility and concentration of the deep level in a similar way, with an optimal beam equivalent pressure ratio around 7 obtained for GaSb grown at 550 °C, which should correspond to the lowest ratio to maintain a Sb‐stabilized surface reconstruction. Analysis of this result suggests that the deep level seen by us is a complex defect. © 1996 American Institute of Physics.
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71.55.Eq III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Ge segregation during the initial stages of Si1−xGex alloy growth

Glenn G. Jernigan, Phillip E. Thompson, and Conrad L. Silvestre

Appl. Phys. Lett. 69, 1894 (1996); http://dx.doi.org/10.1063/1.117469 (3 pages) | Cited 12 times

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Segregation of Ge in the ‘‘leading edge’’ of Si1−xGex alloys grown by molecular beam epitaxy is investigated using x‐ray photoelectron spectroscopy (XPS). Alloys of 5%, 10%, 20%, and 40% Ge were grown in varying thickness (0–20 nm) at 500 °C to observe segregation during the initial stages of alloy growth. The length of the leading edge was found to decrease with increasing Ge concentration (4.8, 2.8, 2.4, and 2.0 nm, respectively). The amount of segregated Ge was found to increase with Ge concentration. A complete monolayer of Ge was found on the surface for all Ge concentrations and an increasing amount of Ge (20%, 55%, 80%, and 95%, respectively) was found in the second atomic layer.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
79.60.Dp Adsorbed layers and thin films
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