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18 Dec 1989

Volume 55, Issue 25, pp. 2573-2675

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Capture of photoexcited carriers by a laser structure

B. Deveaud, F. Clérot, A. Regreny, K. Fujiwara, K. Mitsunaga, and J. Ohta

Appl. Phys. Lett. 55, 2646 (1989); http://dx.doi.org/10.1063/1.101962 (3 pages) | Cited 28 times

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The capture of photoexcited carriers in different laser structures is investigated by subpicosecond luminescence spectroscopy. The capture time at 20 and 80 K is monitored by the decay of the luminescence of the confinement layers. It is found to range between 2 and 3 ps for both linear and parabolic grading, and to be much longer in nongraded structures. The improvement of the capture in the case of graded structures is due to the quasi‐electric field experienced by the carriers, and might allow the devices to run at much higher frequencies.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
72.80.Ey III-V and II-VI semiconductors

Growth of single‐crystal metastable (GaAs)1−x(Si2)x alloys on GaAs and (GaAs)1−x(Si2)x/GaAs strained‐layer superlattices

D. H. Mei, Y.‐W. Kim, D. Lubben, I. M. Robertson, and J. E. Greene

Appl. Phys. Lett. 55, 2649 (1989); http://dx.doi.org/10.1063/1.102300 (3 pages) | Cited 15 times

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Epitaxial zinc blende structure metastable (GaAs)1−x(Si2)x alloys have been grown with 0<x<0.3 on As‐stabilized GaAs(100) substrates by a hybrid sputter deposition/evaporation technique. The films, typically 2–3 μm thick, were deposited at 570 °C with growth rates between 0.7 and 1 μm h−1. Alloys with 0<x<0.12 were defect‐free as judged by plan‐view and cross‐sectional transmission electron microscopy (TEM and XTEM) with x‐ray diffraction peak widths approximately the same as that of the substrate, 30 arcsec 2θ. XTEM lattice images showed smooth abrupt interfaces. (GaAs)1−x(Si2)x alloys with x>0.12 exhibited increasing evidence of interfacial defects associated with lattice strain when grown on GaAs. However, defect‐free alloys with x up to 0.3 were obtained using (GaAs)1−x(Si2)x/GaAs strained‐layer superlattice buffer layers to provide a better lattice match.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.Dv Composition, segregation; defects and impurities
81.15.Cd Deposition by sputtering

Valley selective tunneling transistor based on valley discontinuities in AlGaAs heterostructures

Jasprit Singh

Appl. Phys. Lett. 55, 2652 (1989); http://dx.doi.org/10.1063/1.101963 (3 pages)

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The conduction‐band discontinuities in AlxGa1−xAs/AlyGa1−yAs heterostructure for various valleys (Γ, L, X) are utilized to conceive of a valley selective tunneling transistor. At low temperature, the perpendicular tunneling current is very small because of the large Γ‐Γ discontinuity and the small prefactor for Γ to X tunneling. However, if the valley population is altered by applying a lateral bias to the emitter, one can dramatically alter the perpendicular current since the X‐X discontinuity is nonexistent and the L‐L discontinuity is very small. By choosing proper values of x and y in the heterostructure, a very large current (power) change can be produced in the on and off states.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Gk Tunneling

Photoelectrochemical etching of n‐InP in a thin‐film cell

H. Grebel, B. Iskandar, and K. G. Sheppard

Appl. Phys. Lett. 55, 2655 (1989); http://dx.doi.org/10.1063/1.101964 (3 pages) | Cited 6 times

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The laser‐induced photoelectrochemical etching of n‐InP using a thin‐film cell has been studied. A minimum in the reaction time was found as a function of etchant concentration for a given laser intensity. External potential biasing enhanced the reaction only for relatively low etchant concentrations.
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81.65.-b Surface treatments
82.45.-h Electrochemistry and electrophoresis
82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light
79.20.Ds Laser-beam impact phenomena

Saturation of the light‐induced defect density in hydrogenated amorphous silicon

H. R. Park, J. Z. Liu, and S. Wagner

Appl. Phys. Lett. 55, 2658 (1989); http://dx.doi.org/10.1063/1.101965 (3 pages) | Cited 75 times

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We report new experimental results on the saturation of the light‐induced defect density in hydrogenated (and fluorinated) amorphous silicon. The films were illuminated near room temperature up to 5000 h with bandpass filtered red light at a carrier generation rate G of 5×1020 cm−3 s−1, or up to 20 h with Kr+ laser light (λ=647.1 nm) at G=3×1022 cm−3 s−1. The bulk defect densities Ns saturate in both cases in the vicinity of 1017 cm−3. The saturation values are almost independent either of G or of temperature in the range from room temperature to about 70 °C. The illumination time to reach saturation is approximately proportional to 1/G2. These results are discussed within the framework of existing models for the light‐induced defects.
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61.72.Bb Theories and models of crystal defects
72.80.Ng Disordered solids
72.40.+w Photoconduction and photovoltaic effects
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Wet chemical etching of high‐temperature superconducting Y‐Ba‐Cu‐O films in ethylenediaminetetraacetic acid

F. K. Shokoohi, L. M. Schiavone, C. T. Rogers, A. Inam, X. D. Wu, L. Nazar, and T. Venkatesan

Appl. Phys. Lett. 55, 2661 (1989); http://dx.doi.org/10.1063/1.102366 (3 pages) | Cited 28 times

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A new wet chemical etchant for high‐temperature superconducting films is reported, which leaves transition temperature unaffected within experimental accuracy (1 K) and does not require reoxygenation. The solution consists of ethylenediaminetetraacetic acid (EDTA) in water, and is suitable for micropatterning using standard photolithography. We have fabricated 3–50 μm patterns on laser‐deposited Y‐Ba‐Cu‐O films. The bulk of the films etches at 0.14 μm/min in a saturated solution at room temperature. Porous surface layers are removed three times faster than the dense portions of the films. Etch rate depends linearly on the solution concentration and exponentially on the solution temperature. These rates are reduced if etching is interrupted and the samples are exposed to atmosphere.
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74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.65.-b Surface treatments

New family of thallium cuprate superconductors not containing calcium or barium: TlSrn+1−xLnxCunO2n+3+δ (Ln=La, Pr, or Nd)

A. K. Ganguli, V. Manivannan, A. K. Sood, and C. N. R. Rao

Appl. Phys. Lett. 55, 2664 (1989); http://dx.doi.org/10.1063/1.102255 (3 pages) | Cited 12 times

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The first two members of the new TlSrn+1−xLnxCunO2n+3+δ (Ln=La, Pr, or Nd) series of superconducting cuprates possessing 1021 and 1122 type structures are described. The n=1 (1021) members with Tcs around 40 K have electrons or holes as the majority charge carriers depending on x. The n=2 (1122) cuprate (Ln=Pr or Nd) shows a Tc in the 80–90 K range.
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74.10.+v Occurrence, potential candidates
74.70.-b Superconducting materials other than cuprates
74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition

Oxygen concentration of Eu1Ba2Cu3O7−x in vacuum: An atom probe study

H. B. Elswijk, A. J. Melmed, and P. P. Camus

Appl. Phys. Lett. 55, 2667 (1989); http://dx.doi.org/10.1063/1.102367 (3 pages) | Cited 3 times

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Atom Probe mass analysis, at 85 K, using a wide‐angle instrument was used to measure the oxygen content and metallic stoichiometry of the near‐surface region of the superconducting ceramic oxide Eu1Ba2Cu3O7−x (x≂0.1) after vacuum exposure at room temperature. Routine specimen preparation, handling, and field‐ion imaging produced a specimen which had already lost oxygen such that its measured surface oxygen content corresponded to x=0.73 and the metallic stoichiometry of the surface was not the expected 1:2:3 but was enhanced in Ba and Eu. The specimen was subsequently exposed to vacuum for up to 80 h at room temperature and no additional loss of oxygen was detected. It was concluded that either (1) a stoichiometric low‐oxygen surface also would not have lost oxygen or (2) the nonstoichiometric layer forms a barrier for subsequent oxygen loss.
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74.70.-b Superconducting materials other than cuprates
68.35.Fx Diffusion; interface formation
66.30.H- Self-diffusion and ionic conduction in nonmetals
68.35.Dv Composition, segregation; defects and impurities

Optical plasma monitoring of Y‐Ba‐Cu‐O rf sputter target transients

J. D. Klein and A. Yen

Appl. Phys. Lett. 55, 2670 (1989); http://dx.doi.org/10.1063/1.102368 (3 pages) | Cited 12 times

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The plasma emission spectra resulting from rf sputtering Y‐Ba‐Cu‐O targets were observed as a function of sputter time. Although most lines of the observed spectra are not attributable to target species, peaks associated with each of the cation elements were resolved. The Ba and Cu peaks can be used as tracking indicators of process conditions. For example, switching from an O2/Ar sputter atmosphere to pure Ar enhanced the Ba peak much more than that associated with Cu. The emission spectra from a newly fabricated target exhibited a slow first‐order transient response in seeking equilibrium with the rf plasma. The transient response of a previously sputtered target is also first order but has a much shorter time constant.
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74.78.-w Superconducting films and low-dimensional structures
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
81.15.Cd Deposition by sputtering
74.70.-b Superconducting materials other than cuprates

Beam breakup in recirculating induction accelerators

Y. Y. Lau and D. G. Colombant

Appl. Phys. Lett. 55, 2673 (1989); http://dx.doi.org/10.1063/1.101966 (3 pages) | Cited 2 times

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Estimates of beam breakup instability (BBU) growths are given for multiturn recirculating induction accelerators currently under active study. The dispersion relation based on a simple model shows that BBU growth cannot be completely suppressed by just reducing the quality factor Q alone. Various methods of BBU control are discussed.
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29.20.-c Accelerators
29.27.Eg Beam handling; beam transport
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