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18 Apr 1988

Volume 52, Issue 16, pp. 1285-1363

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Widely tunable active Bragg reflector integrated lasers in InGaAsP‐InP

Björn Broberg and Stefan Nilsson

Appl. Phys. Lett. 52, 1285 (1988); http://dx.doi.org/10.1063/1.99140 (3 pages) | Cited 5 times

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Monolithic InGaAsP‐InP lasers comprising an active Bragg reflector integrated with a separately pumped wide‐band gain region have been developed. The lasers operate in a dynamic single mode in the 1.55 μm wavelength region. By adjusting the current through the Bragg reflector, the wavelength can be tuned. The maximum tuning range is 11.6 nm.
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42.60.Fc Modulation, tuning, and mode locking
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Px Semiconductor lasers; laser diodes

Linear electro‐optic effect in barium metaborate

H. Nakatani, W. Bosenberg, L. K. Cheng, and C. L. Tang

Appl. Phys. Lett. 52, 1288 (1988); http://dx.doi.org/10.1063/1.99680 (3 pages) | Cited 8 times

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We report the first measurement of the linear electro‐optic coefficients of crystalline barium metaborate. The largest electro‐optic coefficient r22 was found to be 2.5 pm/V, about four times smaller than the r63 of potassium dihydrogen phosphate (KDP). The dispersion of the electro‐optic coefficient was also measured and found to be in excellent agreement with predicted values using the anharmonic oscillator model. Implications of the result on the point group symmetry of barium metaborate are also discussed.
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78.20.Jq Electro-optical effects

Femtosecond luminescence spectroscopy with 60 fs compressed pulses

T. C. Damen and Jagdeep Shah

Appl. Phys. Lett. 52, 1291 (1988); http://dx.doi.org/10.1063/1.99141 (3 pages) | Cited 24 times

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We report compression of the pulses from a synchronously pumped Rh 6G dye laser to 60 fs using a fiber‐prism compressor. Average power in excess of 150 mW has been obtained. Using this compressed laser and the sum‐frequency‐generation technique, we have demonstrated the capability of measuring luminescence spectra with 65 fs time resolution. Initial results on GaAs and AlGaAs are presented.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Rz Doped-insulator lasers and other solid state lasers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.55.Cr III-V semiconductors
42.55.Mv Dye lasers

High‐efficiency extraction study of an electron beam pumped ArF laser amplifier with an atmospheric‐pressure Ar‐rich mixture

Young‐Woo Lee, Hiroshi Kumagai, Shu‐ichi Ashidate, and Minoru Obara

Appl. Phys. Lett. 52, 1294 (1988); http://dx.doi.org/10.1063/1.99142 (3 pages) | Cited 3 times

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The characteristics of an electron beam excited ArF laser amplifier were investigated from the small‐signal region to the strongly saturated region (≥10 MW/cm2) as a function of Ar concentration. A single‐pass (L=50 cm) amplifier experiment was performed with atmospheric Ar/F2 and Ne/Ar/F2 gas mixtures pumped by an intense electron beam (1.3 MV, 90 kA, 65 ns full width half‐maximum). The extracted intensity (output intensity minus input intensity) from this single‐pass amplifier was maximized at input intensities ranging from 6.7 to 9.5 MW/cm2. The power efficiencies obtained were 13, 14.4, and 15.7%, and the extraction efficiencies were 65, 59.7, and 59.4% for Ar concentrations of 40, 70, and 99.6%, respectively. The amplifier parameters (small‐signal gain g0, nonsaturable absorption coefficient α, and saturated intensity Is) were estimated for each mixture using a Rigrod analysis [J. Appl. Phys. 36, 2487 (1965)].
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Losses in Y‐junction semiconductor laser arrays

William Streifer, David F. Welch, Josef Berger, Peter S. Cross, and Don R. Scifres

Appl. Phys. Lett. 52, 1297 (1988); http://dx.doi.org/10.1063/1.99143 (3 pages) | Cited 2 times

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Losses in Y‐junction semiconductor laser arrays are shown to affect not only the thresholds and differential efficiencies, but also the array near‐field mode patterns, threshold discrimination, and radiation patterns.
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42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Px Semiconductor lasers; laser diodes

Violet cw neodymium upconversion laser

R. M. Macfarlane, F. Tong, A. J. Silversmith, and W. Lenth

Appl. Phys. Lett. 52, 1300 (1988); http://dx.doi.org/10.1063/1.99681 (3 pages) | Cited 74 times

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We have observed cw laser action on a new transition (4D3/2→4I11/2) of the Nd3+ ion at 380 nm. This was demonstrated in Nd:LaF3 using an upconversion pumping scheme in which near infrared (788 nm) and visible (591 nm) pump photons from cw dye lasers produce stepwise excitation of the Nd3+ ion. In addition, lasing was observed with a single pump source at wavelengths around 578 nm using doubly resonant, sequential absorption of two yellow photons. Single‐mode, cw operation with an output power of 12 mW was measured at 20 K with 1% output coupling and pump powers of several hundred mW. At 77 K the maximum power dropped to 4 mW.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Electron‐beam‐pumped two‐dimensional semiconductor laser array with tilted mirror resonator

F. Tong, R. M. Osgood, A. Sanchez, and V. Daneu

Appl. Phys. Lett. 52, 1303 (1988); http://dx.doi.org/10.1063/1.99144 (3 pages)

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The spatial and spectral emission characteristics of a two‐dimensional CdS laser array, pumped by a high‐energy electron beam, have been experimentally investigated. The near‐field emission from each cell or array element is found to arise from a virtual line located behind the cell. The results are consistent with a geometric ray model of a tilted mirror resonator.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Electrical properties of a CdTe/InSb hetero metal‐insulator‐semiconductor structure

K. Shiina, Y. Tanaka, O. Sugiura, S. Oda, and M. Matsumura

Appl. Phys. Lett. 52, 1306 (1988); http://dx.doi.org/10.1063/1.99145 (2 pages) | Cited 10 times

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Electrical properties of a metal/CdTe/InSb metal‐insulator‐semiconductor structure have been investigated by capacitance‐voltage and conductance‐voltage measurements for the first time at 77 K. Interfaces of both p‐ and n‐type InSb substrates can be controlled from accumulation states to inversion states. Distribution of interface state density evaluated by the Terman method is U shaped with the minimum value of 1012 cm−2 eV−1.
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73.40.Lq Other 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

Infrared absorption study of N–H bonds in plasma‐deposited silicon oxynitride films

C. M. M. Denisse, J. F. M. Janssen, F. H. P. M. Habraken, and W. F. van der Weg

Appl. Phys. Lett. 52, 1308 (1988); http://dx.doi.org/10.1063/1.99682 (3 pages) | Cited 9 times

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A study of the infrared (IR) absorption by N–H bonds in plasma‐deposited silicon oxynitride films is presented. Emphasis in this study is placed on the absorption strength for the N–H stretching mode per bond, i.e., the absorptivity. It is found that the absorptivity strongly peaks at an oxygen‐to‐nitrogen ratio of O/(O+N)=0.2. A tentative explanation for the unusually high IR absorption strength in relation to the structure of the material is given.
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78.30.Hv Other nonmetallic inorganics
78.66.-w Optical properties of specific thin films

Low‐temperature amorphous‐to‐crystalline transformation of CoSi2 films

A. Cros, K. N. Tu, D. A. Smith, and B. Z. Weiss

Appl. Phys. Lett. 52, 1311 (1988); http://dx.doi.org/10.1063/1.99683 (3 pages) | Cited 23 times

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Amorphous‐to‐crystalline transformation of e‐gun co‐deposited CoSi2 films occurs from 150 to 200 °C, as observed by in situ resistivity measurement and transmission electron microscopy. Resistivity changes abruptly from 1500 to 110 μΩ cm as the amorphous film transforms into circular crystallites that are circular before impingement occurs. A room‐temperature resistivity of 30 μΩ cm was obtained by annealing the film to 500 °C.
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68.55.-a Thin film structure and morphology
73.61.At Metal and metallic alloys
64.70.K- Solid-solid transitions
68.35.Rh Phase transitions and critical phenomena

Lateral diffusion of mercury during laser annealing of HgMnTe and other HgTe‐based materials

F. G. Moore and R. E. Kremer

Appl. Phys. Lett. 52, 1314 (1988); http://dx.doi.org/10.1063/1.99146 (3 pages) | Cited 4 times

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The diffusion of mercury in HgTe‐related materials has played a major role in the development of devices utilizing the unique features of this family of materials. The study of mercury diffusion, however, has been limited to diffusion perpendicular to the surface (i.e., into or out of the sample). We present evidence showing that when samples undergo laser annealing, substantial amounts of mercury are displaced laterally as well. This lateral diffusion was observed with the use of thermal probe mapping of slices of HgMnTe and HgCdTe.
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66.30.Lw Diffusion of other defects
68.35.Fx Diffusion; interface formation
66.30.Fq Self-diffusion in metals, semimetals, and alloys
72.20.Pa Thermoelectric and thermomagnetic effects

Interaction of a polycrystalline silicon/SiO2/silicon substrate under thermal/electrical fields

T. C. Chou and K. N. Tu

Appl. Phys. Lett. 52, 1317 (1988); http://dx.doi.org/10.1063/1.99684 (3 pages) | Cited 2 times

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Electric current induced breakdown phenomenon of silicon dioxide film was studied by annealing the sandwich samples of polycrystalline Si/SiO2 /Si substrate at 700 °C under electric currents. Cross‐sectional transmission electron microscopy revealed two interesting results: (1) the aggregation of voids into large holes at the interface of polycrystalline Si/SiO2 , and (2) the nucleation and growth of crystalline Si in the silicon dioxide layer. The crystalline Si was either of single crystalline or polycrystalline forms, depending on the nucleating interfaces. Local melting as a result of Joule heating was observed. The breakdown of the oxide is mainly attributed to the loss of oxide integrity as a result of heterogeneous Joule heating. The nucleation and growth of crystalline Si in the amorphous oxide layer suggest the direct decomposition of SiO2 during the oxide breakdown process.
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77.22.Jp Dielectric breakdown and space-charge effects
73.61.Ng Insulators
73.40.Ty Semiconductor-insulator-semiconductor structures
68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics

Photovoltaic detection of infrared light in a GaAs/AlGaAs superlattice

A. Kastalsky, T. Duffield, S. J. Allen, and J. Harbison

Appl. Phys. Lett. 52, 1320 (1988); http://dx.doi.org/10.1063/1.99147 (3 pages) | Cited 54 times

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We report the observation of photovoltaic infrared photodetection in an n‐type GaAs/AlGaAs superlattice within the optical range 3.6–6.2 μm. A built‐in graded AlGaAs barrier (∼0.2 eV) provides charge polarization in the sample by allowing the optically excited electrons in the second miniband of the superlattice to diffuse over this barrier. The optical polarization of the infrared signal is consistent with the selection rules applicable to the superlattice. The infrared photoresponse results from first‐to‐second miniband as well as shallow donor‐to‐second miniband photoexcitations within the superlattice. Donor‐to‐second miniband photoexcitation is dominant at low temperatures (<25 K).
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73.50.Pz Photoconduction and photovoltaic effects
85.60.Gz Photodetectors (including infrared and CCD detectors)
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors

Carrier confinement photoconductive detector

B. Jalali, H. L. Evans, and E. S. Yang

Appl. Phys. Lett. 52, 1323 (1988); http://dx.doi.org/10.1063/1.99148 (3 pages) | Cited 1 time

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We propose a new device, the carrier confinement photoconductive detector, in which an improvement in performance over a conventional photoconductor is achieved by confinement of photogenerated carriers in the active channel. The confinement can be realized by placing a layer of a wide band‐gap semiconductor between the channel and ohmic contact. Analytical and numerical analyses show that gain‐bandwidth improvement of 100% can be achieved by using the GaAl/AlGaAs system.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
73.50.Pz Photoconduction and photovoltaic effects
73.61.Ey III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Epitaxial Al2O3 films on Si by low‐pressure chemical vapor deposition

Makoto Ishida, Ichiro Katakabe, Tetsuro Nakamura, and Norio Ohtake

Appl. Phys. Lett. 52, 1326 (1988); http://dx.doi.org/10.1063/1.99685 (3 pages) | Cited 58 times

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Heteroepitaxial Al2O3 films were grown successfully on (100)Si substrates at substrate temperatures above 1000 °C by low‐pressure chemical vapor deposition with the use of N2 bubbled Al(CH3)3 and N2O. From reflection high‐energy electron diffraction analysis, the epitaxial films were found to be γ‐Al2O3 with an orientation relation of (100)Al2O3//(100)Si. Capacitors with 700‐Å‐thick Al2O3 films as gate insulators were fabricated and showed high‐frequency capacitance‐voltage characteristics without hysteresis. An interface state density of 1.7×1011 cm−2 eV−1 was observed by using quasistatic capacitance‐voltage measurements. The leakage current was 9.7×10−11 A/cm2 at a gate voltage of 3.0 V.
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68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.61.Ng Insulators
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Short‐wavelength (∼625 nm) room‐temperature continuous laser operation of In0.5(AlxGa1−x)0.5P quantum well heterostructures

D. W. Nam, D. G. Deppe, N. Holonyak, R. M. Fletcher, C. P. Kuo, T. D. Osentowski, and M. G. Craford

Appl. Phys. Lett. 52, 1329 (1988); http://dx.doi.org/10.1063/1.99149 (3 pages) | Cited 11 times

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Data are presented demonstrating very‐short‐wavelength (625 nm) room‐temperature (300 K) continuous (cw) photopumped laser operation of In1−y(AlxGa1−x)yP‐In1−y (AlxGa1−x)yP quantum well heterostructures grown lattice matched (y≊0.5) on a GaAs substrate via metalorganic chemical vapor deposition. In addition, 300 K pulsed laser operation (Jth∼104 A/cm2, 625 nm) of diodes fabricated from the same crystal is described.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Px Semiconductor lasers; laser diodes
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.45.+h Stimulated emission

Two‐dimensional behavior of molecular beam epitaxy grown HgTe

R. J. Justice, D. G. Seiler, W. Zawadzki, R. J. Koestner, and M. W. Goodwin

Appl. Phys. Lett. 52, 1332 (1988); http://dx.doi.org/10.1063/1.99150 (3 pages)

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Two‐dimensional electronic properties of HgTe films (∼2 μm thick) grown by molecular beam epitaxy on CdTe substrates have been investigated by using the Shubnikov–de Haas effect. Electron densities, effective masses, and Dingle temperatures of three electric subbands in an accumulation layer near the HgTe‐CdTe interface have been determined for two samples with different total densities. The results exhibit behavior typical of an asymmetric triangular potential well and a pronounced band nonparabolicity.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ga II-VI semiconductors
73.30.+y Surface double layers, Schottky barriers, and work functions

Stress reduction and doping efficiency in B‐ and Ge‐doped silicon molecular beam epitaxy films

Hiroyuki Hirayama, Toru Tatsumi, and Naoaki Aizaki

Appl. Phys. Lett. 52, 1335 (1988); http://dx.doi.org/10.1063/1.99151 (3 pages) | Cited 9 times

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Lattice defects in boron highly doped silicon molecular beam epitaxy films (B:2×1020 cm−3) were reduced by a simultaneous doping of germanium and boron. The defect reduction mechanism was investigated with surface defect observation, x‐ray diffraction, and Raman spectroscopy. The growth rate of Si and the doping level of Ge and B were controlled precisely, and the suitable germanium‐to‐boron ratio was determined. At a germanium‐to‐boron ratio of 4:1, a drastic decrease of the defect density was observed, and the doping efficiency was improved.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.60.Bs Mechanical and acoustical properties
68.35.Dv Composition, segregation; defects and impurities

NiAl/n‐GaAs Schottky diodes: Barrier height enhancement by high‐temperature annealing

T. Sands, W. K. Chan, C. C. Chang, E. W. Chase, and V. G. Keramidas

Appl. Phys. Lett. 52, 1338 (1988); http://dx.doi.org/10.1063/1.99152 (3 pages) | Cited 30 times

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A metallurgically stable and laterally uniform contact to n‐GaAs with an enhanced barrier height (0.99 V) and an ideality factor of 1.10 has been achieved with a NiAl bimetallic metallization. This barrier height, as measured by the forward current‐voltage technique after annealing for 20 s at 650 °C, is higher than the reported barrier heights of refractory metallizations to n‐GaAs. Auger electron spectroscopy (AES) sputter profiles reveal an Al‐Ga exchange reaction after high‐temperature (500–950 °C) rapid thermal annealing. From these results, the barrier height enhancement is attributed to the formation of an Al1−xGaxAs layer at the NiAl/n‐GaAs interface. The thermal stability and low electrical resistivity of the NiAl phase, the enhanced barrier height on n‐GaAs, and the ease of patterning the as‐deposited Ni/Al/Ni layered structure by lift‐off techniques make NiAl a very promising gate contact material for GaAs metal‐semiconductor field‐effect transistors and related devices.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts
73.40.Ei Rectification
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Measurement of the valence‐band discontinuities for molecular organic semiconductor/inorganic semiconductor heterojunctions

F. F. So and S. R. Forrest

Appl. Phys. Lett. 52, 1341 (1988); http://dx.doi.org/10.1063/1.99153 (3 pages) | Cited 1 time

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Using the temperature dependence of the forward‐biased current‐voltage characteristics as well as internal photoemission, we directly measure the barrier potential and valence‐band discontinuity energy (ΔEv ) of isotype heterojunctions formed between thin films of the crystalline organic semiconductor: 3,4,9,10‐perylenetetracarboxylic dianhydride (PTCDA) and p‐Si. We find ΔEv =(0.50±0.02) eV. This, to our knowledge, is the first report of a measurement of a band discontinuity energy between a crystalline organic semiconductor and an inorganic semiconductor. These results are consistent with predictions of a current model involving diffusion and drift in the organic‐on‐inorganic (OI) semiconductor device. This model is employed to calculate ΔEv using previously obtained barrier energies for several different PTCDA/inorganic semiconductor devices. In all cases, values of the barrier diffusion potential and ΔEv are considerably smaller than apparent barrier energies obtained previously using pure thermionic emission theory to explain transport of charge over the OI barrier.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Effects of processing conditions on negative bias temperature instability in metal‐oxide‐semiconductor structures

D. Lu, G. A. Ruggles, and J. J. Wortman

Appl. Phys. Lett. 52, 1344 (1988); http://dx.doi.org/10.1063/1.99154 (3 pages) | Cited 4 times

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Radiation from electron beam metallization has been found to result in damage to metal‐oxide‐semiconductor structures, which, when not properly annealed out, can lead to severe negative bias temperature instability (NBTI), even at room temperature. Similarly, rapid thermal annealing (RTA) after oxidation can result in significant room‐temperature instability. The post‐metal‐annealing behavior of this RTA‐induced instability depends on the high‐temperature annealing ambient (Ar vs O2). Processing in O2 can also lead to significant NBTI; however, following such steps by an Ar anneal at the same temperature can negate the effect, and in some cases, lead to an overall reduction in NBTI. An electrical current flows during the stressing measurement and can be correlated with the development of oxide positive charge. This finding supports a model for charge buildup during NBT stressing in which holes from the Si substrate become trapped in intrinsic hole traps located within the oxide.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.Tv Field effect devices
81.40.Rs Electrical and magnetic properties related to treatment conditions

Dark‐line observations in failed quantum well lasers

R. G. Waters and R. K. Bertaska

Appl. Phys. Lett. 52, 1347 (1988); http://dx.doi.org/10.1063/1.99640 (2 pages) | Cited 6 times

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The electron‐beam‐induced current technique has been used to disclose dark‐line patterns in degraded AlxGa1−xAs quantum well lasers. At least four distinct types of pattern exist, each being characteristic of a particular device structure.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Px Semiconductor lasers; laser diodes
85.30.De Semiconductor-device characterization, design, and modeling

Observation of electron quantum interference effects due to virtual states in a double‐barrier heterostructure at room temperature

Robert C. Potter and Amir A. Lakhani

Appl. Phys. Lett. 52, 1349 (1988); http://dx.doi.org/10.1063/1.99155 (3 pages) | Cited 24 times

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Strong electron quantum interference effects have been observed at room temperature in the current‐voltage characteristics of a double‐barrier, wide‐well, lattice‐matched In0.52Al0.48As /In0.53Ga0.47As heterostructure tunneling device. A total of 22 oscillations was observed in the differential conductance. A model is proposed which attributes ten of the oscillations to the usual resonant tunneling via the subbands and the rest to the presence of virtual states that exist in the well and second barrier regions.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
73.40.Gk Tunneling
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Surface photovoltage spectroscopy of surface states on indium phosphide

Y. Byun and B. W. Wessels

Appl. Phys. Lett. 52, 1352 (1988); http://dx.doi.org/10.1063/1.99156 (3 pages) | Cited 2 times

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Indium phosphide photoelectrodes have been studied in situ using surface photovoltage spectroscopy. The observed spectra were a strong function of electrode surface conditions. Electronic properties of the chemically induced surface states correlated well with previously reported values determined by surface photovoltage spectroscopy measurements in vacuum. Metal deposits of Cu and Ag were found to induce deep surface states at 0.9 eV above the valence‐band edge.
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73.20.At Surface states, band structure, electron density of states
81.65.-b Surface treatments
82.47.-a Applied electrochemistry
73.25.+i Surface conductivity and carrier phenomena

Superconductive aluminum/YBa2Cu3Ox composites stabilized by oxygen/fluorine donors

In‐Gann Chen, S. Sen, and D. M. Stefanescu

Appl. Phys. Lett. 52, 1355 (1988); http://dx.doi.org/10.1063/1.99686 (3 pages) | Cited 16 times

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A fabrication technique for producing bulk and irregular‐shaped aluminum/high Tc superconductor composites by traditional powder metallurgy method is reported. During the course of fabrication, the oxygen stoichiometry can be maintained at the desired level in order to retain superconductivity by addition of certain metal oxides or metal carbonates with low oxidation tendency, e.g., Ag2O, Ag2CO3, and CdO. Moreover, replacement of oxygen with fluorine is also possible by addition of certain unstable fluorides like AgF. Superconductivity measurements of Al/YBa2Cu3Ox random composites with additions of different oxygen or fluorine donors show a similiar or improved Tc in comparison to the pure 123 compound. The concept of oxygen/fluorine donor can also be used in other fabrication techniques of metal/123 composites to stabilize the oxygen/fluorine stoichiometry.
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74.70.-b Superconducting materials other than cuprates
81.05.Mh Cermets, ceramic and refractory composites
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