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17 Feb 1992

Volume 60, Issue 7, pp. 793-914

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Luminescence from Si/Si1−xGex heterostructures and superlattices

G. A. Northrop, D. J. Wolford, and S. S. Iyer

Appl. Phys. Lett. 60, 865 (1992); http://dx.doi.org/10.1063/1.106512 (3 pages) | Cited 6 times

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A detailed study of near‐gap photoluminescence (PL) from strained Si1−xGex alloy layers (x=0.01–0.05) and Si/Si0.95Ge0.05 multiquantum‐wells (MQWs) has failed to show either free or dopant‐bound excitons in as‐prepared molecular beam epitaxial (MBE) layers. Low‐temperature PL was, however, successfully induced in these same heterostructures by the selective introduction of relatively shallow (137 and 186 meV) radiation‐damage bound‐exciton centers, I1 and G, (respectively). The I1 center, in particular, produced alloy‐broadened spectra which are shown clearly to emanate from the epitaxial layers, with separate and distinguishable components originating from both Si and Si1−xGex (x=0.01–0.05). This is among the first such reports of luminescence verifiably originating from within a Si/Si1−xGex multiple heterostructure.
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78.66.-w Optical properties of specific thin films
71.55.Ht Other nonmetals
61.80.Jh Ion radiation effects

InAs p‐n diodes grown on GaAs and GaAs‐coated Si by molecular beam epitaxy

W. Dobbelaere, J. De Boeck, P. Heremans, R. Mertens, G. Borghs, W. Luyten, and J. Van Landuyt

Appl. Phys. Lett. 60, 868 (1992); http://dx.doi.org/10.1063/1.106490 (3 pages) | Cited 12 times

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InAs p‐n diodes have been grown on GaAs and GaAs‐coated Si substrates by molecular beam epitaxy. Transmission electron microscopy cross sections of the epilayers demonstrate a good structural quality. Photodiodes were obtained using a Be (p=5×1016 cm−3) and Si (n=3×1016 cm−3) doping scheme. The diodes exhibited 77 K zero‐bias resistance area products of 2200 Ω cm2 for InAs/GaAs and 1500 Ω cm2 for InAs/GaAs/Si. The spectral response of the devices peaked at 2.95 μm with Johnson noise limited detectivities D∗ of 7.0×1011 cm Hz1/2/W for InAs/GaAs and 5.8×1011 cm Hz1/2/W for InAs/GaAs/Si. These results clearly demonstrate the feasibility of the monolithic integration of InAs infrared detectors and GaAs or Si read‐out electronics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
85.60.Dw Photodiodes; phototransistors; photoresistors

Polarization effect on infrared absorption of oxygen precipitates in silicon

A. Borghesi, B. Pivac, and A. Sassella

Appl. Phys. Lett. 60, 871 (1992); http://dx.doi.org/10.1063/1.107434 (3 pages) | Cited 9 times

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High‐spatial resolution Fourier transform infrared spectroscopy permitted us to study the effects of incident light polarization on the absorption band related to aggregates of SiO2 disk‐shaped precipitates present in annealed (100) Czochralski silicon samples. This is the first report documenting the strong dependence of such a band intensity on light polarization. Experimental results were compared with the simulation obtained using the effective medium theory. From this comparison we deduce that the precipitates only lie on the planes among {100} which are parallel to the wafer surface. This result can be related to the difference between the 〈100〉 direction and those crystallographically equivalent, introduced by the ingot growth process.
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78.30.-j Infrared and Raman spectra
78.40.Fy Semiconductors
78.30.Hv Other nonmetallic inorganics
61.72.sd Impurity concentration
61.72.sh Impurity distribution
61.72.sm Impurity gradients

Optical bleaching of metastable defects in amorphous silicon

Gautam Ganguly

Appl. Phys. Lett. 60, 874 (1992); http://dx.doi.org/10.1063/1.107435 (3 pages) | Cited 2 times

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Sub‐band‐gap absorption due to metastable defects induced by intense visible illumination in hydrogenated amorphous silicon is bleached when treated with low intensity, intensely absorbed, ultraviolet light. The bleaching effect is shown to occur in the bulk and is nonthermal. It is proposed that the energy from the surface absorbed light can be transferred to the bulk through phonons generated by cooling of photo injected hot carriers.
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78.30.-j Infrared and Raman spectra
78.40.Fy Semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
63.20.kp Phonon-defect interactions

Shallow ohmic contacts to n‐type GaAs and AlxGa1−xAs

L. R. Zheng, S. A. Wilson, D. J. Lawrence, S. I. Rudolph, S. Chen, and G. Braunstein

Appl. Phys. Lett. 60, 877 (1992); http://dx.doi.org/10.1063/1.106491 (3 pages) | Cited 7 times

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Sequential deposition of Pd/AuGe/Ag/Au and rapid thermal annealing are used to form shallow ohmic contacts to n‐GaAs and n‐AlxGa1−xAs. Ion backscattering measurements and cross‐sectional transmission electron microscopy show limited metal‐substrate reaction and uniform interfaces. The metallization on GaAs displays good electrical properties with a contact resistivity of 2.0×10−6 Ω cm2 at a carrier concentration of 2×1017 cm−3. The contacts formed on Al0.55Ga0.45As have a contact resistivity of 2.1×10−5 Ω cm2 at a carrier concentration of 7.5×1017 cm−3.
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73.40.Ns Metal-nonmetal contacts
66.30.Ny Chemical interdiffusion; diffusion barriers
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Carrier diffusion effects in time‐resolved photoluminescence

D. W. Bailey and C. J. Stanton

Appl. Phys. Lett. 60, 880 (1992); http://dx.doi.org/10.1063/1.106492 (3 pages) | Cited 9 times

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We model time‐resolved photoluminescence in GaAs using an ensemble Monte Carlo method coupled with a k⋅p calculation of the band structure. We show that on a picosecond scale, carrier diffusion perpendicular to the layer significantly reduces the density at the surface and consequently has a first‐order effect on luminescence measurements. To illustrate this we compare the calculated luminescence, with and without diffusion, to experimental data.
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78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
72.10.Bg General formulation of transport theory
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Photoluminescence and structure properties of GaAs/ZnSe quantum wells

S. Zhang and N. Kobayashi

Appl. Phys. Lett. 60, 883 (1992); http://dx.doi.org/10.1063/1.106493 (3 pages) | Cited 9 times

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By improving the quality of the GaAs well layer on a ZnSe barrier, we were able to observe the quantum size effect in photoluminescence of ZnSe/GaAs/ZnSe quantum wells. After solid phase epitaxy of 2‐ML GaAs on ZnSe epilayer, migration‐enhanced epitaxy (MEE) of the GaAs well layer was carried out while the growth temperature was elevated in steps. Photoluminescence from the obtained quantum wells has been appreciably improved by this method. The photoluminescence spectra show a systematic shift to higher energies as the well width is reduced, clearly demonstrating the size effect in the ZnSe‐GaAs system. By comparing the experimental data with calculated emission energies, the valence‐band and conduction‐band discontinuities between ZnSe and GaAs in the 〈001〉 direction have been determined to be 1.27±0.02 and 0.03±0.02 eV, respectively.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
72.80.Ey III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

High‐quality eutectic‐metal‐bonded AlGaAs‐GaAs thin films on Si substrates

R. Venkatasubramanian, M. L. Timmons, T. P. Humphreys, B. M. Keyes, and R. K. Ahrenkiel

Appl. Phys. Lett. 60, 886 (1992); http://dx.doi.org/10.1063/1.106494 (3 pages) | Cited 7 times

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Device quality GaAs‐AlGaAs thin films have been obtained on Si substrates, using a novel approach called eutectic‐metal‐bonding (EMB). This involves the lattice‐matched growth of GaAs‐AlGaAs thin films on Ge substrates, followed by bonding onto a Si wafer. The Ge substrates are selectively removed by a CF4/O2 plasma etch, leaving high‐quality GaAs‐AlGaAs thin films on Si substrates. We have obtained a minority‐carrier lifetime of 103 ns in a EMB GaAs‐AlGaAs double heterostructure on Si, which is nearly forty times higher than the state‐of‐the‐art lifetime for heteroepitaxial GaAs on Si, and represents the largest reported minority‐carrier lifetime for a freestanding GaAs thin film. In addition, a negligible residual elastic strain in the EMB GaAs‐AlGaAs films has been determined from Raman spectroscopy measurements.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.30.-j Infrared and Raman spectra
68.55.-a Thin film structure and morphology

Photoluminescence of porous silicon buried underneath epitaxial GaP

J. C. Campbell, C. Tsai, K.‐H. Li, J. Sarathy, P. R. Sharps, M. L. Timmons, R. Venkatasubramanian, and J. A. Hutchby

Appl. Phys. Lett. 60, 889 (1992); http://dx.doi.org/10.1063/1.106495 (3 pages) | Cited 9 times

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Recent observations of visible, room‐temperature photoluminescence in porous Si have stimulated research aimed at the realization of efficient, Si‐based electroluminescent devices. To achieve electroluminescence, it may be beneficial to generate carriers with sufficient energy to populate the states of the quantum‐confined Si structures. A viable method to accomplish this is to utilize a wide‐band‐gap heterojunction injector, such as GaP. Toward that end, we report the successful formation of porous Si buried underneath GaP islands, and we demonstrate that the buried porous Si layer exhibits strong photoluminescence (λ≊7000 Å).
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78.55.Hx Other solid inorganic materials
78.66.-w Optical properties of specific thin films
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

ZnSe based multilayer pn junctions as efficient light emitting diodes for display applications

H. Jeon, J. Ding, A. V. Nurmikko, W. Xie, M. Kobayashi, and R. L. Gunshor

Appl. Phys. Lett. 60, 892 (1992); http://dx.doi.org/10.1063/1.106496 (3 pages) | Cited 35 times

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pn junction characteristics and LED action in ZnSe‐based multilayers grown by molecular beam epitaxy is demonstrated. In particular, we show that (Zn,Cd)Se/ZnSe/Zn(S,Se) structures containing (Zn,Cd)Se quantum wells, grown on p‐type GaAs epilayers, and designed with a heavily doped n+‐ZnSe top contact layer may be appropriate for display device applications in the blue‐green portion of the spectrum.
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85.60.Jb Light-emitting devices
85.60.Pg Display systems
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors

Electrical tunability of infrared detectors using compositionally asymmetric GaAs/AlGaAs multiquantum wells

E. Martinet, F. Luc, E. Rosencher, Ph. Bois, and S. Delaitre

Appl. Phys. Lett. 60, 895 (1992); http://dx.doi.org/10.1063/1.106497 (3 pages) | Cited 26 times

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For the first time, an electrically tunable infrared photoconductor is made with GaAs/AlGaAs asymmetric step multiquantum wells, using the linear Stark shift of the intersubband transition. An applied electric field excursion of ±40 kV/cm is sufficient to shift the peak responsivity wavelength from 8.5 to 13.5 μm. The photoresponse tunability is studied by comparing photocurrent and absorption spectra for different applied electric fields.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
78.20.Jq Electro-optical effects

Joining of high current bulk Y‐Ba‐Cu‐O superconductors

K. Salama and V. Selvamanickam

Appl. Phys. Lett. 60, 898 (1992); http://dx.doi.org/10.1063/1.106498 (3 pages) | Cited 24 times

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A new fabrication method which makes it possible to enlarge the size of small, but high quality, grain‐aligned superconductors has been developed. This method involves solid state joining of high current density bulk YBa2Cu3Ox samples prepared by melt‐processing. The joined samples exhibit superconductivity above 90 K and are found to be capable of carrying currents in excess of 150 A at 77 K. The interface of the joined samples is found to sustain current densities (Jc) in excess of 6000 A/cm2 at zero field and in excess of 4000 A/cm2 at 1.5 T. Also, the magnetic field dependence of Jc of the joined samples is similar to that of the individual samples. Since this joining method is not limited by the size of the superconductors that can be joined, the favorable transport and magnetic properties render this process suitable for applications requiring high temperature superconductors in bulk forms.
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81.20.-n Methods of materials synthesis and materials processing
74.70.-b Superconducting materials other than cuprates
81.40.Rs Electrical and magnetic properties related to treatment conditions

Li‐doped Bi three‐layered superconducting whiskers

Ichiro Matsubara, Toru Ogura, Hiroshi Yamashita, Makoto Kinoshita, and Tomoji Kawai

Appl. Phys. Lett. 60, 901 (1992); http://dx.doi.org/10.1063/1.106499 (2 pages) | Cited 2 times

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Li‐doped Bi2Sr2Ca2Cu3O10 (2223) whiskers of single crystals with several millimeters length have been successfully prepared and it is revealed that Li‐doping is effective for increasing critical temperature (Tc) of the 2223 phase. By annealing Bi2Sr2CaCu2O8 (2212) whiskers in a calcined powder with a composition of Bi2Sr2Ca4Cu6Pb0.5LixOy (x=0.2, 0.3) only within the very narrow temperature region, the conversion from the 2212 phase to the 2223 phase and Li‐doping are achieved at the same time. The Tc value of the Li‐doped 2223 whiskers (108.1 K) is reproducibly 1.1 K higher than that of undoped 2223 whiskers prepared by the same method using a calcined powder without Li.
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74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.70.-b Superconducting materials other than cuprates
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
61.72.up Other materials

Subnanosecond photoresponse of a YBaCuO thin film to infrared and visible radiation by quasiparticle induced suppression of superconductivity

A. D. Semenov, G. N. Gol’tsman, I. G. Gogidze, A. V. Sergeev, E. M. Gershenzon, P. T. Lang, and K. F. Renk

Appl. Phys. Lett. 60, 903 (1992); http://dx.doi.org/10.1063/1.106500 (3 pages) | Cited 37 times

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We observed subnanosecond photoresponse of a structured superconducting YBa2Cu3O7−δ thin film to infrared and visible radiation. We measured the voltage response of a current biased film (thickness 700 Å) in a resistive state to radiation pulses. From our results we conclude a response time of about 90 ps and a responsivity of about 4×1010 Ω/J. We attribute the response to Cooper pair breaking and suppression of the superconducting energy gap induced by nonequilibrium quasiparticles.  
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
74.70.-b Superconducting materials other than cuprates
74.78.-w Superconducting films and low-dimensional structures
78.66.-w Optical properties of specific thin films
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures

Magnetic field imaging by using magnetic force scanning tunneling microscopy

R. D. Gomez, E. R. Burke, A. A. Adly, and I. D. Mayergoyz

Appl. Phys. Lett. 60, 906 (1992); http://dx.doi.org/10.1063/1.107442 (3 pages) | Cited 9 times

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Magnetic fields on previously recorded magnetic disk are measured and analyzed using a modified scanning tunneling microscope. The technique employs the interaction of local magnetic field with a flexible thin‐film magnetic probe. The dependence of resolution and image contrast on spatial orientation of the probe with respect to the sample is theoretically investigated. The predictions of this model, in limiting cases, are supported and illustrated by experimental results. A method for a controlled batch fabrication of probe tips is also discussed.
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75.70.Rf Surface magnetism
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
07.50.-e Electrical and electronic instruments and components
07.55.-w Magnetic instruments and components

Laser surface modification for selective electroplating of metal: A 2.5 m/s laser direct write process

Vincent Malba and Anthony F. Bernhardt

Appl. Phys. Lett. 60, 909 (1992); http://dx.doi.org/10.1063/1.106501 (3 pages) | Cited 3 times

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A very fast laser direct write process is described. The process involves laser modification of an insulating seed multilayer to form a conducting surface which can be electroplated. The seed layer is composed of an adhesion layer of TiW, a conducting layer of Au, and a top insulating layer of α‐Si. The laser forms a Au‐Si mixture without substantially affecting the adhesion layer. Writing speeds of 2.5 m/s have been demonstrated. The laser patterning can be performed in air, and the process works over a broad range of laser power (Pmax/Pmin ∼ 5).
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85.40.Hp Lithography, masks and pattern transfer
85.40.Ls Metallization, contacts, interconnects; device isolation
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Excimer laser mixing of Ti layers on Si3N4 ceramic substrates

T. R. Jervis, M. Nastasi, and K. M. Hubbard

Appl. Phys. Lett. 60, 912 (1992); http://dx.doi.org/10.1063/1.107436 (3 pages) | Cited 6 times

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We have used pulsed excimer laser radiation at 248 nm to mix Ti layers into Si3N4 substrates. Mixed layers show formation of small grain TiN in a Si3N4 but no evidence of Ti‐Si compounds or free Si. Low fluence (∼1.0 J cm−2) processing results in minimal mixing as TiN formation at the interface impedes further diffusion. At higher fluence (≳2 J cm−2) complete and quite uniform mixing occurs. The mixed layer is of the order of 0.5 μm thick.
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81.30.-t Phase diagrams and microstructures developed by solidification and solid-solid phase transformations
64.75.-g Phase equilibria
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.65.-b Surface treatments
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