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2 Mar 1992

Volume 60, Issue 9, pp. 1037-1146

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Photoluminescence excitation measurements of the absorption band gap in heavily carbon‐doped GaAs

Lei Wang, B. J. Aitchison, and N. M. Haegel

Appl. Phys. Lett. 60, 1111 (1992); http://dx.doi.org/10.1063/1.106460 (3 pages) | Cited 5 times

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Photoluminescence excitation (PLE) spectroscopy has been used to study the optical absorption in epitaxial layers of heavily carbon‐doped GaAs. Shifts of the PLE spectra with temperature and doping were observed. The location of the Fermi level was estimated to be 0.08, 0.22, and 0.24 eV below the top of the valence band in samples doped to 6.2×1019 cm−3, 1.6×1020 cm−3, and 4.1×1020 cm−3, respectively.
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78.55.Cr III-V semiconductors
78.30.-j Infrared and Raman spectra
78.40.Fy Semiconductors

Etching characteristics of AlxGa1−xAs in (NH4)2Sx solutions

Jong‐Wook Seo, Terry Koker, Sambhu Agarwala, and Ilesanmi Adesida

Appl. Phys. Lett. 60, 1114 (1992); http://dx.doi.org/10.1063/1.106461 (3 pages) | Cited 15 times

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The etching of GaAs and AlxGa1−xAs have been characterized in (NH4)2Sx solution with various excess sulfur concentrations and for temperatures ranging from 20 to 60 °C. The etch rate varies with the concentration of excess sulfur and is highest at 60 °C using a 4% excess sulfur solution. The etch rate of AlxGa1−xAs increases exponentially with increasing Al mole fraction. Activation energies of 19.8 and 15.9 kcal/mole are obtained for GaAs and Al0.3Ga0.7As in 4% (NH4)2Sx, respectively. These high values and the linear time dependence of etch rates signify that the etching process of AlxGa1−xAs in (NH4)2Sx solutions is predominantly reaction‐rate limited. Possible chemical processes involved in the etching and the formation of a passivating sulfur layer are discussed.
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81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer
85.40.Ls Metallization, contacts, interconnects; device isolation

Activation and diffusion characteristics of implanted Si and Be in Al0.5In0.5P

S. J. Pearton, W. S. Hobson, J. M. Kuo, H. S. Luftman, A. Katz, and F. Ren

Appl. Phys. Lett. 60, 1117 (1992); http://dx.doi.org/10.1063/1.106434 (3 pages) | Cited 4 times

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The electrical activation characteristics of implanted Si and Be in Al0.5In0.5P grown lattice matched to GaAs by either organometallic vapor phase epitaxy or gas‐source molecular beam epitaxy were investigated as a function of ion dose (1013–1015 cm−2), annealing time (3–60 s) and annealing temperature (600–950 °C). Limiting sheet electron densities of 9×1012 cm−2 for 100 keV Si implants and sheet hole densities of 7×1012 cm−2 for 40 keV Be implants were obtained for optimum 10 s anneals at 850 or 800 °C, respectively. Co‐implantation of P with Be failed to substantially improve the Be activation. Apparent activation energies for electrical activation of Si of 0.74±0.05 eV and 0.68±0.05 eV for Be were obtained from the temperature dependence of the saturated carrier density. The implanted Be displayed extensive redistribution upon annealing at 800 °C for 10 s, whereas implanted Si showed no measurable motion under any of our conditions.
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72.80.Ey III-V and II-VI semiconductors
71.55.Eq III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
66.30.J- Diffusion of impurities

Space‐charge distribution and trapping kinetics in amorphous silicon solar cells

R. Könenkamp, S. Muramatsu, S. Matsubara, and T. Shimada

Appl. Phys. Lett. 60, 1120 (1992); http://dx.doi.org/10.1063/1.106435 (3 pages) | Cited 2 times

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Using electron time‐of‐flight experiments we have determined the electric field profile and the electron transport efficiency in amorphous silicon solar cells. In optimized devices we find a correlation between the space‐charge distribution and the trapping behavior at the p‐i junction, indicating that charged defects in the space‐charge region determine both, the electric field distribution and the trapping kinetics. From their capture cross section the charged states are identified as positively charged dangling bonds.
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85.60.-q Optoelectronic devices
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.50.Pz Photoconduction and photovoltaic effects
72.40.+w Photoconduction and photovoltaic effects

Backside secondary ion mass spectrometry study of a Ge/Pd ohmic contact to InP

S. A. Schwarz, M. A. A. Pudensi, T. Sands, T. J. Gmitter, R. Bhat, M. Koza, L. C. Wang, and S. S. Lau

Appl. Phys. Lett. 60, 1123 (1992); http://dx.doi.org/10.1063/1.106428 (3 pages) | Cited 13 times

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High‐resolution SIMS (secondary ion mass spectrometry) depth profiles of Ge/Pd ohmic contacts on InP are obtained by sputter‐etching from the back (semiconductor) side. The samples contain an InGaAs‐etch stop layer, to allow chemical thinning, and InGaAsP marker layers, which allow alignment and calibration of the depth profiles on the nm scale. At 200 °C, a Pd‐In‐P alloy layer is observed to form at the contact interface. The thickness of this layer is dependent on the amount of metallic Pd available for reaction. Subsequent processing at 325 °C results in the partial dissolution of this alloy layer, as PdGe forms at the contact interface, and regrowth of the liberated InP. Ge is detected in the regrown region but is not observed to diffuse into the substrate. Ge epitaxy is not observed at the contact interface at 325 °C, in contrast to the behavior of the Ge/Pd‐GaAs contact. The experimental evidence suggests that regrowth is a key step in the formation of the ohmic contact.
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68.35.Fx Diffusion; interface formation
68.35.Dv Composition, segregation; defects and impurities
68.55.Nq Composition and phase identification

New all‐optical reflection modulator based on a doubly resonant hetero‐nipi saturable Bragg reflection

P. J. Poole, C. C. Phillips, and O. H. Hughes

Appl. Phys. Lett. 60, 1126 (1992); http://dx.doi.org/10.1063/1.107454 (3 pages) | Cited 3 times

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Very large fractional reflectivity changes (30%) under optical pump densities of ≊3 mW/cm2 are found in a novel GaAs/Al0.35Ga0.65As hetero‐nipi structure grown by MBE. This high sensitivity originates in the interaction between the n=1 heavy‐hole excitonic resonances in the hetero‐nipi and an optical Bragg resonance, designed into the structure through its optical periodicity. The dynamics of the nonlinearity are shown to be dominated by the ‘‘giant ambipolar diffusion’’ mechanism for in‐plane carrier transport, and the implications of this for device applications are discussed.
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42.79.Hp Optical processors, correlators, and modulators
42.65.Pc Optical bistability, multistability, and switching, including local field effects
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors

Strain relaxation of compositionally graded InxGa1−xAs buffer layers for modulation‐doped In0.3Ga0.7As/In0.29Al0.71As heterostructures

J. C. P. Chang, Jianhui Chen, J. M. Fernandez, H. H. Wieder, and K. L. Kavanagh

Appl. Phys. Lett. 60, 1129 (1992); http://dx.doi.org/10.1063/1.106429 (3 pages) | Cited 54 times

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Modulation‐doped In0.3Ga0.7As/In0.29Al0.71As heterostructures have been grown on GaAs substrates by molecular beam epitaxy using a compositionally step‐graded InxGa1−xAs buffer layer. We found that the buffer layer produces essentially total relaxation with <2×106/cm2 dislocations present in the In0.3Ga0.7As layer. The structural perfection of this layer is reflected in the electrical and galvanomagnetic properties of its two‐dimensional electron‐gas channel which has a sheet‐electron density of 1.2×1012/cm2, peak mobilities of 9 300 cm2/V s at room temperature and 31 000 cm2/V s at 77 K, and a mobility anisotropy of ∼4% along orthogonal 〈110〉 directions.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.Dv Composition, segregation; defects and impurities

Liquid phase epitaxy of cubic FeSi2 on (111) Si induced by pulsed laser irradiation

M. G. Grimaldi, P. Baeri, C. Spinella, and S. Lagomarsino

Appl. Phys. Lett. 60, 1132 (1992); http://dx.doi.org/10.1063/1.106430 (3 pages) | Cited 26 times

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Epitaxial βFeSi2 layers thermally grown on (111) Si substrates have been irradiated by 25 ns ruby laser pulses in the energy density range 0.3–0.7 J/cm2. Rutherford backscattering analyses in combination with the channeling effect have shown that the silicide stoichiometry does not change for irradiations up to an energy density of 0.5 J/cm2, while alignment of the irradiated silicide along the [111] substrate normal direction is observed. Transmission electron diffraction in the plan view configuration showed that this silicide phase has a cubic symmetry with a lattice parameter very similar to that of Si. Diffraction patterns taken along different poles of the substrate indicated that the epitaxial phase is 180° rotated about the [111] normal direction like the B type NiSi2 and CoSi2 silicides.
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81.30.-t Phase diagrams and microstructures developed by solidification and solid-solid phase transformations
81.10.Fq Growth from melts; zone melting and refining
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

On the role of mobility and saturated velocity in the dynamic operation of p‐i‐n and metal‐semiconductor‐metal photodetectors

Sandip Tiwari and Michael A. Tischler

Appl. Phys. Lett. 60, 1135 (1992); http://dx.doi.org/10.1063/1.106431 (3 pages) | Cited 8 times

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We have employed the temperature dependence of the response of lateral p‐i‐n and metal‐semiconductor‐metal photodetectors fabricated with Ga0.47In0.53As active regions to determine the role of low and high‐field transport properties of electrons and holes in the speed and frequency response. The p‐i‐n structures exhibit a response with two characteristic time constants and show a significantly larger improvement in response time at lower temperatures than that expected from improvements in saturated velocities alone. It is suggested that upon excitation by photons, the initial stage of the response is characterized by low‐field ambipolar conditions with electron transport and collection dominating the response. This is followed by high‐field unipolar conditions where hole transport and collection dominates the response. Thus, low‐field mobility, which has a stronger temperature dependence, is also important to the operation of photodetectors.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Sx Metal-semiconductor-metal structures

Sr2RuO4: A metallic substrate for the epitaxial growth of YBa2Cu3O7−δ

F. Lichtenberg, A. Catana, J. Mannhart, and D. G. Schlom

Appl. Phys. Lett. 60, 1138 (1992); http://dx.doi.org/10.1063/1.106432 (3 pages) | Cited 66 times

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Single crystals of Sr2RuO4 were grown by the floating zone melting technique. The crystals have the K2NiF4 structure and display a metallic resistivity behavior in the a‐b‐plane between 300 and 4.2 K (ρab≂10−4 Ω cm at 300 K). The in‐plane lattice mismatch between YBa2Cu3O7−δ (001) and Sr2RuO4 (001) is smaller than 1.3%, better than that to SrTiO3 {100}. Epitaxial films of YBa2Cu3O7−δ with Tc(R=0) as high as 86 K have been grown on Sr2RuO4 crystals. The epitaxial growth of YBa2Cu3O7−δ on Sr2RuO4 was revealed by four‐circle x‐ray diffraction as well as by transmission electron microscopy.
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74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
68.55.-a Thin film structure and morphology
81.10.Fq Growth from melts; zone melting and refining

Tl‐Ca‐Ba‐Cu‐O step‐edge Josephson junctions

J. S. Martens, T. E. Zipperian, G. A. Vawter, D. S. Ginley, V. M. Hietala, and C. P. Tigges

Appl. Phys. Lett. 60, 1141 (1992); http://dx.doi.org/10.1063/1.107458 (3 pages) | Cited 3 times

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There has been considerable progress in the development of nonhysteretic Josephson junction microelectronic technologies for YBaCuO. Such a technology for Tl‐Ca‐Ba‐Cu‐O junctions would be interesting because of the higher operating temperatures and the very different grain boundary structures in the different cuprate superconductors. We have successfully made step‐edge junctions with TlCaBaCuO grown on ion‐milled LaAlO3. Nonhysteretic grain boundary‐based junctions have been demonstrated with critical current‐normal state resistance products exceeding 5 mV at 77 K, critical current densities ranging from 500 to 25 000 A/cm2, and critical current versus field profiles suggesting very uniform junctions. Yield has exceeded 70% on over 250 junctions tested and operation has been demonstrated to 100 K.
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85.25.Cp Josephson devices
74.70.-b Superconducting materials other than cuprates
74.50.+r Tunneling phenomena; Josephson effects

Epitaxial growth of BaTiO3 thin films by plasma‐enhanced metalorganic chemical vapor deposition

C. S. Chern, J. Zhao, L. Luo, P. Lu, Y. Q. Li, P. Norris, B. Kear, F. Cosandey, C. J. Maggiore, B. Gallois, and B. J. Wilkens

Appl. Phys. Lett. 60, 1144 (1992); http://dx.doi.org/10.1063/1.106433 (3 pages) | Cited 30 times

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High‐quality BaTiO3 thin films have been epitaxially grown on (001) LaAlO3 and (001) NdGaO3 substrates by plasma‐enhanced metalorganic chemical vapor deposition at a substrate temperature of 680 °C. X‐ray diffraction θ–2θ, ω, and ϕ scan results all indicate that single‐crystalline BaTiO3 thin films were epitaxially grown on the substrates with 〈100〉 orientation perpendicular to the substrates. The high degree of epitaxial crystallinity is further confirmed by Rutherford backscattering spectrometry which gives a minimum yield of 7.5% and 11% for films deposited on LaAlO3 and NdGaO3, respectively. Cross‐section high‐resolution electron microscopy images also showed that the layer epitaxy of BaTiO3 was characterized by an atomically abrupt film/substrate interface. Scanning electron micrographs showed that these films had very smooth surface morphologies.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.80.-e Ferroelectricity and antiferroelectricity
77.55.-g Dielectric thin films
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