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17 Apr 1995

Volume 66, Issue 16, pp. 2013-2142

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Rapid thermal annealing of low‐temperature GaAs layers

Zuzanna Liliental‐Weber, X. W. Lin, J. Washburn, and W. Schaff

Appl. Phys. Lett. 66, 2086 (1995); http://dx.doi.org/10.1063/1.113911 (3 pages) | Cited 27 times

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Electron microscopy studies of annealed GaAs layers grown by molecular beam epitaxy at low temperature (200 °C) were used to monitor growth of As precipitates. Ostwald ripening kinetics was used to deduce a migration enthalpy of 1.4±0.3 eV for the diffusion mediating defect. A conclusive picture of the dominant diffusion mechanism can be given, attributing this value to the migration enthalpy of gallium vacancies (VGa), which is well established by other experiments. The present studies indicate that growth of As precipitates is driven by supersaturation of VGa. © 1995 American Institute of Physics.
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61.72.Qq Microscopic defects (voids, inclusions, etc.)
66.30.Lw Diffusion of other defects
68.60.Dv Thermal stability; thermal effects

Composition modulated structures in bulk‐growth Hg0.8Cd0.2Te

X. Z. Liao and T. S. Shi

Appl. Phys. Lett. 66, 2089 (1995); http://dx.doi.org/10.1063/1.113912 (3 pages) | Cited 1 time

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High‐resolution transmission electron microscopy and selected area electron diffraction have been used to study Hg0.8Cd0.2Te wafer. Two kinds of chemical composition modulated structures were found. One is a one‐dimensional modulation with modulated wave vector q∗=(a∗−b∗)/5.6 and the other two‐dimensional modulation with modulated wave vectors q1∗=(a∗−b∗)/5.6 and q2∗=(a∗−b∗)/11.2−0.22c∗. Both structures have a common modulated wavelength of 2.54 nm. © 1995 American Institute of Physics.
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81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
61.66.Fn Inorganic compounds
68.55.-a Thin film structure and morphology

Measurement of the recombination velocity at single crystalline/polycrystalline GaAs interfaces using time‐resolved photoluminescence

Kazuhiro Mochizuki, Jun‐ichi Kasai, and Tomonori Tanoue

Appl. Phys. Lett. 66, 2092 (1995); http://dx.doi.org/10.1063/1.113913 (3 pages) | Cited 1 time

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The recombination velocity at single crystalline/polycrystalline Be‐doped GaAs interfaces is measured using time‐resolved photoluminescence. Samples with AlGaAs/GaAs double heterostructures are grown by molecular beam epitaxy on GaAs substrates patterned with SiO2. For a Be doping level of 3×1016 cm−3, the interface recombination velocity at 77 K is in the range of (2 to 10)×6 cm/s, and it is independent of the polycrystal grain size. The latter is explained by assuming that the carrier capture cross section is constant on the polycrystal grain surface. © 1995 American Institute of Physics.
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73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics

Luminescence of low‐temperature GaAs in a GaAs/In0.2Ga0.8As multiple quantum well structure

T. M. Cheng, C. Y. Chang, and J. H. Huang

Appl. Phys. Lett. 66, 2095 (1995); http://dx.doi.org/10.1063/1.113914 (3 pages) | Cited 1 time

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The luminescence of GaAs layers grown by molecular beam epitaxy at low substrate temperature (230 °C) in a GaAs/In0.2Ga0.8As multiple quantum well structure is presented. The near‐band‐gap emission and defect‐related emission are observed for samples annealed at high temperature (800–900 °C), but are not observed for samples annealed at lower temperature (600–700 °C). The luminescence shows a strong correlation with the spacing between As precipitates based on the transmission electron microscope observations. The evolution of luminescence of annealed low‐temperature (LT) GaAs can be reasonably explained by the buried Schottky model. © 1995 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
71.55.Eq III-V semiconductors

Femtosecond electron transport in quantum well laser structures with step‐graded confinement layers

S. Marcinkevičius, U. Olin, J. Wallin, K. Streubel, and G. Landgren

Appl. Phys. Lett. 66, 2098 (1995); http://dx.doi.org/10.1063/1.113915 (3 pages) | Cited 3 times

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Time‐resolved photoluminescence measurements of electron transport are reported in InGaAsP/InP graded‐gap separate‐confinement quantum well laser structures with a steplike grading profile. It is found that electron transfer over the graded‐gap region occurs on a subpicosecond time scale. The upper time limit for the electrons to pass one step of 22 nm width is 250 fs. The fast transfer times imply that the electron transport across the graded region is not affected by the presence of the steps. © 1995 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.47.-p Spectroscopy of solid state dynamics
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Estimation of HgCdTe band‐gap variations by differentiation of the absorption coefficient

V. Ariel, V. Garber, D. Rosenfeld, and G. Bahir

Appl. Phys. Lett. 66, 2101 (1995); http://dx.doi.org/10.1063/1.113916 (3 pages) | Cited 11 times

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A new simple nondestructive method for band‐gap estimation in HgCdTe layers is presented in this work. The theoretical approach is based on a qualitative empirical model that assumes two different regions of absorption in HgCdTe. The border between the two regions, which indicates the approximate value of the band gap, is determined by differentiation of the absorption coefficient in respect to the photon energy. The approach is verified by experimental measurements on several HgCdTe layers grown by different techniques. First, the transmission is measured by Fourier transform infrared (FTIR) spectroscopy at room temperature; then, the measured data is smoothed and the absorption coefficient extracted. The absorption coefficient is then differentiated twice in respect to the photon energy which allows estimation of the average band gap and band‐gap variations within the HgCdTe layer. It appears that this simple procedure can assist in monitoring the quality of HgCdTe layers and help predicting the cutoff wavelength of HgCdTe photodiodes. © 1995 American Institute of Physics.
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78.66.Hf II-VI semiconductors
71.20.Nr Semiconductor compounds
71.20.Ps Other inorganic compounds

Band bleaching and growth dynamics in 45%GeO2–55%SiO2 films

Kelly Simmons‐Potter and Joseph H. Simmons

Appl. Phys. Lett. 66, 2104 (1995); http://dx.doi.org/10.1063/1.113917 (3 pages) | Cited 9 times

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Photoinduced changes in the ultraviolet absorption bands of GeO2–SiO2 glasses have a clear significance in photosensitive processes. In this letter, the dynamics of bleaching and growth of absorption bands in highly photosensitive germanosilicate thin films following exposure to 248 nm excimer laser radiation are discussed. Strong evidence is found in support of a single‐photon process for the bleaching of a band at 238 nm and growth of a band at 202.5 nm as a source of photosensitivity. Calculated changes in refractive index are eight times greater than those found in two‐photon‐induced grating experiments. This suggests avenues for enhancement of photosensitive effects through proper materials conditioning. © 1995 American Institute of Physics.
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42.70.Ce Glasses, quartz
78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Improvement of SiO2/Si interface by low‐temperature annealing in wet atmosphere

N. Sano, M. Sekiya, M. Hara, A. Kohno, and T. Sameshima

Appl. Phys. Lett. 66, 2107 (1995); http://dx.doi.org/10.1063/1.113918 (3 pages) | Cited 10 times

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A postannealing technique was developed in order to improve the quality of SiO2 films formed by a parallel‐plate remote plasma chemical vapor deposition. The wave number of the antisymmetric stretching mode of Si–O–Si bonding in the SiO2 film increased from 1058 to 1069 cm−1 by an annealing in H2O vapor at 270 °C. It was estimated that averaged bonding angle of Si–O–Si was widened from 137.8° to 141.0°. The annealing in the H2O vapor ambient at 270 °C for 30 min efficiently reduced the interface trap density to 2.0×1010 cm−2 eV−1 and the effective oxide charges density from 7×1011 to 5×109 cm−2 for a metal‐oxide‐semiconductor (MOS) diode using the SiO2 film. © 1995 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.-b Surface treatments
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Delayed and continuous nucleation of islands in GaAs molecular beam epitaxy revealed by in situ scanning electron microscopy

J. Osaka, N. Inoue, and Y. Homma

Appl. Phys. Lett. 66, 2110 (1995); http://dx.doi.org/10.1063/1.113919 (3 pages) | Cited 5 times

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In situ scanning electron microscopy reveals delayed and continuous nucleation of two‐dimensional islands in the molecular beam epitaxy of GaAs. It is found that the islands do not appear until about 1/3 of a monolayer is deposited. The mechanism is discussed in terms of site dependent successive atomic layer growth processes. Nucleation continues till the islands start to coalesce. © 1995 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology

Spatial distribution of electric‐field domains in n‐doped semiconductor superlattices

S. H. Kwok, U. Jahn, J. Menniger, H. T. Grahn, and K. Ploog

Appl. Phys. Lett. 66, 2113 (1995); http://dx.doi.org/10.1063/1.113920 (3 pages) | Cited 5 times

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The spatial arrangement of electric‐field domains in heavily doped GaAs‐AlAs superlattices was investigated by depth‐resolved cathodoluminescence (CL). By measuring the CL spectra for different excitation energies of the electrons, it is shown that the high‐field domain is located near the anode. A quantitative analysis of the CL intensities suggests that there is only one domain boundary in the sample. © 1995 American Institute of Physics.
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78.60.Hk Cathodoluminescence, ionoluminescence
73.40.Gk Tunneling
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Conduction mechanism in arsenic implanted GaAs

H. Fujioka, E. R. Weber, and A. K. Verma

Appl. Phys. Lett. 66, 2116 (1995); http://dx.doi.org/10.1063/1.113921 (3 pages) | Cited 3 times

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We have investigated the electrical properties of heavily arsenic implanted GaAs, which has structural properties similar to low temperature GaAs. The electrical conduction in the lateral direction is dominated by hopping in a defect band and the resistivity after a 600 °C anneal is on the order of 103 Ω cm. However, the resistivity measured on an n‐i‐n structure in the direction perpendicular to the surface is on the order of 109 Ω cm. This huge difference in resistivity can be explained by the lack of an electrical contact to the defect band in the n‐i‐n structure. The activation energy of the resistivity in the n‐i‐n structure is 0.74 eV. This value is close to that for bulk undoped semi‐insulating wafers, in which the Fermi level is pinned at the midgap donor, EL2. A current transient spectroscopy study of this material reveals an electron trap with an activation energy of 0.82 eV, identical to the EL2. © 1995 American Institute of Physics.
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61.80.Jh Ion radiation effects
72.80.Ey III-V and II-VI semiconductors
71.55.Eq III-V semiconductors

Molecular‐beam epitaxial growth of CdTe(112) on Si(112) substrates

T. J. de Lyon, D. Rajavel, S. M. Johnson, and C. A. Cockrum

Appl. Phys. Lett. 66, 2119 (1995); http://dx.doi.org/10.1063/1.113922 (3 pages) | Cited 33 times

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High crystalline quality epitaxial CdTe(112)B/ZnTe films were deposited by molecular‐beam epitaxy directly onto vicinal Si(112) substrates, without use of GaAs interfacial layers. The films were characterized with x‐ray diffraction, optical microscopy, and wet chemical defect etching. Single crystal, twin‐free CdTe(112)B films exhibit structural quality exceeding that previously reported for CdTe(112)B heteroepitaxy on GaAs/Si(112) or GaAs(112)B substrates. X‐ray rocking curve full width at half‐maximum of 72 arcsec for CdTe(224) reflection and near‐surface etch pit densities (EPD) of 2×106 cm−2 have been observed for 8‐μm‐thick CdTe films. EPD depth profiles indicate that the threading dislocation density decreases with increasing II–VI epilayer thickness up to approximately 5 μm thickness and saturates at 2×106 cm−2 for thickness exceeding 5 μm. The CdTe epilayer orientation was observed to tilt 2° away from the Si(112) substrate orientation toward the [001] direction. © 1995 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology

Evolution of electronic properties at the p‐GaAs(Cs,O) surface during negative electron affinity state formation

V. L. Alperovich, A. G. Paulish, H. E. Scheibler, and A. S. Terekhov

Appl. Phys. Lett. 66, 2122 (1995); http://dx.doi.org/10.1063/1.113923 (3 pages) | Cited 11 times

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The evolution of surface band bending and surface photovoltage was monitored in situ by photoreflectance spectroscopy during activation of the surface of epitaxial GaAs to the state of negative electron affinity by successive deposition of cesium and oxygen in a standard ‘‘yo‐yo’’ technique. Considerable variations of the band bending (by approximately 0.3 eV) and surface photovoltage (by three orders of magnitude) were observed. It was found that the maximum of photoemission quantum yield corresponded to unexpectedly small value of the band bending φs=0.3 eV, as compared to widely accepted value of approximately 0.5 eV. © 1995 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.30.+y Surface double layers, Schottky barriers, and work functions
79.60.-i Photoemission and photoelectron spectra

Se chemical passivation and annealing treatment for GaAs Schottky diode

Huaiqi Xu, Saïd Belkouch, Cetin Aktik, and Wolfgang Rasmussen

Appl. Phys. Lett. 66, 2125 (1995); http://dx.doi.org/10.1063/1.113924 (3 pages) | Cited 5 times

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A Se chemical passivation [(NH4)2S+Se] for GaAs Schottky diodes is presented. We have found that our (NH4)2S+Se passivated Schottky diodes have more than one order of magnitude higher forward current density than the (NH4)2Sx passivated ones. In rapid thermal annealing treatment, an initial decrease and then increase of forward current density for (NH4)2Sx passivated diodes is observed. For the (NH4)2S+Se and (NH4)OH treated diodes, a steady decrease of Schottky barrier height with increased annealing temperature is observed. With or without annealing treatment, the (NH4)2S+Se passivated diodes have the lowest barrier height. © 1995 American Institute of Physics.  
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.20.At Surface states, band structure, electron density of states
81.65.-b Surface treatments

Alternating current transport and magnetic losses in Ag‐sheathed (Bi,Pb)2Sr2Ca2Cu3Ox wires

T. Fukunaga, T. Abe, A. Oota, S. Yuhya, and M. Hiraoka

Appl. Phys. Lett. 66, 2128 (1995); http://dx.doi.org/10.1063/1.113925 (3 pages) | Cited 9 times

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The ac losses are investigated on the Ag‐sheathed (Bi,Pb)2Sr2Ca2Cu3Ox superconducting wires in the rod and tape forms through an ac transport method and an ac magnetic method at 77 K. Experimental results show that the ac losses at 50 Hz for both rod and tape samples are mainly dominated by the hysteresis loss independent of the measuring method. However, the tape sample yields ac transport losses larger than the ac magnetic losses by about one order of magnitude, while the rod sample shows no difference between them. This discrepancy is explained by the difference in the geometry between both samples, which affects only the ac magnetic losses. © 1995 American Institute of Physics.
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84.71.Mn Superconducting wires, fibers, and tapes
74.72.-h Cuprate superconductors
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

High‐quality c‐axis oriented superconducting Nd1+xBa2−xCu3O7−d thin films deposited by the laser ablation method

Massoud Badaye, Furen Wang, Yukio Kanke, Kensuke Fukushima, and Tadataka Morishita

Appl. Phys. Lett. 66, 2131 (1995); http://dx.doi.org/10.1063/1.113926 (3 pages) | Cited 35 times

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High‐quality single phase Nd1+xBa2−xCu3O7−d thin films have been fabricated on SrTiO3 substrates by the laser ablation method. The resistivity of the deposited films are usually lower than that of the YBCO film. The Tc(onset) and Tc(R=0) in the optimized thin films are as high as 91 and 88 K, respectively. The crystallinity of our films are higher than the best YBCO films ever reported. The rocking curve FWHM of the (005) peaks in our thin films is typically 0.05°, which is superior to the best reported YBCO films. © 1995 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
81.15.Fg Pulsed laser ablation deposition

Specific capacitance of Nb/AlOx/Nb Josephson junctions with critical current densities in the range of 0.1–18 kA/cm2

M. Maezawa, M. Aoyagi, H. Nakagawa, I. Kurosawa, and S. Takada

Appl. Phys. Lett. 66, 2134 (1995); http://dx.doi.org/10.1063/1.113927 (3 pages) | Cited 25 times

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The specific capacitance Cs of Nb/AlOx/Nb Josephson tunnel junction has been measured by means of the superconducting quantum interference device (SQUID) resonance technique. We have investigated the junctions with critical current densities Jc in the range of 0.1–18 kA/cm2 and found that 1/Cs linearly depends on a logarithm of Jc. This suggests that the barrier thickness is moderately uniform in the junction area and increases continuously during growth. The results also show that increasing Jc reduces time constants of the junction. © 1995 American Institute of Physics.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.50.+r Tunneling phenomena; Josephson effects
85.25.Cp Josephson devices

Characteristics of oxygen over‐reduced Nd1.85Ce0.15CuO4−y films

S. N. Mao, Wu Jiang, X. X. Xi, Qi Li, J. L. Peng, R. L. Greene, T. Venkatesan, D. Prasad Beesabathina, L. Salamanca‐Riba, and X. D. Wu

Appl. Phys. Lett. 66, 2137 (1995); http://dx.doi.org/10.1063/1.113928 (3 pages) | Cited 8 times

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We have studied the oxygen doping effect in thin Nd1.85Ce0.15CuO4−y (NCCO) films. Contrary to the common believe that the disappearance of superconductivity in the over‐reduced NCCO samples is a consequence of phase decomposition, we found that there exists an over‐reduced region in which the crystallographic structure of the film remains essentially the same as in the optimum‐oxygen doped region, but the film becomes insulating. Rutherford backscattering spectroscopy channeling analysis reveals that the oxygen over‐reduction increases atomic distortion in the lattice. This work provides strong support to previous transport studies by Jiang et al. [Phys. Rev. Lett. 73, 1291 (1994)], which suggested the existence of both electron and hole carriers in superconducting NCCO. © 1995 American Institute of Physics.
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74.62.Dh Effects of crystal defects, doping and substitution
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.72.-h Cuprate superconductors

Growth‐induced uniaxial in‐plane magnetic anisotropy for ultrathin Fe deposited on MgO(001) by oblique‐incidence molecular beam epitaxy

Yongsup Park, Eric E. Fullerton, and S. D. Bader

Appl. Phys. Lett. 66, 2140 (1995); http://dx.doi.org/10.1063/1.113929 (3 pages) | Cited 38 times

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In‐plane uniaxial magnetic anisotropy is observed in the magnetic hysteresis loops of ultrathin Fe films grown on MgO(001) by means of oblique‐incidence molecular beam epitaxy. The films are deposited from an angle of 45° from the surface normal in the (100) azimuth toward the [100]. The easy axis of magnetization is perpendicular to the incident Fe‐beam direction. A strong structural asymmetry is observed in x‐ray photoelectron diffraction and attributed to an oriented morphology that drives the growth‐induced magnetic anisotropy. © 1995 American Institute of Physics.
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75.70.-i Magnetic properties of thin films, surfaces, and interfaces
75.50.Bb Fe and its alloys
75.30.Gw Magnetic anisotropy
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
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