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8 Mar 1993

Volume 62, Issue 10, pp. 1035-1166

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Transport mechanisms in low‐resistance ohmic contacts to p‐InP formed by rapid thermal annealing

T. Clausen and O. Leistiko

Appl. Phys. Lett. 62, 1108 (1993); http://dx.doi.org/10.1063/1.108757 (2 pages) | Cited 9 times

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Thermionic emission across a very small effective Schottky barrier (0–0.2 eV) are reported as being the dominant transport process mechanism in very low‐resistance ohmic contacts for conventional AuZn(Ni) metallization systems to p‐InP formed by rapid thermal annealing. The barrier modulation process is related to interdiffusion and compound formation between the metal elements and the InP. The onset of low specific contact resistance is characterized by a change in the dominant transport mechanism; from predominantly a combination of thermionic emission and field emission to purely thermionic emission.
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73.40.Cg Contact resistance, contact potential
73.30.+y Surface double layers, Schottky barriers, and work functions
85.30.Hi Surface barrier, boundary, and point contact devices

Microscale elastic‐strain determination by backscatter Kikuchi diffraction in the scanning electron microscope

K. Z. Troost, P. van der Sluis, and D. J. Gravesteijn

Appl. Phys. Lett. 62, 1110 (1993); http://dx.doi.org/10.1063/1.108758 (3 pages) | Cited 35 times

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It is shown that backscatter Kikuchi diffraction in the scanning electron microscope can be used for the determination of elastic strain with μm resolution. From the shift of Kikuchi bands in backscatter Kikuchi diffraction patterns of epitaxial Si1−xGex layers on Si(100) the perpendicular elastic strain was determined to be 2.5% for x=0.34 and at 1.0% for x=0.16 with an accuracy of about 0.1%. The values found on a μm scale were in good agreement with high‐resolution x‐ray diffraction measurements averaging over mm distances.
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61.05.J- Electron diffraction and scattering
68.55.-a Thin film structure and morphology

Interpretation of photoluminescence excitation spectroscopy of porous Si layers

Lei Wang, M. T. Wilson, and N. M. Haegel

Appl. Phys. Lett. 62, 1113 (1993); http://dx.doi.org/10.1063/1.108759 (3 pages) | Cited 29 times

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Photoluminescence excitation (PLE) measurements allow one to obtain direct information on the absorption processes in porous Si leading to the strong visible luminescence which has recently been reported. This technique does not need a free‐standing porous Si sample, but the effect of layer thickness should be included in the interpretation of PLE data. In our PLE spectra, two separate absorption edges are observed and the initial one shifts to higher energies with storage time. The trends of these changes are consistent with the quantum wire model.
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78.55.Hx Other solid inorganic materials
78.66.Li Other semiconductors

Relative free energies of Si surfaces

D. M. Follstaedt

Appl. Phys. Lett. 62, 1116 (1993); http://dx.doi.org/10.1063/1.108760 (3 pages) | Cited 51 times

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Cavities are formed by ion implanting (001) Si with He and annealing at 800 °C to enlarge and to remove the He. Subsequent annealing at 600 °C results in cavities with well‐defined facets as seen in [110] cross section with transmission electron microscopy. The most frequently observed facets are {111} planes. A rounded surface is seen about the [001] direction of all cavities, and (110) facets are seen less frequently. The cavities allow the equilibrium crystal shape of Si to be examined and the relative free energies of the observed planes to be measured. The surface free energies of {001} and {110} planes are found to be 1.09±0.07 and 1.07±0.03 times that of {111} planes, respectively.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Md Surface thermodynamics, surface energies

Bound‐to‐bound intersubband transitions in a δ‐doped p‐type Si/SixGe1−x/Si quantum well

S. K. Chun, D. S. Pan, and K. L. Wang

Appl. Phys. Lett. 62, 1119 (1993); http://dx.doi.org/10.1063/1.108761 (3 pages) | Cited 4 times

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The absorption spectrum in p‐type Si/Si0.6Ge0.4/Si structure with a δ‐doped quantum well grown on Si(001) substrate is calculated using a multiband model. We have generalized the previous treatment of the depolarization effect in n‐type Si to include subband multiplicity, nonparabolicity, and valence band anisotropy. An implicit formula for the effective plasma frequency was used to conveniently include these effects in the calculation. We found that it is necessary to treat the depolarization effect in the complicated couplings among valence bands in order to explain the observed spectrum.
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78.66.Li Other semiconductors
78.30.Hv Other nonmetallic inorganics
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Saturation of multiplication factor in InGaAsP/InAlAs superlattice avalanche photodiodes

Toshiaki Kagawa, Yuichi Kawamura, and Hidetoshi Iwamura

Appl. Phys. Lett. 62, 1122 (1993); http://dx.doi.org/10.1063/1.108762 (3 pages) | Cited 3 times

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The saturation of the multiplied photocurrent at an intense illumination was studied for InGaAsP/InAlAs superlattice avalanche photodiodes. The dependence of the multiplication factor on the illumination intensity is small in comparison with conventional bulk APDs because the ionization rate ratio is larger. The multiplication factor decreases at an intense illumination mainly because of the space charge effect.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
73.50.Fq High-field and nonlinear effects
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Positive charge and interface state creation at the Si‐SiO2 interface during low‐fluence and high‐field electron injections

Abdellah Mir and Dominique Vuillaume

Appl. Phys. Lett. 62, 1125 (1993); http://dx.doi.org/10.1063/1.108763 (3 pages) | Cited 10 times

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Positive charge and interface state creation at the Si‐SiO2 interface has been studied when low‐fluence electron injections (lower than 10−3 C/cm2) are performed at high‐field (higher than 7 MV/cm) across the oxide. Temperature dependencies for the formation of both types of interface defects are examined in the range 90–300 K. It is found that positive charge formation is temperature independent, while interface state creation is thermally activated. The former result (no temperature dependence) is consistent with impact ionization in SiO2, while the latter (temperature dependence) is explained by a trap creation due to hydrogen‐related species diffusion. These results show that both mechanisms can occur together, and that they trigger two different kinds of damage at the Si‐SiO2 interface.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.20.Hb Impurity and defect levels; energy states of adsorbed species
79.20.Kz Other electron-impact emission phenomena

Picosecond carrier lifetime in erbium‐doped‐GaAs

S. Gupta, S. Sethi, and P. K. Bhattacharya

Appl. Phys. Lett. 62, 1128 (1993); http://dx.doi.org/10.1063/1.108764 (3 pages) | Cited 16 times

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The dependence of free‐carrier lifetime on erbium concentration has been measured in molecular‐beam epitaxial GaAs epilayers doped with erbium. A gradual reduction in the lifetime is observed with increased dopant incorporation. For a high doping concentration in the range of 1019 cm−3 or greater, a carrier lifetime of ∼1 ps is obtained. Due to the high resistivity of these epilayers, they can also be used as a photoconductive switch, with good responsivity. This leads to new and novel applications for rare‐earth doped III‐V semiconductors.
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73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.50.Pz Photoconduction and photovoltaic effects

Ion implantation induced defects in SiO2: The applicability of the positron probe

M. Fujinami and N. B. Chilton

Appl. Phys. Lett. 62, 1131 (1993); http://dx.doi.org/10.1063/1.108765 (3 pages) | Cited 25 times

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Boron ion implantation‐induced defects in SiO2 were investigated using slow positron annihilation spectroscopy and electron spin resonance (ESR). The defects caused by ion implantation are manifest as a particularly low S parameter in the region of the SiO2 layer in which B implantation damage occurs. The annealing behavior of the defect responsible for positron trapping was studied. The defect to which the positron is sensitive is found to be unobservable in ESR measurements. The defect is suggested to be dissolved O2 or a charged Frenkel defect, such as the negative nonbridging‐oxygen hole center (≡Si—O−).
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61.80.Jh Ion radiation effects
78.70.Bj Positron annihilation

Infrared photoconductor fabricated with HgTe/CdTe superlattice grown by molecular beam epitaxy

Yueming Qiu, Li He, Jie Li, Shixin Yuan, C. R. Becker, and G. Landwehr

Appl. Phys. Lett. 62, 1134 (1993); http://dx.doi.org/10.1063/1.108766 (3 pages) | Cited 7 times

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An infrared photoconductor fabricated with a HgTe/CdTe superlattice grown on a GaAs substrate by molecular beam epitaxy is described here for the first time. The growth procedure, device fabrication, and measurement results are described. The results show that the device has relatively high uniformity and 1000 K black‐body detectivity 2.4×109 cm Hz1/2 W−1. The photoconductivity decay method was used for determining carrier lifetime of the HgTe/CdTe superlattice, the measured lifetime is 12 μs at 77 K, which is the longest lifetime ever reported for HgTe/CdTe superlattices and we believe that the increase of lifetime is mainly due to the reduction of dimensions.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
73.50.Pz Photoconduction and photovoltaic effects
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Ultralow damage depth by electron cyclotron resonance plasma etching of GaAs/InGaAs quantum wells

T. Bickl, B. Jacobs, J. Straka, and A. Forchel

Appl. Phys. Lett. 62, 1137 (1993); http://dx.doi.org/10.1063/1.108767 (3 pages) | Cited 5 times

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Dry etch induced damage of GaAs/InGaAs/GaAs heterostructures in an electron cyclotron resonance (ECR) argon discharge has been investigated as a function of additional radio frequency self‐biasing of the sample and process pressure in argon ECR discharges. We used depth resolved photoluminescence measurements to determine the influence of the etch process on the samples. We observe a decreasing damage depth for smaller bias voltages reaching its lowest value of 1.7 nm at 20 V bias and a pressure of 0.15 Pa. For lower pressures we observe a strong increase of the damage, which is attributed predominantly to high energetic vacuum ultraviolet radiation from the ECR region.
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61.80.Jh Ion radiation effects
81.65.-b Surface treatments
78.55.Cr III-V semiconductors

p+/n/n+ InP solar cells directly on Si substrates

M. K. Lee, D. S. Wuu, and R. H. Horng

Appl. Phys. Lett. 62, 1140 (1993); http://dx.doi.org/10.1063/1.108768 (3 pages) | Cited 4 times

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p+/n/n+ InP solar cells have been fabricated directly on (100) Si substrates by low‐pressure organometallic vapor phase epitaxy. The best experimental cell without an antireflection coating exhibits an air mass one efficiency of 11.9%. The corresponding open‐circuit voltage, short‐circuit current, and fill factor are 0.78 V, 22.47 mA/cm2, and 0.63, respectively. An electrical characterization identifying loss mechanism is proposed.
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84.60.Jt Photoelectric conversion
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.66.Fd III-V semiconductors

Determination of electron recombination parameters in GaAs/AlGaAs quantum wells by impedance spectroscopy

F. Luc, E. Rosencher, and B. Vinter

Appl. Phys. Lett. 62, 1143 (1993); http://dx.doi.org/10.1063/1.108769 (3 pages) | Cited 13 times

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We show that the capture process between a three‐dimensional (3D) gas and a two‐dimensional quantum well are unambiguously characterized by impedance spectroscopy. The contact layer of an asymmetrical semiconductor‐insulator‐semiconductor diode provides the 3D gas to the conduction band of an AlGaAs barrier which interacts near thermal equilibrium with a GaAs quantum well (QW). This approach is validated by an excellent agreement between experimental results and theoretical expectations regarding the influence of electric field and temperature. We show that the natural quantity which describes this recombination is the recombination velocity in the QW, which is found to be ≊8×104 cm/s for a 60 Å GaAs/Al0.22Ga0.78As quantum well at 100 K for an electric field of 3 kV/cm, which corresponds to a capture probability of 0.013. Results indicate a decrease of the recombination velocity in the quantum well with an increasing applied electric field.
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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

Spatially resolved Raman spectroscopy of a step graded GexSi1−x strain relief structure

J. C. Tsang, F. H. Dacol, P. M. Mooney, J. O. Chu, and B. S. Meyerson

Appl. Phys. Lett. 62, 1146 (1993); http://dx.doi.org/10.1063/1.108770 (3 pages) | Cited 4 times

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The structure of a strain relief region between a Si substrate and a low dislocation density Ge film has been measured by Raman spectroscopy. The composition of the structure has been determined with ≂1000 Å resolution in the growth direction, and the upper portions shown to be largely relaxed. The presence of microscopic inhomogeneities in these alloys is suggested.
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68.55.-a Thin film structure and morphology
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.30.-j Infrared and Raman spectra

Study of characteristics of photoluminescence spectra in double‐barrier resonant tunneling structures

T. H. Wang, X. B. Mei, C. Jiang, Y. Huang, J. M. Zhou, and G. Z. Yang

Appl. Phys. Lett. 62, 1149 (1993); http://dx.doi.org/10.1063/1.108771 (3 pages) | Cited 3 times

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We have investigated photoluminescence of double‐barrier diodes under various bias voltages and observed the saturation of the broadening of the photoluminescence lines. We have also studied the integrated photoluminescence intensity with increasing applied voltages near resonant voltages for high quality samples at low temperature (4.2 K). The results of the 77 K photoluminescence experiments confirm those at 4.2 K. The saturation of the broadening is due to weak hole localization; however, the saturation of the integrated photoluminescence intensity is mainly due to reduced nonradiative recombination. Our results suggest that the hole localization may arise from interface roughness.
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78.55.Cr III-V semiconductors
73.40.Gk Tunneling
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.Fz Weak or Anderson localization

Enhancement and stabilization of porous silicon photoluminescence by oxygen incorporation with a remote‐plasma treatment

Y. Xiao, M. J. Heben, J. M. McCullough, Y. S. Tsuo, J. I. Pankove, and S. K. Deb

Appl. Phys. Lett. 62, 1152 (1993); http://dx.doi.org/10.1063/1.108772 (3 pages) | Cited 43 times

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We report a treatment that enhances and stabilizes the photoluminescence (PL) from porous Si films. Films prepared by anodization in a 50% HF/ethanol solution were annealed at 450 °C in vacuum, exposed to air, and then exposed to a remote‐hydrogen plasma. Infrared absorption spectroscopy revealed that the concentration of oxygen, rather than hydrogen, was increased by the processing steps, and that silicon dihydride species had been eliminated from the surface. The PL from a treated film was initially ∼30 times more intense than from the as‐etched films. The PL intensity increased with illumination time in air until a steady‐state intensity was reached.
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78.55.Hx Other solid inorganic materials
81.40.Tv Optical and dielectric properties related to treatment conditions
81.65.-b Surface treatments

Optical absorption evidence of a quantum size effect in porous silicon

I. Sagnes, A. Halimaoui, G. Vincent, and P. A. Badoz

Appl. Phys. Lett. 62, 1155 (1993); http://dx.doi.org/10.1063/1.108773 (3 pages) | Cited 81 times

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This study presents optical transmission measurements performed on free‐standing homogeneous porous silicon (PS) films of different porosities and substrate doping levels. The absorption coefficient curves deduced from these measurements, taking into account the total quantity of matter in the PS film, exhibit significant blue shift (up to 500 meV). These shifts, well correlated with the crystallite size variations with porosity and substrate doping observed by electron microscopy and gas adsorption experiments, are attributed to quantum size effects in the silicon microcrystallites.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Db Elemental semiconductors and insulators

Identification of nonbolometric photoresponse in YBa2Cu3O7−δ thin films based on magnetic field dependence

F. A. Hegmann and J. S. Preston

Appl. Phys. Lett. 62, 1158 (1993); http://dx.doi.org/10.1063/1.109613 (3 pages) | Cited 11 times

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Optically induced transient voltages across a current‐biased bridge structure fabricated from an epitaxial YBa2Cu3O7−δ thin film are reported. A novel technique consisting of applying a small magnetic field perpendicular to the sample was used to identify any bolometric contribution to the photoresponse. Comparison to resistance versus temperature curves with and without the field establishes a slow component in the photoresponse as bolometric and unambiguously identifies a fast component as a nonthermal transient.
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74.25.N- Response to electromagnetic fields
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors

Peltier refrigerator using a high Tc superconductor

M. G. Fee

Appl. Phys. Lett. 62, 1161 (1993); http://dx.doi.org/10.1063/1.108774 (3 pages) | Cited 5 times

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A prototype Peltier refrigerator junction for operation at around liquid nitrogen temperatures has been built consisting of a thermoelectrically active bismuth‐antimonide alloy leg and a thermoelectrically passive superconducting YBa2Cu3O7−δ leg. The junction has shown a maximum cooling of 5.35 K below a heat sink held at 79 K. Improvements in materials and design and operation in a magnetic field could result in cooling of up to 16 K.  
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85.25.Qc Superconducting surface acoustic wave devices and other superconducting devices
72.20.Pa Thermoelectric and thermomagnetic effects
74.78.Fk Multilayers, superlattices, heterostructures

Secondary ion mass spectrometry study for Josephson junction with Nb/AlOx‐Al/Nb structure

Shin’ichi Morohashi, Yuji Kataoka, Takeshi Imamura, and Shinya Hasuo

Appl. Phys. Lett. 62, 1164 (1993); http://dx.doi.org/10.1063/1.108775 (3 pages) | Cited 5 times

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We studied the interface changes of niobium (Nb) Josephson junction structures (Nb/Al/Nb and Nb/AlOx‐Al/Nb) using secondary ion mass spectrometry (SIMS). Using a cesium (Cs+) primary beam, CsM+ ions (M=H, O, OH, Nb, and Al) were monitored for cesium bombardment. In the SIMS depth profile, the CsH+ and CsO+ intensity indicated accumulation at junction interfaces, where these intensities were larger for the Al/Nb base electrode interface than for the Nb counterelectrode/Al interface. We think a layer of absorbed water vapor with a thickness a few nm, is formed on the junction interface, and is attributed to chamber outgassing. In the Nb/Al/Nb structure, the annealing changes for the Al/Nb base electrode interface were smaller than those for the Nb counterelectrode/Al interface. We confirmed that the absorbed water vapor layer plays an important role in the junction structure, that is, it acts as a barrier for grain boundary diffusion between Nb and Al.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
74.40.-n Fluctuation phenomena
85.25.Cp Josephson devices
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