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6 Feb 1995

Volume 66, Issue 6, pp. 653-777

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Negative photoconductivity in semiconductor heterostructures

A. S. Chaves and H. Chacham

Appl. Phys. Lett. 66, 727 (1995); http://dx.doi.org/10.1063/1.114113 (3 pages) | Cited 26 times

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Literature data on negative photoconductivity in GaAs/AlGaAs modulation doped heterojunctions and InAs/AlGaSb undoped quantum wells are explained in terms of electron–hole pair generation in the large gap layer, with subsequent charge separation and majority carrier annihilation in the well. This effect can be classified in two different limits, depending on the position of the quasi‐Fermi level μ in the large gap layer. The limit with μ on the conduction band corresponds to the GaAs/AsGaAs heterostructures, and we are able to reproduce quantitatively the available experimental results. We also show that the limit with μ on the middle of the gap corresponds to the InAs/AlGaSb heterostructures. © 1995 American Institute of Physics.
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72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects
71.55.Eq III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Hot electron transport in SiO2 probed with a scanning tunnel microscope

R. Ludeke, A. Bauer, and E. Cartier

Appl. Phys. Lett. 66, 730 (1995); http://dx.doi.org/10.1063/1.114114 (3 pages) | Cited 32 times

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Hot electrons injected with a scanning tunnel microscope (STM) tip into Pt/SiO2/Si(100) structures were detected as a collector current in the Si by using a STM configuration known as ballistic electron emission microscopy. The collector current, observed for STM tip potentials ≳4 V and for oxide biases ≥0 V, is direct evidence for electron transmission through the conduction band of the SiO2. Negative oxide biases delayed the onset of current to correspondingly higher tip potentials. A simple model was used to extract the energy and bias dependent transmission probabilities from the experimental data for a 62 Å SiO2 layer. The results are compared with Monte Carlo calculations. © 1995 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.61.Ng Insulators
73.50.Fq High-field and nonlinear effects

Passivation of an n‐type GaAs surface with an As2S3 film

Yoichi Mada and Kazumi Wada

Appl. Phys. Lett. 66, 733 (1995); http://dx.doi.org/10.1063/1.114115 (3 pages) | Cited 3 times

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This letter describes the passivation of an n‐type GaAs surface using an arsenic trisulfide (As2S3) film. Metal–insulator—semiconductor diodes were fabricated with an evaporated As2S3 film as an insulator. In the inversion region, the capacitance–voltage curve shows deep depletion, that coincides with the depletion theory. In the accumulation region, surface Fermi level movement is blocked 0.25 eV below the conduction‐band minimum due to a high density of interface states. The minimum interface state density is found to be about 1–2×1011 eV−1 cm−2. © 1995 American Institute of Physics.
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73.20.-r Electron states at surfaces and interfaces
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Room temperature optical absorption characteristics of GaAs/AlGaAs multiple quantum well structures under external anisotropic strain

Man‐fang Huang, Elsa Garmire, Afshin Partovi, and Minghwei Hong

Appl. Phys. Lett. 66, 736 (1995); http://dx.doi.org/10.1063/1.114116 (3 pages) | Cited 7 times

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We report the room temperature anisotropic absorption characteristics of a GaAs/AlGaAs multiple quantum well structure under biaxial anisotropic strain that was achieved by bonding to an x‐cut LiTaO3 substrate at 150 °C, with the [110] and [1☒10] directions of the multiple quantum well along the y and z axes of LiTaO3, respectively. A stronger heavy hole excitonic feature can be observed when the polarization of the incident light is in the compression direction, which thus results in larger quantum confined Stark effect. An absorption coefficient change of 0.6 μm−1 was observed for an applied field of 7.4 V/μm. This change in absorption coefficient is 1.5 times the value obtainable from a multiple quantum well without strain. © 1995 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Very strong negative differential resistance real‐space transfer transistor using a multiple δ‐doping GaAs/InGaAs pseudomorphic heterostructure

C. L. Wu, W. C. Hsu, M. S. Tsai, and H. M. Shieh

Appl. Phys. Lett. 66, 739 (1995); http://dx.doi.org/10.1063/1.114117 (3 pages) | Cited 6 times

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We present the observation of an effective real‐space transfer process of hot electrons resulting in a very strong negative differential resistance in GaAs/In0.25Ga0.75As/GaAs pseudomorphic heterostructure by growing symmetrically double δ‐doping layers on both sides of the InGaAs channel. By Hall measurements, the proposed structure shows carrier mobility as high as 4500 (14 100) cm2/V s at 300 (77) K which is suitable for high‐frequency operations. Meanwhile, this structure with a 5×100 μm2 emitter channel reveals extremely sharp charge injection, broad current valley range (≳3 V), high transconductance (over 23.5 S/mm), high current driving capability, and high peak‐to‐valley current ratio (up to 156 000). We also carried out secondary‐ion mass spectrometry profiles to confirm the quality of the proposed structure. © 1995 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Mx High-frequency effects; plasma effects
73.61.Ey III-V semiconductors

Spatial distribution of light‐induced defects in hydrogenated amorphous silicon

Jiang‐Huai Zhou, Minoru Kumeda, and Tatsuo Shimizu

Appl. Phys. Lett. 66, 742 (1995); http://dx.doi.org/10.1063/1.114118 (3 pages) | Cited 6 times

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We have deduced the spatial distribution of defects in light‐soaked hydrogenated amorphous silicon (a‐Si:H) from the thickness dependence of the areal defect density using a large number of film thicknesses, ranging from 0.05 to 8.7 μm. The light soaking was done with strong white light generated by a Xe lamp with an infrared‐cut filter and the defects were measured using electron spin resonance. The distribution of defects is found to be highly nonuniform and has an inverse power‐law form Nv(x)=Ax−α, where Nv(x) is the defect density at depth x measured from the surface, and A and α (≊0.6) are constants and depend on the light‐soaking time. Our results show unambiguously that the Staebler–Wronski effect is a bulk effect, however the regions close to the surface are affected much more by light soaking than the regions deep in the bulk of the sample. © 1995 American Institute of Physics.
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71.55.Jv Disordered structures; amorphous and glassy solids
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Electroluminescence and photoluminescence of Ge‐implanted Si/SiO2/Si structures

K. V. Shcheglov, C. M. Yang, K. J. Vahala, and Harry A. Atwater

Appl. Phys. Lett. 66, 745 (1995); http://dx.doi.org/10.1063/1.114080 (3 pages) | Cited 41 times

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Electroluminescent devices were fabricated in SiO2 films containing Ge nanocrystals formed by ion implantation and precipitation during annealing at 900 °C, and the visible room‐temperature electroluminescence and photoluminescence spectra were found to be broadly similar. The electroluminescent devices have an onset for emission in reverse bias of approximately −10 V, suggesting that the mechanism for carrier excitation may be an avalanche breakdown caused by injection of hot carriers into the oxide. The electroluminescent emission was stable for periods exceeding 6 h. © 1995 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.66.Sq Composite materials

Role of misfit dislocations on pseudomorphic high electron mobility transistors

M. Meshkinpour, M. S. Goorsky, G. Chu, D. C. Streit, T. R. Block, and M. Wojtowicz

Appl. Phys. Lett. 66, 748 (1995); http://dx.doi.org/10.1063/1.114081 (3 pages) | Cited 20 times

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The relationship between structural defects and device performance of In0.21Ga0.79As/(Al,Ga)As high electron mobility transistors with different In0.21Ga0.79As channel thicknesses (75–300 Å) was analyzed. Using triple axis x‐ray diffraction and transmission electron microscopy, we determined that the presence of misfit dislocations along only one of the 〈110〉 directions did not impair device performance. In fact, the sample with the highest cutoff frequency possessed the misfit dislocations along one 〈110〉 direction. However, for thicker samples, with an orthogonal array of misfit dislocations, the device parameters were significantly degraded. We also determined that x‐ray diffuse scattering correlates strongly with device performance, making this nondestructive technique useful for device performance evaluation. © 1995 American Institute of Physics.  
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.30.Tv Field effect devices
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Fabrication of lateral npn‐phototransistors with high gain and sub‐μm spatial resolution

P. Baumgartner, C. Engel, G. Abstreiter, G. Böhm, and G. Weimann

Appl. Phys. Lett. 66, 751 (1995); http://dx.doi.org/10.1063/1.114082 (3 pages) | Cited 9 times

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A novel kind of phototransistor with high gain and sub‐μm spatial resolution is fabricated by focused laser beam‐induced Zn doping of an n‐modulation doped GaAs/Al0.4Ga0.6As quantum well structure. To produce this lateral npn‐structure, p‐doped lines are directly written over a mesa without degrading the quality of the sample. The local Zn doping causes an effective potential barrier for electrons. Photogenerated holes reduce this barrier and amplify the thermionic electron current. Spatially resolved photocurrent measurements show typical responsivities above 103 A/W and linewidths as small as 605 nm. © 1995 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.40.Hp Lithography, masks and pattern transfer

Second subband population in δ‐doped Al0.48In0.52As/Ga0.47In0.53As heterostructures

Ikai Lo, W. C. Mitchel, M. Ahoujja, J.‐P. Cheng, A. Fathimulla, and H. Mier

Appl. Phys. Lett. 66, 754 (1995); http://dx.doi.org/10.1063/1.114083 (3 pages) | Cited 19 times

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We have observed the population of the second two‐dimensional electron subband in δ‐doped Al0.48In0.52As/Ga0.47In0.53As heterostructures by Shubnikov–de Haas measurements. After illuminating the samples at low temperature, the electron density increases from 17.3 to 18.2×1011 cm−2 for the first subband and from 3.6 to 4.1×1011 cm−2 for the second subband. The population of the second subband begins when the first subband is filled at a density of 10.3×1011 cm−2. The effective mass of the second subband is equal to (0.045±0.003)m0, indicating significant band nonparabolicity in the Ga0.47In0.53As well. © 1995 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
73.50.Pz Photoconduction and photovoltaic effects

Reactivity at the Al/Si3N4 interfaces

J. Avila and J. L. Sacedón

Appl. Phys. Lett. 66, 757 (1995); http://dx.doi.org/10.1063/1.114084 (3 pages) | Cited 3 times

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The reactivity of the Al/Si3N4/Si(100) system has been studied using x‐ray photoelectron spectroscopy (XPS). The Si3N4 overlayer was prepared on Si(100) by N ion implantation and subsequent annealing. The deposition at 673 K of Al on a 18 Å Si3N4 overlayer leads to the total reduction of the Si3N4 overlayer and the aluminum nitridation. The reaction also takes place at room temperature (RT) but to a lesser degree. The stability of a RT formed Al/Si3N4/Si structure was examined by increasing the sample temperature up to 673 K. In this way, the near complete reduction of a 24 Å Si3N4 overlayer was obtained. These results show the instability of the Al/Si3N4 interface at moderate annealing temperatures. © 1995 American Institute of Physics.
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68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
85.40.Hp Lithography, masks and pattern transfer

Thermally stable, low specific resistance (1.30×10−5 Ω cm2) TiC Ohmic contacts to n‐type 6Hα‐SiC

A. K. Chaddha, J. D. Parsons, and G. B. Kruaval

Appl. Phys. Lett. 66, 760 (1995); http://dx.doi.org/10.1063/1.114085 (3 pages) | Cited 28 times

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An array of transfer length measurement (TLM) structures was formed on an electrically isolated (0001) n+6Hα‐SiC epilayer. The n+6Hα‐SiC epilayer contained an in situ incorporated nitrogen concentration of 4×1019 cm−3. The specific contact resistance (ρc), sheet resistance (Rs), contact resistance (Rc), and transfer length (LT) were calculated from resistance (RT) versus contact spacing (d) measurements obtained from 17 TLM structures. The linear curves used for these calculations were fit to the RT versus d data by calculating the standard error of linear regression of RT on d; where, the average correlation coefficient with a straight line was 1.0000 and the average standard error of linear regression of RT on d was 0.08 Ω. The resulting average values were: ρc=1.30×10−5 Ω cm2, Rs=14.4 Ω/square, Rc=1.6 Ω, and LT=9.5 μm. The (111) TiC contacts, epitaxially grown by chemical vapor deposition, were thermally and chemically stable at 1400 °C. The TiC contacts could not be scratched with a tungsten carbide scriber, nor delaminated from the 6Hα‐SiC substrate. © 1995 American Institute of Physics.
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73.40.Cg Contact resistance, contact potential
73.40.Ns Metal-nonmetal contacts
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Subpicosecond, resonant refractive index changes in germanium near 1.5 μm

G. Mak and H. M. van Driel

Appl. Phys. Lett. 66, 763 (1995); http://dx.doi.org/10.1063/1.114086 (3 pages) | Cited 4 times

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The refractive index changes have been time resolved in crystalline Ge near the direct‐band‐gap (0.8 eV, 1.55 μm) following femtosecond pulse excitation at room temperature. Measurements were made for 1.485<λ<1.55 μm using degenerate pump‐probe transmission and reflection spectroscopy with 120 fs pulses from an optical parametric oscillator. Resonant excitation leads to large refractive index changes (≳10−3 for 1017 cm−3 carrier density) dominated by band filling and carrier screening effects. Unlike the much slower recovery observed in direct gap semiconductors, the refractive index change disappears with a time constant of 230 fs due to intervalley scattering of electrons to the lower energy L valley in this indirect‐gap semiconductor. © 1995 American Institute of Physics.
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78.47.-p Spectroscopy of solid state dynamics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.65.Pc Optical bistability, multistability, and switching, including local field effects

Electrochemical etching of Si(001) in NH4F solutions: Initial stage and {111} microfacet formation

Shueh‐Lin Yau, Kazutoshi Kaji, and Kingo Itaya

Appl. Phys. Lett. 66, 766 (1995); http://dx.doi.org/10.1063/1.114087 (3 pages) | Cited 31 times

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In situ scanning tunneling microscopy (STM) has been used to examine the etching of an n‐Si(001) electrode in 0.1 M NH4F. Cathodic polarization facilitated chemical etching of Si(001) to give {111} microfacets as a result of the tendency of Si to form a monohydride terminated surface. Time‐dependent in situ STM atomic images were obtained to demonstrate the preferential etching at the kinks and steps. From the results of the time‐dependent imaging, local etching rates were evaluated for the specific crystallographic directions. A Si(001):H‐(1×1) square structure was also obtained, demonstrating the presence of dihydride configuration in the beginning of the etching. © 1995 American Institute of Physics.
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81.65.-b Surface treatments
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)

Josephson effects in YBa2Cu3Oy grain boundary junctions on (100)MgO bicrystal substrates

Kiejin Lee and Ienari Iguchi

Appl. Phys. Lett. 66, 769 (1995); http://dx.doi.org/10.1063/1.114088 (3 pages) | Cited 12 times

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The grain boundary YBa2Cu3Oy(YBCO) Josephson junctions are fabricated on (100)MgO bicrystal substrates with a misorientation angle of 24° and the microwave properties of Josephson effects are studied up to millimeter‐wave range. Strong [100]//[010] and [010]//[100] in‐plane orientations are observed at the junction interface of a YBCO film, whose microscopic geometries are discussed in connection with the observed Josephson effects. The directly observed maximum Josephson microwave self‐radiation powers from the junction at receiver frequencies of fREC=22 GHz and 47 GHz are 3.2×10−12 W and 5.6×10−14 W, respectively. The observed characteristic voltage (Vc) is 4.4 mV, corresponding to the frequency of about 2 THz at 4.2 K. © 1995 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects
85.25.Cp Josephson devices
74.78.-w Superconducting films and low-dimensional structures

Aging of critical currents and irreversibility line in melt textured YBa2Cu3O7

B. Martínez, F. Sandiumenge, S. Piñol, N. Vilalta, J. Fontcuberta, and X. Obradors

Appl. Phys. Lett. 66, 772 (1995); http://dx.doi.org/10.1063/1.114089 (3 pages) | Cited 8 times

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The critical currents and the irreversibility line of bulk melt textured YBa2Cu3O7 have been found to evolve with the increase of the oxygenation time. A strong field‐dependent reduction of the critical currents is observed which finally leads to a downward shift of the irreversibility line. Transmission electron microscopy micrographs of aged samples display a huge increase in the concentration of stacking faults near the microcracks and at the YBa2Cu3O7‐Y2BaCuO5 interfaces. Low field ac susceptibility measured with H∥ab shows a strong reduction of the screening capability thus meaning that nonsuperconducting planar defects parallel to the ab planes have been created. We suggest that an enhanced two‐dimensional behavior of the vortex flux lattice occurs when H∥c as a consequence of this layered defective structure. © 1995 American Institute of Physics.
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74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.72.-h Cuprate superconductors

Optical detection of local field in vinylidene fluoride copolymer

Kazushige Hasegawa, Akihiro Tomioka, and Kenjiro Miyano

Appl. Phys. Lett. 66, 775 (1995); http://dx.doi.org/10.1063/1.114090 (3 pages) | Cited 1 time

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Electro‐absorption spectroscopy has been used to monitor the local field in a ferroelectric copolymer of vinylidene fluoride and trifluoroethylene. The local‐field factor deduced is in good agreement with the previous numerical simulation. © 1995 American Institute of Physics.
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77.80.-e Ferroelectricity and antiferroelectricity
77.84.Jd Polymers; organic compounds
78.20.Jq Electro-optical effects
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