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28 Mar 1994

Volume 64, Issue 13, pp. 1601-1743

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Low temperature electron cyclotron resonance plasma etching of GaAs, AlGaAs, and GaSb in Cl2/Ar

S. J. Pearton, F. Ren, and C. R. Abernathy

Appl. Phys. Lett. 64, 1673 (1994); http://dx.doi.org/10.1063/1.111827 (3 pages) | Cited 9 times

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Sidewall etching of GaAs, AlGaAs, and GaSb in electron cyclotron resonance Cl2/Ar discharges is found to be completely suppressed by cooling the semiconductor sample to −30 °C during the process. Vertical etch rates of ≳1500 Å min−1 at 1 mTorr and −50 V dc bias are obtained for all three materials under conditions where the lateral etch rates are negligible. Ex situ chemical analysis of the sidewall shows substantially increased Cl‐containing residue on low temperature etched samples, which can be removed by a 5 min H2 plasma clean‐up step. The exploitation of temperature to control undercutting enables use of simpler gas chemistries because there is no need to form a sidewall polymer.
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81.65.-b Surface treatments
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)

Optical anisotropy and spin polarization in ordered GaInP

Su‐Huai Wei and Alex Zunger

Appl. Phys. Lett. 64, 1676 (1994); http://dx.doi.org/10.1063/1.111828 (3 pages) | Cited 23 times

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Spontaneous CuPt‐like ordering of GaxIn1−xP causes a splitting at the valence band maximum (VBM) and induces an anisotropy in the intensities of the transitions between these split VBM components and the conduction band minimum. We calculate these intensities as function of ordering parameter η, and show that the transition intensities depend strongly on the light polarization math and the degree of long‐range order η in the sample. Furthermore, for sufficiently ordered single‐subvariant sample, 100% spin polarization of emitted photoelectrons is predicted.  
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78.66.Fd III-V semiconductors
71.70.Ch Crystal and ligand fields

Kinetic pattern formation of Gd‐silicide films in lateral growth geometry

G. Molnár, G. Petô, Z. E. Horváth, and E. Zsoldos

Appl. Phys. Lett. 64, 1679 (1994); http://dx.doi.org/10.1063/1.111829 (2 pages) | Cited 4 times

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The solid phase reaction of gadolinium thin film and silicon substrate was investigated in lateral growth geometry with the help of periodic titanium protective stripes by optical microscopy. In the lateral reaction zone the shape of the interface between gadolinium and Gd silicide was very complicated and showed pattern formation. This silicide growth can be described as a kinetic process modified by the structure of the Gd film in contrast to the previously proposed simple nucleation.
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68.55.-a Thin film structure and morphology
68.35.Fx Diffusion; interface formation
82.40.Bj Oscillations, chaos, and bifurcations

Cyclotron effective mass of holes in Si1−xGex/Si quantum wells: Strain and nonparabolicity effects

J.‐P. Cheng, V. P. Kesan, D. A. Grutzmacher, and T. O. Sedgwick

Appl. Phys. Lett. 64, 1681 (1994); http://dx.doi.org/10.1063/1.111830 (3 pages) | Cited 12 times

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The Ge‐composition dependence of cyclotron effective mass of quasi‐two‐dimensional holes in strained Si1−xGex/Si quantum well structures has been investigated by far‐infrared magneto‐optical spectroscopy at low temperatures and high magnetic fields up to 23 T. The in‐plane effective mass determined from cyclotron resonance energies is much less than that of unstrained Si1−xGex alloys and decreases systematically from 0.40me to 0.29me as the Ge composition increases from x=0.13 to x=0.37, indicating the importance of the strain effect on the valence‐band structure. The nonparabolicity correction is significant in explaining the discrepancy between the measured values and the calculated band‐edge masses.
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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
78.66.Db Elemental semiconductors and insulators
78.66.Li Other semiconductors

Detection of hydrogen‐plasma‐induced defects in Si by positron annihilation

P. Asoka‐Kumar, H. J. Stein, and K. G. Lynn

Appl. Phys. Lett. 64, 1684 (1994); http://dx.doi.org/10.1063/1.111831 (3 pages) | Cited 17 times

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We report a positron annihilation study of defects created in Si by rf hydrogen‐plasma exposure at 275 °C. Analysis of positron annihilation spectroscopy data indicates voidlike structures in a defective ayer extending to ≊14 nm from the surface at a concentration of 1.9±0.5×1020 cm−3. The Doppler broadening parameter for the annihilation gamma rays is strongly correlated to the hydrogen coverage of the void surfaces, voids remain in the Si to at least 800 °C while the hydrogen is desorbed from their surfaces between 600 and 800 °C.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.70.Bj Positron annihilation
81.65.-b Surface treatments

Candela‐class high‐brightness InGaN/AlGaN double‐heterostructure blue‐light‐emitting diodes

Shuji Nakamura, Takashi Mukai, and Masayuki Senoh

Appl. Phys. Lett. 64, 1687 (1994); http://dx.doi.org/10.1063/1.111832 (3 pages) | Cited 1271 times

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Candela‐class high‐brightness InGaN/AlGaN double‐heterostructure (DH) blue‐light‐emitting diodes (LEDs) with the luminous intensity over 1 cd were fabricated. As an active layer, a Zn‐doped InGaN layer was used for the DH LEDs. The typical output power was 1500 μW and the external quantum efficiency was as high as 2.7% at a forward current of 20 mA at room temperature. The peak wavelength and the full width at half‐maximum of the electroluminescence were 450 and 70 nm, respectively. This value of luminous intensity was the highest ever reported for blue LEDs.  
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85.60.Jb Light-emitting devices
85.40.Hp Lithography, masks and pattern transfer
78.60.Fi Electroluminescence
78.66.Fd III-V semiconductors

Temperature‐dependent study of spin‐dependent recombination at silicon dangling bonds

D. Vuillaume, D. Deresmes, and D. Stiévenard

Appl. Phys. Lett. 64, 1690 (1994); http://dx.doi.org/10.1063/1.111833 (3 pages) | Cited 7 times

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Electrical detection of magnetic resonance is used in a large temperature range (150–350 K) to analyze the spin‐dependent recombination properties of silicon dangling bonds at the Si‐SiO2 interface (created by high‐field electron injections) and of silicon dangling bond clusters in bulk silicon (created by electron irradiations). Quite different temperature spin‐dependent recombination behaviors are observed for these two kinds of silicon dangling bonds. These features are related to the respective behaviors of their nonradiative capture processes, which are independently determined by deep level transient spectroscopy. Moreover, we show that only the Pb0 center is observed at the Si‐SiO2 interface after high‐field electron injection. The Pb1 center is not observed by electrically detected magnetic resonance in this large temperature range.
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61.43.Dq Amorphous semiconductors, metals, and alloys

High efficiency chemical etchant for the formation of luminescent porous silicon

Michael T. Kelly, Jonathan K. M. Chun, and Andrew B. Bocarsly

Appl. Phys. Lett. 64, 1693 (1994); http://dx.doi.org/10.1063/1.111834 (3 pages) | Cited 24 times

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Hydrofluoric acid solutions containing high concentrations of the ion NO+ produce an etchant capable of reproducibly generating a porous silicon layer on both single‐crystal and polycrystalline silicon surfaces. Room‐temperature photoluminescence from porous silicon that has been chemically etched in such solutions has been observed. The photoluminescent intensity is superior to that obtained using HNO3/HF based stain etches. Reproducibility with respect to etch induction time, and the quality of the porous silicon layer are also improved when compared to classic stain etchants. Although, prior work has suggested that HNO2 is the active oxidant in silicon stain etching processes, the present work points to NO+ as the active species.
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78.55.Hx Other solid inorganic materials
81.65.-b Surface treatments
78.66.Db Elemental semiconductors and insulators
82.45.-h Electrochemistry and electrophoresis

Reduced phosphorus loss from InP surface during hydrogen plasma treatment

Sathya Balasubramanian, Vikram Kumar, and N. Balasubramanian

Appl. Phys. Lett. 64, 1696 (1994); http://dx.doi.org/10.1063/1.111835 (3 pages) | Cited 16 times

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A new method for plasma hydrogenation of InP with a reduced phosphorus loss is reported. The loss of P from InP surface is suppressed by the use of a sacrificial InP wafer kept directly in the plasma while the test sample is kept away from it in a downstream geometry. It is shown using photoluminescence that the P vacancy related transitions are considerably reduced for InP hydrogenated in the presence of a sacrificial wafer when compared to the one hydrogenated without it. The results suggest the utility of the sacrificial InP wafer in providing a P overpressure during H plasma exposure.
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78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors

Fabrication of three‐terminal resonant tunneling devices in silicon‐based material

A. Zaslavsky, K. R. Milkove, Y. H. Lee, K. K. Chan, F. Stern, D. A. Grützmacher, S. A. Rishton, C. Stanis, and T. O. Sedgwick

Appl. Phys. Lett. 64, 1699 (1994); http://dx.doi.org/10.1063/1.111838 (3 pages) | Cited 2 times

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Laterally gated three‐terminal resonant tunneling devices have been fabricated from Si/Si1−xGex double‐barrier structures grown by atmospheric pressure chemical vapor deposition. The gate is insulated from the submicrometer vertical channel by a low‐temperature oxide and the entire fabrication scheme is compatible with current silicon technology. At T=77 K the resonant peak current can be modulated by 25% by applying a moderate gate voltage; at T=4.2 K, current modulation reaches 50%. We present calculations demonstrating that devices fabricated from optimized Si/Si1−xGex structures will pinch off fully at moderate gate voltages and operate at liquid nitrogen temperatures.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Gk Tunneling

Si/Ge/S multilayer passivation of GaAs(100) for metal‐insulator‐semiconductor capacitors

Z. H. Lu, D. Landheer, J.‐M. Baribeau, L. J. Huang, and W. W. Lau

Appl. Phys. Lett. 64, 1702 (1994); http://dx.doi.org/10.1063/1.111839 (3 pages) | Cited 18 times

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We describe a new multilayer passivation method on GaAs(100), an ex situ method that doesn’t require GaAs epitaxy. Thin 20 Å Si films or thin films consisting of 15 Å Si and 5 Å Ge were grown on (NH4)2S cleaned and S passivated GaAs(100) wafers. High‐energy resolution x‐ray photoelectron spectroscopy has been used to study the chemical structure of the buried GaAs surfaces. As and Ga 3d core level studies show that the surface is free of gallium and arsenic oxides as well as elementary As. The Ga‐S‐Ga bridge bond termination is found preserved on the buried GaAs surface. SiNx/Si/Ge/S/GaAs and SiNx/Si/S/GaAs capacitors have been made and analyzed using quasistatic and high frequency capacitance‐voltage measurements. Using the high‐low method, an interface state density of about 1012 cm−2 eV−1 is obtained. The modulation of the surface potential is the highest reported for a method not requiring GaAs epitaxy.
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84.32.Tt Capacitors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.40.Rs Electrical and magnetic properties related to treatment conditions

Picosecond carrier escape by resonant tunneling in pseudomorphic InGaAs/GaAsP quantum well modulators

N. M. Froberg, A. M. Johnson, K. W. Goossen, J. E. Cunningham, M. B. Santos, W. Y. Jan, T. H. Wood, and C. A. Burrus

Appl. Phys. Lett. 64, 1705 (1994); http://dx.doi.org/10.1063/1.111840 (3 pages) | Cited 3 times

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We have used time‐resolved transmission and photocurrent measurements at 1.06 μm to study carrier sweepout in strain‐relaxed InGaAs/GaAs and strain‐balanced InGaAs/GaAsP quantum well modulators. Our results show carrier sweepout on a picosecond time scale from both structures, in agreement with the high saturation intensities measured for these devices. Carrier escape from the InGaAs/GaAs structure is facilitated by a low band offset and occurs in tens of picoseconds even without external bias. In the InGaAs/GaAsP structure, which has a much larger band offset, resonant tunneling reduces the sweepout time from 1.8 ns at zero bias to 10 ps at −6 V.
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73.40.Gk Tunneling
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.47.-p Spectroscopy of solid state dynamics
85.60.-q Optoelectronic devices

Strained In0.40Al0.60As window layers for indium phosphide solar cells

R. K. Jain, G. A. Landis, D. M. Wilt, and D. J. Flood

Appl. Phys. Lett. 64, 1708 (1994); http://dx.doi.org/10.1063/1.111990 (3 pages) | Cited 5 times

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The efficiency of indium phosphide solar cells might be improved by a wide‐band‐gap window layer. In this work we calculate the performance of InP solar cells with a strained (pseudomorphic) In0.40Al0.60As window layer. Calculations show that the efficiencies of baseline and optimized p+n cells are increased to more than 22% and 24% (AM0, 25 °C), respectively, for In0.40Al0.60As window layer of 10 nm thickness. Comparatively little improvement is found for n+p cells.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Pz Photoconduction and photovoltaic effects
73.61.Ey III-V semiconductors

Negative differential resistance at room temperature in δ ‐doped diodes grown by Si‐molecular beam epitaxy

M. R. Sardela, H. H. Radamson, and G. V. Hansson

Appl. Phys. Lett. 64, 1711 (1994); http://dx.doi.org/10.1063/1.111813 (3 pages) | Cited 7 times

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Negative differential resistance effects at room temperature in delta‐doped diodes grown by silicon‐molecular beam epitaxy are reported. High tunneling current densities (≊4 kA/cm2) and peak‐to‐value ratios close to 1.1 were achieved.
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85.60.Jb Light-emitting devices
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Electronic mobility gap structure and deep defects in amorphous silicon‐germanium alloys

Thomas Unold, J. David Cohen, and Charles M. Fortmann

Appl. Phys. Lett. 64, 1714 (1994); http://dx.doi.org/10.1063/1.111814 (3 pages) | Cited 9 times

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Amorphous hydrogenated silicon‐germanium alloys have been studied using a variety of junction‐capacitance techniques to establish the dependence of the mobility gap electronic structure and the density of deep defects on the germanium content. The Urbach tail slope is observed to be nearly constant over the whole alloy range. The energy position of the dominant deep defect band near midgap is deduced and evidence for a shallower unoccupied defect band undergoing a large lattice relaxation is also observed. The total density of deep defects is found to increase exponentially with increasing germanium content and the details of this increase are shown to be consistent with a weak bond to dangling bond conversion model.
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71.55.Ht Other nonmetals

Pressure dependence of deep level transitions in AgGaSe2

In‐Hwan Choi and Peter Y. Yu

Appl. Phys. Lett. 64, 1717 (1994); http://dx.doi.org/10.1063/1.111815 (3 pages) | Cited 5 times

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Polarized optical absorption in single crystals of AgGaSe2 has been measured as a function of hydrostatic pressure. Two polarized absorption peaks due to defects are reported. The pressure dependence of these peaks suggests that they are due to deep centers. These deep center absorption peaks merged into the fundamental absorption edge under high pressure.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.-j Infrared and Raman spectra
78.40.Fy Semiconductors

Dynamics of beam defocusing and induced absorption in CdZnTe alloys

B. Hönerlage, D. Ohlmann, M. Benhmida, R. Lévy, and J. B. Grun

Appl. Phys. Lett. 64, 1720 (1994); http://dx.doi.org/10.1063/1.111790 (3 pages) | Cited 1 time

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We study the optical nonlinear properties of bulk Cd0.13Zn0.87Te monocrystals at room temperature near the band gap. In time‐resolved test and pump experiments, they manifest themselves by a defocalization and an induced absorption of the test beam in the presence of the pump beam. By measuring the spatial intensity profile of the test pulse transmitted through the sample, we determine the real and the imaginary parts of the refractive index as functions of the photon energy and time delay between pump and test pulses.
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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)
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Impurity‐mediated growth and characterization of thin pseudomorphic germanium layers in silicon

H. J. Osten, E. Bugiel, B. Dietrich, and W. Kissinger

Appl. Phys. Lett. 64, 1723 (1994); http://dx.doi.org/10.1063/1.111791 (3 pages) | Cited 2 times

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We deposited thin germanium layers (among 4 and 12 monolayers thick) in silicon with antimony‐mediated molecular beam epitaxy. All layers were investigated with Raman spectroscopy, electroreflectance measurements, and transmission electron microscopy in the lattice‐imaging mode. The layers are continuous, no islanding could be observed even for the 1.8‐nm‐thick layers. Raman spectroscopic and electroreflectance measurements indicate some relaxation of the strained Ge layers. The interface between germanium layers and silicon buffer and cap layer are not sharp; significant intermixing could be detected.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.-a Thin film structure and morphology
68.55.Nq Composition and phase identification

Temperature dependence of the electron energy gap of high TC superconductors studied by work function spectroscopy

S. Westermeyr, R. Müller, J. Scholtes, and H. Oechsner

Appl. Phys. Lett. 64, 1726 (1994); http://dx.doi.org/10.1063/1.111989 (3 pages)

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Work function measurements with the so‐called onset technique have been used to study the temperature‐dependent behavior of the electron energy gap of YBa2Cu3O7−x superconducting films. In the temperature range from TC down to 30 K a BCS‐like behavior with gap width 2Δ0 at T=0 between 38 and 62 meV is found.
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74.78.-w Superconducting films and low-dimensional structures
73.30.+y Surface double layers, Schottky barriers, and work functions
68.37.-d Microscopy of surfaces, interfaces, and thin films

Direct observation of Josephson self‐radiation in Bi2Sr2Ca2Cu3Oy break junctions above 77 K

Kiejin Lee, Ienari Iguchi, Takeshi Hikata, and Ken‐ichi Sato

Appl. Phys. Lett. 64, 1729 (1994); http://dx.doi.org/10.1063/1.111792 (3 pages) | Cited 7 times

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We have directly observed the Josephson self‐radiation emitted from a Bi2Sr2Ca2Cu3Oy break junction at receiver frequencies fREC=11 and 47 GHz above liquid‐nitrogen temperature. The results on the current‐voltage characteristics, the dV/dI vs I curves, the harmonic Josephson self‐radiation, and the dependence of critical current on microwave self‐radiation power are well interpreted in terms of the current biased resistively shunted junction model. The maximum first‐harmonic self‐radiation powers at receiver frequencies fREC=11 and 47 GHz were P(I) =3×10−13 and P(I)=1×10−13 W at 77 K, respectively.
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74.50.+r Tunneling phenomena; Josephson effects
74.72.-h Cuprate superconductors

Determination of density of trap states at Y2O3‐stabilized ZrO2/Si interface of YBa2Cu3O7−δ /Y2O3‐stabilized ZrO2/Si capacitors

Jianmin Qiao, Kuohsu Wang, and Cary Y. Yang

Appl. Phys. Lett. 64, 1732 (1994); http://dx.doi.org/10.1063/1.111793 (3 pages) | Cited 2 times

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YBa2Cu3O7−δ/yttria‐stabilized zirconia (YSZ)/silicon superconductor‐insulator‐semiconductor capacitors are characterized with current‐voltage and capacitance‐voltage (C‐V) measurements at different temperatures between 223 and 80 K. As a result of ‘‘freezing’’ of mobile ions in YSZ, effects of trapped charge at the YSZ/Si interface dominate the device electrical properties at superconducting temperatures. Density of interface states and its temperature dependence are determined using a modified high frequency C‐V method, in which the temperature dependences of band gap, Fermi level, and active dopant and intrinsic carrier concentrations are considered. At superconducting temperatures, e.g., 80 K, the interface state density within the band gap is reduced to lower than 1×1011 cm−2 eV at midgap. The low interface state density at the YSZ/Si interface is important for acceptable performance and reliability devices made up of such capacitors.
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84.32.Tt Capacitors
74.78.-w Superconducting films and low-dimensional structures
85.30.De Semiconductor-device characterization, design, and modeling
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Fast growth of Bi2Sr2Ca2Cu3O10+x and Bi2Sr2CaCu2O8+x thin crystals at the surface of KCl fluxes

G. Balestrino, E. Milani, A. Paoletti, A. Tebano, Y. H. Wang, A. Ruosi, R. Vaglio, M. Valentino, and P. Paroli

Appl. Phys. Lett. 64, 1735 (1994); http://dx.doi.org/10.1063/1.111794 (3 pages)

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We report a novel technique to grow crystals of the high‐temperature superconductor Bi2Sr2Ca2Cu3O10+x and Bi2Sr2CaCu2O8+x (2223 and 2212 BSCCO phases), both pure and Pb substituted. The technique, based on chemical transport in a thermal gradient in molten KCl, is simple and inexpensive, and yields a continuous output of crystals, with growth times of a few minutes, i.e., orders of magnitude shorter than conventional flux methods. Depending on melt aging, crystals of either the pure 2223 or the pure 2212 BSCCO phases are obtained, having zero‐resistance temperature of 105 and 90 K, respectively, and a transport critical current density of 104 A cm−2 at liquid nitrogen temperature.
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74.78.-w Superconducting films and low-dimensional structures
81.10.Fq Growth from melts; zone melting and refining

Tapping mode atomic force microscopy in liquids

P. K. Hansma, J. P. Cleveland, M. Radmacher, D. A. Walters, P. E. Hillner, M. Bezanilla, M. Fritz, D. Vie, H. G. Hansma, C. B. Prater, J. Massie, L. Fukunaga, J. Gurley, and V. Elings

Appl. Phys. Lett. 64, 1738 (1994); http://dx.doi.org/10.1063/1.111795 (3 pages) | Cited 287 times

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Tapping mode atomic force microscopy in liquids gives a substantial improvement in imaging quality and stability over standard contact mode. In tapping mode the probe‐sample separation is modulated as the probe scans over the sample. This modulation causes the probe to tap on the surface only at the extreme of each modulation cycle and therefore minimizes frictional forces that are present when the probe is constantly in contact with the surface. This imaging mode increases resolution and reduces sample damage on soft samples. For our initial experiments we used a tapping frequency of 17 kHz to image deoxyribonucleic acid plasmids on mica in water. When we imaged the same sample region with the same cantilever, the plasmids appeared 18 nm wide in contact mode and 5 nm in tapping mode.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
42.79.Pw Imaging detectors and sensors

Vanishing Freedericksz transition threshold voltage in a chiral nematic liquid crystal

Karl A. Crandall, Michael R. Fisch, Rolfe G. Petschek, and Charles Rosenblatt

Appl. Phys. Lett. 64, 1741 (1994); http://dx.doi.org/10.1063/1.111796 (3 pages) | Cited 14 times

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A negative dielectric anisotropy cholesteric liquid crystal, oriented homeotropically in a wedged capacitance cell, was subjected to an applied electric field. The Freedericksz transition threshold voltage was found to depend on the local thickness of the sample, and was found to vanish at a thickness of order 3/2 P, where P is the pitch of the cholesteric in the bulk. The results are consistent with a continuum elastic theory. A discussion of the technological ramifications is presented.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
85.60.-q Optoelectronic devices
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