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25 Mar 1996

Volume 68, Issue 13, pp. 1745-1873

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Room‐temperature stimulated emission in GaN/AlGaN separate confinement heterostructures grown by molecular beam epitaxy

T. J. Schmidt, X. H. Yang, W. Shan, J. J. Song, A. Salvador, W. Kim, Ö. Aktas, A. Botchkarev, and H. Morkoç

Appl. Phys. Lett. 68, 1820 (1996); http://dx.doi.org/10.1063/1.116024 (3 pages) | Cited 31 times

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Strong near‐ultraviolet stimulated emission was observed at room temperature in GaN/AlGaN separate confinement heterostructures (SCH) grown by molecular beam epitaxy (MBE) on sapphire substrates. The MBE grown GaN/AlGaN SCH samples exhibited stimulated emission threshold pumping powers as low as 90 kW/cm2 at room temperature under the excitation of a frequency‐tunable nanosecond laser system with a side‐pumping configuration. This represents an order of magnitude reduction over bulklike GaN. Our results suggest that the carrier confinement and waveguiding effects of the SCH samples result in a substantial decrease in the stimulated emission threshold. © 1996 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.45.+h Stimulated emission
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Atomic steps on a silicon (001) surface tilted toward an arbitrary direction

Lei Zhong, Akimichi Hojo, Yoshiro Aiba, Katuhiro Chaki, Jun Yoshikawa, and Kenro Hayashi

Appl. Phys. Lett. 68, 1823 (1996); http://dx.doi.org/10.1063/1.116025 (3 pages) | Cited 6 times

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In this letter, we show that the misorientation of a vicinal (001) surface annealed in hydrogen is accommodated by a pair of near‐Sa steps which are evolved in two perpendicular {110} independently and coordinately. We demonstrate that the deviation of surface orientation in a tiny area can be readily evaluated by inspecting the local variation of the near‐Sa step pair. We finally indicate that the atomic steps on a surface annealed in argon exhibit in contrast, no conformity with the misorientation towards an azimuth other than {110}. © 1996 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)

Generation of hole traps in thin silicon oxide layers under high‐field electron injection

Tomasz Brożek and Chand R. Viswanathan

Appl. Phys. Lett. 68, 1826 (1996); http://dx.doi.org/10.1063/1.116026 (3 pages) | Cited 10 times

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The letter reports an observation of a new degradation mechanism in thermal silicon dioxide layers on silicon, namely generation of hole traps under high‐field stressing of metal‐oxide‐semiconductor (MOS) structure. Excess hole trapping due to newly generated hole traps is observed by substrate hot‐hole injection in 9 nm oxide of p‐channel MOS transistors after high‐field Fowler‐Nordheim stress followed by standard post‐metallization annealing in nitrogen. The concentration of generated traps has a weak stress‐polarity dependence and increases with electron fluence during degrading stress. Relaxation behavior under switching oxide fields indicates that the nature of hole trapping sites is different from anomalous positive charge centers. © 1996 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.Ng Insulators
85.30.De Semiconductor-device characterization, design, and modeling

Role of hydrogen in doping of GaN

Jörg Neugebauer and Chris G. Van de Walle

Appl. Phys. Lett. 68, 1829 (1996); http://dx.doi.org/10.1063/1.116027 (3 pages) | Cited 115 times

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We investigate the interactions between hydrogen and dopant impurities in GaN, using state‐of‐the‐art first‐principles calculations. Our results for energetics and migration reveal a fundamental difference in the behavior of hydrogen between p‐type and n‐type material; in particular, we explain why hydrogen concentrations in n‐type GaN are low, and why hydrogen has a beneficial effect on acceptor incorporation in p‐type GaN. Our results identify the conditions under which hydrogen can be used to control doping in semiconductors in general. © 1996 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors

Voltage‐tunable two‐color detection by interband and intersubband transitions in a p‐i‐n‐i‐n structure

H. Schneider, C. Schönbein, and G. Bihlmann

Appl. Phys. Lett. 68, 1832 (1996); http://dx.doi.org/10.1063/1.116028 (3 pages) | Cited 6 times

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We report on a novel class of voltage‐tunable two‐color detectors, based on a quantum‐well intersubband photodetector (QWIP) and a p‐i‐n photodiode in a p‐i‐n‐i‐n configuration. In this approach, the two constituting detector structures can be optimized independently because of their different conductance characteristics. The detection concept is demonstrated for the case of an 8‐10μm GaAs/AlGaAs QWIP and a 850 nm p‐i‐n diode containing In0.08Ga0.92As quantum wells. © 1996 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.66.Fd III-V semiconductors
85.60.Gz Photodetectors (including infrared and CCD detectors)

Photocurrent multiplication in hydrogenated amorphous silicon staircase photodiode films

Kazuaki Sawada, Shinya Akata, Toshinori Takeuchi, and Takao Ando

Appl. Phys. Lett. 68, 1835 (1996); http://dx.doi.org/10.1063/1.116029 (3 pages) | Cited 2 times

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The available multiplication of photocurrent was observed in the a‐Si:H/a‐Si1−xCx:H staircase photodiode film which was fabricated by a high‐vacuum plasma enhanced chemical vapor deposition on a heavily doped n‐type silicon substrate. It was found that the saturated maximum gain is about 6 for the staircase photodiode having three conduction band steps. The fabrication process and device characteristics are reported in this letter. © 1996 American Institute of Physics.
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73.61.Jc Amorphous semiconductors; glasses
78.66.Jg Amorphous semiconductors; glasses
85.60.Dw Photodiodes; phototransistors; photoresistors

Dynamical switching behavior of n‐i‐p‐i modulator structures

U. Pfeiffer, M. Kneissl, B. Knüpfer, N. Müller, P. Kiesel, G. H. Döhler, and J. S. Smith

Appl. Phys. Lett. 68, 1838 (1996); http://dx.doi.org/10.1063/1.116030 (3 pages) | Cited 3 times

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We report on the ac switching behavior of surface‐normal electro‐optical modulators based on hetero‐n‐i‐p‐i structures. We have investigated systematically the way the transition times scale with device dimensions and present a straightforward theoretical model including sheet resistivities of n and p layers as well as contact resistances. The model is in excellent agreement with experimental data. With a voltage swing as low as 3.7 V, we achieved a single path contrast ratio in excess of 2:1 and maximum 3 dB frequencies larger than 250 MHz. © 1996 American Institute of Physics.
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42.79.Hp Optical processors, correlators, and modulators
78.66.Fd III-V semiconductors

Pd/Zn/Pd/Au and Pd/Zn/Au/LaB6/Au ohmic contacts to p‐type In0.53Ga0.47As

P. Ressel, P. W. Leech, G. K. Reeves, W. Zhou, and E. Kuphal

Appl. Phys. Lett. 68, 1841 (1996); http://dx.doi.org/10.1063/1.116031 (3 pages) | Cited 1 time

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The resistivity and interfacial characteristics of Pd/Zn/Pd/Au and Pd/Zn/Au/LaB6/Au contacts to p‐In0.53Ga0.47As have been investigated. Annealing of the contacts at 375–425 °C yielded a minimum in specific contact resistance, ρc, of 2×10−7 Ω cm2 for the Pd/Zn/Pd/Au contacts and 1×10−6 Ω cm2 for the Pd/Zn/Au/LaB6/Au configuration. The measurement of ρc for the Pd/Zn/Pd/Au system is the lowest reported for an ohmic contact to p‐In0.53Ga0.47As doped to ≤1×1019 cm−3. In the Pd/Zn/Au/LaB6/Au scheme, the minimum in ρc was the same whether the Zn was incorporated as a structural layer or as Zn ions implanted into the interfacial Pd. At ≥375 °C, the LaB6 layer limited the indiffusion of Au and the degradation of the In0.53Ga0.47As substrate. © 1996 American Institute of Physics.
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73.40.Cg Contact resistance, contact potential
85.40.Ls Metallization, contacts, interconnects; device isolation

Screening effects on the band‐gap renormalization of strained InGaAs/InGaAsP quantum well lasers lattice matched to GaAs

Seoung‐Hwan Park and Doyeol Ahn

Appl. Phys. Lett. 68, 1844 (1996); http://dx.doi.org/10.1063/1.116032 (3 pages) | Cited 3 times

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The screening effects on the band‐gap renormalization (BGR) of strained InGaAs/InGaAsP (Eg=1.6 eV) QW lasers lattice matched to GaAs are investigated theoretically, taking into account the valence‐band mixing and multisubband effects. These results are also compared with those of InGaAs/GaAs QW lasers. Without the screening effect, the BGR significantly depends on both the carrier density and the In composition. On the other hand, with the screening effect, these dependencies are expected to be reduced considerably. The BGR with the screening effect in InGaAs/GaAs lasers show weaker dependence on the In composition compared to InGaAs/InGaAsP lasers. © 1996 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Observation of lateral confinement effect in Ge quantum wires self‐aligned at step edges on Si(100)

H. Sunamura, N. Usami, Y. Shiraki, and S. Fukatsu

Appl. Phys. Lett. 68, 1847 (1996); http://dx.doi.org/10.1063/1.116033 (3 pages) | Cited 26 times

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Spontaneous formation of step‐edge Ge quantum wires and lateral quantum confinement effect are clearly observed in Si submonolayer‐Ge/Si heterostructures grown on Si(100). By depositing submonolayer equivalent Ge (Q), the Ge atoms are found to line up in a wire‐like fashion at the 〈011〉 step edges as revealed by plan‐view transmission electron microscopy. Photoluminescence (PL) peak energy shift with Q due to lateral quantum confinement of holes is clearly observed, and PL features characteristic of the quasi‐one‐dimensional system are also addressed. © 1996 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.55.Cr III-V semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Low interface trap density for remote plasma deposited SiO2 on n‐type GaN

H. C. Casey, G. G. Fountain, R. G. Alley, B. P. Keller, and Steven P. DenBaars

Appl. Phys. Lett. 68, 1850 (1996); http://dx.doi.org/10.1063/1.116034 (3 pages) | Cited 90 times

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Metal‐oxide‐semiconductor capacitors were prepared with remote plasma‐enhanced chemical vapor deposition of SiO2 at ∼300 °C on an n‐type GaN epitaxial layer grown by atmospheric pressure metalorganic chemical‐vapor deposition on a sapphire substrate. No hysteresis was observed in the high‐frequency capacitance‐voltage (C−V) measurements, and the measured C−V curve agreed with the C−V behavior calculated for an ideal oxide with the same flat‐band voltage as the measured C–V curve. The absence of hysteresis and stretchout in the measured C–V curve and the increase of capacitance with incident ultraviolet light while in deep depletion suggest a low concentration of interface traps. These results demonstrate previous predictions of the absence of Fermi‐level stabilization at the interface for the ionic crystal GaN. © 1996 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

ab‐plane anisotropy of the critical currents in twinned YBa2Cu3O7−δ superconductors

H. Safar, S. Foltyn, H. Kung, M. P. Maley, J. O. Willis, P. Arendt, and X. D. Wu

Appl. Phys. Lett. 68, 1853 (1996); http://dx.doi.org/10.1063/1.116035 (3 pages) | Cited 16 times

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We show that the in‐plane critical current density of heavily twinned YBa2Cu3O7−δ thick films is anisotropic, depending on the relative orientation between the transport electrical current and the twin boundary mosaic. We demonstrate that the critical current density in an applied magnetic field can be substantially increased by producing conductors with twin boundaries tilted 45° with respect to the electrical current flow. We show that these findings can be readily incorporated to improve the critical currents of biaxially textured YBa2Cu3O7−δ thick films deposited on metallic substrates. © 1996 American Institute of Physics.
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74.25.Sv Critical currents
74.72.-h Cuprate superconductors

Low noise YBa2Cu3O7−x SQUID magnetometers operated with additional positive feedback

D. Drung, E. Dantsker, F. Ludwig, H. Koch, R. Kleiner, John Clarke, S. Krey, D. Reimer, B. David, and O. Doessel

Appl. Phys. Lett. 68, 1856 (1996); http://dx.doi.org/10.1063/1.116036 (3 pages) | Cited 25 times

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Three magnetometers based on dc superconducting quantum interference devices (SQUIDs) fabricated from YBa2Cu3O7−x have been operated in a magnetically shielded room using a flux‐locked loop involving additional positive feedback with bias current reversal. Two of these devices, integrated multiloop dc SQUIDs with outer diameters of 7 mm, achieved white noise levels of 10 fT/√Hz for bicrystal junctions and 30 fT/√Hz for step‐edge junctions. The third magnetometer involved a flux transformer with a 10×10 mm2 pickup coil connected to a 16‐turn input coil which was inductively coupled to a bicrystal SQUID. This device achieved a white noise of 16.2 fT/√Hz. High quality magnetocardiograms were obtained without signal averaging. © 1996 American Institute of Physics.
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07.55.Ge Magnetometers for magnetic field measurements
85.25.Dq Superconducting quantum interference devices (SQUIDs)

Properties of NdBa2Cu3O7−δ thin film prepared by off‐axis rf sputtering

In‐Seon Kim, Kyu Won Lee, Yong Ki Park, and Jong‐Chul Park

Appl. Phys. Lett. 68, 1859 (1996); http://dx.doi.org/10.1063/1.116037 (3 pages) | Cited 13 times

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Thin films of NdBa2Cu3O7−δ(NdBCO) were fabricated on SrTiO3 substrates by an off‐axis rf sputtering. Disk shaped targets of 5 cm in diameter were prepared with stoichiometric composition of NdBCO by sintering at 1273 K in air. The sintered body was single phase and exhibited Tc(R=0)=92 K. The effects of several deposition parameters on the superconducting NdBCO thin films, e.g., gas pressure, substrate temperature, oxygen annealing process, and rf power were studied. The x‐ray diffraction pattern showed the deposited thin films were highly c‐axis oriented without any impurity phase. Thin films with Tc(R=0)=87 K could be obtained reproducibly at optimized conditions. Critical current density (Jc) of the patterned thin film was 106–107 A/cm2 at low temperature. © 1996 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
81.15.Cd Deposition by sputtering

A low‐noise micromachined millimeter‐wave heterodyne mixer using Nb superconducting tunnel junctions

Gert de Lange, Brian R. Jacobson, and Qing Hu

Appl. Phys. Lett. 68, 1862 (1996); http://dx.doi.org/10.1063/1.116038 (3 pages) | Cited 3 times

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A heterodyne mixer with a micromachined horn antenna and a superconductor‐insulator‐ superconductor (SIS) tunnel junction as mixing element is tested in the W‐band (75–115 GHz) frequency range. Micromachined integrated horn antennas consist of a dipole antenna suspended on a thin Si3N4 dielectric membrane inside a pyramidal cavity etched in silicon. The mixer performance is optimized by using a backing plane behind the dipole antenna to tune out the capacitance of the tunnel junction. The lowest receiver noise temperature of 30±3 K (without any correction) is measured at 106 GHz with a 3‐dB bandwidth of 8 GHz. This sensitivity is comparable to the state‐of‐the‐art waveguide and quasi‐optical SIS receivers, showing the potential use of micromachined horn antennas in imaging arrays. © 1996 American Institute of Physics.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors

Study of the leakage field of magnetic force microscopy thin‐film tips using electron holography

B. G. Frost, N. F. van Hulst, E. Lunedei, G. Matteucci, and E. Rikkers

Appl. Phys. Lett. 68, 1865 (1996); http://dx.doi.org/10.1063/1.116039 (3 pages) | Cited 4 times

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Electron holography is applied for the study of the leakage field of thin‐film ferromagnetic tips used as probes in magnetic force microscopy. We used commercially available pyramidal tips covered on one face with a thin NiCo film, which were then placed in a high external magnetic field directed along the pyramid axis. Good agreement between simulated and experimental electron phase difference maps allows to measure the local flux from the ferromagnetic tips and therefore to evaluate the perturbation induced by the microprobe stray field on the sample area. © 1996 American Institute of Physics.
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07.79.Pk Magnetic force microscopes
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
FREE

Comment on ‘‘Iron diffusivity in silicon: Impact of charge state’’ [Appl. Phys. Lett. 66, 860 (1995)]

T. Heiser and A. Mesli

Appl. Phys. Lett. 68, 1868 (1996); http://dx.doi.org/10.1063/1.116040 (2 pages) | Cited 4 times

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Abstract Unavailable
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61.72.uf Ge and Si
66.30.J- Diffusion of impurities
FREE

Response to ‘‘Comment on ‘Iron diffusivity in silicon: Impact of charge state’ ’’ [Appl. Phys. Lett. 68, 1868 (1996)]

Sergei Koveshnikov and George Rozgonyi

Appl. Phys. Lett. 68, 1870 (1996); http://dx.doi.org/10.1063/1.116041 (2 pages) | Cited 2 times

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Abstract Unavailable
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61.72.uf Ge and Si
66.30.J- Diffusion of impurities
FREE

Comment on ‘‘Normal incidence second‐harmonic generation in L‐valley AlSb/GaSb/Ga1−xAlxSb/AlSb stepped quantum wells’’ [Appl. Phys. Lett. 65, 2048 (1994)]

M. Załużny and V. Bondarenko

Appl. Phys. Lett. 68, 1872 (1996); http://dx.doi.org/10.1063/1.116125 (1 page) | Cited 2 times

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Abstract Unavailable
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.66.Fd III-V semiconductors
FREE

Response to ‘‘Comment on ‘Normal incidence second‐harmonic generation in L‐valley AlSb/GaSb/Ga1−xAlxSb/AlSb stepped quantum wells’ ’’ [Appl. Phys. Lett. 68, 1872 (1996)]

L. R. Ram‐Mohan, J. R. Meyer, H. Xie, and W. I. Wang

Appl. Phys. Lett. 68, 1873 (1996); http://dx.doi.org/10.1063/1.116126 (1 page) | Cited 2 times

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Abstract Unavailable
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.66.Fd III-V semiconductors
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