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9 Dec 1996

Volume 69, Issue 24, pp. 3623-3756

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Atomic‐scale structure and electronic properties of GaN/GaAs superlattices

R. S. Goldman, R. M. Feenstra, B. G. Briner, M. L. O’Steen, and R. J. Hauenstein

Appl. Phys. Lett. 69, 3698 (1996); http://dx.doi.org/10.1063/1.117193 (3 pages) | Cited 29 times

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We have investigated the atomic‐scale structure and electronic properties of GaN/GaAs superlattices produced by nitridation of a molecular beam epitaxially grown GaAs surface. Using cross‐sectional scanning tunneling microscopy (STM) and spectroscopy, we show that the nitrided layers are laterally inhomogeneous, consisting of groups of atomic‐scale defects and larger clusters. Analysis of x‐ray diffraction data in terms of fractional area of clusters (determined by STM), reveals a cluster lattice constant similar to bulk GaN. In addition, tunneling spectroscopy on the defects indicates a conduction band state associated with an acceptor level of NAs in GaAs. Therefore, we identify the clusters and defects as nearly pure GaN and NAs, respectively. Together, the results reveal phase segregation in these arsenide/nitride structures, in agreement with the large miscibility gap predicted for GaAsN. © 1996 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
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
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Reliability of gate oxide grown on nitrogen‐implanted Si substrates

Chuan Lin, Anthony I. Chou, Prasenjit Choudhury, Jack C. Lee, Kiran Kumar, Brian Doyle, and Hamid R. Soleimani

Appl. Phys. Lett. 69, 3701 (1996); http://dx.doi.org/10.1063/1.117194 (3 pages) | Cited 8 times

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Direct nitrogen implant into Si substrate prior to gate oxidation has been proposed to grow multiple gate oxide thicknesses on a single wafer. In this letter, we have studied the reliability of gate oxide grown on nitrogen‐implanted Si substrate. The effects of implant doses, sacrificial oxide thicknesses, and gate oxide thicknesses on gate oxide reliability have been investigated. It was found that there is a tradeoff between oxide thickness control and gate oxide reliability. © 1996 American Institute of Physics.
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85.30.De Semiconductor-device characterization, design, and modeling
85.40.Ry Impurity doping, diffusion and ion implantation technology
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Electron and hole g‐factors in CdTe/CdMgTe quantum wells

Q. X. Zhao, M. Oestreich, and N. Magnea

Appl. Phys. Lett. 69, 3704 (1996); http://dx.doi.org/10.1063/1.117195 (3 pages) | Cited 17 times

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Single CdTe/CdMgTe quantum well (QW) structures are investigated by stationary and time‐resolved photoluminescence in the presence of an applied magnetic field. We study the dependence of the electron and the hole g factors on the well width by combining Zeeman measurements and the recently developed spin quantum beats technique. The experimental results show that both the electron and the hole g factors have the same sign in wide QWs and increase with decreasing well width. The electron spin phase relaxation time is about 250 ps in our QW structures. © 1996 American Institute of Physics.
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78.20.Ls Magneto-optical effects
78.66.Hf II-VI semiconductors
78.47.-p Spectroscopy of solid state dynamics
78.55.Et II-VI semiconductors

Dead space approximation for impact ionization in silicon

A. Spinelli, A. Pacelli, and A. L. Lacaita

Appl. Phys. Lett. 69, 3707 (1996); http://dx.doi.org/10.1063/1.117196 (3 pages) | Cited 24 times

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We demonstrate the validity of the dead space approximation for impact ionization in silicon. Monte Carlo simulations are used to obtain realistic ionization probabilities, and the corresponding avalanche gain in constant field structures is computed. We show that the hard‐threshold dead space model is in good agreement with a more refined model taking into account soft‐threshold effects, if an effective threshold energy of 3 eV is adopted for electrons. We also show that hole nonlocal effects do not significantly affect the result. © 1996 American Institute of Physics.
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72.20.Ht High-field and nonlinear effects
72.80.Cw Elemental semiconductors
85.30.De Semiconductor-device characterization, design, and modeling

N incorporation in GaP and band gap bowing of GaNxP1−x

W. G. Bi and C. W. Tu

Appl. Phys. Lett. 69, 3710 (1996); http://dx.doi.org/10.1063/1.117197 (3 pages) | Cited 41 times

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We report a study on the N incorporation in GaP grown by gas‐source molecular beam epitaxy using a N radical beam source. Contrary to theoretical predictions under thermoequilibrium conditions, GaNP with N concentration as high as 16% has been obtained without showing any phase separation, but increasing the growth temperature will result in a decrease of N incorporation. These results indicate that using nonequilibrium growth techniques can achieve GaNP alloys with a N concentration far greater than the thermal equilibrium solubility limit. Optical absorption measurements reveal that although the band gap energy of GaNxP1−x decreases with increasing N concentration, it is still positive for x up to 16%, indicating that the material is not a semimetal but a semiconductor, contrary to theoretical predictions based on the Van Vechten’s quantum dielectric model. © 1996 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Initial, rapid light‐induced changes in hydrogenated amorphous silicon materials and solar cell structures: The effects of charged defects

Lihong Jiao, Hongyue Liu, S. Semoushikina, Yeeheng Lee, and C. R. Wronski

Appl. Phys. Lett. 69, 3713 (1996); http://dx.doi.org/10.1063/1.117198 (3 pages) | Cited 18 times

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Large, rapid light induced changes are reported for photoconductivities, electron mobility‐lifetime products, and forward bias currents in hydrogenated amorphous silicon (a‐Si:H) films and Schottky barrier cell structures. The absence of concurrent changes in subgap absorption and quantum efficiencies are clearly inconsistent with the widely held view that the kinetics of degradation in a‐Si:H materials and cells can be quantified solely in terms of neutral dangling bond defects. The self‐consistent analysis of all the results was carried out for films and Schottky barrier structures by including charged defects and using a three‐Gaussian distribution of donorlike and acceptorlike defect states. Such self‐consistent development of ‘‘operational’’ parameters for these gap states offers a method for reliable and quantitative correlations between solar cell performance and stability with the properties of their bulk materials. © 1996 American Institute of Physics.
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73.50.Pz Photoconduction and photovoltaic effects
73.61.Jc Amorphous semiconductors; glasses
84.60.Jt Photoelectric conversion

Time‐resolved cathodoluminescence study of carrier relaxation in strained (InP)2/(GaP)2 quantum wires

D. H. Rich and Y. Tang

Appl. Phys. Lett. 69, 3716 (1996); http://dx.doi.org/10.1063/1.117199 (3 pages) | Cited 4 times

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The carrier relaxation kinetics and nonlinear optical properties of strain‐induced laterally ordered (InP)2/(GaP)2 quantum wire (QWR) samples were examined with time‐resolved cathodoluminescence. A temperature dependence of the QWR luminescence decay time reveals that thermal activation of carriers in the QWR and transfer to and from In0.49Ga0.51P barriers plays an important role in determining the measured lifetimes. The presence of disorder in the QWRs was found to induce inhomogeneous regions which exhibit large variations in carrier capture and band filling. © 1996 American Institute of Physics.
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78.60.Hk Cathodoluminescence, ionoluminescence
78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Growth of polycrystalline silicon on glass by selective laser‐induced nucleation

D. Toet, B. Koopmans, P. V. Santos, R. B. Bergmann, and B. Richards

Appl. Phys. Lett. 69, 3719 (1996); http://dx.doi.org/10.1063/1.117200 (3 pages) | Cited 17 times

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Polycrystalline silicon on glass substrates was grown by a method based on the creation of nucleation sites using laser crystallization of amorphous silicon followed by thermal annealing at temperatures below 600 °C. Annealing induces the crystallization of the material around the seeds, eventually leading to coalescence of adjacent domains before spontaneous nucleation sets in. Micro‐Raman spectroscopy shows that the seeds experience a tensile stress, which causes a radial birefringence in the surrounding amorphous silicon, detected by optical anisotropy measurements. We conjecture that this stress facilitates the crystallization of the material around the seed upon thermal annealing. © 1996 American Institute of Physics.
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81.15.Np Solid phase epitaxy; growth from solid phases
81.05.Cy Elemental semiconductors
68.55.-a Thin film structure and morphology

Photocurrent multiplication in naphthalene tetracarboxylic anhydride film at room temperature

Tadashi Katsume, Masahiro Hiramoto, and Masaaki Yokoyama

Appl. Phys. Lett. 69, 3722 (1996); http://dx.doi.org/10.1063/1.117201 (3 pages) | Cited 28 times

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A large photocurrent multiplication reaching 130 000‐fold at room temperature has been observed in naphthalene tetracarboxylic anhydride (NTCDA) film sandwiched between metal electrodes. This phenomenon is reasonably interpreted in terms of the tunneling injection of electrons from a metal electrode, which is triggered by the accumulation of photogenerated trapped holes near the metal/organic interface. The combination of an ultrathin NTCDA film with another photoconductive pigment film in a layered structure allowed us to fabricate a photocurrent multiplication device with the desired spectral response. © 1996 American Institute of Physics.
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72.80.Le Polymers; organic compounds (including organic semiconductors)
73.50.Pz Photoconduction and photovoltaic effects
73.61.Ph Polymers; organic compounds
73.40.Sx Metal-semiconductor-metal structures

Local vibrational modes of the Mg–H acceptor complex in GaN

W. Götz, N. M. Johnson, D. P. Bour, M. D. McCluskey, and E. E. Haller

Appl. Phys. Lett. 69, 3725 (1996); http://dx.doi.org/10.1063/1.117202 (3 pages) | Cited 93 times

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Local vibrational modes (LVMs) are reported for Mg‐doped GaN grown by metalorganic chemical vapor deposition. Hetero‐epitaxial layers of GaN:Mg, either as‐grown, thermally activated, or deuterated, were investigated with low‐temperature, Fourier‐transform infrared absorption spectroscopy. The as‐grown material, which was semi‐insulating, exhibits a LVM at 3125 cm−1. Thermal annealing increases the p‐type conductivity, as established with Hall effect measurements, and proportionally reduces the intensity of this LVM. Deuteration of the activated material creates a LVM at 2321 cm−1. The isotopic shift establishes the presence of hydrogen in the vibrating complex. The new LVMs are assigned to the stretch modes of the Mg–H and Mg–D complexes in GaN, with the vibrational frequencies indicative of a strong N–H bond as recently proposed from total‐energy calculations. © 1996 American Institute of Physics.
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78.30.Fs III-V and II-VI semiconductors
73.61.Ey III-V semiconductors
71.55.Eq III-V semiconductors

Growth of 6H and 4H silicon carbide single crystals by the modified Lely process utilizing a dual‐seed crystal method

V. D. Heydemann, N. Schulze, D. L. Barrett, and G. Pensl

Appl. Phys. Lett. 69, 3728 (1996); http://dx.doi.org/10.1063/1.117203 (3 pages) | Cited 16 times

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The influence of polarity on the SiC crystal growth has been demonstrated using a dual‐seed technique to grow on both the C‐ and Si‐face seed simultaneously. For the investigated range of growth conditions, 4H‐SiC crystals were grown on the C‐face of 6H‐SiC seed crystals with on‐axis orientation, when the growth rate exceeded 1.2 g/h. We were never able to grow 4H‐SiC on the Si‐ face of 6H‐ or 4H‐SiC seed crystals under these growth conditions. The incorporation of nitrogen is shown to be 2–3 times higher in crystals grown on the C‐face than on the Si‐face, and is independent of both polytype and 8° off‐axis orientation. The addition of more than 15% silicon powder to the SiC sublimation source resulted in polycrystalline growth. © 1996 American Institute of Physics.
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81.10.Bk Growth from vapor
71.55.Ht Other nonmetals
81.05.Hd Other semiconductors

Faraday–Stark optoelectronic effect

Z. K. Lee, D. Heiman, H. Wang, C. G. Fonstad, M. Sundaram, and A. C. Gossard

Appl. Phys. Lett. 69, 3731 (1996); http://dx.doi.org/10.1063/1.117204 (3 pages) | Cited 2 times

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An optoelectronic effect based on Faraday or Kerr rotation and the quantum‐confined Stark shift is demonstrated. It is novel in that the degree of rotation is controlled by an electric field as opposed to a magnetic field. By applying an electric field to a quantum well structure, the Faraday rotation can be tuned into resonance, thereby varying the rotation angle of plane polarized light. We have observed a resonant rotation of 10° in GaAs at a magnetic field of 1 T. By applying a gate voltage of 2 V to a GaAs/AlGaAs superlattice structure, we observed a change in rotation of 1.3° at 2 K. The Faraday–Stark effect could be useful in electrically controlled light switches and high‐speed optical modulators. © 1996 American Institute of Physics.
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78.20.Ls Magneto-optical effects
78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors

Noise characteristics of thin multiplication region GaAs avalanche photodiodes

C. Hu, K. A. Anselm, B. G. Streetman, and J. C. Campbell

Appl. Phys. Lett. 69, 3734 (1996); http://dx.doi.org/10.1063/1.117205 (3 pages) | Cited 61 times

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It is well known that the gain‐bandwidth product of an avalanche photodiode can be increased by utilizing a thin multiplication region. Previously, measurements of the excess noise factor of InP/InGaAsP/InGaAs avalanche photodiodes with separate absorption and multiplication regions indicated that this approach could also be employed to reduce the multiplication noise. This letter presents a systematic study of the noise characteristics of GaAs homojunction avalanche photodiodes with different multiplication layer thicknesses. It is demonstrated that there is a definite ‘‘size effect’’ for multiplication regions less than approximately 0.5 μm. A good fit to the experimental data has been achieved using a discrete, nonlocalized model for the impact ionization process. © 1996 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
72.70.+m Noise processes and phenomena
72.20.Ht High-field and nonlinear effects

Enhancement of deep acceptor activation in semiconductors by superlattice doping

E. F. Schubert, W. Grieshaber, and I. D. Goepfert

Appl. Phys. Lett. 69, 3737 (1996); http://dx.doi.org/10.1063/1.117206 (3 pages) | Cited 41 times

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The thermal activation of acceptors in wide‐gap semiconductors can be very low due to large acceptor activation energies. It is shown that superlattice doping, i.e., the composition modulation of a uniformly doped ternary semiconductor, can enhance the acceptor activation by more than one order of magnitude. © 1996 American Institute of Physics.
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71.55.-i Impurity and defect levels
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Band offset transitivity in AlGaAs/InGaP/InGaAsP heterostructures on a GaAs substrate

Yong‐Hoon Cho, Byung‐Doo Choe, and H. Lim

Appl. Phys. Lett. 69, 3740 (1996); http://dx.doi.org/10.1063/1.117207 (3 pages) | Cited 9 times

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The conduction‐band offset ΔEc of Al0.3Ga0.7As/In0.1Ga0.9As0.8P0.2 lattice matched to a GaAs substrate was measured by capacitance‐voltage analysis. To examine the transitivity of the band offset in the AlGaAs/InGaP/InGaAsP system, the band offsets of Al0.3Ga0.7As/In0.5Ga0.5P and In0.5Ga0.5P/In0.1Ga0.9As0.8P0.2 were investigated. The value of ΔEc for the Al0.3Ga0.7As/In0.1Ga0.9As0.8P0.2 heterostructure, estimated by adding the measured ΔEc values in Al0.3Ga0.7As/In0.5Ga0.5P and in In0.5Ga0.5P/In0.1Ga0.9As0.8P0.2, agrees well with the value measured directly. We thus conclude that the transitivity rule holds well for the band offsets of an AlGaAs/InGaP/InGaAsP system lattice matched to a GaAs substrate. © 1996 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
71.20.Nr Semiconductor compounds

Properties of Schottky contacts of aluminum on strained Si1−x−yGexCy layers

Jian Mi, Ashawant Gupta, Cary Y. Yang, Jintian Zhu, Paul K. L. Yu, Patricia Warren, and Michel Dutoit

Appl. Phys. Lett. 69, 3743 (1996); http://dx.doi.org/10.1063/1.117208 (3 pages) | Cited 3 times

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Schottky contacts of Al/Si1−x−yGexCy were fabricated using conventional Si technology. Effects of thermal processing of the alloys on the electrical properties of the Al/Si1−x−yGexCy Schottky diodes were investigated. Current–voltage (I–V), capacitance–voltage (C–V), and x‐ray diffraction measurements were performed. These thick alloy films (100–150 nm) experienced strain relaxation upon annealing at 700 °C. Nearly ideal I–V and C–V behaviors were obtained for strain‐compensated samples. I–V and C–Vcharacteristics show evidence of dislocation‐related traps for strain‐relaxed samples. Carbon incorporation improves the I–V and C–V characteristics by lessening the extent of lattice relaxation due to thermal processing. © 1996 American Institute of Physics.
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73.30.+y Surface double layers, Schottky barriers, and work functions
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.40.Ns Metal-nonmetal contacts

Controlled growth of bulk bicrystals and the investigation of microstructure‐property relations of YBa2Cu3Ox grain boundaries

V. R. Todt, X. F. Zhang, D. J. Miller, M. St. Louis‐Weber, and V. P. Dravid

Appl. Phys. Lett. 69, 3746 (1996); http://dx.doi.org/10.1063/1.117209 (3 pages) | Cited 35 times

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A new method to prepare bicrystals with well defined planar interfaces in YBa2Cu3Ox (Y123) has been developed. The bicrystal misorientation is controlled by dual seeding using Nd1+xBa2−xCu3Oy single crystals. The grain boundary plane orientation is influenced by the positioning of the seeds and by control of the temperature gradient. The macro‐, meso‐, and microscopic planarity of the grain boundaries has been established by optical and electron microscopy. In addition, a difference in critical current density between the low (≤10°) and the high (≥20°) misorientation angle regime of nearly two orders of magnitude has been established in a series of [001]‐tilt grain boundaries. Thus, this type of grain boundary may allow a less ambiguous interpretation of the relationship between microstructure and transport properties than is possible from bicrystal thin film boundaries by eliminating the potential variations in properties associated with a varying grain boundary plane. © 1996 American Institute of Physics.
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74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.72.-h Cuprate superconductors
61.72.Mm Grain and twin boundaries

Measurement of rapidly varying electric fields through parity oscillations in the Rydberg states of hydrogenic atoms

N. E. Shafer‐Ray and R. N. Zare

Appl. Phys. Lett. 69, 3749 (1996); http://dx.doi.org/10.1063/1.117180 (3 pages) | Cited 1 time

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Oscillations are shown to exist in the inversion symmetry of the electronic wave function of a hydrogenic atom coherently excited to a Rydberg state by a short pulse of laser radiation in a uniform electric field. The dependence of these oscillations on field strength is shown to scale as n2 where n is the principal quantum number. The possibility of using these oscillations to measure electric signals on picosecond timescales (terahertz frequencies) is suggested. © 1996 American Institute of Physics.
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32.80.Rm Multiphoton ionization and excitation to highly excited states
32.60.+i Zeeman and Stark effects

Nanometer‐scale recording on an organic‐complex thin film with a scanning tunneling microscope

L. P. Ma, Y. L. Song, H. J. Gao, W. B. Zhao, H. Y. Chen, Z. Q. Xue, and S. J. Pang

Appl. Phys. Lett. 69, 3752 (1996); http://dx.doi.org/10.1063/1.117181 (2 pages) | Cited 32 times

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Nanometer‐scale recording on an organic‐complex thin film with a scanning tunneling microscope (STM) under ambient conditions is demonstrated. The recording marks are made by applying external voltage pulses between the tip and the highly ordered pyrolytic graphite substrate. A 30×30 nm2 STM image with recorded marks is given. The average recorded mark is 1.3 nm in diameter, which corresponds to a data storage density of about 1013 bits/cm2. The current–voltage characteristics measured by the STM show an insulator behavior for the unrecorded regions, and a conductor behavior for the recorded regions, which indicates that the data are recorded by local change of the electrical property of the films. © 1996 American Institute of Physics.
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07.79.Cz Scanning tunneling microscopes
73.61.Ph Polymers; organic compounds
85.30.-z Semiconductor devices

Nondestructive evaluation of the oxidation stresses through thermal barrier coatings using Cr3+ piezospectroscopy

R. J. Christensen, D. M. Lipkin, D. R. Clarke, and K. Murphy

Appl. Phys. Lett. 69, 3754 (1996); http://dx.doi.org/10.1063/1.117182 (3 pages) | Cited 80 times

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The stresses in the aluminum oxide formed during high‐temperature oxidation of a bond‐coated superalloy are shown to be measurable through zirconia thermal barrier coatings. The basis for the measurements is the piezospectroscopic shift in the R‐line fluorescence (photoluminescence) from Cr3+ impurities incorporated into the growing aluminum oxide scale. Measurements through the thermal barrier coating are feasible because (partially stabilized) zirconia coatings have some transparency at both the excitation and at fluorescence frequencies. © 1996 American Institute of Physics.
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81.70.Bt Mechanical testing, impact tests, static and dynamic loads
81.65.Mq Oxidation
78.55.Hx Other solid inorganic materials
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