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30 Nov 1998

Volume 73, Issue 22, pp. 3181-3305

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Incorporation of indium during molecular beam epitaxy of InGaN

T. Böttcher, S. Einfeldt, V. Kirchner, S. Figge, H. Heinke, D. Hommel, H. Selke, and P. L. Ryder

Appl. Phys. Lett. 73, 3232 (1998); http://dx.doi.org/10.1063/1.122728 (3 pages) | Cited 35 times

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We report on the incorporation of In during growth of InxGa1−xN by molecular beam epitaxy under varying In/Ga flux ratios and with different film thicknesses. The incorporation efficiency studied by energy dispersive x-ray microanalysis, high-resolution x-ray diffraction and photoluminescence spectroscopy is strongly affected by the chosen fluxes of Ga and N and is limited by the excess of nitrogen compared to gallium. Furthermore, thick films exhibit a decrease of the In content in growth direction. The behavior can be explained by considering the different stabilities of the two binary compounds InN and GaN. © 1998 American Institute of Physics.  
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Nq Composition and phase identification
61.66.Bi Elemental solids
61.66.Dk Alloys
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Persistent photoconductivity in Si delta-doped GaAs at low doping concentration

C. Y. Chen, Tineke Thio, K. L. Wang, K. W. Alt, and P. C. Sharma

Appl. Phys. Lett. 73, 3235 (1998); http://dx.doi.org/10.1063/1.122729 (3 pages) | Cited 5 times

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In addition to the persistent photoconductivity (PPC) attributed to DX centers in GaAs delta-doped with Si, a weak PPC (WPPC) with a PPC carrier density independent of Si-doping concentration has been generally reported at ambient atmosphere, but the nature of the deep states responsible has not been elucidated. Here, we present the results of a detailed study of the WPPC in δ-GaAs:Si at low-doping densities, NSi ≈ 1–3×1012 cm−2, and ambient pressure. It is concluded that the WPPC does not arise from DX centers but from another deep defect, which is DX-like in the sense that it can be metastably excited. The presence of two distinct DX-like states is apparent from two separate annealing temperatures of the PPC, Ta ≈ 50 K and Tb ≈ 230 K; to the best of our knowledge, the latter is the highest annealing temperature observed in the AlGaAs:Si system. © 1998 American Institute of Physics.
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72.40.+w Photoconduction and photovoltaic effects
72.80.Ey III-V and II-VI semiconductors
71.55.Eq III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments

Depth-resolved cathodoluminescence study of ZnxCd1−xSe epilayer grown on (001) InP by metal organic chemical vapor phase deposition

X. B. Zhang, H. K. Won, and S. K. Hark

Appl. Phys. Lett. 73, 3238 (1998); http://dx.doi.org/10.1063/1.122730 (3 pages) | Cited 5 times

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Optical properties of zincblende structured ZnxCd1−xSe epilayer grown on InP by metal organic chemical vapor phase deposition at temperatures of 360, 400, and 440 °C are investigated with low temperature cathodoluminescence spectroscopy (CL). Both near band gap and deep level emissions are found for the samples grown at 400 °C and above, but deep level emissions are absent for the sample grown at 360 °C. We conclude that the growth temperature should be kept below the temperature at which InP begins to decompose and diffusion of III–V constituents into the epilayer occurs. Evidence of this diffusion comes from an analysis of depth resolved CL studies, which shows that the deep level emissions occur mainly at the epilayer/substrate interface. By monitoring the ratio of the intensity of the deep level emissions to that of the near band emissions, we find that this ratio is larger for samples grown at high temperatures than those at low temperatures. Indium diffusion from the substrate into the epilayer is most likely the source of these deep levels. © 1998 American Institute of Physics.
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78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
81.15.Kk Vapor phase epitaxy; growth from vapor phase
66.30.Ny Chemical interdiffusion; diffusion barriers
71.55.Gs II-VI semiconductors

Electrochemical fabrication of n-Si/Au Schottky junctions

G. Oskam, D. van Heerden, and P. C. Searson

Appl. Phys. Lett. 73, 3241 (1998); http://dx.doi.org/10.1063/1.122731 (3 pages) | Cited 23 times

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We report on the electrochemical deposition of gold films onto n-type silicon. Gold deposition occurs through progressive nucleation and diffusion limited growth. A high density of gold nuclei was obtained by using a short potential pulse to −1.6 V(Ag/AgCl), and subsequent growth was performed at about −1.1 V(Ag/AgCl) where the growth rate is kinetically limited. Transmission electron microscopy showed that high quality, continuous gold films were formed with an average grain size on the order of 50–70 nm. The electrical properties of the electrochemically deposited Si/Au Schottky junctions are comparable to junctions prepared by evaporation or sputtering techniques. © 1998 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
81.15.Pq Electrodeposition, electroplating
81.05.Bx Metals, semimetals, and alloys
68.55.-a Thin film structure and morphology

Structure and hydrogen content of stable hot-wire-deposited amorphous silicon

A. M. Brockhoff, E. H. C. Ullersma, H. Meiling, F. H. P. M. Habraken, and W. F. van der Weg

Appl. Phys. Lett. 73, 3244 (1998); http://dx.doi.org/10.1063/1.122732 (3 pages) | Cited 8 times

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Thin-film transistors incorporating a hot-wire chemical-vapor-deposited silicon layer have been shown to exhibit superior electronic stability as compared to glow-discharge-deposited amorphous silicon devices. Hot-wire-deposited silicon films of various thicknesses (37–370 nm) on silicon dioxide were investigated. The films are structurally inhomogeneous. Raman measurements and transmission electron microscopy show that isolated cone-shaped crystals grow within a primarily amorphous layer. The amorphous interface region has a low hydrogen content of 2.0±0.2 at. %, while the films exhibit an enhanced hydrogen concentration in the surface region. The bond-angle distribution in the amorphous phase is comparable to that of device-quality glow-discharge-deposited amorphous silicon. © 1998 American Institute of Physics.
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61.43.Dq Amorphous semiconductors, metals, and alloys
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Gc Amorphous semiconductors
81.05.Cy Elemental semiconductors
85.30.Tv Field effect devices
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.66.Jg Amorphous semiconductors; glasses

Evidence on the formation of a heavily Ge-doped layer in Pd/Ge-based ohmic contact to pseudomorphic high electron mobility transistor

Jong-Lam Lee and Yi-Tae Kim

Appl. Phys. Lett. 73, 3247 (1998); http://dx.doi.org/10.1063/1.122733 (3 pages)

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Microstructural evidence on the formation of a heavily Ge-doped layer below Pd/Ge-based ohmic contact to AlGaAs/InGaAs pseudomorphic high electron mobility transistor was obtained. The contact resistivity is decreased by two orders of magnitude as InGaAs channel is intermixed. This originates from the formation of Au2Al and Au7Ga2 compounds below the contacts during annealing, via production of group III vacancies. The vacancies play a role in producing free electrons by the incorporation of Ge atoms, resulting in intermixing of InGaAs as well as reduction of contact resistivity. © 1998 American Institute of Physics.
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85.30.Tv Field effect devices
73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing

Electron paramagnetic resonance evidence for reversible transformation of thermal donor into shallow donor-type center in hydrogen-implanted silicon

B. Rakvin, B. Pivac, R. Tonini, F. Corni, and G. Ottaviani

Appl. Phys. Lett. 73, 3250 (1998); http://dx.doi.org/10.1063/1.122734 (3 pages) | Cited 1 time

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Electron paramagnetic resonance spectrum of the proton-related thermal donor (TD) assigned as NL8 paramagnetic center has been detected at 110 K after heat treatment of the hydrogen-implanted Czochralski-Si at 773 K. The effect of temperature on reversible transformations of the anisotropic spectrum of NL8 center into the isotropic singlet line was studied in the temperature region from 110 to 240 K. The analysis of the singlet provides an evidence that this signal originates from the proton-related shallow donor type at g = 1.9987. The changes in the linewidth have been used to evaluate the parameters [1/τ = 0.66×1012 exp(−ΔE/kT);ΔE = 169 meV] for thermally activated electron emission to the conduction band from the second donor state of the NL8 center. These results represent direct experimental evidence of reversible transformation of the TD+ charged center into the shallow donor-type center. © 1998 American Institute of Physics.
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76.30.Lh Other ions and impurities
71.55.Cn Elemental semiconductors
61.72.uf Ge and Si
61.72.Cc Kinetics of defect formation and annealing

Gallium vacancies and the growth stoichiometry of GaN studied by positron annihilation spectroscopy

K. Saarinen, P. Seppälä, J. Oila, P. Hautojärvi, C. Corbel, O. Briot, and R. L. Aulombard

Appl. Phys. Lett. 73, 3253 (1998); http://dx.doi.org/10.1063/1.122735 (3 pages) | Cited 40 times

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We have applied positron spectroscopy to study the formation of vacancy defects in undoped n-type metal organic chemical vapor deposition grown GaN, where the stoichiometry was varied. Ga vacancies are found in all samples. Their concentration increases from 1016 to 1019 cm−3 when the V/III molar ratio increases from 1000 to 10 000. In nitrogen rich conditions Ga lattice sites are thus left empty and Ga vacancies are abundantly formed. The creation of Ga vacancies is accompanied by the decrease of free electron concentration from 1020 to 1016 cm−3, demonstrating their role as compensating centers. © 1998 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.J- Point defects and defect clusters
78.70.Bj Positron annihilation
61.66.Bi Elemental solids
61.66.Dk Alloys
71.55.Eq III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Simultaneous phase separation and basal-plane atomic ordering in InxGa1−xN

Michio Shimotomai and Akihiko Yoshikawa

Appl. Phys. Lett. 73, 3256 (1998); http://dx.doi.org/10.1063/1.122736 (3 pages) | Cited 5 times

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Reported discrepancy of phase separation in InxGa1−xN films between experimental studies and theoretical calculations based on the usual regular solution model is discussed from the standpoint of phase diagram. The inclusion of higher-order pairwise interactions in the theoretical model may allow the system to undergo a spinodal decomposition in an asymmetrical manner as revealed by experiments. It is suggested that basal-plane atomic ordering in the In-rich precipitates should accompany the decomposition. © 1998 American Institute of Physics.
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64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation
81.30.Dz Phase diagrams of other materials
68.55.Nq Composition and phase identification
61.66.Fn Inorganic compounds

Very large continuous-wave-laser-induced optical absorption in porous silicon films: Evidence for thermal effects

Hideki Koyama and Philippe M. Fauchet

Appl. Phys. Lett. 73, 3259 (1998); http://dx.doi.org/10.1063/1.122737 (3 pages) | Cited 10 times

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A very large optical absorption increase induced by continuous-wave laser irradiation is reported for free-standing porous silicon films oxidized at 800–950 °C. A maximum reversible optical-density change of 2.5 is obtained with a pump laser intensity of ∼ 20W/cm2. The induced absorption is found to be strongly decreased when the sample is attached to materials with a higher thermal conductivity. The experimental results can be satisfactory fitted with an empirical formula for the thermally induced absorption increase in bulk crystalline Si. These results strongly suggest that the observed nonlinearity is originating from thermally induced band gap shrinking in Si micro/nanostructures. © 1998 American Institute of Physics.
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78.66.Db Elemental semiconductors and insulators
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects

Superlattice AlAs/AlInAs-oxide current aperture for long wavelength InP-based vertical-cavity surface-emitting laser structure

N. Ohnoki, F. Koyama, and K. Iga

Appl. Phys. Lett. 73, 3262 (1998); http://dx.doi.org/10.1063/1.122738 (3 pages) | Cited 7 times

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A superlattice AlAs/AlInAs structure which can be formed on an InP substrate is proposed and demonstrated for use in oxide confinement long wavelength surface emitting lasers. The large strain of AlAs layers is relaxed by the use of a superlattice structure showing no defects and uniform oxidations. Also, an AlAs layer on an InP substrate provides us with a relatively large heterobarrier, and will be useful for improving temperature characteristics of long-wavelength vertical-cavity surface-emitting lasers. A current aperture of a few micrometers in diameter was formed by precisely controlling the oxidation time. We have demonstrated a current confinement by this oxide aperture. Low-threshold long-wavelength vertical-cavity surface-emitting lasers with this oxide confinement structure are expected. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Quantum real-space transfer in semiconductor heterostructures

Rui Q. Yang

Appl. Phys. Lett. 73, 3265 (1998); http://dx.doi.org/10.1063/1.122739 (3 pages) | Cited 3 times

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Quantum real-space transfer of carriers in semiconductor heterostructures, which relies solely on the wave nature of electrons governed by quantum mechanics, is investigated. In quantum-well structures where electron effective mass varies spatially, the confined electron wave function can be modified by changing the longitudinal momentum via an external electric field parallel to the quantum-well plane. This shifts electrons perpendicularly to another layer having a different effective mass. Issues associated with realistic scattering are identified for unambiguously demonstrating this quantum real-space transfer in practical situations. Specific quantum-well structures for realizing the quantum real-space transfer are proposed with calculations. Potential applications of the quantum real-space transfer are discussed. © 1998 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
73.61.Ey III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

A photomodulated reflectance study of InAs/GaAs self-assembled quantum dots

G. L. Rowland, T. J. C. Hosea, S. Malik, D. Childs, and R. Murray

Appl. Phys. Lett. 73, 3268 (1998); http://dx.doi.org/10.1063/1.122740 (3 pages) | Cited 24 times

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Photomodulated reflectance (PR) spectra have been measured for self-assembled InAs/GaAs quantum dot (QD) structures consisting of a pair of QD layers, with a GaAs spacer either 50 or 100 Å thick. The PR clearly reveals five confined-state QD transitions, at both 80 and 300 K, as well as features from the two-dimensional confining and GaAs layers. The measured QD transition energies correlate well with photoluminescence spectra at 13 K, using high laser excitation powers to incur level filling. Annealing one of the samples produces a strong blueshift in the QD transitions. © 1998 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.20.-e Optical properties of bulk materials and thin films
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Measurement of the AlGaInAs/AlGaAs conduction-band offset using ballistic electron emission spectroscopy

S. Bhargava, C. Zheng, J. Ko, M. A. Chin, L. A. Coldren, and V. Narayanamurti

Appl. Phys. Lett. 73, 3271 (1998); http://dx.doi.org/10.1063/1.122741 (2 pages) | Cited 3 times

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Ballistic electron emission spectroscopy (BEES) has been used to determine the conduction-band offset between a 10-nm-thick Al0.12In0.22Ga0.66As (Q) strained layer and a ternary Al0.2Ga0.8As (T) barrier located beneath the surface. A three-sample process was used so that the known, reproducible Au/GaAs Schottky barrier would be the top layer of all measured structures. BEES thresholds obtained for Au/GaAs, Au/GaAs/Q, and Au/GaAs/Q/T were 0.96±0.02, 0.98±0.04, and 1.08±0.04 meV yielding offsets of ∼20 meV for GaAs/Q and ∼100 meV for Q/T. Under the affect of a high-temperature anneal, the Q/T offset was reduced to ∼40 meV. In addition, a structure employing solely Au/GaAs/AlGaAs was used to study transitivity for the Q/T material system. © 1998 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
61.72.Cc Kinetics of defect formation and annealing

Energy-dispersive x-ray imaging of an InGaN/GaN bilayer on sapphire

K. P. O’Donnell, P. G. Middleton, C. Trager-Cowan, C. Young, S. C. Bayliss, I. Fletcher, W. Van der Stricht, I. Moerman, and P. Demeester

Appl. Phys. Lett. 73, 3273 (1998); http://dx.doi.org/10.1063/1.122742 (3 pages) | Cited 7 times

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In this letter we discuss the potential and the limitations of quantitative characterization of the distribution of In and Ga atoms in III–N mixed alloys using energy dispersive x-ray (EDX) analysis. Spatial fluctuations of the indium content in an InGaN epilayer are found to correspond to changes in luminescence efficiency. Large hexagonal pyramids, which appear sparsely in such layers, appear to be relatively deficient in indium. Monte Carlo simulations, used to profile the Ga Ka x-ray fluorescence, highlight several limitations of the EDX technique in this context, but confirm our interpretation of the data. Finally, we identify differential growth rates as a possible explanation for the concentration/efficiency variations in InGaN layers. © 1998 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.55.Nq Composition and phase identification
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
02.50.Ng Distribution theory and Monte Carlo studies
02.70.Rr General statistical methods

Electron diffusion length and lifetime in p-type GaN

Z. Z. Bandić, P. M. Bridger, E. C. Piquette, and T. C. McGill

Appl. Phys. Lett. 73, 3276 (1998); http://dx.doi.org/10.1063/1.122743 (3 pages) | Cited 33 times

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We report on electron beam induced current and current–voltage (I–V) measurements on Schottky diodes on p-type doped GaN layers grown by metal organic chemical vapor deposition. A Schottky barrier height of 0.9 eV was measured for the Ti/Au Schottky contact from the I–V data. A minority carrier diffusion length for electrons of (0.2±0.05) μm was measured for the first time in GaN. This diffusion length corresponds to an electron lifetime of approximately 0.1 ns. We attempted to correlate the measured electron diffusion length and lifetime with several possible recombination mechanisms in GaN and establish connection with electronic and structural properties of GaN. © 1998 American Institute of Physics.
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73.61.Ey III-V semiconductors
81.05.Ea III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
72.80.Ey III-V and II-VI semiconductors
68.55.-a Thin film structure and morphology
73.30.+y Surface double layers, Schottky barriers, and work functions
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