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22 Oct 2001

Volume 79, Issue 17, pp. 2681-2850

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Improved mobilities and resistivities in modulation-doped p-type AlGaN/GaN superlattices

Erik L. Waldron, John W. Graff, and E. Fred Schubert

Appl. Phys. Lett. 79, 2737 (2001); http://dx.doi.org/10.1063/1.1410340 (3 pages) | Cited 28 times

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The transport properties of modulation, shifted modulation, and uniformly doped Al0.20Ga0.80N/GaN superlattices are presented. The modulation-doped sample is doped only in the AlGaN barriers. The shifted-modulation-doped sample has its dopants shifted by one-quarter period. Measurements reveal a strong improvement in mobility and resistivity for the modulation-doped and shifted-modulation-doped structures versus the uniformly doped structure. The modulation-doped sample has a mobility of 9.2 and 36 cm2/V s at 300 and 90 K respectively and a very low resistivity of 0.20 and 0.068 Ω cm at 300 and 90 K, respectively. Capacitance–voltage profiling shows multiple two-dimensional hole gases. The results are consistent with a reduction of neutral impurity scattering for modulation-doped structures as compared to uniformly doped structures. © 2001 American Institute of Physics.
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73.63.-b Electronic transport in nanoscale materials and structures
72.80.Ey III-V and II-VI semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance
61.72.uj III-V and II-VI semiconductors

Controlled oxygen doping of GaN using plasma assisted molecular-beam epitaxy

A. J. Ptak, L. J. Holbert, L. Ting, C. H. Swartz, M. Moldovan, N. C. Giles, T. H. Myers, P. Van Lierde, C. Tian, R. A. Hockett, S. Mitha, A. E. Wickenden, D. D. Koleske, and R. L. Henry

Appl. Phys. Lett. 79, 2740 (2001); http://dx.doi.org/10.1063/1.1403276 (3 pages) | Cited 15 times

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High-quality (0001) and (0001)-GaN films were grown by plasma-assisted molecular-beam epitaxy to study the dependence of oxygen incorporation on polarity and oxygen partial pressure. Oxygen incorporates at a rate ten times faster on nitrogen-polar GaN than on the Ga polarity. Oxygen doping is controllable, reproducible, and produces low compensation material up to concentrations of at least 1018 cm−3 with higher levels showing significant compensation. Layers containing oxygen at levels above 1022 cm−3 exhibit severe cracking while oxygen concentrations less than 1021 cm−3 do not introduce significant strain. The oxygen incorporation rate has a weak dependence on Ga overpressure during Ga-stable growth but dramatically increases for conditions approaching N-stable growth. © 2001 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
52.77.Dq Plasma-based ion implantation and deposition
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.Ey III-V semiconductors

Self-assembled heterojunction between electrodeposited PbS nanoparticles and indium tin oxide substrate

K. K. Nanda and S. N. Sahu

Appl. Phys. Lett. 79, 2743 (2001); http://dx.doi.org/10.1063/1.1413223 (3 pages) | Cited 15 times

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Self-assembled heterojunction was fabricated by means of an electrochemical deposition of PbS nanoparticles on indium tin oxide substrate. The current–voltage and capacitance–voltage studies confirmed the formation of a heterojunction. A large current and large capacitance were observed in the case of a device from particle of smaller size which is believed to be due to the large surface area contact. The rectifying behavior of the heterojunction was found to be weak as compared to the usual p–n junction. © 2001 American Institute of Physics.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Ei Rectification
73.63.Bd Nanocrystalline materials

Impurity-controlled dopant activation: Hydrogen-determined site selection of boron in silicon carbide

B. Aradi, P. Deák, N. T. Son, E. Janzén, W. J. Choyke, and R. P. Devaty

Appl. Phys. Lett. 79, 2746 (2001); http://dx.doi.org/10.1063/1.1410337 (3 pages) | Cited 13 times

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The geometry and formation energy of substitutional B and Al dopants as well as their complexes with hydrogen have been calculated in 4H–SiC using first-principles methods. Our results show that boron selecting the silicon site and, therefore, getting activated as a shallow acceptor depends on the presence of hydrogen which is promoted into the crystal by boron itself. Without hydrogen, boron would mostly be incorporated at the carbon site. Aluminum does not show this behavior: it always selects the silicon site and is incorporated independently of hydrogen. © 2001 American Institute of Physics.
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71.55.Ht Other nonmetals
61.72.S- Impurities in crystals

Localized variations in electronic structure of AlGaN/GaN heterostructures grown by molecular-beam epitaxy

K. V. Smith, E. T. Yu, C. R. Elsass, B. Heying, and J. S. Speck

Appl. Phys. Lett. 79, 2749 (2001); http://dx.doi.org/10.1063/1.1410342 (3 pages)

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Local electronic properties in a molecular-beam-epitaxy-grown AlxGa1−xN/GaN heterostructure field-effect transistor epitaxial layer structure are probed using depth-resolved scanning capacitance microscopy. Theoretical analysis of contrast observed in scanning capacitance images acquired over a range of bias voltages is used to assess the possible structural origins of local inhomogeneities in electronic structure, which are shown to be concentrated in areas where Ga droplets had formed on the surface during growth. Within these regions, there are significant variations in the local electronic structure that are attributed to variations in both AlxGa1−xN layer thickness and Al composition. Increased charge trapping is also observed in these regions. © 2001 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.30.Tv Field effect devices
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
71.20.Nr Semiconductor compounds
73.20.At Surface states, band structure, electron density of states

Defect-induced lateral chemical heterogeneity at Ni/GaN interfaces and its effect on the electronic properties of the interface

A. Barinov, L. Gregoratti, B. Kaulich, M. Kiskinova, and A. Rizzi

Appl. Phys. Lett. 79, 2752 (2001); http://dx.doi.org/10.1063/1.1404411 (3 pages) | Cited 9 times

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Scanning photoemission microscopy (SPEM) has been used to investigate the effect of morphological defects in GaN films grown on a 6H–SiC substrate on the composition and electronic properties of Ni/GaN interfaces in the temperature range of 25–600 °C. The SPEM imaging and spectroscopy identified a direct relation between the defects and the development of spatial heterogeneity in the interfacial composition, best pronounced after moderate annealing at 300 °C. The Schottky barrier height measured at these heterogeneous interfaces changes with advancement of the Ni–GaN reaction at elevated temperatures but exhibits negligible spatial variations. © 2001 American Institute of Physics.
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68.35.Ct Interface structure and roughness
73.20.At Surface states, band structure, electron density of states
73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
61.72.Cc Kinetics of defect formation and annealing

Intersubband absorption dynamics in coupled quantum wells

T. Müller, R. Bratschitsch, G. Strasser, and K. Unterrainer

Appl. Phys. Lett. 79, 2755 (2001); http://dx.doi.org/10.1063/1.1413728 (3 pages) | Cited 16 times

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We apply an interband pump/intersubband probe technique to monitor the temporal evolution of the electron population in the first and second subband of an undoped GaAs/AlGaAs asymmetric double quantum well after interband optical excitation. The spacing between the two subbands is smaller than the longitudinal optical phonon energy. The time dependence of the intersubband absorption can be explained by a simple rate equation model. We extract an intersubband lifetime of T21 = 100 ps and a recombination time of τ = 410 ps at an excitation density of nS = 2×1011 cm−2. © 2001 American Institute of Physics.
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73.21.Fg Quantum wells
78.67.De Quantum wells
78.66.Fd III-V semiconductors
73.25.+i Surface conductivity and carrier phenomena
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Influence of tensile and compressive strain on the band gap energy of ordered InGaP

J. Novák, S. Hasenöhrl, M. I. Alonso, and M. Garriga

Appl. Phys. Lett. 79, 2758 (2001); http://dx.doi.org/10.1063/1.1413725 (3 pages) | Cited 3 times

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The band gap energy of ordered and strained InxGa1−xP as a function of ternary composition was studied. Epitaxial growth using a metalorganic vapor phase epitaxy technique at a reactor pressure of 20 mbar and Tg = 580 °C allowed us to prepare a set of samples with nearly constant ordering parameter η. Optical measurements were performed at room temperature using a rotating polarizer ellipsometer with a spectral energy range 1.4–5.1 eV. Comparing the experimental data with the theory, we have shown that the band gap energy Eg dependence on composition closely follows the prediction of Wei and Zunger [S. Wei and A. Zunger, Phys. Rev. B 49, 14337 (1994)]. This prediction is more valid as the commonly used parabolic interpolation of Eg between InP and GaP values. © 2001 American Institute of Physics.
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71.20.Nr Semiconductor compounds
68.60.Bs Mechanical and acoustical properties
78.66.Fd III-V semiconductors
78.40.Fy Semiconductors
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors

Reduction of doping and trap concentrations in 4H–SiC epitaxial layers grown by chemical vapor deposition

Tsunenobu Kimoto, Satoshi Nakazawa, Koichi Hashimoto, and Hiroyuki Matsunami

Appl. Phys. Lett. 79, 2761 (2001); http://dx.doi.org/10.1063/1.1413724 (3 pages) | Cited 42 times

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High-purity and thick 4H–SiC(0001) epilayers have been grown by a horizontal hot-wall chemical vapor deposition (CVD) system, which was designed and built at the authors’ group. The background donor concentration has decreased by reducing pressure during CVD, and a low donor concentration of 1–3×1013 cm−3 was achieved by CVD growth at 80 Torr. The free exciton peaks dominated in low- and room-temperature photoluminescence spectra without titanium or point-defect related peaks. The electron mobility reaches 981 cm2/V s at room temperature and 46 200 cm2/V s at 42 K. The total trap concentration could be reduced to 4.7×1011 cm−3 by increasing the input C/Si ratio. © 2001 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Hd Other semiconductors
71.55.Ht Other nonmetals
73.61.Le Other inorganic semiconductors
78.66.Li Other semiconductors
78.55.Hx Other solid inorganic materials
73.50.Dn Low-field transport and mobility; piezoresistance
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Selective growth of GaN on a SiC substrate patterned with an AlN seed layer by ammonia molecular-beam epitaxy

H. Tang, J. A. Bardwell, J. B. Webb, S. Moisa, J. Fraser, and S. Rolfe

Appl. Phys. Lett. 79, 2764 (2001); http://dx.doi.org/10.1063/1.1413956 (3 pages) | Cited 5 times

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Highly selective growth of GaN on 4H–SiC using the SiC substrate as a pseudomask has been demonstrated using the ammonia molecular-beam-epitaxy technique. A total lack of nucleation on the bare SiC surface was observed under typical GaN growth conditions. The nucleation of the GaN layer occurred preferentially from a patterned thin (300 Å) AlN seed layer, which had been predeposited on the SiC surface using the magnetron-sputter-epitaxy technique and patterned into parallel stripes by photolithography and chemically assisted ion-beam etching. Evidence of lateral overgrowth was observed by scanning electron microscopy and x-ray diffraction studies. The GaN stripes grown show extremely smooth side facets due to the lateral growth. © 2001 American Institute of Physics.
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81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.65.Cf Surface cleaning, etching, patterning
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