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  • 1
    Electronic Resource
    Electronic Resource
    Ultraviolet photoenhanced wet etching of GaN in K2S2O8 solution (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 4142-4149 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The mechanism of the UV photoenhanced wet etching of GaN is determined. The UV photoenhanced wet etching does not require an electrical contact to be made to the sample, and nitrides deposited on insulating substrates (such as sapphire) can be etched, unlike photoelectrochemical (PEC) wet etching. The present technique relies on adding an appropriate oxidizing agent, in this case, peroxydisulfate (S2O82−), to KOH solutions. In a similar mechanism to PEC wet etching, the regions of low defect density are preferentially etched, leaving regions of high electron recombination such as threading dislocations relatively intact. The threading dislocations may be physically broken off, either by stirring or by a postetch sonication of the sample in KOH solution. Smoothly etched surfaces can be obtained under the proper conditions. A noble metal mask acts in a catalytic manner, yielding etch rates approximately one order of magnitude greater than those observed using inert masks. The essential role of the free radicals, originating from the peroxydisulfate ion, in the etching reaction is confirmed. The etching reaction is more rapid for more heavily n-type doped samples, and insulating C-doped layers act as an etch stop layer. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1352684
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  • 2
    Electronic Resource
    Electronic Resource
    Physical characterization of ultrathin anodic silicon oxide films (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 3114-3122 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ultrathin oxides formed on p-type (100) Si using anodic oxidation in dilute aqueous NH4OH solution have been characterized by Fourier transform infrared spectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS), and x-ray reflectometry. The aim of the work was to optimize the growth and annealing conditions for fabrication of ultrathin gate oxides. Two alternate growth conditions (potentiostatic and galvanostatic) could be used to grow oxides of thickness between 3 and 16 nm. There was very little difference between the two types of oxides; however, the FTIR asymmetric stretch maximum νm was at slightly higher frequencies and this band was slightly narrower for potentiostatic oxides compared to galvanostatic oxides of the same thickness. For both types of films, νm increased with film thickness, while the corresponding full width at half-maximum decreased. As-grown ∼11-nm-thick films of both types contain 3.8±0.3% -OH (bound as isolated silanol) and 5.0±0.4% -OH (bound as H2O and/or associated silanol) by mass, and have a density of 2.05±0.03 g cm−3 compared with a density of 2.27±0.03 g cm−3 measured for thermal oxides. Thus, the composition of the as-grown anodic oxides can be written as SiO1.93(OH)0.14⋅0.18H2O. Discounting the H content, this converts to an O/Si ratio of 2.25±0.02, which can be compared to the O/Si ratio of 2.27±0.06 measured for as-grown films by XPS. Potentiostatically grown ∼11-nm-thick films were annealed at temperatures between 300 and 900 °C in forming gas. Two different stages were observed as a function of anneal temperature. At temperatures below 500 °C, water and/or associated silanol was ejected from the films. This resulted in a maximum in the stress and/or disorder in the oxides at anneal temperatures of 500 °C. At temperatures above 500 °C, the remainder of the silanol was removed from the films; some kind of stress relief occurred. The oxides became stoichiometric at temperatures 700 °C and above.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357493
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  • 3
    Electronic Resource
    Electronic Resource
    Growth and characterization of anodic oxides on Si(100) formed in 0.1 M hydrochloric acid (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 8761-8769 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Anodic oxides of thickness 1–10 nm have been grown on Si(100) using anodic oxidation at room temperature. The electrolyte was 0.1 M HCl. The effects of the anodic potential, growth time, external visible illumination intensity, substrate doping type, and density on the oxide thickness were determined. Coulometric and etching experiments suggest that no silicon is lost to the 0.1 M HCl solution. Under sufficient visible illumination, the oxide thickness was independent of dopant level for n-type substrates and only weakly dependent for p-type substrates. These results suggest that this technique can be used for accurate dopant profiling, when combined with cyclical etch back and four-point probe electrical measurements. In the dark, the oxide thickness was substantially reduced for n-type substrates. This suggests that this technique can be used for lateral delineation of n- and p-type regions on patterned wafers. The as grown oxides were characterized by x-ray photoelectron spectroscopy, ellipsometry, and x-ray reflectometry. The substrates were characterized by Mott–Schottky analysis which, together with electrochemical polarization curves, assisted in a qualitative description of the oxide growth as a function of doping density and type. Flatband potentials obtained from Mott–Schottky analysis were obtained at pH 1.1 and 11.7, and show a pH dependence of approximately 60 mV/pH unit, which in contrast to previously reported data indicates an ideal behavior. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362502
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  • 4
    Electronic Resource
    Electronic Resource
    Thin anodic oxides formed on GaAs in aqueous solutions (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 7303-7311 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin (0–250 A(ring)) anodic oxides were formed on p-GaAs (100) in aqueous solutions (borate buffer, pH 8.4 and 0.3 M NH4H2PO4, pH 4.4). The thickness, composition, and electrochemical behavior were characterized by x-ray photoelectron spectroscopy, secondary ion mass spectrometry, ellipsometry, and electrochemical impedance spectroscopy. In borate buffer, oxide growth results in a two-layer structure with an outer As2O3-rich layer and ion transfer is mainly diffusion controlled. From the potential dependence of the film thickness a growth rate of 25 A(ring)/V was determined. Due to the formation of a Ga-phosphate precursor layer in NH4H2PO4, films grow under field control which results in a time dependence of oxide thickness and composition. Under pseudosteady state conditions a growth rate of 28 A(ring)/V was obtained. Films formed in NH4H2PO4 have, except for the outer phosphate layer, a fairly uniform composition in depth with a significant enrichment of Ga2O3, and show a 40 times higher specific charge transfer resistance than films formed in borate buffer. The superior quality of the oxide formed in NH4H2PO4 is also reflected in its high stability against H2O etch. In addition, substrate pretreatment and the effects of oxide washing on composition were investigated and the importance of an appropriate preparation of samples for ex situ analysis is demonstrated. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361524
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  • 5
    Electronic Resource
    Electronic Resource
    Mechanism of the growth of native oxide on hydrogen passivated silicon surfaces (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 446-447 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The native oxide growth in water on HF etched, hydrogen passivated silicon surfaces has been studied by 18O labeling techniques, with analysis by secondary ion mass spectrometry, Fourier transform infrared spectroscopy, and x-ray photoelectron spectroscopy. It is shown that (approximately-greater-than)85% of the oxygen in the native oxide originates from H2O and not from dissolved O2. The role of the dissolved O2/H2O couple is to anodically polarize the electrode, thus driving the H2O/Si-oxide reaction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111124
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  • 6
    Electronic Resource
    Electronic Resource
    Dopant delineation on Si(100) using anodic oxidation and atomic force microscopy (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 2840-2842 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A procedure has been developed for delineation of lateral variations in the doping of Si(100). The procedure relies on the fact that the thickness of electrochemically grown oxide depends on the dopant density and type. By growing the oxide and then etching it off in cycles, the silicon is selectively removed according to the doping density. By using atomic force microscopy, the electrically effective n+, n, and p-type regions of the sample are delineated. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116342
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  • 7
    Electronic Resource
    Electronic Resource
    Growth of high mobility GaN and AlGaN/GaN high electron mobility transistor structures on 4H-SiC by ammonia molecular-beam epitaxy (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 3845-3847 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ammonia molecular-beam epitaxy has been used to grow high-quality epilayers of GaN and AlGaN/GaN heterostructure field-effect transistor (HFET) structures on insulating 4H-SiC. The growth process, which used a magnetron sputter epitaxy deposited buffer layer of AlN, has been described previously. Ex situ pretreatment of the SiC substrate was found to be unnecessary. For a single 2.0 μm thick silicon doped epilayer, a room temperature (RT) electron mobility of 500 cm2/Vs was measured at a carrier density of 6.6×1016 cm−3. For the HFET structure, a room temperature mobility of 1300 cm2/Vs at a sheet carrier density of 3.3×1012 cm−2 was observed, increasing to 11 000 cm2/Vs at 77 K. The surface morphology of the layers indicated a coalesced mesa structure similar to what we observed for growth on sapphire, but with a lower overall defect density and correspondingly larger grain size. The observation of well-resolved Shubnikov de Haas oscillations at fields as low as 3 T indicated a relatively smooth interface. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1379785
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  • 8
    Electronic Resource
    Electronic Resource
    Semi-insulating C-doped GaN and high-mobility AlGaN/GaN heterostructures grown by ammonia molecular beam epitaxy (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 953-955 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A method of growing semi-insulating GaN epilayers by ammonia molecular beam epitaxy through intentional doping with carbon is reported. Thick GaN layers of high resistivity are an important element in GaN-based heterostructure field-effect transistors. A methane ion source was used as the carbon dopant source. The cracking of the methane gas by the ion source was found to be the key to the effective incorporation of carbon. High-quality C-doped GaN layers with resistivities greater than 106 Ω cm have been grown with high reproducibility and reliability. AlGaN/GaN heterostructures grown on the C-doped semi-insulating GaN-based layers exhibited a high-mobility two-dimensional electron gas at the heterointerface, with room-temperature mobilities typically between 1000 and 1200 cm2/V s, and liquid-nitrogen-temperature mobilities up to 5660 cm2/V s. The carrier density was almost constant, with less than 3% change over the measured temperature range. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.124252
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  • 9
    Electronic Resource
    Electronic Resource
    Selective growth of GaN on a SiC substrate patterned with an AlN seed layer by ammonia molecular-beam epitaxy (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 2764-2766 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1413956
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  • 10
    Electronic Resource
    Electronic Resource
    Properties of carbon-doped GaN (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 757-759 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The properties of carbon-doped GaN epilayers grown by molecular-beam epitaxy have been studied by temperature-dependent resistivity, Hall-effect measurements, x-ray diffraction, and by photoluminescence spectroscopy. Carbon doping was found to render the GaN layers highly resistive (〉108 Ω cm) and quench the band edge excitonic emissions. Yellow luminescence is still present in carbon-doped GaN layers. The highly resistive state is interpreted as being caused by direct compensation by the carbon acceptors and by the consequently enhanced potential barrier at the subgrain boundaries. Evidence of dislocations joining to form potential barriers along the subgrain boundaries was observed in photoassisted wet etching experiments on electrically conducting GaN layers. GaN films grown on insulating carbon-doped base layers are of excellent transport and optical properties. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1345816
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