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24 Jan 2000

Volume 76, Issue 4, pp. 397-519

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Photoenhanced wet oxidation of gallium nitride

L.-H. Peng, C.-H. Liao, Y.-C. Hsu, C.-S. Jong, C.-N. Huang, J.-K. Ho, C.-C. Chiu, and C.-Y. Chen

Appl. Phys. Lett. 76, 511 (2000); http://dx.doi.org/10.1063/1.125804 (3 pages) | Cited 28 times

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We investigate the photo-oxidation process and the corresponding passivation effects on the optical properties of unintentionally doped n-type gallium nitride (GaN). When illuminated with a 253.7 nm mercury line source, oxidation of GaN is found to take place in aqueous phosphorus acid solutions with pH values ranging from 3 to 4. At room temperature, the photo-oxidation process is found reaction-rate limited and has a peak value of 224 nm/h at pH=3.5. Compared with the as-grown GaN layers, threefold enhancement in the photocurrent and photoluminescence response are observed on the oxidized GaN surfaces. These results are attributed to the surface passivation effects due to the deep ultraviolet-enhanced wet oxidation on GaN. © 2000 American Institute of Physics.
Show PACS
81.65.Mq Oxidation
81.65.Rv Passivation
81.05.Ea III-V semiconductors
82.50.-m Photochemistry
72.40.+w Photoconduction and photovoltaic effects
73.25.+i Surface conductivity and carrier phenomena
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
78.55.Cr III-V semiconductors

Picosecond photoacoustics using common-path interferometry

Mehrdad Nikoonahad, Shing Lee, and Haiming Wang

Appl. Phys. Lett. 76, 514 (2000); http://dx.doi.org/10.1063/1.125805 (3 pages) | Cited 5 times

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A pump-probe technique based on the detection of optical phase changes at the surface is described. A common-path interferometer in which the reference and probe pulses interrogate the surface immediately (∼500 ps) before and after the pump pulse is demonstrated. The primary application of this system is film thickness measurement in integrated circuit processing. Pulses 60 to 100 fs wide, from a Ti-sapphire laser at 800 nm, are brought to a 5 μm focus on the surface, resulting in picosecond acoustic pulses in the film. Echoes from film interfaces, upon arrival at the surface, lead to a phase change in the probe beam which is measured. Results from tungsten, aluminum, and copper film structures are presented. © 2000 American Institute of Physics.
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43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
07.60.Ly Interferometers
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Microtip-assisted metal–insulator transition in a layered chalcogenide

W. Yamaguchi, O. Shiino, T. Endo, K. Kitazawa, and T. Hasegawa

Appl. Phys. Lett. 76, 517 (2000); http://dx.doi.org/10.1063/1.125806 (3 pages) | Cited 1 time

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The layered compound 1T–TaS1.7Se0.3 forms a nanoscale domain structure, separated by mesh-like domain walls, above its bulk metal–insulator transition temperature TMI of ∼ 180 K. Scanning tunneling microscopy and spectroscopy of the compound demonstrated that each metallic domain can be converted to insulating one by successive scans of the probe tip just above TMI. This tip-assisted phenomenon is consistently explained by assuming that the domain structure arises from irregular distortion of charge density waves, and that the stacking pattern of charge density waves plays an essential role in the metal–insulator transition. © 2000 American Institute of Physics.
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72.60.+g Mixed conductivity and conductivity transitions
71.30.+h Metal-insulator transitions and other electronic transitions
71.45.Lr Charge-density-wave systems
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
61.46.-w Structure of nanoscale materials
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