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ABSTRACT: The spatial variations of transconductance in AlGaN/GaN heterostructures were mapped using a conducting tip atomic force microscope. The conducting tip locally modulates the two-dimensional electron gas (2DEG) while the change in the drain current was monitored as a function of tip position. A spatial resolution of 250 nm was obtained. This technique enables us to investigate the role of defects in transistor performance. In particular, when biased near the depletion of the 2DEG, the transconductance map displays a cell structure, with low signal regions correlating with the positions of negatively charged threading dislocations. © 2003 American Institute of Physics.
Applied Physics Letters 01/2004; · 3.84 Impact Factor
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ABSTRACT: Using a two-photon laser-scanning microscope (LSM), the spectral and intensity variations of photoluminescence (PL) in a lateral
epitaxially overgrown GaN film were mapped with submicron resolution. The PL results are correlated with the carrier-density
variation obtained by confocal-Raman microscopy and the surface Fermi-level positions measured by scanning Kelvin-force microscopy.
Near-bandgap emission spectra taken in the wing regions provide support for the previously proposed, compensated-impurity
band, which arises from the incorporation of a high concentration of impurities, resulting in a carrier density of ∼1020 cm−3.
Journal of Electronic Materials 04/2003; 32(5):322-326. · 1.47 Impact Factor
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ABSTRACT: We designed and built a unique instrument that combines a two-photon laser scanning microscope (LSM) with an inverted atomic force microscope (AFM). Local photoluminescence (PL) spectroscopy and three-dimensional lithography are demonstrated using the two-photon LSM. High spatial resolution topographic images from the AFM can be recorded simultaneously with the PL images of the same region, allowing us to correlate PL variation and surface features of the sample. The wavelength of the short-pulse laser excitation can be varied continuously from 700 to 800 nm while the detection setup is optimized for signals between 350 and 650 nm. We demonstrate the performance of this instrument by examining the spatial variation of PL signals in GaN samples and by fabricating photonic crystal structures in polymer films. © 2003 American Institute of Physics.
Review of Scientific Instruments 02/2003; 74(3):1211-1216. · 1.37 Impact Factor
