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Research paper thumbnail of Enhanced vertical and lateral hole transport in high aluminum-containing AlGaN for deep ultraviolet light emitters

Applied Physics Letters, 2013

Improved p-type conductivity is demonstrated in AlGaN:Mg superlattice (SL) cladding layers with a... more Improved p-type conductivity is demonstrated in AlGaN:Mg superlattice (SL) cladding layers with average Al composition ∼60%. The vertical conductivity ranges from 6.6 × 10−5 S/cm at a DC current of 1 mA to ∼0.1 S/cm at 550 mA and approaches the lateral conductivity that was obtained from Hall-effect measurements. The effective acceptor activation energy (EA) in the SL was determined to be 17 meV, nearly 10× smaller than EA in homogeneous p-GaN. The devices sustain current densities of 11 kA/cm2 under DC and up to 21 kA/cm2 under pulsed operation.

Research paper thumbnail of Erratic dislocations within funnel defects in AlN templates for AlGaN epitaxial layer growth

Applied Physics Letters, 2009

We report our transmission electron microscopy observations of erratic dislocation behavior withi... more We report our transmission electron microscopy observations of erratic dislocation behavior within funnel-like defects in the top of AlN templates filled with AlGaN from an overlying epitaxial layer. This dislocation behavior is observed in material where phase separation is also observed. Several bare AlN templates were examined to determine the formation mechanism of the funnels. Our results suggest that they are formed prior to epitaxial layer deposition due to the presence of impurities during template re-growth. We discuss the erratic dislocation behavior in relation to the 2 presence of the phase-separated material and the possible effects of these defects on the optoelectronic properties.

Research paper thumbnail of The structural quality of AlxGa1−xN epitaxial layers grown by digitally alloyed modulated precursor epitaxy determined by transmission electron microscopy

Applied Physics Letters, 2009

Al x Ga 1-x N layers of varying composition (0.5 < x Al < 1.0) grown in the digitallyalloyed modu... more Al x Ga 1-x N layers of varying composition (0.5 < x Al < 1.0) grown in the digitallyalloyed modulated precursor epitaxial regime employing AlN and GaN binary sub-layers by metal organic chemical vapor deposition on AlN templates were characterized by transmission electron microscopy techniques. Fine lamellae were observed in bright field images that indicate a possible variation in composition due to the modulated nature of growth. In higher Ga content samples (x Al < 0.75), a compositional inhomogeniety associated with thicker island regions was observed, which is determined to be due to large Ga-rich areas formed at the base of the layer. Possible causes for the separation of Ga-rich material are discussed in the context of the growth regime used.

Research paper thumbnail of Ordered Nanowire Array Blue/Near-UV Light Emitting Diodes

Research paper thumbnail of Digitally alloyed modulated precursor flow epitaxial growth of AlxGa1−xN layers with AlN and AlyGa1−yN monolayers

Journal of Crystal Growth, 2009

We propose a new growth scheme of digitally alloyed modulated precursor flow epitaxial growth (DA... more We propose a new growth scheme of digitally alloyed modulated precursor flow epitaxial growth (DA-MPEG) using metalorganic and hydride precursors for the growth of Al x Ga 1Àx N layers with high-Al content at relatively low temperatures. The growth of high-quality, high-Al content Al x Ga 1Àx N layers (x Al 450%) that are composed of AlN and Al y Ga 1Ày N monolayers on AlN/sapphire template/substrates by DA-MPEG was demonstrated. The overall composition of the ternary Al x Ga 1Àx N material by DA-MPEG can be controlled continuously by adjusting the Column III mole fraction of the atomic Al y Ga 1Ày N sublayer. X-ray diffraction and optical transmittance results show that the AlGaN materials have good crystalline quality. The surface morphology of DA-MPEG AlGaN samples measured by atomic force microscopy are comparable to high-temperature-grown AlGaN and are free from surface features such as nano-pits.

Research paper thumbnail of Geiger-Mode Operation of GaN Avalanche Photodiodes Grown on GaN Substrates

IEEE Photonics Technology Letters, 2009

Research paper thumbnail of Improvement of quantum efficiency by employing active-layer-friendly lattice-matched InAlN electron blocking layer in green light-emitting diodes

Applied Physics Letters, 2010

Improvement of the internal quantum efficiency in green-light emitting diodes has been achieved u... more Improvement of the internal quantum efficiency in green-light emitting diodes has been achieved using lattice-matched InAlN electron-blocking layers. Higher electroluminescence intensities have been obtained due to better electron confinement in the device active region. The device efficiency has also been found to significantly depend on the InAlN growth temperature. Optimized InAlN growth at ~840 °C results in a lower growth

Research paper thumbnail of Threshold voltage control of InAlN/GaN heterostructure field-effect transistors for depletion- and enhancement-mode operation

Applied Physics Letters, 2010

ABSTRACT

Research paper thumbnail of Enhanced vertical and lateral hole transport in high aluminum-containing AlGaN for deep ultraviolet light emitters

Applied Physics Letters, 2013

Improved p-type conductivity is demonstrated in AlGaN:Mg superlattice (SL) cladding layers with a... more Improved p-type conductivity is demonstrated in AlGaN:Mg superlattice (SL) cladding layers with average Al composition ∼60%. The vertical conductivity ranges from 6.6 × 10−5 S/cm at a DC current of 1 mA to ∼0.1 S/cm at 550 mA and approaches the lateral conductivity that was obtained from Hall-effect measurements. The effective acceptor activation energy (EA) in the SL was determined to be 17 meV, nearly 10× smaller than EA in homogeneous p-GaN. The devices sustain current densities of 11 kA/cm2 under DC and up to 21 kA/cm2 under pulsed operation.

Research paper thumbnail of Erratic dislocations within funnel defects in AlN templates for AlGaN epitaxial layer growth

Applied Physics Letters, 2009

We report our transmission electron microscopy observations of erratic dislocation behavior withi... more We report our transmission electron microscopy observations of erratic dislocation behavior within funnel-like defects in the top of AlN templates filled with AlGaN from an overlying epitaxial layer. This dislocation behavior is observed in material where phase separation is also observed. Several bare AlN templates were examined to determine the formation mechanism of the funnels. Our results suggest that they are formed prior to epitaxial layer deposition due to the presence of impurities during template re-growth. We discuss the erratic dislocation behavior in relation to the 2 presence of the phase-separated material and the possible effects of these defects on the optoelectronic properties.

Research paper thumbnail of The structural quality of AlxGa1−xN epitaxial layers grown by digitally alloyed modulated precursor epitaxy determined by transmission electron microscopy

Applied Physics Letters, 2009

Al x Ga 1-x N layers of varying composition (0.5 < x Al < 1.0) grown in the digitallyalloyed modu... more Al x Ga 1-x N layers of varying composition (0.5 < x Al < 1.0) grown in the digitallyalloyed modulated precursor epitaxial regime employing AlN and GaN binary sub-layers by metal organic chemical vapor deposition on AlN templates were characterized by transmission electron microscopy techniques. Fine lamellae were observed in bright field images that indicate a possible variation in composition due to the modulated nature of growth. In higher Ga content samples (x Al < 0.75), a compositional inhomogeniety associated with thicker island regions was observed, which is determined to be due to large Ga-rich areas formed at the base of the layer. Possible causes for the separation of Ga-rich material are discussed in the context of the growth regime used.

Research paper thumbnail of Ordered Nanowire Array Blue/Near-UV Light Emitting Diodes

Research paper thumbnail of Digitally alloyed modulated precursor flow epitaxial growth of AlxGa1−xN layers with AlN and AlyGa1−yN monolayers

Journal of Crystal Growth, 2009

We propose a new growth scheme of digitally alloyed modulated precursor flow epitaxial growth (DA... more We propose a new growth scheme of digitally alloyed modulated precursor flow epitaxial growth (DA-MPEG) using metalorganic and hydride precursors for the growth of Al x Ga 1Àx N layers with high-Al content at relatively low temperatures. The growth of high-quality, high-Al content Al x Ga 1Àx N layers (x Al 450%) that are composed of AlN and Al y Ga 1Ày N monolayers on AlN/sapphire template/substrates by DA-MPEG was demonstrated. The overall composition of the ternary Al x Ga 1Àx N material by DA-MPEG can be controlled continuously by adjusting the Column III mole fraction of the atomic Al y Ga 1Ày N sublayer. X-ray diffraction and optical transmittance results show that the AlGaN materials have good crystalline quality. The surface morphology of DA-MPEG AlGaN samples measured by atomic force microscopy are comparable to high-temperature-grown AlGaN and are free from surface features such as nano-pits.

Research paper thumbnail of Geiger-Mode Operation of GaN Avalanche Photodiodes Grown on GaN Substrates

IEEE Photonics Technology Letters, 2009

Research paper thumbnail of Improvement of quantum efficiency by employing active-layer-friendly lattice-matched InAlN electron blocking layer in green light-emitting diodes

Applied Physics Letters, 2010

Improvement of the internal quantum efficiency in green-light emitting diodes has been achieved u... more Improvement of the internal quantum efficiency in green-light emitting diodes has been achieved using lattice-matched InAlN electron-blocking layers. Higher electroluminescence intensities have been obtained due to better electron confinement in the device active region. The device efficiency has also been found to significantly depend on the InAlN growth temperature. Optimized InAlN growth at ~840 °C results in a lower growth

Research paper thumbnail of Threshold voltage control of InAlN/GaN heterostructure field-effect transistors for depletion- and enhancement-mode operation

Applied Physics Letters, 2010

ABSTRACT

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