42 research outputs found
Analytical Study of KOH Wet Etch Surface Passivation for III-Nitride Micropillars
III-Nitride micropillar structures show great promise for applications in
micro light-emitting diodes and vertical power transistors due to their
excellent scalability and outstanding electrical properties. Typically,
III-Nitride micropillars are fabricated through a top-down approach using
reactive ion etch which leads to roughened, non-vertical sidewalls that results
in significant performance degradation. Thus, it is essential to remove this
plasma etch induced surface damage. Here, we show that potassium hydroxide
(KOH) acts as a crystallographic etchant for III-Nitride micropillars,
preferentially exposing the vertical m-plane, and effectively removing
dry etch damage and reducing the structure diameter at up to 36.6 nm/min. Both
KOH solution temperature and concentration have a dramatic effect on this wet
etch progression. We found that a solution of 20% AZ400K (2% KOH) at 90 C is
effective at producing smooth, highly vertical sidewalls with RMS surface
roughness as low as 2.59 nm, ideal for high-performance electronic and
optoelectronic devices.Comment: 7 pages, 7 figure
Carrier lifetimes in green emitting InGaN/GaN disksâinânanowire and characteristics of green light emitting diodes
Improvement in the internal quantum efficiency (IQE) of InGaN/GaN disksâinânanowires by surface passivation is demonstrated. The highest IQE achieved through surface passivation for green emitting (λ=540 nm) InGaN/GaN disksâinânanowires is âŒ53%. Radiative and nonradiative carrier lifetimes are calculated for asâgrown and surface passivated green emitting disksâinânanowires. Passivated green sample exhibits a room temperature radiative lifetime of âŒ748 ps, which is much smaller than that of equivalent quantum wells. Electroluminescence measurements on passivated green light emitting diodes containing InGaN disks demonstrate no roll over or efficiency droop up to 375 A/cm 2 , and exhibit a blueâshift of 7 nm in peak wavelength. An enhancement in the light output due to surface passivation is observable in the relative external quantum efficiency of the surface passivated devices as compared with the asâgrown samples. (© 2013 WILEYâVCH Verlag GmbH & Co. KGaA, Weinheim)Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98222/1/812_ftp.pd
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Electron tomography of (In,Ga)N insertions in GaN nanocolumns grown on semi-polar (112Ì 2) GaN templates
We present results of scanning transmission electron tomography on GaN/(In,Ga)N/GaN nanocolumns (NCs) that grew uniformly inclined towards the patterned, semi-polar GaN( 11 2 Ì 2 ) substrate surface by molecular beam epitaxy. For the practical realization of the tomographic experiment, the nanocolumn axis has been aligned parallel to the rotation axis of the electron microscope goniometer. The tomographic reconstruction allows for the determination of the three-dimensional indium distribution inside the nanocolumns. This distribution is strongly interrelated with the nanocolumn morphology and faceting. The (In,Ga)N layer thickness and the indium concentration differ between crystallographically equivalent and non-equivalent facets. The largest thickness and the highest indium concentration are found at the nanocolumn apex parallel to the basal planes
Electron tomography of (In,Ga)N insertions in GaN nanocolumns grown on semi-polar (11(2)over-bar2) GaN templates
We present results of scanning transmission electron tomography on GaN/(In,Ga)N/GaN nanocolumns (NCs) that grew uniformly inclined towards the patterned, semi-polar GaN( 112Ì 2 ) substrate surface by molecular beam epitaxy. For the practical realization of the tomographic experiment, the nanocolumn axis has been aligned parallel to the rotation axis of the electron microscope goniometer. The tomographic reconstruction allows for the determination of the three-dimensional indium distribution inside the nanocolumns. This distribution is strongly interrelated with the nanocolumn morphology and faceting. The (In,Ga)N layer thickness and the indium concentration differ between crystallographically equivalent and non-equivalent facets. The largest thickness and the highest indium concentration are found at the nanocolumn apex parallel to the basal planes