The epitaxial lateral overgrowth (ELO) gallium nitride (GaN) was grown with high fill factor using metal organic
chemical vapor deposition (MOCVD). The inductively coupled plasma (ICP) etching of ELO-GaN based on
Cl2/Ar/SiCl4 gas mixture was performed. Surface properties of ELO-GaN subjected to ICP etching have been
investigated and optimized etching condition in ELO-GaN with ICP etching is presented. Radiofrequency (RF) power
and the flow rate of Cl2 gas were modified during the experiments. The window region, wing region and the edge region
of ELO-GaN pattern present different etching characteristics. Different etching conditions were studied to get the
minimized plasma-induced damage, relatively high etching rates, and excellent surface profiles. Etch depths of the
etched ELO-GaN with smooth surface up to about 19 μm were achieved. The most suitable three-step etching condition
is discussed with the assessment based on the morphology observation of the etched surface of ELO-GaN patterns.
We report the internal quantum efficiency (IQE) and external quantum efficiency (EQE) of m-plane InGaN-based
LEDs and c-plane LEDs emitting at 400 nm. According to excitation density dependent photoluminescence (PL)
measurements, the IQE values for the m-plane LEDs are approximately 70% higher than that for c-plane reference
LEDs with the same structure (multiple-quantum well active region with 3nm In0.01Ga0.99N barriers) and similar
emission wavelength (400nm) albeit on sapphire substrate. Electroluminescence (EL) measurements reveal that the
external quantum efficiency (EQE) from both LEDs shows negligible droop under electrical injection due to the
employment of thin In0.01Ga0.99N barriers, i.e. coupled quantum wells, in the active regions. However, with
increasing current, the EL intensity of the m-plane LEDs increases more rapidly than that of the c-plane LEDs, with
the EL intensity reaching its peak value at ~240 Acm-2 for the m-plane LEDs and ~420 Acm-2 for the c-plane LEDs.
Consistent with the IQE values obtained from the PL measurements, the m-plane LEDs exhibit ~ 60% higher EQE
values than the c-plane counterparts. It is also worth to mention that increasing the emission wavelength (from 400
nm to 435 nm) for the m-plane LEDs does not affect the efficiency retention at high injection levels.
The concept of non-polar (11bar00) m-plane GaN on Si substrates has been demonstrated by initiating growth on the
vertical (1bar1bar1) sidewalls of patterned Si(112) substrates using metalorganic chemical vapor deposition. The Si(112)
substrates were wet-etched to expose {111} planes using stripe-patterned SiNx masks oriented along the [1bar10] direction.
Only the vertical Si (1bar1bar1) sidewalls were allowed to participate in GaN growth by masking other Si{111} planes using
SiO2, which led to m-plane GaN films. Growth initiating on the Si (1bar1bar1) planes normal to the surface was allowed to
advance laterally and also vertically towards full coalescence. The full width at half maximum values for the GaN mplane
x-ray diffraction rocking curves were 9 and 27 arcmin when rocked toward the GaN a-axis (parallel to stripes) and
the GaN c-axis (perpendicular to stripes), respectively. Room-temperature photoluminescence showed strong band-edge
emission with an intensity comparable to that of laterally overgrown c-plane GaN. InGaN double heterostructure active
layers grown on these m-GaN templates on Si exhibited two times higher internal quantum efficiencies as compared to
their c-plane counterparts at comparable carrier densities. These results demonstrate a promising method to obtain highquality
non-polar m-GaN films on large area, inexpensive Si substrates.
High brightness InGaN light emitting diodes (LEDs) require high quantum efficiency and its retention at high injection
levels. The efficiency drop at a high injection levels in InGaN light emitting diodes (LEDs) has been attributed, e.g. to
polarization field on polar c-plane InGaN and the heavy effective hole mass which impedes high hole densities and
transport in the active quantum wells. In this study, we carried out a comparative investigation of the internal quantum
efficiency (IQE) of InGaN active region in LED structures using resonant optical excitation for layers with polar (0001)
orientation on c-plane sapphire, and nonpolar (1-100) m-plane orientation, the latter on specially patterned Si and on m-plane bulk GaN. Analysis of the resonant photoluminescence (PL) intensity as a function of the excitation power
indicate that at comparable generated carrier concentrations the IQE of the m-plane InGaN on Si is approximately a
factor of 2 higher than that of the highly optimized c-plane layer. At the highest laser excitation level employed
(corresponding carrier concentration n ~ 1.2 x 1018 cm-3), the m-plane LED structure on Si has an IQE value of
approximately 65%. We believe that the m-plane would remain inherently advantageous, particularly at high electrical
injection levels, even with respect to highly optimized c-plane varieties. The observations could be attributed to the lack
of polarization induced field and the predicted increased optical matrix elements.
The internal quantum efficiency (IQE) and relative external quantum efficiency (EQE) in InGaN LEDs emitting at 400
nm with and without electron blocking layers (EBLs) on c-plane GaN and m-plane GaN were investigated in order to
shed some light on any effect of polarization charge induced field on efficiency killer carrier spillover. Without an EBL
the EQE values suffered considerably (by 80 %) for both orientations, which is clearly attributable to carrier spillover.
Substantial carrier spillover in both polarities, therefore, suggests that the polarization charge is not the major factor in
efficiency degradation observed, particularly at high injection levels. Furthermore, the m-plane variety with EBL did not
show any discernable efficiency degradation up to a maximum current density of 2250 Acm-2 employed while that on cplane
showed a reduction by ~ 40 %. In addition, IQE of m-plane LED structure determined from excitation power
dependent photoluminescence was ~80 % compared to 50 % in c-plane LEDs under resonant and moderate excitation
condition. This too is indicative of the superiority of m-plane LED structures, most probably due to relatively larger
optical matrix elements for m-plane orientation.
Vertical double heterostructures based on GaN were prepared and investigated for their current voltage characteristics
and compared to theory. In our quest to observe negative differential resistance (NDR) phenomenon based on quantum
mechanical tunneling to, we fabricated resonant tunneling diode (RTD) like structures grown on low defect density and
high quality templates prepared by metal organic chemical vapor deposition using in situ SiN nanonetwork induced
epitaxial lateral overgrowth. The measured threading dislocation density of the template was in the range of 107 cm-2.
Inductively coupled plasma reactive ion etching (ICP-RIE) where in enhanced chemical etching mode was used for
reducing the detrimental surface defects on the mesa walls which otherwise contribute to current. Double barrier
structures with varying barrier and quantum well thicknesses as well as doping profiles were tested for their I-V
characteristics. The rectifying phenomenon occurred as a result of depletion region in GaN above the top Al(Ga)N layer
and asymmetric barrier shape of GaN RTD-like structure due to polarization. With the aid of calculated band structure
and resultant doping profile optimization, we now observe what appears to be resonant increase in current, the source of
which is not yet clear, at quantum states of the well.
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