Semipolar (1-101) GaN layers were grown by metal-organic chemical vapor deposition on patterned (001) Si substrates.
The effects of reactor pressure and substrate temperature on optical properties of (1-101) GaN were studied by steadystate
and time-resolved photoluminescence. The optical measurements revealed that the optical quality of (1-101)-
oriented GaN is comparable to that of c-plane GaN film grown on sapphire. Slow decay time constants, representative of
the radiative recombination, for semipolar (1-101)GaN grown at 200 Torr are found to be very long (~1.8 ns), comparable
to those for the state-of-art c-plane GaN templates grown using in situ epitaxial lateral overgrowth through silicon nitride
nano-network. Defect distribution in the GaN stripes was studied by spatially resolved cathodeluminescence
measurements. The c+-wing regions of the GaN stripes were found to be dominated by a (D0,X) emission. Only a thin
slice of emission around 3.42 eV related to basal stacking faults was revealed in c--wing regions.
We report on the effects of substrate temperature and surface morphology of p-GaN templates on the
properties of ZnO:Ga (GZO) layers grown by plasma-assisted molecular beam epitaxy. Substrate temperature varying
from 200 °C to 450°C was found to have only a moderate effect on the electrical properties of GZO films but it greatly
affects the surface morphology of the GZO films. The surface morphology and growth mode of GZO were also found to
be considerably affected by the surface morphology of underlying p-GaN templates. On p-GaN templates with a smooth
surface (RMS = 0.4 nm) featured by clear atomic steps, GZO layers grew in 2D growth mode and exhibited smooth
surfaces with RMS roughness of 2 nm. In contrast, on p-GaN without clear atomic steps but having comparable surface
roughness of 0.6 nm, GZO layers grew in 3D growth mode and exhibited rough surface (RMS roughness of ~17.0-20.0
nm). The results of surface roughness are consistent with those from TEM measurements. The lowest resistivity of
~2.3×10-4 Ω·cm for as-grown GZO layers has been achieved at substrate temperature of 350°C, while the data for 2D
GZO layers was affected by a parallel conduction channel from underneath GaN and require further studies. Although
the differences in electrical properties and surface morphology existed, the GZO layers grown on different p-GaN
templates showed optical transparency higher than 90% in the visible spectral range. The performance of 3D GZO layers
as p-electrode was tested in InGaN light emitting diodes.
InGaN light emitting diodes (LEDs), which have become key components of the lighting technology owing to
their improved power conversion efficiencies and brightness, still suffer from efficiency degradation at high
injection levels. Experiments showing sizeable impact of the barrier height provided by an electron blocking layer
(EBL) or the electron cooling layer prior to electron injection into the active region strongly suggest that the electron
overflow resulting from ballistic and quasi-ballistic transport is the major cause of efficiency loss with increasing
injection. Our previous report using a first order simple overflow model based on hot electrons and constant LO
phonon scattering rates describes well the experimental observations of electron spillover and the associated
efficiency degradation in both nonpolar m-plane and polar c-plane LEDs with different barrier height EBLs and
electron injection layers. LEDs without EBLs show three to five times lower efficiencies than those with
Al0.15Ga0.85N EBLs due to significant electron overflow to the p-type region in the former. For effective means of
thermalization in the active region within their residence time and possibly longitudinal optical phonon lifetime, the
electrons were cooled prior to their injection via a staircase electron injector, i.e. an InGaN staircase structure with
step-wise increased In composition. The investigated m-plane and c-plane LEDs with incorporation of staircase
electron injector show comparable electroluminescence performance regardless of the status of EBL. This paper
discusses hot electron effects on efficiency loss, means to cool the electrons prior to injection.
Non-polar (1-100 ) and semipolar (1-101)GaN layers were grown on (112) and (001) Si substrates, respectively, by metalorganic
chemical vapor deposition. In both cases, grooves aligned parallel to the <110> Si direction were formed by
anisotropic wet etching to expose vertical {111}Si facets for growth initiation. The effect of growth conditions (substrate
temperature, chamber pressure, ammonia and trimethylgallium flow rates) on the growth habits of GaN was studied. It
was found that low pressure and low ammonia flow rate are beneficial for m-facet formation, while high ammonia flow
rate promotes formation of (1-101) facets. Steady-state and time-resolved photoluminescence measurements revealed that
the optical quality of (1-101) oriented GaN is comparable to that of c-plane GaN film grown on sapphire. The nonpolar
(1-100 ) GaN shows only weak emission and fast non-radiative recombination rate. The poor optical quality of the mplane
GaN can be explained by carbon incorporation during the growth under low pressure. Although further
optimization of the growth conditions for better optical quality is required, preliminary results obtained for semipolar
(1-101) -oriented GaN are encouraging.
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