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The optical quality of semipolar (1 101)GaN layers was explored by time- and polarization-resolved photoluminescence spectroscopy. High intensity bandedge emission was observed in +c-wing regions of the stripes as a result of better structural quality, while -c-wing regions were found to be of poorer optical quality due to basal plane and prismatic stacking faults (BSFs and PSFs) in addition to a high density of TDs. The high optical quality region formed on the +cwings was evidenced also from the much slower biexponential PL decays (0.22 ns and 1.70 ns) and an order of magnitude smaller amplitude ratio of the fast decay (nonradiative origin) to the slow decay component (radiative origin) compared to the -c-wing regions. In regard to defect-related emission, decay times for the BSF and PSF emission lines at 25 K (~ 0.80 ns and ~ 3.5 ns, respectively) were independent of the excitation density within the range employed (5 – 420 W/cm2), and much longer than that for the donor bound excitons (0.13 ns at 5 W/cm2 and 0.22 ns at 420 W/cm2). It was also found that the emission from BSFs had lower polarization degree (0.22) than that from donor bound excitons (0.35). The diminution of the polarization degree when photogenerated carriers recombine within the BSFs is another indication of the negative effects of stacking faults on the optical quality of the semipolar (1101)GaN. In addition, spatial distribution of defects in semipolar (1101)-oriented InGaN active region layers grown on stripe patterned Si substrates was investigated using near-field scanning optical microscopy. The optical quality of -c- wing regions was found to be worse compared to +c-wing regions due to the presence of higher density of stacking faults and threading dislocations. The emission from the +c-wings was very bright and relatively uniform across the sample, which is indicative of a homogeneous In distribution.

Nonpolar m -plane GaN layers were grown on patterned Si (112) substrates by metal-organic chemical vapor deposition (MOCVD). A two-stage growth procedure involving a low-pressure (30 Torr) first stage to ensure formation of the m -plane facets and a high-pressure stage (200 Torr) for improvement of optical quality was employed. The layers grown in two steps show improvement of the optical quality: the near-bandedge photoluminescence (PL) intensity is about 3 times higher than that for the layers grown at low pressure, and deep emission is considerably weaker. However, emission intensity from m- GaN is still lower than that of polar and semipolar ( 1100 ) reference samples grown under the same conditions. To shed light on this problem, spatial distribution of optical emi ssion over the c+ and ci wings of the nonpolar GaN/Si was studied by spatially resolved cathodoluminescence and near-field scanning optical microscopy. Keywords: GaN, nonpolar, m-plane, Si substrate, MOCVD, time-resolved photoluminescence, near-field scanning optical microscopy

Diffusion lengths of photo-excited carriers along the c-direction were determined from photoluminescence (PL) measurements in p- and n-type GaN epitaxial layers grown on c-plane sapphire by metal-organic chemical vapor deposition. The investigated samples incorporate a 6 nm thick In 0.15 Ga 0.85 N active layer capped with either 500 nm p-GaN or 1300 nm n-GaN. The top GaN layers were etched in steps and PL from the InGaN active region and the underlying layers was monitored as a f unction of the top GaN thickness upon pho togeneration near the surface region by above bandgap excitation. Taking into consideration the absorption in the active and underlying layers, the diffusion lengths at 295 K and at 15 K were measured to be about 92 7r nm and 68 7r nm for Mg-doped p-type GaN and 432 30r nm and 316 30r nm for unintentionally doped n-type GaN, respectively. Cross-sectional cathodoluminescence line-scan measurement was performed on a separate sample and the diffusion length in n-type GaN was measured to be 280 nm. Keywords: Diffusion length, GaN, Photoluminescence, Cathodoluminescence.

Semipolar (11macron01) GaN layers and GaN/InGaN LED structures were grown by metal-organic chemical vapor deposition on patterned (001) Si substrates. Optical properties of the semipolar samples were studied by steady-state and time-resolved photoluminescence (PL). Photon energies and intensities of emission lines from steady-state PL as well as carrier decay times from time-resolved PL were correlated with the distributions of extended defects studied by spatially resolved cathodoluminescence and nearfield scanning optical microscopy. Intensity of donor-bound exciton (DX) emission from both coalesced and non-coalesced semipolar layers is comparable to that of state-of-art c-plane GaN template. To gain insight into the contribution from near surface region and deeper portion of the layers to carrier dynamics in polar c-plane and semipolar (11macron01) GaN, time-resolved PL was measured with two different excitation wavelengths of 267 and 353 nm, which provide different excitation depths of about 50 nm and 100 nm, respectively. Time-resolve PL data indicate that the near-surface layer is relatively free from nonradiative centers (point and/or extended defects), while deeper region of the semipolar film (beyond of ~100 nm in depth) is more defective, giving rise to shorter decay times.

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.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Formation of defects in semipolar (11¯01)-oriented GaN layers grown by metal-organic chemical vapor deposition on patterned Si (001) substrates and their effects on optical properties were investigated by steady-state and time-resolved photoluminescence (PL) and spectrally and spatially resolved cathodoluminescence (CL). Near-band edge emission is found to be dominant in the c+-wings of semipolar (11¯01)GaN, which are mainly free from defect-related emission lines, while the c– wings contain a large number of basal stacking faults. When the advancing c+ and c— fronts meet to coalesce into a continuous film, the existing stacking faults contained in c— wings continue to propagate in the direction perpendicular to the c-axis and, as a result, the region dominated by stacking fault emission is extended to the film surface. Additional stacking faults are observed within the c+ wings, where the growing c+ wings of GaN are in contact with the SiO2 masking layer. Out-diffusion of oxygen/silicon species and conce...