Exciton localization on basal stacking faults in a-plane epitaxial lateral overgrown GaN grown by hydride vapor phase epitaxy

Abstract

We present a detailed study of the luminescence at 3.42 eV usually observed in a-plane epitaxial lateral overgrowth ͑ELO͒ GaN grown by hydride vapor phase epitaxy on r-plane sapphire. This band is related to radiative recombination of excitons in a commonly encountered extended defect of a-plane GaN: I 1 basal stacking fault. Cathodoluminescence measurements show that these stacking faults are essentially located in the windows and the N-face wings of the ELO-GaN and that they can appear isolated as well as organized into bundles. Time-integrated and time-resolved photoluminescence, supported by a qualitative model, evidence not only the efficient trapping of free excitons ͑FXs͒ by basal plane stacking faults but also some localization inside I 1 stacking faults themselves. Measurements at room temperature show that FXs recombine efficiently with rather long luminescence decay times ͑360 ps͒, comparable to those encountered in high-quality GaN epilayers. We discuss the possible role of I 1 stacking faults in the overall recombination mechanism of excitons.

Development of m-plane GaN anisotropic film properties during MOVPE growth on LiAlO2 substrates

“…In-plane and out-of-plane lattice constants were determined from the peak positions taking the distorted hexagonal crystal symmetry into account [9]. Beside the symmetric (1-100) reflection, we chose the (3-302), , and the (2-1-10) and (3-1-20) planes for evaluation in [0001] and [11][12][13][14][15][16][17][18][19][20] direction of GaN, respectively. A low-temperature photoluminescence spectroscopy setup equipped with a 325 nm HeCd laser and polarization filter was used for optical characterization.…”

“…High-resolution X-ray diffraction (HRXRD), X-ray rocking curve (XRC) scans, and XRD reciprocal space mapping (RSM) were employed to check phase purity, strain and crystal quality of the deposited material. The anisotropy of strain was determined by measurements of a set of symmetrical and asymmetrical reciprocal lattice points along [0001] and [11][12][13][14][15][16][17][18][19][20] direction. For this purpose, a number of 2Theta/Omega scans were performed for different Omega offsets with a Ge(220)-channel-cut crystal for incident and diffracted beam conditioning.…”

“…Simultaneously, the X-ray rocking curve (XRC) full width at half maximum (FWHM) values become strongly dependent on incident X-ray beam direction beyond this critical thickness. Anisotropic in-plane compressive strain is initially present and gradually relaxes mainly in the [11][12][13][14][15][16][17][18][19][20] direction when growing thicker films. Low-temperature photoluminescence (PL) spectra are dominated by the GaN near-band-edge peak and show only weak signal related to basal plane stacking faults (BSF).…”

“…A surface roughening is observed caused by the increased size of hillock-like features. Additionally, small steps which are perfectly aligned in (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) planes appear for samples with a thickness of ~0.5 µm and above. Simultaneously, the X-ray rocking curve (XRC) full width at half maximum (FWHM) values become strongly dependent on incident X-ray beam direction beyond this critical thickness.…”

“…(100) LiAlO 2 is an interesting option for this approach because of the very low lattice mismatch with m-plane (1-100) GaN. It amounts to -1.7 % and -0.3 % in [11][12][13][14][15][16][17][18][19][20] and [0001] direction of GaN, respectively, giving rise to anisotropic strain in the layer [3]. In addition to that, the material is produced by the comparably cheap Czochralski pulling method.…”