Valence subband structures of (101̄0)-GaN/AlGaN strained quantum wells calculated by the tight-binding method

Abstract

The effect of biaxial strain on the valence bands in (101̄0)-GaN/AlGaN quantum wells (QWs) is theoretically investigated, using the sp3 tight-binding method. The effective mass around the valence band edge in unstrained (101̄0) QWs is reduced to about 1/2 that of (0001) QWs. Under compressive strain, the subband non-parabolicity near the band edge is further reduced due to heavy-hole/light-hole splitting. The optical matrix elements of [112̄0] polarization in these QWs are twice as large as those in (0001) QWs. The reduced effective mass and large optical matrix elements in the (101̄0) QWs are an advantage for short-wavelength laser diodes based on wurtzite GaN.

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).…”

“…(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.…”

“…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.…”