Surface striation, anisotropic in-plane strain, and degree of polarization in nonpolar m-plane GaN grown on SiC

Abstract

We report the roles of island coalescence rate and strain relaxation in the development of anisotropic in-plane strains, striation feature, and subsequent degree of polarization in NH3-flow-rate-dependent m-plane GaN. In the high-NH3-flow-rate samples, the results of cathodoluminescence, polarized Raman and in situ optical reflectance measurements reveal that a slower coalescence and unrelieved lattice misfit strain lead to larger anisotropic in-plane strains, striated surface and luminescence patterns, and a lower density of basal-plane stacking fault (BSF) and prismatic stacking fault (PSF). In contrast, a lower NH3 flow rate leads to more rapid island coalescence and fully relaxed lattice misfit strain such that relaxed in-plane strains, a reduced striation surface, and a higher density of BSF and PSF are observed. It is suggested that the anisotropic in-plane strains, striation feature, and BSF and PSF density are consequences of how rapidly coalescence occurs and the degree of relaxation of lattice misfit strain. In addition, the simulation results of the k · p perturbation approach confirm a larger anisotropic strain results in a smaller degree of polarization. The research results provide important information for optimized growth of nonpolar III-nitrides.

Anisotropic strain relaxation and the resulting degree of polarization by one- and two-step growth in nonpolar a-plane GaN grown on r-sapphire substrate

“…All the observed modes agree with the polarization selection rules. 3 The two dotted lines (531.8 and 568.0 cm À1 ) show the phonon frequencies A 1 (TO) and E 2 -high, respectively, for strain-free GaN. The frequency shifts Dx ¼ ðx À x 0 Þ can be described as a function of in-plane strain De yy and De zz : 12 …”

“…3 C 11 ¼ 390, C 12 ¼ 145, and C 13 ¼ 106 GPa are the elastic stiffness constants. 3 A 1 (TO) mode in the xðzzÞ x configuration and E 2 (high) mode in the xðyyÞ x configuration are chosen to estimate the in-plane strains by calculating Eqs. (1) and (2).…”

“…3,16 The oscillator strength and degree of polarization from the conduction band to the highest ðE 1 Þ, second highest ðE 2 Þ, and third highest ðE 3 Þ valence band are calculated in terms of anisotropic in-plane strains e yy and e zz . Simulations are performed using in-house code written for Matlab software.…”

“…[1][2][3][4] These nitride devices are generally grown along the polar c-axis, where the huge built-in electric field decreases the overlap between the electron and hole wave functions and degrades the device performance. 3 The growth of wurtzite III-nitrides along the nonpolar direction can overcome the quantum-confined Stark effect and enhance the radiative efficiency of LEDs. 3 Nonpolar III-nitrides grown on foreign substrates show high densities of threading dislocation (TD), basal stacking fault (BSF), and prismatic stacking fault (PSF).…”

“…3 The growth of wurtzite III-nitrides along the nonpolar direction can overcome the quantum-confined Stark effect and enhance the radiative efficiency of LEDs. 3 Nonpolar III-nitrides grown on foreign substrates show high densities of threading dislocation (TD), basal stacking fault (BSF), and prismatic stacking fault (PSF). [5][6][7][8] Defect reduction of III-nitride films is a key issue to fabricate high quality devices.…”