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

Abstract

Anisotropic strain relaxation and the resulting degree of polarization of the electronic transition in nonpolar a-plane GaN using one-and two-step growth are studied. By using two-step growth, a slower coalescence and a longer roughening-recovery process lead to larger anisotropic strain relaxation, a less striated surface, and lower densities of basal stacking fault (BSF) and prismatic stacking fault (PSF). It is suggested that anisotropic in-plane strains, surface striation, and BSF and PSF densities in nonpolar a-GaN are consequences of the rate of coalescence, the period of roughening-recovery process, and the degree of anisotropic strain relaxation. In addition, the two-step growth mode can enhance the degree of polarization of the electronic transition. The simulation results of the kÁp perturbation approach show that the oscillator strength and degree of polarization of the electronic transition strongly depend on the in-plane strains upon anisotropic in-plane strain relaxation. The research results provide important information for optimized growth of nonpolar III-nitrides. By using two-step growth and by fabricating the devices on the high-quality nonpolar free-standing GaN substrates, high-efficiency nonpolar a-plane InGaN LEDs can be realized. Nonpolar a-plane InGaN/GaN LEDs can exhibit a strongly polarized light to improve the contrast, glare, eye discomfort and eye strain, and efficiency in display application. V C 2013 AIP Publishing LLC. [http://dx.

Experimental and theoretical study of polarized photoluminescence caused by anisotropic strain relaxation in nonpolar a-plane textured ZnO grown by a low-pressure chemical vapor deposition

“…16 The degree of polarization of PL in a-plane ZnO should be maintained even when passed through the textured surface layer. Similar to nonpolar a-plane GaN in our previous study, 11 it is suggested that anisotropic in-plane strains, sample quality, and degree of polarization of PL in nonpolar a-ZnO are consequences of the degree of anisotropic strain relaxation. By using the kÁp perturbation approach to simulate the electronic band of nonpolar a-plane ZnO, the transition energy, 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 bands are calculated in terms of anisotropic in-plane strains e yy and e zz .…”

“…By using the kÁp perturbation approach to simulate the electronic band of nonpolar a-plane ZnO, the transition energy, 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 bands are calculated in terms of anisotropic in-plane strains e yy and e zz . 11,17 The material parameters of ZnO, such as energy parameters, valence band deformation potentials, and elastic stiffness constants, are adopted from Refs. 18 and 19.…”

“…[7][8][9][10] In addition, polarized emission in non-polar a-plane gallium nitride (GaN) attributed to anisotropic inplane strain has also been observed. 11 The phenomenon has been identified by strain-dependent electronic band structure modification through the kÁp perturbation approach. 11 The oscillator strength and degree of polarization of the electronic transition have been shown to strongly depend on the in-plane strains.…”

“…11 The phenomenon has been identified by strain-dependent electronic band structure modification through the kÁp perturbation approach. 11 The oscillator strength and degree of polarization of the electronic transition have been shown to strongly depend on the in-plane strains. Although the argument of valence band structure modification has been adopted to qualitatively explain the polarized optical properties in nonpolar a-plane ZnO, electronic band structures are not theoretically calculated in terms of the in-plane strains.…”

Efficient carrier relaxation and fast carrier recombination of N-polar InGaN/GaN light emitting diodes

“…[1][2][3][4][5][6] The carrier localization effect caused by indium aggregation and the quantum-confined Stark effect (QCSE) resulting from a strain-induced piezoelectric field in those devices, generally grown along the Ga-polar c-axis [0001], were shown to determine the optical properties and device characteristics. [1][2][3][4][5][6] In spite of successful applications in optoelectronic devices, Ga-polar III-nitrides show some limitations. Because the optimal growth temperatures for the growth of GaN and InN are different, the low-quality, high-In InGaN exhibits a higher defect density and lower green light efficiency, i.e., the well-known "green gap."…”