Modification of the valence band structures of polar and nonpolar plane wurtzite-GaN by anisotropic strain

Abstract

The influence of anisotropic strain on the valence band structure and related properties, including excitonic transition energies, transition polarization selection rules, band-edge hole effective masses, and exciton reduced effective masses, of polar and nonpolar plane GaN are systematically investigated using the well-known k⋅p Hamiltonian approach. We re-examine the band deformation potentials D3 and D4, and interband hydrostatic deformation potentials a1 and a2, and find that they take the values 9.4, −4.7, −3.0, and −12.4 eV, respectively. In order to correctly interpret the optical properties of GaN, the spin-orbit coupling effect cannot be neglected. Our numerical calculations show that pure linear polarization light emissions and absorptions can be obtained. In addition, the two topmost valence subbands can be effectively separated to reduce the band-edge density of state by manipulating the strain states in GaN epilayers, which is favorable for laser diode design. Furthermore, the band-edge hole effective masses exhibit significant in-plane anisotropy and are sensitive to the residual strain, while the influence of the residual strain on the exciton reduced effective masses is relatively weak.

Stacking fault‐related luminescence features in semi‐polar GaN

“…It appears as an almost horizontal line marking the intersection of the c plane with the a plane cross-section, thus confirming the earlier assignment to BSFs [3,5]. The slightly noisy background is caused by the partially overlapping luminescence from donor-bound excitons (D 0 , X), which is red shifted due to strain [11] in that part of the stripes which was grown above the SiO 2 mask (wing region). At the very top of the cross-section, directly above the SiO 2 mask opening (column region), the material quality is best.…”

Studies about wafer bow of freestanding GaN substrates grown by hydride vapor phase epitaxy

“…Hence the bowing of the crystal planes could be directly determined irrespective of any thickness variations which might disturb optical curvature measurements. The strain in the samples at the final surface could additionally be determined from the position of the donor-bound excitonic line measured by lowtemperature photoluminescence (PL; T % 15 K) following the data published by Fu et al [7]. The ex situ measurements have been typically performed on small pieces of the 2 00 wafers comparable in size and shape which we assumed to be spherically bowed, whereas the curvature of strongly bowed wafers may be influenced by the wafer size for larger areas.…”

Photoreflectance investigation of band gap renormalization and the Burstein–Moss effect in Si doped GaN grown by MOVPE

“…To accurately evaluate the interplay between BGR and BM, it is necessary hence to correct the value of the measured energy band gap by removing the contribution of strain. In connection with the current study, the strain-dependent energy corrections E s Δ are calculated as follows [4,[25][26][27]:…”

“…Å are the unstrained bulk GaN lattice parameters [28]. Here we take the values of a 1 , a 2 , D 3 and D 4 to be À 3 eV, À 12.4 eV, À9.4 eV and À4.7 eV, which are accurately determined by Fu et al using more precise results obtained from high-quality strain-free GaN films [26]. It should be emphasized that these values are somewhat different from the ones determined recently by Ishii et al [29] using reflectance measurements.…”

“…(7), the evolution of the band gap energy with electron concentration was calculated. The band gap energy of the intrinsic GaN E g0 ( ) was taken to be 3.434 eV [26]. It is found that the theoretical values overestimate the experimental ones as shown in Fig.…”