Optical and structural study of deformation states in the GaN/AlN superlattices

Abstract

We report on the effect of strain on the optical and structural properties of 5-, 10-, and 20-period GaN/AlN superlattices (SLs) deposited by plasma-assisted molecular beam epitaxy. The deformation state in SLs has been studied by high resolution transmission electron microscopy (HRTEM), X-ray diffraction, and micro-Raman, Fourier transform infrared (FTIR), and photoluminescence spectroscopy. HRTEM images showed that the structural quality of the SL layers is significantly improved and the interfaces become very sharp on the atomic level with an increase of the SL periods. A combined analysis through XRD, Raman, and FTIR reflectance spectroscopy found that with increasing number of SL periods, the strain in the GaN quantum wells (QWs) increases and the AlN barrier is relaxed. Based on the dependence of the frequency shift of the E2High and E1TO Raman and IR modes on the deformation in the layers, the values of the biaxial stress coefficients as well as the phonon deformation potentials of these modes in both GaN and AlN were determined. With increasing number of SL periods, the QW emission considerably redshifted in the range lower than the GaN band gap due to the quantum confined Stark effect. The influence of strain obtained by the XRD, Raman, and FTIR spectra on the structural parameters and QW emission of GaN/AlN SLs with different numbers of periods is discussed.

Thermomechanical stress in GaN‐LEDs soldered onto Cu substrates studied using finite element method and Raman spectroscopy

“…AuSn was simulated using hyperbolic sine-type Garofalo model [47] (coefficient constants are 4.62Á10 15 , 2Á10 −5 , 2.07, and 1.02Á10 5 ). GaN T A B L E 1 Phonon deformation potential (PDP), [37][38][39][40] stiffness, [29] and elastic coefficients of wurtzite GaN PDP coefficients (cm −1 ) [37][38][39][40] Stiffness coefficients (GPa) [29] Elastic coefficients (×10 −3 GPa −1 ) a −911(54) [37] C 11 366.9 ± 0. −920 ± 60 [39] c 379 [38] was modeled with an anisotropic elasticity like the stiffness matrix used in Equation 11.…”

“…PDP parameters from different literature sources are reported in Table 1. [37,39,40] They were used in Equation 11) for calculation of different curves of variation of Raman shift (continuous lines in Figure 5). All values are from experimental measurements, with a lower uncertainty in the most recent papers.…”

“…[37] The other coefficients were measured by analyzing GaN epitaxial layers with different amounts of residual strain. [39,40] In this study, the mathematical model was used to obtain the in-plane stress by using the variation of Raman shift in case of mechanical loading. Therefore, the set of Callsen et al [37] was selected for the application in Equation 11.…”

The Effect of Interface Diffusion on Raman Spectra of Wurtzite Short-Period GaN/AlN Superlattices

“…The Raman spectrum of zinc-blende GaN/AlN SLs contains only two optical phonons, while the spectrum of wurtzite GaN/AlN SL contains six optical phonon lines, which is a favorable factor for the development of quantitative diagnostic methods. There are a number of works where Raman spectroscopy was used to quantitatively evaluate important structural parameters of short-period GaN/AlN SLs like their period, thickness of the GaN and AlN layers, sign and magnitude of strain in individual layers comprising SLs [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ]. However, as far as we know, there are no studies yet on the possibility of estimating the degree of interface diffusion in wurtzite short-period GaN/AlN SLs from the data of Raman spectroscopy.…”

Energy transport analysis in a Ga0.84In0.16N/GaN heterostructure using microscopic Raman images employing simultaneous coaxial irradiation of two lasers

“…The parameters to analyze the mode energies are listed in Table I. [39][40][41][42][43][44][45][46] Here, we assume that the shift of mode energy Dx by strain is expressed as 2ae xx þ be zz , which is transformed to…”