Cross‐sectional and surface Raman mapping of thick GaN layers

Abstract

Raman scattering spectroscopy was utilized for investigation of the structural properties of thick GaN layers. These layers with thickness ~ 40 µm have been grown by HVPE technique on the sapphire substrates. The investigations have been focused on the strain distribution in GaN layer cross-section as a function of distance from an interface sapphire/GaN and mapping of the surface and of the inner layer, near the sapphire/GaN interface. From the observed phonon shifts in the Raman spectra strain differences lower than 6.4×10corresponding to stress differences of 240 MPa were estimated across the thick GaN epitaxial layer. The measurements exhibit that strain in the layer causes changes in the Raman spectra and allow determining the relaxation process in the crystal. The obtained results confirmed, that the mode frequencies in the measured Raman spectra in both directions (parallel or perpendicular to the growth direction) for layer thicknesses over 30 µm are comparable with typical values for bulk material and match the low strain in the structure due to relaxation processes.

Stress control by micropits density variation in strained AlGaN/GaN/SiN/AlN/Si(111) heterostructures

“…On figure strain variation of GaN layer can be observed due to shifts of GaN E 2 H peaks. Similar effect was observed for GaN by other research groups . Summary of parameters concluded from microRaman spectra studies can be found in Table .…”

Gallium Nitride Based Electrode for High‐Temperature Supercapacitors

“…[ 24 ] In addition, the Raman spectrum of porous GaN emerged A 1 (TO) and E 1 (TO) stretching modes with signal ≈527 and 554 cm −1 respectively, which ascribed to the large number of defects introduced in the electrochemistry etching process. [ 25 ] The Fourier transform infrared spectrum (Figure S6, Supporting Information) of GaN, GaN/NCO‐2 heterostructure and NCO further identify the above conclusions. The stretching mode of GaN, MO, along with MN is gathered.…”

Vacancy-modified few-layered GaN crystal for novel high-temperature energy storage

“…19 In addition to the E 2 (high) phonon vibration modes, the A 1 (TO) phonon vibration mode with a peak at 529.3 cm −1 and the E 1 (TO) phonon vibration mode with a peak at 558.8 cm −1 are observed, because of the exposure of more defects on the different GaN-2.5 h crystal surfaces. 20 According to previous reports, the vibration modes of 417.2 cm −1 and 657 cm −1 are caused by vacancies inside the lattice and defect level occurring in the conduction band minimum (CBM) of the GaN crystal. 21,22 In Fig.…”