Investigation of cracks in GaN films grown by combined hydride and metal organic vapor-phase epitaxial method

Abstract

Cracks appeared in GaN epitaxial layers which were grown by a novel method combining metal organic vapor-phase epitaxy (MOCVD) and hydride vapor-phase epitaxy (HVPE) in one chamber. The origin of cracks in a 22-μm thick GaN film was fully investigated by high-resolution X-ray diffraction (XRD), micro-Raman spectra, and scanning electron microscopy (SEM). Many cracks under the surface were first observed by SEM after etching for 10 min. By investigating the cross section of the sample with high-resolution micro-Raman spectra, the distribution of the stress along the depth was determined. From the interface of the film/substrate to the top surface of the film, several turnings were found. A large compressive stress existed at the interface. The stress went down as the detecting area was moved up from the interface to the overlayer, and it was maintained at a large value for a long depth area. Then it went down again, and it finally increased near the top surface. The cross-section of the film was observed after cleaving and etching for 2 min. It was found that the crystal quality of the healed part was nearly the same as the uncracked region. This indicated that cracking occurred in the growth, when the tensile stress accumulated and reached the critical value. Moreover, the cracks would heal because of high lateral growth rate.

Porous Quaternary Al0.1In0.1Ga0.8N Film Formation via Photoelectrochemical Etching in HF:C2H5OH Electrolyte

“…Hydrostatic strains associated with point defects have been calculated using equation (15) in Ref. by considering out‐of‐plane strain (ε zz ) and in‐plane strain (ε xx/yy ) components of the films . It could be observed that the films etched in 1:1 and 1:2 solution demonstrated larger ε h values while the films etched in 1:3 and 1:4 showed smaller ε h values than the nonporous film (Fig.…”

“…Raman measurement was used to measure in‐plane biaxial stress relaxation using the following expression:where ∆ԝ , E 2 (high), K R , and σ is Raman shift with respect to nonporous sample, E 2 (high) phonon mode, proportionality factor, and in‐plane biaxial stress relaxation, respectively. The K R values in the range of 4.223 to 4.235, which lied within the reported range for GaN (4.2), InN (9.0), and AlN (4.0) was determined using linear interpolation method by taking into consideration of c (inset of Fig.…”

Surface Alteration of Planar P-Type Gallium Nitride to Porous Structure Using 50 Hz Alternating Current-Assisted Photo-Electrochemical Etching Route

“…Besides a variation in the Raman scattering intensity, shifting of E 2 (high) peak that was related to the in-plane biaxial stress relaxation 45 has been detected in the porous p-GaN films obtained by etching at different AC current. It could be conveniently observed from Figure 12 that the E 2 (high) peaks were shifted to a lower frequency for all the porous films with respect to the non-porous film, signifying the presence of tensile stress in the porous films.…”

Structure, optical spectra and biaxial stress of (0002) AlN epilayers grown on c‐sapphire by high‐temperature chemical vapor deposition

“…4c and d. The FWHM of the Raman mode was always used to evaluate crystal quality [21,29] because it was mainly influenced by point defects and dislocations for nitride films [31][32][33]. As Fig.…”