Bending in HVPE GaN free‐standing films: effects of laser lift‐off, polishing and high‐pressure annealing

Abstract

We have studied the effects of laser lift-off and polishing processes on the bending of free-standing HVPE grown GaN thick films. Their structural characteristics were accessed by reciprocal space mapping and lattice parameters measurements as well as by Raman scattering and photoluminescence. The in-plane strain difference between the two faces was found to have determining effect on the bending of the freestanding films. Removing the high-defect-density near-interface region either by melting caused by laser lift-off, or by polishing, or by point defects dissociation caused by high-pressure annealing was found to lead to flattening of the strain distribution along the film thickness and a significant reduction of the bending of the free-standing films.

Self‐separation of thick two inch GaN layers grown by HVPE on sapphire using epitaxial lateral overgrowth with masks containing tungsten

“…Different lattice constants between the backside and the surface of the separated layers have been considered to cause the bowing of freestanding GaN [6]. However, no clear dependency of this difference from the separation temperature was found here.…”

Free‐standing GaN substrates fabricated by a combination of substrate fracturing and chemical lift‐off

“…Bending of as-grown free-standing 500 μm-thick GaN layer was of concave shape and its typical bending radius measured 2.5 m with stylus measurement system. We note that this value is even larger than reported values of asgrown free-standing GaN layer obtained by laser lift-off (1.21 m) [10] and by self-separation (0.43 m) [10]. Figure 4 shows room-temperature CL spectra of freestanding GaN thick layers with various thicknesses.…”

Fabrication of 2-Inch Free-Standing GaN Substrate on Sapphire With a Combined Buffer Layer by HVPE

“…First, a GaN template with a low temperature GaN buffer layer (LT-GaN), grown with metal organic chemical vapor deposition (MOCVD) is used for the re-growth of GaN film in HVPE. Following that, a GaN film, with a thickness of several 100 μm, is then separated from its foreign substrate using self-separation (Lee et al, 2009 ) or the laser lift-off (LLO) technique (Paskova et al, 2006 ). However, the residual strain and lattice distortion caused by hetero-epitaxy could not be completely suppressed using the LT-GaN buffer layer method.…”