Wet Electrochemical Lift-off Method Of GaN Epitaxial Film

GaN-based Light-emitting diodes (LED) possess high brightness, energy consumption, thin volume, long life and other features. Currently, the radiating problem and the low light efficiency limit the development of high-power LED. Electrochemical wet etching to selectively stripping the GaN epitaxial to get the freedom unsupported LED film can effectively solve these problems. Therefore, this paper focuses on the following works.1. Metal organic chemical vapor deposition (MOCVD) growth of Si-doped InGaN/GaN quantum well superlattice sacrificial layer for the LED structure. By light-assisted electrochemical wet-etching of the sample, and the results showed that KOH solution can be laterally etched GaN epitaxial film. But the etching liquid also damage the InGaN/GaN multiple quantum wells (MQWs).2. By MOCVD grow the n-GaN etching sacrificial layer and the InGaN/GaN MQWs GaN epitaxial. AFM test demonstrated that the surface unevenness of the GaN sample is0.855%and the variance is0.310nm, there is no obvious step. The peak of2Theta XRD for (002) plane of the GaN sample center of the scanning curve is no offset, the width at half-height (FWHM) is18.747arcsec. the FWHM of XRD rocking curve for (002) plane and(102) plane are283.43arcsec and342.32arcsec, respectively。So the density screw dislocation and edge dislocation of the GaN epitaxial are7.4×104cm-1and2.8×105cm-1, separately.3. Oxalic acid electrochemical lateral selective etch the GaN sample with the n-GaN sacrificial layer.These results illustrated that only the n-GaN sacrificial layer was etched away by oxalic acid aqueous solutions, while the u-GaN, InGaN/GaN MQWs and p-GaN were remained in the etching process. The PL emission peaks of as-grown and lifted-off samples were at466.603nm and469.791nm origin from MQWs, respectively. The red-shifted peak position to, indicates that the tensile stress relaxation occurred after lift-off. The intensity and full width at half maximum (FWHM) of emission peaks are almost same for both samples. Thus, the freestanding MQWs layer with high optical quality was obtained by this wet electrochemical lift-off method.4. Test the Raman spectra of the GaN sample with n-GaN sacrificial layer before and after being lift-off to investigative the tension varies. the peak of Raman spectrum of the GaN epitaxial before and after being stripped down is566.664cm-1and569.832cm-1, respectively. So the stress of the GaN epitaxial is3.42GPa and-4.689GPa. Owing to the lattice mismatch and thermal mismatch, the GaN epitaxial suffer tensile stress. After epitaxial stripped down from the substrate, the tensile stress gets significant release.