InGaN/AlInN interface with enhanced holes to improve photoelectrochemical etching and GaN device release

We introduce a novel superlattice structure for releasing GaN-based devices with selective photo-electrochemical (PEC) etching by incorporating a lattice-matched AlInN barrier in an InGaN/GaN sacrificial stack. A dopant-free two-dimensional hole gas is formed at the InGaN/AlInN interface due to the band bending and strong polarization discontinuity, which is revealed in simulations. PEC etching using the four period InGaN/AlInN superlattice exhibits almost three times higher etch rate and smoother etched surfaces when compared to conventional InGaN/GaN release layers. A systematic investigation with different AlInN layer thicknesses shows that a thin AlInN layer is able to achieve smooth surface with uniform etch process during the PEC while thicker AlInN exhibits poorer surface morphology although the etch rate was faster. Furthermore, it is found that using HNO₃ as the electrolyte improved the etched surface smoothness compared to KOH when followed by a post-release HCl treatment. This structure will enable the release of high quality GaN layers and the fabrication of novel optical devices.