Direct lift-off and the piezo-phototronic study of InGaN/GaN heterostructure membrane

Internal polarizations, caused by the intrinsic material properties and lattice mismatch during material epitaxial growth, exist inherently in III-nitrides and limit significantly their practical applications. Here, InGaN/GaN single quantum well (SQW) structure grown on sapphire substrate was directly exfoliated by electrochemical (EC) etching. The separated InGaN/GaN SQW heterostructure membranes (SQW-HMs) exhibit substantial relaxation of internal strain and polarization compared to the as-grown samples. To further modulate/tune the internal polarizations and corresponding opto-electronic properties of the SQW-HMs, the piezo-phototronic effect was introduced by applying external stress on the freestanding membrane under ultraviolet (UV) light illumination. The obtained photoluminescence (PL) intensity can be effectively modulated in different manners under tensile and compressive straining conditions. Energy diagrams of the SQW-HMs under free and straining conditions were carefully analyzed to illustrate the working mechanisms of the piezo-phototronic modulations. This research provides a new approach to optimize the performances of III-nitride devices and expand their further applications in optical communications and optical integration systems.