Exploring the effects of tensile and compressive strain on two-dimensional electron gas properties within InGaN quantum wells

With the advent of high-quality AllnGaN quaternary cladding, InGaN quantum wells (QWs) have now been studied under both compressive and tensile strain, as well as no strain at all! This has allowed the experimental investigation of the two-dimensional electron gas (2DEG) properties within InGaN QWs that have been subjected to a full range of strain, opening the doors to a new realm of strain engineering. We present the capacitance–voltage-derived 2DEG properties of several ${\mathrm{In}}_{\mathrm{0.08}}{\mathrm{Ga}}_{\mathrm{0.92}}\mathrm{N}$ QWs subject to various degrees of strain. Strained ${\mathrm{In}}_{\mathrm{0.08}}{\mathrm{Ga}}_{\mathrm{0.92}}\mathrm{N}$ QWs clad with GaN exhibit better 2DEG confinement than their unstrained ${\mathrm{Al}}_{\mathrm{0.24}}{\mathrm{In}}_{\mathrm{0.09}}{\mathrm{Ga}}_{\mathrm{0.67}}\mathrm{N}$ -clad counterparts. For the case of compressive-strained QWs, it was found that the peak 2DEG concentration increases linearly with well width. In contrast, such dependence was not observed for the case of unstrained QWs with lattice-matched cladding. Of further interest, the 2DEGs for compressive and tensile ${\mathrm{In}}_{\mathrm{0.08}}{\mathrm{Ga}}_{\mathrm{0.92}}\mathrm{N}$ QWs are localized at opposite interfaces, which is attributed to strain-induced piezoelectric fields pointing in opposite directions.