Built-in fields in stacked InGaN/GaN quantum dots

The built-in potential φ _tot of an isolated and of three stacked lens-shaped c-plane In _0.2Ga _0.8N/GaN quantum dots (QDs) is calculated using a surface integral approach. There remains disagreement about the sign of the shear strain piezoelectric coefficient e ₁₅, with more recent analysis suggesting e ₁₅ < 0. We show that with e ₁₅ < 0, the potential φ _tot changes sign outside an isolated QD, in contrast to the case with e ₁₅ > 0. This behaviour affects φ _tot in a system of stacked QDs. For small barrier thicknesses between the QDs, the potential in the central QD is strongly reduced compared to an isolated QD, independent of the sign of e ₁₅. Using e ₁₅ < 0 and small barrier thicknesses, the potential in the remaining two QDs is also slightly reduced, while for larger barrier thicknesses almost no reduction is observed.