Effective band gap inhomogeneity and piezoelectric field in InGaN/GaN multiquantum well structures

The emission mechanisms of strained ${\mathrm{In}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}$ quantum wells (QWs) were shown to vary depending on the well thickness, L, and x. The absorption edge was modulated by the quantum confined Stark effect and quantum confined Franz-Keldysh effect (QCFK) for the wells, in which, for the first approximation, the product of the piezoelectric field, $F_{\mathrm{PZ}},$ and L exceed the valence band discontinuity, ${\mathrm{\Delta E}}_V.$ In this case, holes are confined in the triangular potential well formed at one side of the well producing the apparent Stokes-like shift. Under the condition that $F_{\mathrm{PZ}}\mathrm{\times L}$ exceeds the conduction band discontinuity ${\mathrm{\Delta E}}_C,$ the electron-hole pair is confined at opposite sides of the well. The QCFK further modulated the emission energy for the wells with L greater than the three dimensional free exciton Bohr radius $a_B.$ On the other hand, effective in-plane localization of carriers in quantum disk size potential minima, which are produced by nonrandom alloy compositional fluctuation enhanced by the large bowing parameter and $F_{\mathrm{PZ}},$ produces a confined electron-hole pair whose wave functions are still overlapped (quantized excitons) provided that ${\mathrm{L<a}}_B.$