Interface-related exciton-energy blueshift in ${\mathrm{G}\mathrm{a}\mathrm{N}/\mathrm{A}\mathrm{l}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}\mathrm{}$ zinc-blende and wurtzite single quantum wells

The role of nonabrupt interfaces on the confined exciton energy blueshift in zinc-blende and wurtzite ${\mathrm{G}\mathrm{a}\mathrm{N}/\mathrm{A}\mathrm{l}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ single quantum wells (QWs) is investigated. The theoretical calculations are performed taking into account a range of values for the electron and heavy-hole effective masses in both phases, which is compatible to those that have been measured and/or estimated from first principles calculations. The interface related ground state exciton energy blueshift is shown to depend strongly on the nonabrupt interfaces widths in the case of thin QWs ${(}_{<}^{\sim }80\hspace{0.5em}\mathrm{\AA }),$ being a little higher in zinc-blende than in similar wurtzite QWs. For a 50 Å (80 Å) wide ${\mathrm{G}\mathrm{a}\mathrm{N}/\mathrm{A}\mathrm{l}}_{0.3}{\mathrm{Ga}}_{0.7}\mathrm{N}$ single QW whose nonabrupt interfaces have a thickness of 10 Å, the nonabrupt interface related ground state exciton energy blueshift is 26 meV (5 meV) and 19 meV (3 meV) in the zinc-blende and wurtzite phases, respectively. It is shown the impossibility of the sharp interface picture to describe exciton related emission properties of ${\mathrm{G}\mathrm{a}\mathrm{N}/\mathrm{A}\mathrm{l}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ single QWs with a precision better than 10 meV.