Hydrostatic pressure dependence of indirect and direct excitons in InGaN/GaN quantum wells

We analyze the evolution of the exciton recombination energy E-PL and its pressure coefficient dE(PL)/dp, with the laser power density (LPD) exciting excitonic photoluminescence. Two In0.17Ga0.83N/GaN quantum well (QW) structures are used: sample A consisting of a 5.2-nm-wide single QW and sample B consisting of two 2.6-nm-wide QWs separated by a 0.78-nm-thick barrier. Changes of E-PL and dE(PL)/dp with LPD in both structures cover a wide range of magnitude. They switch character in the vicinity of the indirect to direct exciton induced by increasing LPD. In sample B, at low excitation, a negative pressure coefficient of E-PL has been found. Moreover, pressure dependences of E-PL are different for the two samples under study. We examined pressure dependence of the threshold LPD for indirect-direct exciton switching in both samples. The reported observations originate to a high extent from screening of a built-in electric field by carriers externally introduced into the quantum wells. We also note that the universal relation between transition energies and their pressure coefficients (observed previously in InGaN/GaN quantum wells) does not hold for samples modified by screening.