Carrier confinement in GaInN/AlGaN/GaN quantum wells with asymmetric barriers: direction of the piezoelectric field

We present time-resolved measurements on GaInN/GaN quantum wells (QWs) with varying well widths and GaInN/AlGaN/GaN QWs with asymmetric barriers. Our study in GaInN/GaN QWs shows a strong decrease of oscillator strength with increasing well widths in parallel to a red shift of emission peaks, which can be well explained by the piezoelectric field. The measurement in the asymmetric structure reveals enhanced oscillator strength with the AlGaN barrier on top of the GaInN QW indicating the better carrier confinement in such structure. These results allow us to determine unambiguously the sign of the piezoelectric field, which points towards the substrate in a compressively strained QW.