The photoluminescence spectra of (Al,Ga)N/GaN quantum wells grown by molecular-beam epitaxy under Ga-rich and N-rich conditions with growth interruptions at each interface exhibit several excitonic peaks, each of them corresponding to a discrete well width. This is confirmed by the excitation power dependence of the excitonic photoluminescence intensity. Well width fluctuations are then discussed in relation with atomic force microscopy and scanning tunneling microscopy images of the (Al,Ga)N surfaces. From these results, we show that the discrete well width differs by one or two molecular monolayers for growth under N-rich or Ga-rich conditions, respectively. This observation leads us to reconsider the amplitude of the built-in electric field in such structures. Contrary to what has been previously proposed in the literature, it is found identical for Ga-rich and N-rich growth conditions and equal to $\sim 5\text{MV}/\text{cm}$ times the AlN mole fraction.

• Received 27 August 2008

DOI:https://doi.org/10.1103/PhysRevB.79.035328