  We report on photoluminescence (PL) measurements at 85 K for GaN/AlGaN
surface quantum wells (SQW's) with a width in the range of 1.51-2.9 nm. The PL
spectra show a redshift with decreasing SQW width, in contrast to the blueshift
normally observed for conventional GaN QW's of the same width. The effect is
attributed to a strong coupling of SQW confined exciton states with surface
acceptors. The PL hence originates from the recombination of
surface-acceptor-bound excitons. Two types of acceptors were identified.
