InAsN/InGaAs single quantum wells (SQWs) with different nitrogen concentration have been successfully grown on InP substrates by gas source molecular beam epitaxy used rf plasma nitrogen source. Photoluminescence (PL) results of the as-grown samples show red-shifted PL peak energy and rapidly degraded intensity as the nitrogen concentration increases. The roughly estimated maximum nitrogen mole fraction in these samples is 0.4%. Both the PL intensity and linewith of these InAsN/InGaAs SQWs were significantly improved after postgrowth rapid thermal annealing with the optimum temperature at 525-550 degrees C for samples with different nitrogen content. The improvement on 10 K PL intensity can be as high as 230 times, and the room temperature PL intensities of the annealed InAsN SQWs have been comparable to those of InAs SQWs used for laser diodes. Quantum well intermixing (QWI) induced blue-shifted PL spectra were also observed in these samples. The QWI threshold temperature decreases as the nitrogen concentration increases, which indicates that defects created by nitrogen incorporation may enhance the QWI.