Voltage-induced anomalous excitonic photoluminescence from a single heterojunction quantum well

Excitons which coexist with a degenerate two-dimensional electron gas (2DEG) in the same quantum well subband have been observed in the photoluminescence (PL) from the recombination of electrons with localized photoexcited holes. We observe a strong decrease in the exciton PL intensity and the concomitant appearance of another peak around 2 meV lower than the exciton energy when the 2DEG density ∼1.9x1011 cm-2. Over a small range of excitation intensity with the 2DEG density ∼1.9x1011 cm-2, we observe anomalous changes in the PL spectra which are very sensitive to an applied gate voltage and suggest that the lower energy peak can be attributed to biexcitons which have undergone a phase transition into an ordered collective phase