EXCITON AND TRION SPECTRAL-LINE SHAPE IN THE PRESENCE OF AN ELECTRON-GAS IN GAAS ALAS QUANTUM-WELLS/

We studied the photoluminescence of (e1:hh1)1S excitons (X) and negati vely charged excitons (trions, X(-)) in quantum wells (QW's) having a low-density (n(e) < 5 x 10(10) cm(-2)) two-dimensional electron gas (2 DEG) at T less than or equal to 12 K. Mixed type-I-type-II GaAs/AlAs q uantum wells are studied in which the 2DEG is photogenerated in the ty pe-I QW's and n(e) is determined by the excitation intensity. At a giv en temperature and for every excitation intensity the photoluminescenc e spectrum is decomposed into a Lorentzian-shaped X(-) Line and a conv oluted Lorentzian-Gaussian X line. Their intensity ratio is analyzed b y assuming a thermal equilibrium distribution of X and X(-) that is de termined by the chemical potential of the 2PEG. The X(-) linewidth dep endence on ne is analyzed as originating from an increased X(-) dephas ing rate that is caused by trion-electron (X(-)-e) scattering. We pres ent a model of the elastic (X(-)-e) scattering and calculate its rate as a function of n(e) assuming the 2DEG screening wave vector (q(s)) t o be an adjustable parameter. Although of the same order of magnitude, the fitted q(s) values differ from those calculated for the ideal gas model using the Thomas-Fermi approximation. Since, to our knowledge, there is no model for calculating q(s) in the low 2DEG density range s tudied here and T > 0, our spectroscopically extracted q(s)(n(e)) valu es might serve as guidelines for the required theory.