Universal estimation of X− trion binding energy in semiconductor quantum wells R. A. Sergeev, R. A. Suris, G. V. Astakhov, W. Ossau and D. R. Yakovlev Eur. Phys. J. B, 47 4 (2005) 541-547 Published online: 17 November 2005 DOI: 10.1140/epjb/e2005-00362-5