FAR INFRARED MAGNETO-ABSORPTION STUDY OF BARRIER IMPURITIES AND SCREENING IN GaAs/AlGaAs MULTIPLE QUANTUM WELLS E. GLASER, B.V. SHANABROOK, R.J. WAGNER, R.L. HAWKINS, W.J. MOORE and D. MUSSER J. Phys. Colloques, 48 C5 (1987) C5-239-C5-242 DOI: 10.1051/jphyscol:1987550