Determination of potential fluctuations in modulation-doped SiGe-quantum wells from conduction electron spin resonance

The spin resonance of conduction electrons in modulation-doped quantum well s is utilized to determine the density of states. The latter exhibits band tails resulting from potential fluctuations caused mainly by the distributi on of charged impurities. Assuming a Gaussian distribution, we determine th e fluctuation amplitude as a function of carrier density. For low-density s creening becomes ineffective and we find a rapid increase of these fluctuat ions corresponding to the Anderson transition in two dimensions. (C) 1999 E lsevier Science B.V. All rights reserved.