SHUBNIKOV-DEHASS OSCILLATIONS IN A NONUNIFORM 2D ELECTRON-GAS

The decay of Shubnikov-de Haas oscillations in a 2D electron gas (2DEG ) with large-scale fluctuations of the electron density is analyzed th eoretically. It is found that the plot of the amplitude of the Shubnik ov-de Haas oscillations versus the magnetic field acquires a factor in addition to the Dingle factor. This new factor is of the type exp[-(p i2hdeltanBAR/momega(c))2], where deltan is the mean value of the fluc tuations in the electron density. Experimental conditions under which this effect is important have been identified. A numerical criterion i s introduced for determining the level of fluctuations in the density of the 2DEG which can be manifested under given experimental condition s. The criterion depends on the parameters of the sample and on the ex perimental conditions. The theory has been tested experimentally for s electively doped InP/In0.53Ga0.47As heterostructures grown by liquid-p hase epitaxy. Independent experiments showed that these heterostructur es have concentration fluctuations over scales on the order of 100 mum . Comparison of theory and experiment yields the values of the one-par ticle relaxation time in these samples and also the typical value of t he concentration fluctuations of the 2DEG. This typical value is less than 5% of the mean value.