GATE BIAS CONTROLLED CHARGE-DISTRIBUTION IN THE SUBBANDS OF IN0.29AL0.71AS/IN0.3GA0.7AS MODULATION-DOPED HETEROSTRUCTURES

The gate voltage dependent charge distribution within the quantum wells of modulation delta-doped In0.29Al0.71As/In0.3Ga0.7As heterostructures, grown by molecular beam epitaxy and fabricated into front-gated, six-arm, Hall bar configurations, were evaluated by means of resistivity, Hall effect, and Shubnikov-de Haas (SdH) oscillatory magnetoresistance measurements. Delta-doping the barrier layer with Si to 6 X 10(12)/cm2 leads to an apparent electron density, as obtained from Hall measurement made at 1.6 K, n(s) = 2.65 X 10(12)/cm2. The SdH spectra exhibit a gate voltage-dependent transition from one subband to two subbands and the total electron density is in good agreement with that obtained from the Hall data. From a fast Fourier transform of the SdH data and low field magnetoresistance measurements the electron densities and mobilities of the two subbands at V(g) = 0 were found to be n(s1) = 2.39 X 10(12) cm-2, mu1 = 21 800 cm2/V s and n(s2) = 3.96 X 10(11) cm-2, mu2 = 16 000 cm2/V s, respectively.