The effects of spacer thickness and temperature on the transport properties of modulation-doped In0.53Ga0.47As/In0.52Al0.48As heterojunctions

The measurements of resistivity and low-field Hall effect made in the tempe rature range 3.3-295 K have been used to investigate the transport properti es of modulation-doped, lattice-matched In0.53Ga0.47As/In0.52Al0.48As heter ojunctions as a function of the spacer thickness in the range from 0 to 400 Angstrom. It is found that the sheet carrier density determined at tempera tures below about 80 K decreases rapidly with increasing spacer thickness. The low-temperature Hall mobility increases substantially when increasing t he spacer thickness from 0 to 100 Angstrom, and decreases gradually with fu rther increase in spacer thickness. The results suggest that, in addition t o alloy scattering, remote ionized-impurity scattering is a major scatterin g mechanism at low temperatures in the samples with thin spacer layer and t hat background impurity scattering prevails in the samples with spacer thic kness larger than about 100 A. The effect of modulation doping on the mobil ity decreases progressively with increasing temperature: the electron mobil ity becomes practically independent of spacer thickness in the temperature range above about 200 K. The variation of Hall mobility with temperature in the range above 90 K has been used to determine the energy of longitudinal optical phonons that limit the mobility of electrons at high temperatures.