Temperature and electric field dependences of the mobility of electrons in vertical transport in GaAs/Ga_1-yAl_yAs barrier structures containing quantum wells

The mobility of electrons in vertical transport in GaAs/Ga_1-y Al_yAs barrier structures was investigated using geometric magnetoresistance measurements in the dark. The samples studied had Ga_yAl_yAs (0 ≤ y ≤ 0:26) linearly graded barriers between the n⁺-GaAs contacts and the Ga_0:74Al_0:26As central barrier, which contain N_w (=0, 2, 4, 7 and 10) n-doped GaAs quantum wells. The mobility was determined as functions of (i) temperature (80-290 K) at low applied voltage (0.01-0.1 V) and (ii) applied voltage (0.005-1.6 V) at selected temperatures in the range 3.5-290 K. The experimental results for the temperature dependence of low-field mobility suggest that space-charge scattering is dominant in the samples with N_w whereas ionized impurity scattering is dominant in the samples with The effect of polar optical phonon scattering on the mobility becomes significant in all barrier structures at temperatures above about 200 K. The difference between the measured mobility and the calculated total mobility in the samples with observed above 200 K, is attributed to the reflection of electrons from well-barrier interfaces in the quantum wells and interface roughness scattering. The rapid decrease of mobility with applied voltage at high voltages is explained by intervalley scattering of hot electrons.