Magnetotransport in modulation-doped In0.53Ga0.47As/In0.52Al0.48As heterojunctions: in-plane effective mass, quantum and transport mobilities of 2D electrons

Abstract

Shubnikov–de Haas (SdH) and Hall effect measurements, performed in the temperature range between 3.3 and 20 K and at magnetic fields up to 2.3 T, have been used to investigate the electronic transport properties of lattice-matched In0.53Ga0.47As/In0.52Al0.48As heterojunctions. The spacer layer thickness (tS) in modulation-doped samples was in the range between 0 and 400 Å. SdH oscillations indicate that two subbands are already occupied for all samples except for that withtS= 400 Å. The carrier density in each subband, Fermi energy and subband separation have been determined from the periods of the SdH oscillations. The in-plane effective mass (m*) and the quantum lifetime (τq) of 2D electrons in each subband have been obtained from the temperature and magnetic field dependences of the amplitude of SdH oscillations, respectively. The 2D carrier density (N1) in the first subband decreases rapidly with increasing spacer thickness, while that (N2) in the second subband, which is much smaller thanN1 , decreases slightly with increasing spacer thickness from 0 to 200 Å. The in-plane effective mass of 2D electrons is similar to that of electrons in bulk In0.53Ga0.47As and show no dependence on spacer thickness. The quantum mobility of 2D electrons is essentially independent of the thickness of the spacer layer in the range between 0 and 200 Å. It is, however, markedly higher for the samples with a 400 Å thick spacer layer. The quantum mobility of 2D electrons is substantially smaller than the transport mobility which is obtained from the Hall effect measurements at low magnetic fields. The transport mobility of 2D electrons in the first subband is substantially higher than that of electrons in the second subband for all samples with double subband occupancy. The results obtained for transport-to-quantum lifetime ratios suggest that the scattering of electrons in the first subband is, on average, forward displaced in momentum space, while the electrons in the second subband undergo mainly large-angle scattering.