Destruction of Magnetophonon Resonance in High Mobility Heterojunctions from Competition between Elastic and Inelastic Scattering

1Xu Wen, 2D.R. Leadley, 3F.M. Peeters, 3J.T. Devreese, 2R.J. Nicholas, 4J.J. Harris and 5C.T. Foxon

  1. Dept. of Theoretical Physics, Australian National University, Canberra, ACT 0200, Australia
  2. Dept of Physics, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, UK.
  3. Dept. Natuurkunde, Universiteit Antwerpen (UIA), Universiteitsplein 1, B-2610 Antwerpen, Belgium
  4. Department of Electronics and Electrical Engineering, University College, London. UK
  5. Department of Physics, The University, Nottingham. UK

We have previously reported on the curious disappearance of the magnetophonon resonance (MPR) peaks in the resistivity of high mobility GaAs-GaAlAs heterojunctions [1]. While the usual exponentially damped cosine series of oscillations is seen at all magnetic fields in high electron density samples, in low density samples the peaks become much smaller and even disappear at high field. This behaviour becomes more pronounced at lower temperature. In this paper we explain all these tendencies with fully self consistent calculations of the resistivity of several heterojunctions, with different densities and mobilities. The calculation is the first such self consistent calculation at high temperature and is based on the momentum balance equation using only measured sample parameters.

The resistivity in high magnetic field is determined by both elastic and inelastic scattering and depends on the product of scattering rates and density of states (DOS). The DOS also depends on the amount of elastic and inelastic scattering present, hence the requirement for self consistency. When the MPR resonance condition is satisfied the increase in electron-LO phonon scattering decreases the DOS at the centre of each Landau level (LL) and so reduces the elastic scattering contribution to the resistivity. Whether or not a peak is seen at the resonance condition depends on the relative contributions of the elastic and inelastic terms to the resistivity and the DOS.

Elastic scattering arises from impurities and both deformation potential and piezoelectric coupling to acoustic phonons. The impurities are treated as screened 1/r potentials for both the background impurities and remote ionised donors, with the respective densities taken from low field mobility and the measured electron density in each sample. The electron distribution is evaluated at each temperature and field, using Fermi-Dirac statistics, and the full electron Green's function is retained in calculating both the DOS and resistivity. We include both absorption and emission processes in the inelastic electron-LO phonon scattering, which has a dramatic effect on the LLs. Without inelastic scattering the LLs are semi-elliptic and off resonance they remain predominately thus. However, at the MPR condition there is a strong change in shape, especially for the higher unoccupied LLs that constitute the final states of an inelastic scattering event.

Only by using the complete energy distribution of each LL is it possible for the calculations to reproduce all the features of the experimental data.

[1] D.R. Leadley et al. Disappearance of Magnetophonon Resonance ..., Surface Science 305, 327 (1994) from EP2DS-10, Newport 1993

22nd International Conference on the Physics of Semiconductors - Vol. 2, ed. D.J. Lockwood (World Scientific, Singapore, 1995), p. 839.