Nonmonotonous electron mobility due to structurally induced resonant coupling of subband states in an asymmetric double quantum well

R K Nayak,T Sahu,A K Panda,S Das

doi:10.1063/1.4936632

Abstract

We show that sharp nonmonotic variation of low temperature electron mobility μ can be achieved in GaAs/AlxGa1-xAs barrier delta-doped double quantum well structure due to quantum mechanical transfer of subband electron wave functions within the wells. We vary the potential profile of the coupled structure as a function of the doping concentration in order to bring the subbands into resonance such that the subband energy levels anticross and the eigen states of the coupled structure equally share both the wells thereby giving rise to a dip in mobility. When the wells are of equal widths, the dip in mobility occurs under symmetric doping of the side barriers. In case of unequal well widths, the resonance can be obtained by suitable asymmetric variation of the doping concentrations. The dip in mobility becomes sharp and also the wavy nature of mobility takes a rectangular shape by increasing the barrier width. We show that the dip in mobility at resonance is governed by the interface roughness scattering through step like changes in the subband mobilities. It is also gratifying to show that the drop in mobility at the onset of occupation of second subband is substantially supressed through the quantum mechanical transfer of subband wave functions between the wells. Our results can be utilized for performance enhancement of coupled quantum well devices.

Highlights

The low dimensional semiconductor structures have demonstrated fascinating quantum mechanical properties which have been exploited for the realization of novel quantum well devices.[1,2,3,4,5] In an asymmetric double quantum well, where the potential profiles of individual wells differ considerably, the eigen states are localized in the respective wells such that the energy eigen values can be treated independently
When the wells are of equal widths, the dip in mobility occurs under symmetric doping of the side barriers
It is gratifying to show that the drop in mobility at the onset of occupation of second subband is substantially supressed through the quantum mechanical transfer of subband wave functions between the wells

Summary

INTRODUCTION

We show that sharp variation of low temperature electron mobility μ can be obtained near the resonance of subband states through variation of structure parameters in a barrier delta doped GaAs/AlxGa1-xAs asymmetric coupled double quantum well. We vary the doping concentrations of the side barriers to change the potential profile such that the subbands of the double quantum well are brought into resonance.

THEORY

RESULTS AND DISCUSSION

SUMMARY AND CONCLUSION