Disorder effects on resonant tunneling transport in GaAs/(Ga,Mn)As heterostructures

TL;DR

This paper theoretically investigates how disorder affects resonant tunneling in GaAs/(Ga,Mn)As heterostructures, explaining experimental observations and the limited ferromagnetic order due to structural imperfections.

Contribution

It provides a Green's function based model analyzing the interplay of disorder, ferromagnetism, and tunneling, revealing disorder's significant impact on tunneling features.

Findings

Disorder reduces or eliminates negative differential conductance.

Spin polarization in the quantum well is too small for significant exchange splitting.

Theoretical results explain the absence of ferromagnetic order in experiments.

Abstract

Recent experiments on resonant tunneling structures comprising (Ga,Mn)As quantum wells [Ohya et al., Nature Physics 7, 342 (2011)] have evoked a strong debate regarding their interpretation as resonant tunneling features and the near absences of ferromagnetic order observed in these structures. Here, we present a related theoretical study of a GaAs/(Ga,Mn)As double barrier structure based on a Green's function approach, studying the self-consistent interplay between ferromagnetic order, structural defects (disorder), and the hole tunnel current under conditions similar to those in experiment. We show that disorder has a strong influence on the current-voltage characteristics in efficiently reducing or even washing out negative differential conductance, offering an explanation for the experimental results. We find that for the Be lead doping levels used in experiment the resulting spin density polarization in the quantum well is too small to produce a sizable exchange splitting.