In-plane transport properties of heavily delta -doped GaAs n-i-p-i superlattices: Metal-insulator transition, weak and strong localization.

Abstract

We performed intralayer-transport measurements on heavily \ensuremath{\delta}-doped GaAs n-i-p-i superlattices in the temperature range of 4--300 K. The n-layer electron density was varied by applying a bias voltage between the selectively contacted n- and p-type layers. This tunability allowed the observation of the disorder-induced metal-insulator transition in a doping superlattice. We compare the experimental electron-density dependence of the mobility at T=4 K with theoretical predictions. Good agreement is achieved in the metallic regime, solving the multisubband Boltzmann equation in relaxation-time approximation and close to the metal-insulator transition, applying a self-consistent current-relaxation theory. Furthermore, we analyze the electron conductivity data of both the metallic and insulating phases as functions of temperature and magnetic field oriented perpendicular to the doping layers. The magnetic field as well as the temperature dependence of the conductivity give evidence for weak localization of the metallic phase. In the strongly localized insulating regime our data show a transition from activated high temperature to weakly temperature-dependent low-temperature behavior. A detailed model is elaborated which explains this observation as transition from thermally activated transport over critical barriers of the disorder potential to phonon-assisted tunneling. \textcopyright{} 1996 The American Physical Society.