Magneto luminescência em diodos de tunelamento ressonante contendo pontos quânticos de InAs

Abstract

In this work, we have studied the spin polarization of carriers in n-type resonant tunneling diodes (RTDs) of GaAs/AlGaAs which incorporates a single layer of InAs selfassembled quantum dots in the center of the GaAs quantum well (QW) grown on (3 1 1)B oriented GaAs substrates.We have performed electrical and optical measurements in the presence and absence of magnetic _eld. The spin-dependent carrier transport in the structure was investigated by measuring the left- and right-circularly polarized photoluminescence (PL) from InAs dots (QD) and contact layers as a function of the applied voltage, laser intensity and magnetic _eld up to 15 T. Under laser excitation, photogenerated holes tunnel through the QW and can be captured by the QDs and eventually recombine radiatively. Due to this fast carrier capture process, the QD photoluminescence will be very sensitive to the resonant tunneling condition and consequently to the applied bias voltage. We have observed a clear correlation between the current voltage characteristics curve (I(V)) and QD PL intensity for both circular _+ and _�� polarizations even though the spin-splitting of the QD PL emission is negligible and does not show any appreciable variation with the applied voltage. We have also observed that the QD circular polarization degree is always negative and that its value depends on both the applied bias voltage and the light excitation intensity. Our experimental results are explained by the tunneling of minority carriers into the QW, carrier capture into the InAs QDs, carrier accumulation in the QW region, and partial thermalization of minority carriers. The observed control of spin polarization of carriers by light and bias voltage may be explored to design new devices for spintronic applications.