Nanoscale physics

Peculiarities of the bipolar electric transport and terahertz radiation of hot charge carriers in the double tunnel-coupled quantum wells GaAs/InGaAs/GaAs
Vinoslavskii M.M., Belevskii P.A., Vainberg V.V., Pylypchuk O.S., Poroshin V.M.
Solid State Electronics Department, Institute of Physics of the NAS of Ukraine. Prospect Nauki, 46, Kyiv-03028, Ukraine.
E-mail: pavlobelevskiy@gmail.com

The dependences of the electric conduction and terahertz electroluminescence (EL) in the n-InGaAs/GaAs heterostructures with the asymmetrically doped double tunnel-coupled quantum wells (QW) on the lateral (in the QW plane) electric field in presence of the charge carriers with both signs (electrons and holes) have been studied. It is established that the field dependences of the electric current and integral EL intensity qualitatively differ at different thickness of the barrier between QWs. In the case of thick (~50 A) barriers in the field range below the threshold of the Gunn kind instabilities the high frequency current oscillations are observed, and the EL intensity monotonously increases with the field in the whole range (up to 3 kV/cm). At small barrier thicknesses (~30 A) the current oscillations are practically absent, and the EL intensity strongly increases at E>1.5-2 kV/cm. The both phenomena are shown to arise in consequence of heating charge carriers by the electric field. The current oscillations may arise under the conditions of existence of the negative differential conduction which is caused by redistribution of hot carriers between wells. The non-monotonous dependence of the EL intensity vs. electric field is explained by two possible kinds of the radiative transitions in QWs – the indirect transitions inside the side quantization subbands and direct intersubband transitions and by dependence of their contribution into luminescence on the electric field. Manifestation of these effects depends on the thickness of the barrier between wells which determines the ratio of the times of the band-to-band radiative recombination of the minority charge carriers (holes) in the narrow doped wells and their tunneling into the wide undoped wells.