Optical and transport properties of short period InAs/GaAs superlattices near quantum dot formation

TL;DR

This study explores how short-period InAs/GaAs superlattices' optical and electrical properties evolve with layer thickness, revealing quantum dot formation and a transition from metallic to hopping conductivity at certain thicknesses.

Contribution

It provides detailed experimental and theoretical analysis of the optical and transport behavior of InAs/GaAs superlattices near quantum dot formation, highlighting the transition in conduction mechanisms.

Findings

Single subband occupancy observed in photoluminescence and transport data.

Quantum dots form when InAs layer exceeds 2.7 monolayers.

Transition from metallic to variable range hopping conductivity at Q >= 2.7 ML.

Abstract

We have investigated the optical and transport properties of MBE grown short-period superlattices of InAs/GaAs with different numbers of periods (3 <= N <= 24) and a total thickness 14 nm. Bandstructure calculations show that these superlattices represent a quantum well with average composition In_0.16Ga_0.84As. The electron wave functions are only slightly modulated by the superlattice potential as compared to a single quantum well with the same composition, which was grown as a reference sample. The photoluminescence, the resistance, the Shubnikov-de Haas effect and the Hall effect have been measured as a function of the InAs layer thickness Q in the range 0.33 <= Q <= 2.7 monolayers (ML). The electron densities range from 6.8 to 11.5x10^11 cm^-2 for Q <= 2.0 ML. The photoluminescence and magnetotransport data show that only one subband is occupied. When Q >= 2.7 ML quantum dots are formed and the metallic type of conductivity changes to variable range hopping conductivity.