Electron-electron Interaction and Dynamic of Electrons in a Vertically Aligned Double Dot System

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1) We fabricated vertically aligned double dot structures using GaAs/AlGaAs heterostructures and observed two resonance peaks of electrons in both two dots in a far-infrared (FIR) magneto-optical absorption measurements. Under photoexcitation with pulsed bandgap light of AlGaAs layer, the two peaks are shifted toward higher magnetic filed, depending on excitation intensity and delay time. From computer simulations, we confirmed that the peak shift includes information on an interdot coupling of the vertically aligned double dot system.2) For the quantitative investigation of the interdot coupling, we made time resolved photoluminescence (PL) measurement system and time resolved optically detected cyclotron resonance measurement system with ultrashort pulse laser. By using the measuring systems, we investigated emission peak (called as H-band emission) due to 2 dimensional electron gas (2DEG) in GaAs/AlGaAs heterostructures which is a starting material of our dot system. It is confirmed that the emission strongly depend on the wavelength of the excitation light. In this measurement, we illuminated the sample with Ar+ laser, as well as the illumination of the probing Ti:sapphire laser. The former excites electron-hole pairs in AlGaAs layer and is found to change the potential profile confining 2DEG. We have direct evidence the generated holes in AlGaAs layer flow toward GaAs layer and recombine with 2DEG in the time resolved PL measurements.3) In FIR absorption measurement, we found the zero-field spin splitting of electrons in InGaAs/InAlAs heterostructures and could estimate the value of spin-splitting energy Δ_R of a sample as 9 meV. We could show the FIR absorption measurement is quite useful technique for the estimation of Δ_R. We also show the tuning of the value of Δ_R by the bandgap light illumination which changes the confinement potential profile.