K.Y. Chuang

Photovoltaic response for high density InGaAs coupled quantum dots

In order to enhance absorption at infrared range for GaAs based solar cell, we insert the nine-layer of vertically coupled quantum dots (VCQDs) into the active layer. We fine modulated the GaAs spacer thickness of coupled In_0.75Ga_0.25As QDs, and investigated the effects on photovoltaic response. For the open-circuit voltage (V_oc), the values decreases from 0.61 V to 0.55 V as the spacer thickness (d) decreases from d= 15 nm to 5 nm for the nine-layer VCQDs solar cells. The reduction of V_oc for the VCQDs solar cells is attributed to the accumulation of compressive strain energy in the active QD region. For the sample of d=10 nm shows the best performance of current density (J_sc~24 mA/cm²) and efficiency (η~10.6). The J_sc and η are increases by 55% and 112% more than the device without QDs, respectively.

Enhanced TE/TM electro-optic effect in vertically coupled InGaAs quantum dots

We have investigated the electro-optic effect for the vertically coupled InGaAs quantum dots. In addition to large TE-polarized electro-optic coefficient, TM-polarized electro-optic effect is observed. The linear and quadratic electro-optic coefficients are larger than GaAs-base multiple quantum well structures.

Differential absorption spectroscopy for vertically coupled InGaAs quantum dots of p-type modulation doping

We report the differential absorption (Deltaalpha) spectra of the vertically coupled triple-layer InGaAs quantum dots (QDs) at different reverse bias. The results show that the decrease of spacer layer thickness increases the differential absorption. Adding p-type modulation doping further increases the differential absorption amplitude at ground state.

340nm blue-shift in InGaAs/InAlAs quantum dots processed by SiO 2 sputtering and rapid thermal annealing

The atomic intermixing effects on emission wavelength blue-shift for self-assembled InGaAs/InAlAs quantum dots on InP substrate were investigated. A large blue-shift upto 343 nm, from lambda=1632 nm to 1289 nm, was obtained by SiO2 sputtering deposition and rapid thermal annealing at 800degC.

Emission and absorption polarization in InGaAs multiple quantum dots layers of different spacer layer thickness

Triple-layer InGaAs QDs of different spacer layer thickness are characterized by polarized electroluminescence and photocurrent spectroscopy. The results show that the decease of spacer layer thickness increases the TE/TM insensitivity.

Quantum Well Intermixing in InGaAs/InGaAlAs Structures by Using ICP-RIE and SiO2 Sputtering

A quantum well intermixing process combining ICP-RIE and SiO2 sputtering was investigated for the InGaAs/InGaAlAs multi-quantum wells. Optimal conditions including ICP-RIE etching depth, SiO2 deposition, and RTA process were obtained for a 60-nm blueshift.