T. E. Tzeng

Broadband quantum dots-in-a-well solar cells

The conversion efficiency of broadband InGaAs quantum dots-in-a-well (DWell) solar cells has been improved by optimizing the p-type doping and growth temperature for the DWell. The solar efficiency (η) is 130% times of the counterpart of GaAs baseline cell. Moreover we obtain the best photovoltaic result by inserting matrix pattern instead grid pattern and using wet etching to enhance the conversion efficiency. The photovoltaic characteristics shows an efficiency of 10.86%.

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.

In(Ga, Al)As quantum dot/wire growth on InP

The authors have investigated the growth of dots/wires on InP substrates by tuning the In(Ga, Al)As compositions for dots/wires and buffer layers. Dots and wires with compositions including InAs, In0.95Al0.05As, In0.95Ga0.05As, and In0.90Ga0.10As were grown on In0.53Ga0.26Al0.21As and In0.52Al0.48As buffer layers, respectively. In(Ga)As nanostructure grown on InAlAs ternary buffer layer forms elongated dots along the [0-11] direction. On the other hand, In0.95Ga0.05As and In0.90Ga0.10As nanostructures grown on InGaAlAs buffer layer form quantum wire arrays of high uniformity. The In0.90Ga0.10As quantum wires have a photoluminescence spectrum of emission peak at λ∼1680nm and a narrow full width at half maximum of 65meV at 10K. For the growth of In0.95Al0.05As nanostructures, dot formations are observed on the InAlAs and InGaAlAs buffer layers.

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.

Structural and Optical Characteristics of Strain-mediated InGaAs Quantum Dots

Self-assembled In_xGa_1-xAs quantum dots, with In(Ga)As capping layers to mediate the strain distribution were studied by x-ray reciprocal space mapping, TEM, and PL. The In_0.75Ga_0.25As QDs capped with In_0.1Ga_0.9As has a PL emission at lambda = 1.31 mum.

Wide Emission Spectra from Multi-stack InGaAs Quantum Dots

Multi-layer InGaAs quantum dots have been grown and investigated to have 165 nm broad-band emission at lambda=1300 nm by tailoring the In and Ga compositions for the dots and caps in the stacked layers.

Surface morphology and photoluminescence for InAs quantum dots of different growth temperature and capping layer

InAs QDs of eight different grown temperatures are measured by AFM and photoluminescence measurement. PL emission peak at 1.306 mum was obtained for InAs QDs with In0.1Ga0.9As capping layer grown at 510degC