Greg Jolley

Electron-hole recombination properties of In0.5Ga0.5As/GaAs quantum dot solar cells and the influence on the open circuit voltage

Thanks are due to the Australian Research Council for the financial support of this research and the Australian National Fabrication Facility for access to the facilities used in this work.

Temperature dependence of dark current properties of InGaAs/GaAs quantum dot solar cells

Performances of GaAs reference solar cells and 10-layer InGaAs/ GaAs quantum dot solar cells were tested using AM1.5 illumination with results indicate that quantum dot (QD) structures improve the photo-current density compared to reference devices. Systematic measurements of the dark current versus voltage (I–V) characteristics were also carried out as a function of temperatures from 30K to 310K. The QD solar cell (QDSC) displays a more rapid change of dark current with increasing temperature than reference cells. The dark current of QD cells was found to be greatly affected by carrier trapping and recombination by the presence of QDs.

Plasmonic quantum dot solar cells for enhanced infrared response

Enhanced near infrared photoresponse in plasmonic InGaAs/GaAs quantum dot solar cells (QDSC) is demonstrated. Long wavelength light absorption in the wetting-layer and quantum-dot region of the quantum dot solar cell is enhanced through scattering of light by silver nanoparticles deposited on the solar cell surface. Plasmonic light trapping results in simultaneous increase in short-circuit current density by 5.3% and open circuit voltage by 0.9% in the QDSC, leading to an overall efficiency enhancement of 7.6%.

Effects of well thickness on the spectral properties of In0.5Ga0.5As/GaAs/Al0.2Ga0.8As quantum dots-in-a-well infrared photodetectors

We report on the effects of the quantum well (QW) thickness on the spectral response and other characteristics of In0.5Ga0.5As∕GaAs∕Al0.2Ga0.8As quantum dots-in-a-well infrared photodetectors grown by low-pressure metal-organic chemical vapor deposition. The main device properties are observed to have a strong dependence on the QW parameters.

Influence of quantum well and barrier composition on the spectral behavior of InGaAs quantum dots-in-a-well infrared photodetectors

We report on the spectral behavior of two different quantum dots-in-a-well infrared photodetectors grown by low-pressure metal-organic chemical vapor deposition. In0.5Ga0.5As quantum dots embedded in an In0.15Ga0.85As∕GaAs quantum well (QW) or a GaAs∕Al0.2Ga0.8As QW have been incorporated into photodetectors and were characterized. A spectral response in the 3–5μm atmospheric window has been achieved by adopting the GaAs∕Al0.2Ga0.8As QW.

Two-color InGaAs∕GaAs quantum dot infrared photodetectors by selective area interdiffusion

We report the postgrowth fabrication of two-color InGaAs∕GaAs quantum dot infrared photodetectors (QDIPs). By capping half of the as-grown QDIP structure with titanium dioxide (TiO2) and performing rapid thermal annealing under the optimized condition, a blueshifted photoluminescence from the uncapped region was obtained compared with the TiO2 covered region. The corresponding device spectral photoresponse from the two adjacent regions exhibited a shift of 0.8μm around the wavelength of 6μm. This is a result of the simultaneous promotion and suppression of thermal interdiffusion during rapid thermal annealing.We report the postgrowth fabrication of two-color InGaAs∕GaAs quantum dot infrared photodetectors (QDIPs). By capping half of the as-grown QDIP structure with titanium dioxide (TiO2) and performing rapid thermal annealing under the optimized condition, a blueshifted photoluminescence from the uncapped region was obtained compared with the TiO2 covered region. The corresponding device spectral photoresponse from the two adjacent regions exhibited a shift of 0.8μm around the wavelength of 6μm. This is a result of the simultaneous promotion and suppression of thermal interdiffusion during rapid thermal annealing.

The conduction band absorption spectrum of interdiffused InGaAs/GaAs quantum dot infrared photodetectors

Thanks are due to the Australian Research Council for the financial support of this research.

Selective Intermixing of InGaAs/GaAs Quantum Dot Infrared Photodetectors

Quantum dot infrared photodetectors have generated significant interest in recent years. They have the potential to outperform quantum well detectors in terms of normal-incidence responsivity and higher operating temperatures. Here, an InGaAs/GaAs dots-in-a-well detector grown by metal-organic chemical vapor deposition is spectrally tuned by rapid thermal annealing under dielectric layers. Four films are considered: SiO2 deposited by both plasma-enhanced chemical vapor deposition and sputter deposition, as well as TiO2 deposited by electron-beam evaporation and sputter deposition. The devices fabricated after these treatments are compared with an uncapped but annealed reference, and also with an as-grown device. The photoresponse peak in the latter occurs at 7.1 μm, whereas the peak responses of the annealed devices range from 7.4 to 11.0 μm. The films themselves were characterized and their properties related to the photoluminescence and spectral photoresponse of each detector. Peak responsivity, specific detectivity, and dark current were also measured for each device to compare their performance.

Periodic dielectric structures for light-trapping in InGaAs/GaAs quantum well solar cells

We study dielectric diffraction gratings for light-trapping in quantum well solar cells and compare their performance with plasmonic and Lambertian light-trapping structures. The optimum structural parameters are identified for symmetric uni-periodic, symmetric bi-periodic and asymmetric bi-periodic gratings. The enhancement in short-circuit current density from the quantum well region with respect to a reference cell with no diffraction grating is calculated. The ratio of this enhancement to the maximum achievable enhancement (i.e. no transmission losses) is 33%, 75% and 74%, respectively for these structures. The optimum asymmetric and symmetric bi-periodic structures perform closest to Lambertian light-trapping, while all three optimum grating structures outperform optimum plasmonic light-trapping. We show that the short-circuit current density from the quantum well region is further enhanced by incorporating a rear reflector.

Properties of In0.5Ga0.5As/GaAs/ Al0.2Ga0.8As quantum-dots-in-a-well infrared photodetectors

We report on an experimental and theoretical study of the optical and dark current properties of In0.5Ga0.5As/GaAs/Al0.2Ga0.8As quantum-dots-in-a-well infrared photodetectors. In particular, we investigate the spectral tunability of the dot-to-well transitions by quantum well thickness variations. The effects of the quantum well states on the dark current characteristics are also investigated. Modelling of the electron thermal energy distribution suggests the large density of states in the quantum well can lead to a lowering of the dark current activation energy.