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

We report on a detailed analysis of the temperature dependent electrical properties of In0.5Ga0.5As/GaAsquantum dotsolar cells. The effects leading to a reduction in the open circuit voltage are found to be the thermal injection of carriers from the n and p-type layers into the depletion region where they recombine with carriers occupying quantum dot states due to a thermal distribution. The departure of the device studied here from an ideal intermediate band solar cell is discussed.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

MITIGATING THE GLASS-WEAVE EFFECT INSIDE A BGA

For a printed circuit board (PCB) that includes many high-speed differential pairs may be routed the signal integrity (SI) performance of the pairs is to be carefully considered. One factor that may lead to a poorer SI performance, on the PCB itself and within a ball grid array (BGA) that is mounted on the PCB, is the glass-weave effect. To mitigate the impact of the glass-weave effect inside of a BGA, techniques are presented herein that support rotating the BGA by a free angle. With such a BGA rotation, a pair\u27s traces will be rotated by the same angle and, consequently, the glass-weave effect on those traces can be mitigated

Plasmonic quantum dot solar cells for enhanced infrared response

Enhanced near infrared photoresponse in plasmonic InGaAs/GaAs quantum dotsolar cells (QDSC) is demonstrated. Long wavelength light absorption in the wetting-layer and quantum-dot region of the quantum dotsolar cell is enhanced through scattering of light by silver nanoparticles deposited on the solar cellsurface.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%.This work was supported by the Australian Research Council (Grant No. DP1096361)

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

Self-assembledIn₀.₅Ga₀.₅As/GaAsquantum dotsolar cell (QDSC) was grown by metal organic chemical vapor deposition. Systematic measurements of dark current versus voltage (I-V) characteristics were carried out from 30 to 310 K. Compared with the reference GaAssolar cell, the QDSC exhibits larger dark current however its ideality factor (n) was smaller, which cannot be straightly interpreted by the conventional diode models. These results are important for the fundamental understanding of QDSC properties and further implementation of new solar cell designs for improved efficiency.The authors would like to acknowledge financial support from the Australian Research Council and facility support from the Australian National Fabrication Facility ACT node

Analytical expression for the quantum dot contribution to the quasistatic capacitance for conduction band characterization

This paper demonstrates an analytical expression for the quasistatic capacitance of a quantum dot layer embedded in a junction, where the reverse bias is used to discharge the initially occupied energy levels. This analysis can be used to determine the position and the Gaussian homogeneous broadening of the energy levels in the conduction band, and is applied for an InGaAs/GaAs quantum dot structure grown by metal organic chemical vapor deposition. It is shown that the Gaussian broadening of the conduction band levels is significantly larger than the broadening of the interband photoluminescence (PL) transitions involving both conduction and hole states. The analysis also reveals a contribution from the wetting layer both in PL and modeled C-V profiles which is much stronger than in typical molecular beam epitaxy grown dots. The presence of a built-in local field oriented from the apex of the dot toward its base, contrary to the direction expected for a strained dot with uniform composition (negative dipole), is also derived from fitting of the C-V experimental data

Design Methodology for Magnetic Field-Based Soft Tri-Axis Tactile Sensors

Tactile sensors are essential if robots are to safely interact with the external world and to dexterously manipulate objects. Current tactile sensors have limitations restricting their use, notably being too fragile or having limited performance. Magnetic field-based soft tactile sensors offer a potential improvement, being durable, low cost, accurate and high bandwidth, but they are relatively undeveloped because of the complexities involved in design and calibration. This paper presents a general design methodology for magnetic field-based three-axis soft tactile sensors, enabling researchers to easily develop specific tactile sensors for a variety of applications. All aspects (design, fabrication, calibration and evaluation) of the development of tri-axis soft tactile sensors are presented and discussed. A moving least square approach is used to decouple and convert the magnetic field signal to force output to eliminate non-linearity and cross-talk effects. A case study of a tactile sensor prototype, MagOne, was developed. This achieved a resolution of 1.42 mN in normal force measurement (0.71 mN in shear force), good output repeatability and has a maximum hysteresis error of 3.4%. These results outperform comparable sensors reported previously, highlighting the efficacy of our methodology for sensor design

Bmi1 Is a Key Epigenetic Barrier to Direct Cardiac Reprogramming

Direct reprogramming of induced cardiomyocytes (iCMs) suffers from low efficiency and requires extensive epigenetic repatterning, although the underlying mechanisms are largely unknown. To address these issues, we screened for epigenetic regulators of iCM reprogramming and found that reducing levels of the polycomb complex gene Bmi1 significantly enhanced induction of beating iCMs from neonatal and adult mouse fibroblasts. The inhibitory role of Bmi1 in iCM reprogramming is mediated through direct interactions with regulatory regions of cardiogenic genes, rather than regulation of cell proliferation. Reduced Bmi1 expression corresponded with increased levels of the active histone mark H3K4me3 and reduced levels of repressive H2AK119ub at cardiogenic loci, and de-repression of cardiogenic gene expression during iCM conversion. Furthermore, Bmi1 deletion could substitute for Gata4 during iCM reprogramming. Thus, Bmi1 acts as a critical epigenetic barrier to iCM production. Bypassing this barrier simplifies iCM generation and increases yield, potentially streamlining iCM production for therapeutic purposes