Multiple wavelength InGaAs quantum dot lasers using selective area epitaxy

The authors demonstrate multiple wavelength lasers fabricated from InGaAsquantum dots. Selective area epitaxy is used to grow the active region, consisting of five layer stack of InGaAsquantum dots with different band gapenergies in selected regions of the substrate, for fabrication of the lasers. The mechanism responsible for engineering of the band gap of quantum dots is discussed. The performance of the selectively grown lasers is compared to the lasers fabricated from structures grown in a standard, nonselective area growth process.The Australian Research Council is gratefully acknowledged for financial support

Spatially resolved characterization of InGaAs/GaAs quantum dot structures by scanning spreading resistance microscopy

Cross-sectional scanning spreading resistance microscopy (SSRM) is used to investigate stacked InGaAs/GaAs quantum dot(QD)structures with different doping schemes. Spatially resolved imaging of the QDs by SSRM is demonstrated. The SSRM contrast obtained for the QD layers is found to depend on doping in the structure. In the undoped structures both QD-layers and QDs within the layers could be resolved, while in the dopedstructures the QD layers appear more or less uniformly broadened. The origin of the SSRM contrast in the QD layer in the different samples is discussed and correlated with doping schemes.T. Hakkarainen, O. Douhéret, and S. Anand would like to acknowledge the Swedish Research Council VR for fi- nancial support and the Kurt-Alice Wallenberg KAW foundation for financing the microscope. L. Fu, H. H. Tan, and C. Jagadish would like to acknowledge the Australian Research Council ARC for financial support and Australian National Fabrication Facility ANFF for access to the facilities

High temperature rapid thermal annealing of phosphorous ion implanted InAs∕InP quantum dots

The effect of high temperature annealing of the InAs∕InPquantum dots(QDs) containing a thin GaAs interlayer is investigated. The QDs are rapid thermally annealed at 750, 800, 850, and 900°C for 30s. The QDs with the GaAs interlayer show good thermal stability up to 850°C as well as enhanced integrated photoluminescence (PL) intensity and reduced PL linewidth. The effect of high energy(450keV) phosphorous ion implantation at room temperature with doses of 5×10¹¹–5×10¹³ions/cm² with subsequent high temperature (750–850°C)rapid thermal annealing is also studied. A large implantation-inducedenergy shift of up to 309meV (400nm) is observed. The implanted samples annealed at 850°C show reduced PL linewidth and enhanced integrated PL intensity compared to the implanted samples annealed at 750°C.The authors gratefully acknowledge financial support from the Australian Research Council

Proton implantation-induced intermixing of InAs∕InP quantum dots

Protonimplantation-induced intermixing of InAsquantum dots(QDs) capped with InP, GaInAsP, and InP and InGaAs layers grown by metal-organic chemical vapor deposition is investigated. The samples are annealed at 750, 800, 850, and 900°C for 30s and thermal stability of the QDs is studied. The optimum annealing temperature is around 800°C which gives maximum implantation-induced energy shift. The QDs capped with InP layers show the highest implantation-induced energy shift due to strong group V interdiffusion whereas the QDsgrown on and capped with GaInAsP layers show the least implantation-induced energy shift due to weak group V and group III interdiffusion. The QDs capped with InP and InGaAs layers show intermediate implantation-induced energy shift and are less thermally stable compared to the QDsgrown on and capped with GaInAsP layers. The QDs capped with InP layers show enhanced photoluminescence(PL) intensity when implanted with lower proton dose (less than 5×10¹⁴ions/cm²). On the other hand higher proton dose (more than 1×10¹⁴ions/cm²) reduces the PL linewidth in all samples.The authors gratefully acknowledge financial support from the Australian Research Council

Impurity-free disordering of InAs/InP quantum dots

Impurity-free disordering (IFD) of the InAs quantum dots (QDs) capped with either an InP layer or an InGaAs∕InP bilayer is studied. The samples are coated with a SiO₂ or TiO₂ dielectric layer followed by rapid thermal annealing at 700, 750, 800, and 850°C for 30s . A large differential energy shift of 157meV is induced by SiO₂ in the QDs capped with an InGaAs∕InP bilayer. Contrary to the reported results on the suppression of intermixing of GaAs based QDs by TiO₂ , the authors find that intermixing of InAs∕InP QDs is promoted by TiO2 . X-ray photoelectron spectroscopy depth profiles show that both In and P outdiffuse to a TiO₂ layer whereas Ga, In, and P outdiffuse to a SiO₂ layer leading to different degrees of intermixing. The results indicate that a group V interstitial diffusion mechanism might be responsible for IFD of InAs∕InP QDs.The financial support from the Australian Research Council is also gratefully acknowledged

Impossibility to eliminate observer effect in the assessment of adherence in clinical trials.

PURPOSE: To utilize the Travoprost Dosing Aid (DA) in the assessment of patient medication adherence, while also determining whether or not altering the functionality of the DA in three randomized subject groups can reduce observer effect. METHODS: Forty-five subjects were randomized into three groups: two with monitored DAs and one without monitoring. One group of subjects was given a DA that both monitored drop usage and had visual and audible alarms, while the other monitored group included subjects given a DA that had no alarms but continued to monitor drop usage. The third group was given a DA that had no alarm reminders or dose usage monitoring. Subjects were informed that some monitors would not be functional, in an attempt to reduce observer effect, or the effect of being monitored on subject behavior and adherence. A six-item questionnaire was also utilized to assess how the subjects felt about their adherence and DA use. RESULTS: The overall adherence rates were found to be 78% in the fully functional group (95% confidence interval: 70-88) and 76% in the no alarms group (95% confidence interval: 65-89). No association was seen between questionnaire response and medication adherence. The patients in the DA group without alarms had a significantly higher odds ratio of medication adherence if they reported on the questionnaire that using the DA did affect how much they used their drops. CONCLUSION: Though the use of DA was expected to reveal different rates of adherence depending on the functionality of the DA between groups, patients with a nonfunctioning DA did not have a significant difference in medication adherence compared to those given a fully functional DA. This supports that an observer effect was not reduced despite these interventions, and that the subjects adhered to taking their medications as if they had a functioning DA and were being monitored

Pitfalls and Precautions When Using Predicted Failure Data for Quantitative Analysis of Safety Risk in Human Rated Launch Vehicles

No abstract availabl

Temperature dependent photoluminescence in oxygen ion implanted and rapid thermally annealed ZnO/ZnMgO multiple quantum wells

The authors investigate the effect of oxygen implantation and rapid thermal annealing in ZnO∕ZnMgOmultiple quantum wells using photoluminescence. A blueshift in the photoluminescence is observed in the implanted samples. For a low implantation dose, a significant increase of activation energy and a slight increase of the photoluminescence efficiency are observed. This is attributed to the suppression of the point defect complexes and transformation between defect structures by implantation and subsequent rapid thermal annealing. A high dose of implantation leads to lattice damage and agglomeration of defects leading to large defect clusters, which result to an increase in nonradiative recombination.The authors gratefully acknowledge the Australian Research Council for financial support and Swinburne University of Technology for Strategic Initiative funding. One of the authors X.W. acknowledges partial financial support of the Chinese National Natural Science Foundation 10364004 and the Yunnan Natural Science Foundation 2003E0013M

Atomic relocation processes in impurity-free disordered p-GaAs epilayers studied by deep level transient spectroscopy

We have used capacitance–voltage and deep level transient spectroscopy techniques to study the relocation of impurities, such as Zn and Cu, in impurity-free disordered (IFD) p-type GaAs. A four-fold increase in the doping concentration is observed after annealing at 925 °C. Two electrically active defects HA (EV+0.39 eV) and HB2 (EV+0.54 eV), which we have attributed to Cu- and Asi/AsGa-related levels, respectively, are observed in the disordered p-GaAs layers. The injection of galliumvacancies causes segregation of Zndopant atoms and Cu towards the surface of IFD samples. The atomic relocation process is critically assessed in terms of the application of IFD to the band gap engineering of doped GaAs-based heterostructures.Two of the authors ~P.N.K.D. and H.H.T.! acknowledge the financial support of the Australian Research Counci