The final lithography accuracy is determined by what is known as the "on-product" performance, which includes product wafer-related errors and long-term stability. It is evident that on-product performance improvement is absolutely imperative now, and will become even more crucial in coming years. In order to meet customers' future requirements, we have developed the next-generation lithography system focusing on wafer alignment advancements to improve on-product performance.This newly developed wafer alignment system will help customers achieve their aggressive next-generation manufacturing accuracy and productivity requirements. In this paper, we describe the details of the new wafer measurement system and provide supporting performance data.

Our previous research has reported on the development of the first generation of quantum dots-in-a-well (DWELL) focal plane arrays (FPAs), which are based on InAs quantum dots (QDs) embedded in an InGaAs well having GaAs barriers, which have demonstrated spectral tunability via an externally applied bias voltage. More recently, technologies in DWELL devices have been further advanced by embedding InAs QDs in InGaAs and GaAs double wells with AlGaAs barriers, leading to a less strained InAs/InGaAs/GaAs/AlGaAs heterostructure. These lower strain quantum dots-in-a-double-well devices exhibit lower dark current than the previous generation DWELL devices while still demonstrating spectral tunability. This paper compares two different configurations of double DWELL (DDWELL) FPAs to a previous generation DWELL detector and to a commercially available quantum well infrared photodetector (QWIP). All four devices are 320 × 256 pixel FPAs that have been fabricated and hybridized with an Indigo 9705 read-out integrated circuit. Radiometric characterization, average array responsivity, array uniformity and measured noise equivalent temperature difference for all four devices is computed and compared at 60 K. Overall, the DDWELL devices had lower noise equivalent temperature difference and higher uniformity than the first-generation DWELL devices, although the commercially available QWIP has demonstrated the best performance.

We report on selective area growth of InAs and GaAs quantum dots (QDs) on GaAs through ∼20 nm SiO2 windows prepared by block copolymer lithography. We discuss the mechanisms of growth through these masks, highlighting the variation of the resulting morphology (dot size, spacing, uniformity, and areal density) as a function of growth parameters. We have obtained highly uniform arrays of InAs and GaAs QDs with mean diameters and areal densities of 20.6 nm and 1×1011 cm−2, respectively. We have also investigated the optical characteristics of these QDs as a function of temperature and drawn correlations between the optical response and their crystalline quality.

Phonons in GaN quantum dots (QDs) fabricated by Stranski–Krastanov growth are analyzed using Raman scattering and continuum models of phonon confinement. The QD samples are evaluated by Raman spectroscopy with four different excitation energies. Each excitation energy has a different penetration depth, and this makes it possible to distinguish Raman signals associated with the QDs from any other signals. In addition, the phonon frequency shift in GaN QDs are analyzed using theoretical models of the confined geometry and the internal stress, the calculated results are compared to the measured results.

In our research group, we develop novel dots-in-a-well (DWELL) photodetectors that are a hybrid of the quantum dot infrared photodetector (QDIP). The DWELL detector consists of an active region composed of InAs quantum dots embedded in InGaAs quantum wells. By adjusting the InGaAs well thickness, our structure allows for the manipulation of the operating wavelength and the nature of the transitions (bound-to-bound, bound-to-quasibound and bound-to-continuum) of the detector. Based on these principles, DWELL samples were grown using molecular beam epitaxy and fabricated into 320 x 256 focal plane arrays (FPAs) with Indium bumps using standard lithography at the University of New Mexico. The FPA evaluated was hybridized to an Indigo 9705 readout integrated circuit (ROIC) in collaboration with QmagiQ LLC and tested with a CamIRa(TM) system manufactured by SE-IR Corp. From this evaluation, we report the first two-color, co-located quantum dot based imaging system that can be used to take multicolor images using a single FPA. We demonstrated that we can operate the device at an intermediate bias (V-b=-1.25 V) and obtain two color response from the FPA at 77K. Using filter lenses, both MWIR and LWIR responses were obtained from the array at the same bias voltage. The MWIR and LWIR responses are thought to be from bound states in the dot to higher and lower lying states in the quantum well respectively. Temporal NEDT for the DWELL FPA was measured to be 80mK at 77K.

We have investigated the Ga-adlayer mediated growth of GaN quantum dots at 707°C on AlN (0001) by simultaneous use of in situ reflection high-energy electron diffraction and line-of-sight quadrupole mass spectrometry during rf-plasma assisted molecular beam epitaxy (PA-MBE). We have found that the Ga-adsorbate coverage of 1.0 ML (monolayer) is critical in the mediation of a fundamental change in the GaN Stranski-Krastanov (SK) growth mode on AlN. When the Ga-adsorbate coverage was less than 1.0 ML, the SK transition occurred during GaN growth. For larger Ga-adsorbate coverages, the SK transition occurred after the desorption of the Ga coverage in excess of 1.0 ML. We performed variable GaN coverage growth experiments followed by desorption of the Ga adsorbate and subsequent GaN thermal decomposition to determine that the critical GaN coverage for the SK transition was less than 2.0 ML under Ga-droplet PA-MBE growth conditions.

We have investigated the Ga-flux dependence of growth morphology and optical properties of GaN quantum dots (QDs) in AlN(0001). The QDs formed either by Stranski–Krastanov (S–K) or autosurfactant modified S–K growth depending on the incident Ga-flux during rf-plasma assisted molecular beam epitaxy. We correlated reflection high-energy electron diffraction specular intensity transients to the QD dimensions measured by atomic force microscopy. Single QD layers with growth mode dependant size, density, and wetting layer thickness were characterized by room temperature photoluminescence (PL) with a pulsed 193 nm excitation source. We used a self-consistent one-dimensional Schrödinger–Poisson calculation to identify the contribution of wetting layer quantum wells (1–4 monolayer GaN) and QDs in the PL spectra.

We study the effect of different deposition conditions on the properties of In-polar InN grown by plasma-assisted molecular beam epitaxy. GaN buffer layers grown in the Ga-droplet regime prior to the InN deposition significantly improved the surface morphology of InN films grown with excess In flux. Using this approach, In-polar InN films have been realized with room temperature electron mobilities as high as 2250cm2∕Vs. We correlate electron concentrations in our InN films with the unintentionally incorporated impurities, oxygen and hydrogen. A surface electron accumulation layer of 5.11×1013cm−2 is measured for In-polar InN. Analysis of optical absorption data provides a band gap energy of ∼0.65eV for the thickest InN films.

The authors have investigated the adsorption and subsequent desorption of Ga on AlN (0001) with line-of-sight quadrupole mass spectrometry (QMS). The authors present desorption data consistent with a continuous Ga-flux dependent accumulation of a laterally contracted Ga bilayer on AlN (0001) from 0 to 2.7±0.3 ML GaN equivalent coverage, and further Ga accumulation in macroscopic Ga droplets. The temperature dependence of Ga-adsorbate QMS desorption transients was investigated and the authors determined that the desorption activation energies for individual monolayers of the Ga adsorbate on AlN (0001) were similar to Ga desorption from GaN (0001). For the (first) pseudomorphic Ga-adsorbate monolayer on AlN, the authors measured a maximum Ga coverage of 1.0±0.1 ML and desorption activation energy of 6.2±0.3eV. For the (second) laterally contracted Ga monolayer (1.7±0.3 ML) the desorption activation energy was 3.8±0.1eV.

Self-assembled GaN quantum dots are characterized using Raman techniques. The electrical and optical properties of these GaN quantum dots are modeled in light of optoelectronic applications. Strain-induced changes in the phononic properties of these nanostructures are modeled and the strain-induced frequency shifts are compared with Raman measurements. Acoustic phonons in colloidal GaN quantum dots are modeled using a quantized elastic continuum model. Shifts observed in the Raman signatures for different excitation wavelengths provide evidence the Raman signatures of GaN quantum dots are observed.

The impact of the Ga adlayer coverage onto the surface morphologies and pit densities of GaN (0001) films grown by plasma-assisted molecular beam epitaxy (PAMBE) has been studied using quantitative in situ quadrupole mass spectrometry (QMS). As the equilibrium Ga adlayer coverages rise continuously from 0 to 2.5 monolayers (ML) the surface pit densities decrease from ∼2×109 cm-2 to zero, yielding characteristic step-flow and spiral growth hillock features. These results show that there is a direct and quantitative link between Ga adlayer coverage, adatom diffusion and surface defect structure without any discontinuities.

Subjects drew lines proportional in length to their subjective valuation of various amounts of money, available immediately and certainly, relative to a standard amount ranging across groups from $1,000,000 to $10. They also drew lines proportional to their subjective valuation of standard amounts with delays ranging from 1 day to 50 years and with probabilities ranging from 1/10 to 1/10,000,000. Amounts of certain-immediate money equivalent (in terms of drawn line length) to delayed or probabilistic money were determined. The delay and probability discount functions thereby obtained were hyperbolic in form, rather than exponential, consistent with previous findings. Large money amounts were valued higher when they were delayed by a day than when available immediately. Steepness of delay discounting was not systematically related to standard money amount but probabilistic discounting was steeper for higher standard amounts than for lower amounts. Some of these results differ from those obtained with choice procedures. Possible reasons for the differences are discussed. Copyright (C) 2000 John Wiley & Sons, Ltd.

Female college students first played a pseudo-prisoner's dilemma (PPD) game with the experimenter, who followed a fixed strategy. In the first experiment the experimenter's strategies for different groups of subjects were: (a) play tit-for-tat; (b) play randomly; (c) always cooperate; (d) always defect ('cooperation' and 'defection', defined as in an actual prisoner's dilemma game). Only the tit-for-tat group increased cooperation over trials; other groups decreased cooperation. After playing the PPD with the experimenter, subjects played an actual prisoner's dilemma (PD) game with each other. In the PD game, subjects began cooperating moderately but cooperation deteriorated regardless of what the experimenter's strategy had been in the earlier (PPD) game. In a second experiment, subjects again played a PPD game with the experimenter and then played a PD game with each other. Half played one trial at a time as in the first experiment while half played in patterns of four trials at a time. In the PD game, patterning of trials retarded the development of mutual defection regardless of previous experience. The cooperation-preserving effect of patterning of trials in this social task is compared with similar effects on individual tasks involving self-control and risk-aversion. (C) 1998 John Wiley & Sons, Ltd.