Two-dimensional electron gas formation in undoped In[0.75]Ga[0.25]As/In[0.75]Al[0.25]As quantum wells

We report on the achievement of a two-dimensional electron gas in completely undoped In[0.75]Al[0.25]As/In[0.75]Ga[0.25]As metamorphic quantum wells. Using these structures we were able to reduce the carrier density, with respect to reported values in similar modulation-doped structures. We found experimentally that the electronic charge in the quantum well is likely due to a deep-level donor state in the In[0.75]Al[0.25]As barrier band gap, whose energy lies within the In[0.75]Ga[0.25]As/In[0.75]Al[0.25]As conduction band discontinuity. This result is further confirmed through a Poisson-Schroedinger simulation of the two-dimensional electron gas structure.Comment: 17 pages, 6 figures, to be published in J. Vac. Sci. Technol.

Growth variations and scattering mechanisms in metamorphic In0.75Ga0.25As/In-0.75 Al0.25As quantum wells grown by molecular beam epitaxy

Modulation doped metamorphic In0.75Ga0.25As/In0.75Al0.25As quantum wells (QW) were grown on GaAs substrates by molecular beam epitaxy (MBE) with step-graded buffer layers. The electron mobility of the QWs has been improved by varying the MBE growth conditions, including substrate temperature, arsenic over pressure and modulation doping level. By applying a bias voltage to SiO2 insulated gates, the electron density in the QW can be tuned from 1×1011 to 5.3×1011 cm−2. A peak mobility of 4.3×105 cm2V−1s−1 is obtained at 3.7×1011 cm−2 at 1.5 K before the onset of second subband population. To understand the evolution of mobility, transport data is fitted to a model that takes into account scattering from background impurities, modulation doping, alloy disorder and interface roughness. According to the fits, scattering from background impurities is dominant while that from alloy disorder becomes more significant at high carrier density

Improving health care quality for racial/ethnic minorities: a systematic review of the best evidence regarding provider and organization interventions

BACKGROUND: Despite awareness of inequities in health care quality, little is known about strategies that could improve the quality of healthcare for ethnic minority populations. We conducted a systematic literature review and analysis to synthesize the findings of controlled studies evaluating interventions targeted at health care providers to improve health care quality or reduce disparities in care for racial/ethnic minorities. METHODS: We performed electronic and hand searches from 1980 through June 2003 to identify randomized controlled trials or concurrent controlled trials. Reviewers abstracted data from studies to determine study characteristics, results, and quality. We graded the strength of the evidence as excellent, good, fair or poor using predetermined criteria. The main outcome measures were evidence of effectiveness and cost of strategies to improve health care quality or reduce disparities in care for racial/ethnic minorities. RESULTS: Twenty-seven studies met criteria for review. Almost all (n = 26) took place in the primary care setting, and most (n = 19) focused on improving provision of preventive services. Only two studies were designed specifically to meet the needs of racial/ethnic minority patients. All 10 studies that used a provider reminder system for provision of standardized services (mostly preventive) reported favorable outcomes. The following quality improvement strategies demonstrated favorable results but were used in a small number of studies: bypassing the physician to offer preventive services directly to patients (2 of 2 studies favorable), provider education alone (2 of 2 studies favorable), use of a structured questionnaire to assess adolescent health behaviors (1 of 1 study favorable), and use of remote simultaneous translation (1 of 1 study favorable). Interventions employing more than one main strategy were used in 9 studies with inconsistent results. There were limited data on the costs of these strategies, as only one study reported cost data. CONCLUSION: There are several promising strategies that may improve health care quality for racial/ethnic minorities, but a lack of studies specifically targeting disease areas and processes of care for which disparities have been previously documented. Further research and funding is needed to evaluate strategies designed to reduce disparities in health care quality for racial/ethnic minorities

Does Cultural Competency Training of Health Professionals Improve Patient Outcomes? A Systematic Review and Proposed Algorithm for Future Research

BACKGROUND: Cultural competency training has been proposed as a way to improve patient outcomes. There is a need for evidence showing that these interventions reduce health disparities. OBJECTIVE: The objective was to conduct a systematic review addressing the effects of cultural competency training on patient-centered outcomes; assess quality of studies and strength of effect; and propose a framework for future research. DESIGN: The authors performed electronic searches in the MEDLINE/PubMed, ERIC, PsycINFO, CINAHL and Web of Science databases for original articles published in English between 1990 and 2010, and a bibliographic hand search. Studies that reported cultural competence educational interventions for health professionals and measured impact on patients and/or health care utilization as primary or secondary outcomes were included. MEASUREMENTS: Four authors independently rated studies for quality using validated criteria and assessed the training effect on patient outcomes. Due to study heterogeneity, data were not pooled; instead, qualitative synthesis and analysis were conducted. RESULTS: Seven studies met inclusion criteria. Three involved physicians, two involved mental health professionals and two involved multiple health professionals and students. Two were quasi-randomized, two were cluster randomized, and three were pre/post field studies. Study quality was low to moderate with none of high quality; most studies did not adequately control for potentially confounding variables. Effect size ranged from no effect to moderately beneficial (unable to assess in two studies). Three studies reported positive (beneficial) effects; none demonstrated a negative (harmful) effect. CONCLUSION: There is limited research showing a positive relationship between cultural competency training and improved patient outcomes, but there remains a paucity of high quality research. Future work should address challenges limiting quality. We propose an algorithm to guide educators in designing and evaluating curricula, to rigorously demonstrate the impact on patient outcomes and health disparities