Extending the cutoff wavelength of lattice-matched GaInAsSb/GaSb thermophotovoltaics devices

This paper reports the growth, materials characterization, and device performance of lattice-matched GaInAsSb/GaSb thermophotovoltaic (TPV) devices with cutoff wavelength as long as 2.5 {micro}m. GaInAsSb epilayers were grown lattice matched to GaSb substrates by organometallic vapor phase epitaxy (OMVPE) using all organometallic precursors including triethylgallium, trimethylindium, tertiarybutylarsine, and trimethylantimony with diethyltellurium and dimethylzinc as the n- and p-type dopants, respectively. The growth temperature was 525 C. Although these alloys are metastable, a mirror-like surface morphology and room temperature photoluminescence (PL) are obtained for alloys with PL peak emission at room temperature as long as 2.5 {micro}m. In general, however, a trend of decreasing material quality is observed as the wavelength increases. Both the surface roughness and PL full width at half-maximum increase with wavelength. In spite of the dependence of material quality on PL peak emission wavelength, the internal quantum efficiency of TPV devices with cutoff wavelengths of 2.3 to 2.5 {micro}m is as high as 86%

Hydroxyurea and sickle cell anemia: effect on quality of life

BACKGROUND: The Multicenter Study of Hydroxyurea (HU) in Sickle Cell Anemia (MSH) previously showed that daily oral HU reduces painful sickle cell (SS) crises by 50% in patients with moderate to severe disease. The morbidity associated with this disease is known to have serious negative impact on the overall quality of life(QOL) of affected individuals. METHODS: The data in this report were collected from the 299 patients enrolled in the MSH. Health quality of llife (HQOL) measures were assessed in the MSH as a secondary endpoint to determine if the clinical benefit of HU could translate into a measurable benefit perceptible to the patients. HQOL was assessed with the Profile of Mood States, the Health Status Short Form 36 (SF-36), including 4-week pain recall, and the Ladder of Life, self-administered twice 2-weeks apart pre-treatment and every 6 months during the two-year, randomized, double-blind, treatment phase. The effects of factors including randomized treatment, age, gender, pre-treatment crises frequency, Hb-F level mean, daily pain from 4-week pre-treatment diaries, and 2-year Hb-F response level (low or high) were investigated. RESULTS: Over two years of treatment, the benefit of HU treatment on QOL, other than pain scales, was limited to those patients taking HU who maintained a high HbF response, compared to those with low HbF response or on placebo. These restricted benefits occurred in social function, pain recall and general health perception. Stratification according to average daily pain prior to treatment showed that responders to HU whose average daily pain score was 5–9 (substantial pain) achieved significant reduction in the tension scale compared to the placebo group and to non-responders. HU had no apparent effect on other QOL measures. CONCLUSION: Treatment of SS with HU improves some aspects of QOL in adult patients who already suffer from moderate-to-severe SS

Substrate misorientation effects on epitaxial GaInAsSb

The effect of substrate misorientation on the growth of GaInAsSb was studied for epilayers grown lattice-matched to GaSb substrates by low-pressure organometallic vapor phase epitaxy. The substrates were (100) misoriented 2 or 6{degree} toward (110), (111)A, or (111)B. The surface is mirror-like and featureless for layers grown with a 6{degree} toward (111)B misorientation, while, a slight texture was observed for layers grown on all other misorientations. The optical quality of layers, as determined by the full width at half-maximum of photoluminescence spectra measured at 4K, is significantly better for layers grown on substrates with a 6{degree} toward (111)B misorientation. The incorporation of Zn as a p-type dopant in GaInAsSb is about 1.5 times more efficient on substrates with 6{degree} toward (111)B misorientation compared to 2{degree} toward (110) misorientation. The external quantum efficiency of thermophotovoltaic devices is not, however, significantly affected by substrate misorientation

Recent progress in GaInAsSb thermophotovoltaics grown by organometallic vapor phase epitaxy

Studies on the materials development of Ga{sub 1{minus}x}In{sub x}As{sub y}Sb{sub 1{minus}y} alloys for thermophotovoltaic (TPV) devices are reviewed. Ga{sub 1{minus}x}In{sub x}As{sub y}Sb{sub 1{minus}y} epilayers were grown lattice matched to GaSb substrates by organometallic vapor phase epitaxy (OMVPE) using all organometallic precursors including triethylgallium, trimethylindium, tertiarybutylarsine, and trimethylantimony with diethyltellurium and dimethylzinc as the n- and p-type dopants, respectively. The overall material quality of these alloys depends on growth temperature, In content, V/III ratio, substrate misorientation, and to a lesser extent, growth rate. A mirror-like surface morphology and room temperature photoluminescence (PL) are obtained for GaInAsSb layers with peak emission in the wavelength range between 2 and 2.5 {micro}m. The crystal quality improves for growth temperature decreasing from 575 to 525 C, and with decreasing In content, as based on epilayer surface morphology and low temperature PL spectra. A trend of smaller full width at half-maximum for low temperature PL spectra is observed as the growth rate is increased from 1.5 to 2.5 and 5 {micro}m/h. In general, GaInAsSb layers grown on (100) GaSb substrates with a 6{degree} toward (111)B misorientation exhibited overall better material quality than layers grown on the more standard substrate (100)2{degree} toward (110). Consistent growth of high performance lattice-matched GaInAsSb TPV devices is also demonstrated

Limiting phase separation in epitaxial GaInAsSb

GaInAsSb alloys are of great interest for lattice-matched thermophotovoltaic (TPV) devices because of the high performance attainable at 2.2 {micro}m. Extension of the TPV device cutoff wavelength to beyond 2.2 {micro}m is especially desirable since the emissive power of the source is significant at these longer wavelengths. However, the GaInAsSb quaternary alloy system exhibits a miscibility gap in the wavelength range of interest, and no devices with cutoff wavelengths longer than 2.3 {micro}m have been demonstrated. This paper reports the successful growth of GaInAsSb alloys which exhibit room temperature photoluminescence (PL) at wavelengths as long as 2.5 {micro}m. TPV devices with cutoff wavelengths out to 2.5 {micro}m exhibit external quantum efficiencies of 57%. These values are comparable to those measured for 2.2 {micro}m devices

Lattice-matched epitaxial GaInAsSb/GaSb thermophotovoltaic devices

The materials development of Ga{sub 1{minus}x}In{sub x}As{sub y}Sb{sub 1{minus}y} alloys for lattice-matched thermophotovoltaic (TPV) devices is reported. Epilayers with cutoff wavelength 2--2.4 {micro}m at room temperature and lattice-matched to GaSb substrates were grown by both low-pressure organometallic vapor phase epitaxy and molecular beam epitaxy. These layers exhibit high optical and structural quality. For demonstrating lattice-matched thermophotovoltaic devices, p- and n-type doping studies were performed. Several TPV device structures were investigated, with variations in the base/emitter thicknesses and the incorporation of a high bandgap GaSb or AlGaAsSb window layer. Significant improvement in the external quantum efficiency is observed for devices with an AlGaAsSb window layer compared to those without one

An Application of Using Support Vector Machine Based on Classification Technique for Predicting Medical Data Sets

© 2019, Springer Nature Switzerland AG. This paper illustrates the utilise of various kind of machine learning approaches based on support vector machines for classifying Sickle Cell Disease data set. It has demonstrated that support vector machines generate an essential enhancement when applied for the pre-processing of clinical time-series data set. In this aspect, the objective of this study is to present discoveries for a number of classes of approaches for therapeutically associated problems in the purpose of acquiring high accuracy and performance. The primary case in this study includes classifying the dosage necessary for each patient individually. We applied a number of support vector machines to examine sickle cell data set based on the performance evaluation metrics. The result collected from a number of models have indicated that, support vector Classifier demonstrated inferior outcomes in comparison to Radial Basis Support Vector Classifier. For our Sickle cell data sets, it was found that the Parzen Kernel Support Vector Classifier produced the highest levels of performance and accuracy during training procedure accuracy 0.89733, AUC 0.94267. Where the testing set process, accuracy 0.81778, the area under the curve with 0.86556

Ternary and quaternary antimonide devices for thermophotovoltaic applications

Thermophotovoltaic (TPV) devices have been fabricated using epitaxial ternary and quaternary layers grown on GaSb substrates. GaInSb ternary devices were grown by metalorganic vapor phase epitaxy (MOVPE) with buffer layers to accommodate the lattice mismatch, and GaInAsSb lattice-matched quaternaries were grown by MOVPE and by liquid phase epitaxy (LPE). Improved devices are obtained when optical absorption occurs in the p-layer due to the longer minority carrier diffusion length. Thick emitter p/n devices are limited by surface recombination, with highest quantum efficiency and lowest dark current being achieved with epitaxially grown surface passivation layers on lattice-matched MOVPE quaternaries. Thin emitter/thick base n/p devices are very promising, but require improved shallow high-quality n-type ohmic contacts

Higher Rates of Hemolysis Are Not Associated with Albuminuria in Jamaicans with Sickle Cell Disease

BACKGROUND: Albuminuria is a marker of glomerular damage in Sickle Cell Disease (SCD). In this study, we sought to determine the possible predictors of albuminuria in the two more prevalent genotypes of SCD among the Jamaica Sickle Cell Cohort Study participants. METHODS: An age-matched cohort of 122 patients with HbSS or HbSC genotypes had measurements of their morning urine albumin concentration, blood pressure, body mass index, haematology and certain biochemistry parameters done. Associations of albuminuria with possible predictors including hematological parameters, reticulocyte counts, aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) levels were examined using multiple regression models. RESULTS: A total of 122 participants were recruited (mean age 28.6 years ±2.5 years; 85 HbSS, 37 HbSC). 25.9% with HbSS and 10.8% with HbSC disease had microalbuminuria (urine albumin/creatinine ratio  =  30-300 mg/g of creatinine) whereas 16.5% of HbSS and 2.7% of HbSC disease had macroalbuminuria (urine albumin/creatinine ratio>300 mg/g of creatinine). Mean arterial pressure, hemoglobin levels, serum creatinine, reticulocyte counts and white blood cell counts were statistically significant predictors of albuminuria in HbSS, whereas white blood cell counts and serum creatinine predicted albuminuria in HbSC disease. Both markers of chronic hemolysis, i.e. AST and LDH levels, showed no associations with albuminuria in either genotype. CONCLUSIONS: Renal disease, as evidenced by excretion of increased amounts of albumin in urine due to a glomerulopathy, is a common end-organ complication in SCD. It is shown to be more severe in those with HbSS disease than in HbSC disease. Rising blood pressure, lower hemoglobin levels and higher white blood cell counts are hints to the clinician of impending renal disease, whereas higher rates of hemolysis do not appear to play a role in this complication of SCD