Electron traps in thin layers of low-temperature-grown gallium arsenide with As-Sb nanoclusters

Electron traps in low-temperature-grown ～40-nm-thick GaAs layers containing nanometer As-Sb clusters have been studied using deep-level transient spectroscopy. Measurements at various bias voltages and small-amplitude filling pulses have allowed the identification of two groups (T1 and T2) of traps with substantially different thermal electron emission rates. It is shown that the density of traps T2 (with an activation energy of 0.56 ± 0.04 eV and electron capture cross section of 2 × 10^?13?10^?12cm²) is ～2 × 10¹²cm_?2, while the density of traps T1 (0.44 ± 0.02 eV and 2 × 10^?14?10^?13 cm², respectively) is ten times lower. It is assumed that, according to the existence of the two cluster groups observed in the layers under study, traps T2 are associated with clusters 4–7 nm in diameter and traps T1, with clusters up to ～20 nm in diameter.     

Matching degradation of threshold voltage and gate voltage of NMOSFET after Hot Carrier Injection stress

Device degradation modelling is more and more important for reliable circuit design. On MOSFET, the threshold voltage drift in time can lead to circuit performance degradation. In this study, V_T shift due to Hot Carrier Injection stress is accelerated on small width devices. V_T matching is also degraded during stress as a function of V_T deterioration. This width dependence allows explaining gate voltage matching behavior in the sub-threshold area used in low power analog applications.     

Effect of local structural defects on the precipitation of as in the vicinity of InAs quantum dots in a GaAs matrix

Electron-microscopy studies of GaAs structures grown by the method of molecular-beam epitaxy and containing arrays of semiconductor InAs quantum dots and metallic As quantum dots are performed. An array of InAs quantum dots is formed using the Stranski-Krastanow mechanism and consists of five layers of vertically conjugated quantum dots divided by a 5-nm-thick GaAs spacer layer. The array of As quantum dots is formed in an As-enriched GaAs layer grown at a low temperature above an array of InAs quantum dots using postgrowth annealing at temperatures of 400–600°C for 15 min. It is found that, during the course of structure growth near the InAs quantum dots, misfit defects are formed; these defects are represented by 60° or edge dislocations located in the heterointerface plane of the semiconductor quantum dots and penetrating to the surface through a layer of “low-temperature” GaAs. The presence of such structural defects leads to the formation of As quantum dots in the vicinity of the middle of the InAs conjugated quantum dots beyond the layer of “low-temperature” GaAs.     

Mechanisms of InGaAlAs solid solution decomposition stimulated by InAs quantum dots

Mechanisms of InGaAlAs solid solution decomposition stimulated by a purposely deposited layer of InAs quantum dots are studied. Decomposition of the solid solution results in an increase in the effective quantum dot size and the shift of the photoluminescence line to as far as 1.3 μm. When aluminum atoms are added to the solid solution, the effect of In atom “conservation” within the dots is observed, which also causes an increase in the effective dot size. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 34, No. 3, 2000, pp. 330–333. Original Russian Text Copyright ? 2000 by Tsatsul’nikov, Volovik, Bedarev, Zhukov, Kovsh, Ledentsov, Maksimov, Maleev, Musikhin, Ustinov, Bert, Kop’ev, Bimberg, Alferov.     

Apparent chemical composition of nine commercial or semi-commercial whey protein concentrates, isolates and fractions

Summary Analytical results are given for whey powders prepared on a commercial or semi-commercial scale by three companies. Altogether, five preparations enriched in β-lactoglobulin, four whey protein isolates and a fraction enriched in α-lactalbumin were analyzed for protein composition, including %β-lactoglobulin, α-lactalbumin, bovine serum albumin, casein (glyco) macropeptide and the main triglycerides. Protein composition was determined by high pressure gel permeation and reversed phase liquid chromatography and by capillary zone electrophoresis. The extent of modification of the native β-lactoglobulin structure was also measured through the degree of lactosylation and the fraction of accessible free sulphydryl groups. One significant finding was that the calculated recovery of protein following quantitation of the chromatogram or electropherogram was seldom above 90% and occasionally below 60% of that loaded onto the column or capillary, raising doubts as to the reliability of the analytical results. Extrapolation by linear regression to 100% recovery allowed estimates to be made of the true β-lactoglobulin composition of the samples. The nine samples could be placed into three distinct groups with estimated true β-lactoglobulin weight % of 70.9 ± 1.1, 62.0 ± 3.4 and 39.5 ± 4.9. Physico-chemical properties of the group of samples are reported elsewhere (Holt et al ., 1999).     

Validity of residential traffic intensity as an estimate of long-term personal exposure to traffic-related air pollution among adults

The validity of traffic intensity near the home as an estimate for the personal long-term exposure to traffic-related air pollution in an adult population was tested. Personal and near-home outdoor exposure to PM2.5, soot, NO, NO2, and NOx was monitored four to five times during 48 h periods in older adults. A group of 23 participants lived in high traffic intensity streets (>10000 vehicles/(24 h)), and 22 lived in low traffic intensity streets. The relation between average personal exposure and traffic intensity at the residential address was explored by taking indoor sources into account. Large differences in the measured outdoor concentrations between locations in high traffic and low traffic intensity streets were found for soot (68%), NO (127%), and NOx (35%). Differences were smaller for PM2.5 (14%) and NO2 (22%). Slightly elevated ratios were found for personal exposure to soot (1.15; 95% confidence interval (CI), 1.01-1.30)when comparing adults living in high traffic intensity streets with adults living in low traffic intensity streets. For NO, increased personal exposure (1.16) was seen for the same comparison, but this difference failed to reach statistical significance (CI, 0.80-1.66). Traffic intensity on the street of residence predicted personal exposure to soot but not to PM2.5 or nitrogen oxides. Traffic intensity may not correlate well to personal exposure and accordingly substantial misclassification of exposure may occur when traffic intensity is used as an exposure indicator in epidemiological studies. Time spent in traffic and spending time outdoors were associated with increased personal exposure of soot and PM2.5, but not NOx.