Variation of material parameters along the growth direction of liquid encapsulated Czochralski grown GaAs ingots

The variation of material properties along the growth axis of single crystal LEC GaAs ingots is studied. Parameters investigated include concentration and lateral variation of EL2, photoluminescence intensity, resistivity, the concentration of extrinsic shallow acceptors and, after test implantation, the sheet resistivity. Correlations between the observed trends are identified and discussed in terms of compensation and segregation. In general, a very satisfactory homogeneity is found. Remaining variations are identified and evaluated with respect to their device-relevant consequences.     

Pressure and temperature dependence of the electric field gradient (EFG) in CdS

Using the time differential perturbed angular correlation technique (TDPAC), the electric hyperfine interaction of¹¹¹Cd in the II-VI-semiconductor CdS was investigated. The results of the temperature and pressure dependence of the electric field gradient (EFG) are discussed. The binding energyE _b for¹¹¹In at a Cd lattice site and a Cd vacancy (¹¹¹In_Cd–V_Cd–pair) could be estimated to 340 meV±80 meV by means of an Arrhenius-Plot. The disappearance of the 79 MHz and 73 MHz frequencies under a pressure of about 30 kbar could be due to their vacancy character or to the beginning of the phase transition to rocksalt structure.     

Introducing oblique norms into multiple criteria programming

We propose to use block norms to generate nondominated solutions of multiple criteria programs and introduce the new concept of the oblique norm that is specially tailored to handle general problems. We prove the equivalence of finding the properly nondominated solutions of a multiple criteria program and solving its scalarization by means of oblique norms.     

The use of pulsed amperometry combined with ion-exclusion chromatography for the simultaneous analysis of ascorbic acid and sulfite

Initial attempts to monitor ascorbic acid and sulfite, in a beer matrix, by combining ion-exclusion chromatography with a pulsed amperometric detector using a single applied voltage to the platinum working electrode, were unsuccessful. Alternatively, good chromatograms for the separation of the two antioxidants were achieved utilizing a standard, amperometric cell. However, remarkably superior results were observed when this standard cell was operated in a pulsed mode and cleaning cycles were continually applied throughout the analysis. The working electrode stability and precision have been examined. Preliminary spike recovery data indicate acceptable accuracy for the method. Comparisons of this method to standard reference methods are currently ongoing.