RESUMO
We report on engineering impact ionization characteristics of In0.53Ga0.47As/Al0.48In0.52As superlattice avalanche photodiodes (InGaAs/AlInAs SL APDs) on InP substrate to design and demonstrate an APD with low k-value. We design InGaAs/AlInAs SL APDs with three different SL periods (4 ML, 6 ML, and 8 ML) to achieve the same composition as Al0.4Ga0.07In0.53As quaternary random alloy (RA). The simulated results of an RA and the three SLs predict that the SLs have lower k-values than the RA because the electrons can readily reach their threshold energy for impact ionization while the holes experience the multiple valence minibands scattering. The shorter period of SL shows the lower k-value. To support the theoretical prediction, the designed 6 ML and 8 ML SLs are experimentally demonstrated. The 8 ML SL shows k-value of 0.22, which is lower than the k-value of the RA. The 6 ML SL exhibits even lower k-value than the 8 ML SL, indicating that the shorter period of the SL, the lower k-value as predicted. This work is a theoretical modeling and experimental demonstration of engineering avalanche characteristics in InGaAs/AlInAs SLs and would assist one to design the SLs with improved performance for various SWIR APD application.
RESUMO
Systematic theoretical investigations are carried out under the density functional formalism in an effort to understand the initial structural evolution due to the adsorption of ZnTe on As-exposed Si(211). Our calculations indicate that after the adsorption of Zn and Te on the As-exposed Si(211), the stable atomic structure qualitatively follows the ideal atomic structure of Si(211) with alteration of various bond lengths. Since the basic symmetry of the Si(211) is preserved after the adsorption of ZnTe, the deposition of ZnTe on the As terminated Si(211) prior to the deposition of CdTe and HgCdTe is useful for obtaining an ultimate quality layer of HgCdTe on Si(211). Some of our results are compared with the available experimental results, and they are found to agree with each other qualitatively.
RESUMO
The investigation of the fracture behavior of polymers in the environmental scanning electron microscope (ESEM) can provide information about the correlation between the microstructure of a specimen and the macroscopic stress-strain characteristic. As the mechanical properties of polymers change dramatically at the glass transition temperature, cooling of the specimens during the tensile tests can yield very valuable information about the influence of individual components of polymer blends on the fracture behavior of the material. A serious problem in this connection is the poor heat conductivity of polymers. A commercially available cooling platform, which can be mounted on the tensile stage used for the tests was substantially modified to both enhance the heat transfer between platform and specimen, and to minimize the temperature gradient along the specimen. The first experiments on modified polypropylene specimens already delivered some unexpected results. Fibril-like structures appeared at the crack tip that would not be expected at temperatures below the glass transition temperature of the polymer blend.
RESUMO
We consider the effect of reducing the density of final hole states for Auger processes on the Auger rate at room temperature and 77K at densities near lasing thresholds. The system of interest is a strain-compensated superlattice based on the InAs/GaInSb material system with a 3.7 microm band gap. At 77K the Auger lifetime is reduced by two orders of magnitude, while the change at 300K is less than a factor of two. We conclude that final-state optimization in this particular structure, while pronounced at 77K, has little effect at 300K.
