The Role of Excitation Photons Energy in the Photoinduced Carrier Dynamics in InGaAs/InAlAs Superlattice Heterostructures

Technical Physics Letters - The influence of excitation photons energy on the relaxation times of photoexcited carriers is studied. The involved relaxation mechanisms are evaluated and the...     

Ultrafast Dynamics of Photoexcited Charge Carriers in In<Subscript>0.53</Subscript>Ga<Subscript>0.47</Subscript>As/In<Subscript>0.52</Subscript>Al<Subscript>0.48</Subscript>As Superlattices under Femtosecond Laser Excitation

The results of experimental studies of the time dynamics of photoexcited charge carriers in In_0.53Ga_0.47As/In_0.52Al_0.48As superlattices grown by molecular-beam epitaxy on a GaAs substrate with a metamorphic buffer are reported. On the basis of the results of the numerical simulation of band diagrams, the optimal thickness of the In_0.52Al_0.48As barrier layer (4 nm) is chosen. At this thickness, the electron wave functions in In_0.53Ga_0.47As substantially overlap the In_0.52Al_0.48As barriers. This makes it possible to attain a short lifetime of photoexcited charge carriers (τ ~ 3.4 ps) at the wavelength λ = 800 nm and the pumping power 50 mW without doping of the In_0.53Ga_0.47As layer with beryllium. It is shown that an increase in the wavelength to λ = 930 nm (at the same pumping power) yields a decrease in the lifetime of photoexcited charge carriers to τ ~ 2 ps. This effect is attributed to an increase in the capture cross section of trapping states for electrons with lower energies and to a decrease in the occupancy of traps at lower excitation densities.     

MHEMT with a power-gain cut-off frequency of f max = 0.63 THz on the basis of a In0.42Al0.58As/In0.42Ga0.58As/In0.42Al0.58As/GaAs nanoheterostructure

The method of molecular-beam epitaxy is used to grow a In_0.42Al_0.58As/In_0.42Ga_0.58As/In_0.42Al_0.58As nanoheterostructure with a step-graded metamorphic buffer on a GaAs substrate. The root-mean-square value of the surface roughness is 3.1 nm. A MHEMT (metamorphic high-electron-mobility transistor) with a zigzag-like gate of a length of 46 nm is fabricated on the basis of this nanoheterostructure; for this MHEMT, the cutoff frequencies for the current and power gain are f _T = 0.13 THz and f _max = 0.63 THz, respectively.     

Intensification of the bio‐processing of cotton textiles by combined enzyme/ultrasound treatment

Utilization of highly specific enzymes for various textile‐processing applications is becoming increasingly popular because of their ability to replace harsh organic/inorganic chemicals currently used by the textile industry. Thus, a significant decrease in the amount and toxicity of textile wastewater effluents is achievable. It was established that ultrasound does not inactivate the complex structures of enzyme molecules and as a consequence there was significant improvement in the performance of both cellulase and pectinase enzymes. The experimental data indicate that the maximum benefit provided by sonication occurs at relatively low enzyme concentrations. Ultrasonic energy significantly intensified enzymatic activity on various types of cotton fabrics, but it did not contribute to a decrease in tensile strength. The combined enzyme/sonication treatment of cellulosic textiles offers significant advantages such as less consumption of expensive enzymes, shorter processing time, less fiber damage and better uniformity of treatment. Published in 2002 for SCI by John Wiley & Sons, Ltd     

Amplitude-Hyperbolic Method of Passive Location of a Radiation Source

A new method for ranging and locating a radiation source is proposed for a two-position system that detects an amplitude and difference of instances at which a wave arrives at a receiving position. Equations that make it possible to study the procedural error and accuracy characteristics of the method for various observation conditions and the results of a computational experiment are presented. Recommendations on applying this method are given.