Calculation on hot-electron noise in semiconductors

Under hot-electron conditions, noise arises both from fluctuations in the carrier velocity and the carrier collision time. The magnitudes of these two contributions are calculated by the Monte-Carlo method for InSb at 77°K.     

In Situ Quenching Methods Toward exo-Olefin-Terminated Polyisobutylene

exo-Olefin-terminated polyisobutylene was obtained directly from living isobutylene polymerizations by addition of a quenching compound to the living chain ends. Three broad classes of compounds were evaluated including hindered bases such as hindered pyridines and piperidines, N-hydro-2,5-disubstitutedpyrroles, and sulfides, ethers, and silylethers. The proposed mechanism of quenching unique to each class was discussed, with supporting kinetic, spectroscopic, and structure-based evidence presented. Hindered bases were proposed to operate by E2 elimination reaction of free base at the carbenium ion. N-Hydro-2,5-disubstitutedpyrroles were proposed to form the η⁵-2,5-disubstitutedpyrrolyltrichloro-titanium(IV) coordination complex, which serves as the true quencher. Sulfides, ethers, and silylethers were proposed to operate by first converting the PIB chain ends quantitatively to the onium adduct, which is then decomposed to form exo-olefin PIB. Sulfides and ethers were the best performing quenchers of all the types studied, particularly bulky ones such di-tert-butylsulfide and diisopropyl ether.     

Visible (683 to 713 nm) room-temperature AlGaAs vertical cavity surface emitting lasers (VCSELs)

We compare the materials parameters for visible emitting, vertical cavity surface emitting lasers (VCSELs) and conclude that AlGaAs-based materials are a good choice. All-AlGaAs devices were produced by metalorganic vapour phase epitaxy (MOVPE) growth using ultra-high purity source reagents. Lasing was obtained at wavelengths in the range of 683 to 713 nm using four 45 Å wide Al_0.18Ga_0.82 As quantum wells in the active region. A threshold current density of 3.8 kA cm⁻² was measured for a cavity wavelength of 692 nm at room temperature. Growth of the epitaxial mirrors at 5.2 μm/h results in a total device growth time of only two and a half hours.