E. Johannessen

Impurity-related photoluminescence line shape asymmetry in GaAs/AlAs multiple quantum wells: Fractional-dimensional space approach

The optical transitions in 20 nm wide silicon and beryllium δ-doped GaAs/AlAs multiple quantum wells with various doping levels were investigated at different excitation intensities. A fractional dimensionality model was used to describe the free hole-donor and free electron-acceptor transitions in the quantum wells. The measured photoluminescence spectra from samples of different doping level related to donor-impurity or acceptor-impurity induced effects in the photoluminescence lineshape, were compared within the framework of these model calculations. Both experimentally and theoretically it was shown that acceptor and donor related optical transitions and photoluminescence line shapes were related to the difference in the effective masses of holes and electrons. This effect also leads to a difference in the photoluminescence spectra in which the luminescence band for the donor related spectrum is narrower in comparison to the acceptor related spectrum.

Light emission lifetimes in p-type δ-doped GaAs/AlAs multiple quantum wells near the Mott transition

The time resolved photoluminescence of beryllium δ-doped GaAs/AlAs multiple quantum wells have been studied over a range of doping concentrations, in order to investigate possible mechanisms for the carrier radiative recombination, both above and below the Mott metal-insulator transition. It was found that at doping concentrations near the Mott transition (NBe ∼ 3 × 1012 cm−2), the radiative recombination of excitons-bound-to-acceptor impurities as well as free electrons with acceptor impurities, dominated in the Be δ-doped GaAs/AlAs MQWs (LW = 15 nm) that were used in this study. Above the Mott transition, the major contribution was from radiative recombination of free electrons with a two-dimensional hole gas. The radiative lifetime would therefore exhibit different behavior with doping. In lightly doped GaAs/AlAs MQWs, this changed from 0.3–1 ns at 3.6 K to 8 ns at 300 K, whilst in quantum wells above the Mott transition, it changed from ∼0.36 ns at 3.6 K to ∼1 ns at 300 K, and was also weakly dependen...

Design of a Love wave mode device for use in a microfabricated glucose sensor

This paper presents a SiO2/AT-cut quartz Love wave delay line device that have been designed as the transducing element of a glucose biosensor. This delay line device is characterized using a three dimensional (3D) finite element model, which is combined with analytical calculations based on the dispersion equation. It is found that the 3D model with periodic boundary conditions showed good agreement with an equivalent model based on symmetric boundary conditions while consuming less computational power. Besides optimization of the guiding layer thickness and the geometrical parameters of the interdigital transducer, the biosensor phase mass sensitivities are estimated to be 990 cm2/g. This is sufficient to perform a direct detection of glucose interacting with the functionalized surface of the Love wave mode device.