Surface Plasmons for Probing Optical Data of Multi- Layered Thin Films

In this paper, we show how optical excitation of surface plasmons (SPs) can be used to obtain optical and geometrical parameters of specific layers in multi-layered thin film systems. The optimum coupling phenomenon between incoming p-polarized light and SPs appears as a minimum in the reflectance that is calculated using a standard matrix formalism. The sensitive dependence of the reflectance minimum on optical and geometrical parameters suggests that they can be determined accurately by fitting the measured attenuated total reflectance (ATR) to the matrix-calculated reflectance using the Simplex minimization method. The procedure is applied to the multi-layered system: Prism / Air gap / Al-oxide / Al / GaAs. At fixed incident light wavelength, the fitting parameters are the Al-oxide optical constant and the thickness of the air gap, Al-oxide and Al layers. Fortran codes are implemented for the reflectance calculations and the fitting procedures. The results show that the theoretical reflectance fits well the measured ATR at 633 nm wavelength. Moreover, the modeled Al-oxide optical constant at this wavelength agrees well with the literature. However, the reflectance fits are less good at 590 nm and 458 nm wavelengths and their modeled Al-oxide optical constants show a dispersion effect in disagreement with the literature. The modeled geometrical parameters are consistent with the nominal values

I-V-T measurements on GaAs/AlGaAs heterojunctions interpreted on the basis of thermally assisted tunneling

I-V-T data is routinely used to determine the conduction band discontinuity in heterojunction structures. In the present paper, capacitance-voltage and current-voltage-temperature measurements performed on AlGaAs/GaAs isotype heterojunctions are presented and analysed over a wide temperature range (77 K-300 K). Considering thermionic emission alone when analysing I-V-T data resulted in several problems. The Richardson plot $[\ln(J_0/T^2) vs. 1/T]$, in particular while suggesting that the thermally activated process is of importance in the overall conduction mechanism, shows two distinct linear regions of different slope over two temperature ranges. Also the derived activation energies and hence the band discontinuity from I-V-T data is very much lower than the value obtained from C-V profiling which is in very good agreement with values routinely published in literature. However, the results obtained from both I-V-T and C-V data are reconciled when considering a simple analytical expression for the current based on the assumption that thermally assisted tunneling is the dominant current generating mechanism over most of the temperature range