The experimental error in the angle of incidence strongly affects the film optical constants and thickness sought from the ellipsometric data, particularly when the film is thinner than 200 Å. This angle should therefore be accurately measured and this has been a frequently faced difficulty, especially in fixed-angle-of-incidence and in situ ellipsometers. We describe in this paper two numerical calibration procedures evaluating the angle of incidence from the ellipsometric data and measured on well-identified film-substrate reflecting structures either with a known or with an unknown film refractive index. The procedures rapidly determine the angle of incidence independently of the film thickness. An error analysis shows that the angle of incidence can thus be determined with an uncertainty of a few hundredths of a degree from ellipsometers inducing the same order of angular errors. The thickness ranges of films yielding such lower uncertainties are deduced from the error analysis. The effect of substrate real index error on this uncertainty is studied in particular. The supplementary results produced therein may be used in data interpretation while checking the angle of incidence if it is accurately measured by some other method. The procedures may also be easily adopted to variably damped least-squares (VDLS) algorithms employed in real-time monitoring of films during growth. The calibration procedures are illustrated for all these aspects with experimental data from real reflecting systems.

Schottky barriers have been formed by vacuum evaporation of Cu on to CdS thin films. The behaviour of these samples has been investigated as a function of time and annealing by standard electrical methods: current-voltage analysis, capacitance-voltage analysis and analysis of the spectral dependence of the photoemission currents. The impurity profile deduced from the reverse differential capacitance shows evidence of copper diffusion occurring between 20 and 200 degrees C. An activation energy of 0.72 eV is found for the temperature dependence of the diffusion coefficient. The Cu-CdS interface has also been investigated by looking at the photovoltaic mechanisms in connection with the different heat treatments. Capacitance measurements performed under junction illumination have been used to obtain the true donor density after copper diffusion.

No abstract

The passivation of InP surfaces has been investigated by growing native thin film oxides with RF plasma oxidation in order to realise high-speed InP metal-insulator-semiconductor field effect transistors (MISFETS). The electrical properties of the InP interface have been analysed by variable-frequency C-V and G-V measurements using the well-established, high-frequency capacitance method, the low-frequency capacitance method and the AC conductance method. In this paper, we report the results obtained for unannealed and postmetallisation-annealed diodes. In addition to the improvement in C-V hyteresis, annealing has the effect of reducing the value of interface state density. Also, it alters the interface electrical properties such as time constant and energy position in the gap. The dispersion of interface state time constant in the depletion region resulting from the potential surface fluctuations has been observed. Also noted is a dispersion of C-V characteristics in the positive bias region. Good correlation has been obtained between theory and the measured conductance curves as a function of frequency at different values of the surface potential. More information about the electrical transport properties of the minority carriers in the weak inversion can be obtained by measuring inversion equivalent parallel conductance G , as a function of temperature. An activation energy of 0.66 eV have been obtained for temperatures above 90 'C.

No abstract