Note: Modification of an FTIR spectrometer for optoelectronic characterizations.

We propose a very simple system to be adapted to a Fourier Transform Infra-Red (FTIR) spectrometer with which three different types of characterizations can be done: the Fourier transform photocurrent spectroscopy, the recording of reflection-transmission spectra of thin film semiconductors, and the acquisition of spectral responses of solar cells. In addition to gather three techniques into a single apparatus, this FTIR-based system also significantly reduces the recording time and largely improves the resolution of the measured spectra compared to standard equipments.

An automated steady state photocarrier grating experiment.

The design of an automated steady state photocarrier grating (SSPG) experiment is presented that matches most of the requirements of an industrial environment. We first briefly recall the bases of the SSPG technique and that the minority carrier diffusion length deduced from this experiment is a key parameter in the fabrication of thin film solar devices. We then underline the main drawbacks of the use of the classical SSPG technique as an industrial and systematic characterization technique mostly that all the adjustments have to be done manually. We show that this issue can be overcome to end with a compact (90 × 60 cm(2)), fast, reliable, and easy-to-use system that could become a routine characterization technique for research laboratories and thin film solar industry. We illustrate the possibilities of this new system by showing some of the results obtained with it on very different thin films.

The influence of hopping on modulated photoconductivity.

We have developed equations taking into account both multiple-trapping and hopping processes for describing transport phenomena in disordered semiconductors. These equations have been introduced into a numerical simulation to model the steady state dark conductivity and photoconductivity as well as the modulated photoconductivity. The influence of parameters such as the density of states and attempt-to-hop frequency on the results of these experiments has been investigated. Steady state and modulated photoconductivity experiments have been performed on a hydrogenated amorphous silicon film in the temperature range 18-300 K and the results have been compared with those from the numerical simulation. This comparison shows that the latter provides a suitable interpretation of the experimental behaviours observed in both experiments.

Characterization of defect levels in semi-insulating 6H-SiC by means of photoinduced transient spectroscopy and modulated photocurrent technique.

Parameters of electrically active defect centres in vanadium-doped 6H silicon carbide (6H-SiC:V) were investigated by means of the photoinduced transient spectroscopy (PITS) and modulated photocurrent (MPC) method. After a short description of the two techniques, experimental results are presented and briefly compared. Our aim is mainly to understand and explain these experimental results. In particular, in the PITS technique a shallow level seems to be at the origin of negative photoconductivity. Besides, in the same temperature range hole and electron levels can be detected at the same time. Finally, the detection of a given level seems to depend on the photon flux used to perform the PITS experiment. As far as the MPC experiment is concerned, it has put into evidence a very efficient shallow level. A numerical calculation was developed to simulate both experiments in order to understand the experimental results. By means of this simulation, we have explained all the phenomena observed experimentally in each technique and we propose a simple model for the distribution of electrically active defect centres in 6H-SiC:V crystals.