ASSESSMENT OF DEEP LEVELS IN PHOTOREFRACTIVE MATERIALS BY TRANSIENT PHOTOELECTRIC METHODS

Depending on their characteristics (energy, concentration, ...) locali zed imperfection levels, directly or indirectly, determine the propert ies of photorefractive materials. The aim of this paper is to present a summarized description of the principles of characterization techniq ues allowing the assessment of deep traps in high resistivity material s. Since this review paper addresses people working in the field of ph otorefractivity it will be necessary to first recall the characteristi c parameters to be measured and to describe the underlying physical pr ocesses and their modelisation. The experiments which are basically of spectroscopic nature are subdivided in thermal and optical methods. T hey use as a tool the analysis of the current transient resulting resp ectively from the thermally or optically stimulated release of trapped carriers. The report will focus on PICTS (Photo Induced Current Trans ient Spectroscopy), a thermal method which so far allows the most comp lete trap characterization. A description of the principles of the exp eriments and of the different data processing modes will be given. Som e important experimental aspects will also be discussed. A few represe ntative results will be presented as an illustration.