Assessment of deep levels in photorefractive materials by transient photoelectric methods

(Received 3 December 1992, revised 7 April 1993, accepted 21 April 1993)

Abstract

Depending on their characteristics (energy, concentration, ...) localized imperfection levels, directly or indirectly, determine the properties of photorefractive materials. The aim of this paper is to present a summarized description of the principles of characterization techniques allowing the assessment of deep traps in high resistivity materials. Since this review paper addresses people working in the field of photorefractivity it will be necessary to first recall the characteristic parameters to be measured and to describe the underlying physical processes and their modelisation. The experiments which are basically of spectroscopic nature are subdivided in thermal and optical methods. They use as a tool the analysis of the current transient resulting respectively from the thermally or optically stimulated release of trapped carriers. The report will focus on PICTS (Photo Induced Current Transient Spectroscopy), a thermal method which so far allows the most complete trap characterization. A description of the principles of the experiments and of the different data processing modes will be given. Some important experimental aspects will also be discussed. A few representative results will be presented as an illustration.