INJECTION SPECTROSCOPY OF LOCALIZED STATES IN THIN INSULATING LAYERS ON SEMICONDUCTOR SURFACES

An overview of charge injection techniques for studies of localized el ectron states in insulators is presented. These states control most im portant electrical properties of the materials, especially their thin layers and the multilayered structures containing them. Electronic pro perties of thin insulating layers are usually different from those of bulk material because in vicinity of an interface the thin film is sub jected to action of structural strain, spatial confinement, extra ener gy release during growth or deposition, e.c. All these factors substan tialliy affect the spectrum of localized electron states (intrinsic de fects, dopants, impurities) and influence their spatial distribution. The interfaces often exhibit an unusual behaviour relative the defect generation and an impurity transport and segregation comparing with a bulk of insulator. The characterization of these states in thin-layere d systems suffers from low sensitivity of both electron and optical sp ectroscopies to shallow electron states those have to be detected on t he background of the signal from substrate. Nevertheless, the problem may be resolved by means of charge carrier injection into the insulati ng layer followed by monitoring of the charge becomes trapped. The loc alized states are detected by this way as a potential wells for the in jected a mobile charge carriers. In thin layers the mean path of injec ted electron (hole) with respect to interaction with such a trap may g reatly exceed thickness of the layer. In offers possibility to use lin ear modes for the trapping and detrapping analysis. We will show that under these conditions the charge-injection methods provide the most i mportant phenomenological parameters of a localized state: the density per unit area, in-depth location, cross section for capture of carrie rs or recombination, energy position of the trapped carrier level in t he insulator bandgap, e.c. On the base of these possibilities a non-de structive methods for characterization of extrinsic and intrinsic defe cts states are developed. Various charge injection and charge detectio n methods are compared. It shows unambiguously the advantages of using a semiconducting substrate for the insulator trapping studies. The li mits of the linear models applicability are discussed in detail and th e effects arising from the non-linear correlation phenomena are analyz ed.