Photocapacitance and photoreflectance characterization of Pb/sub 3/O/sub 4/ photoelectrets

High resistivity with density of deep traps in Pb/sub 3/O/sub 4/ layers is suitable for photoelectret applications. Recently the Pb/sub 3/O/sub 4/ physical characterization was found to be of interest due to anomalies of structural and electrical properties. Photocapacitance (PC) spectra, that is, dependence of photoresponses /spl Delta/C(/spl lambda/), where /spl lambda/ - the wavelength of falling irradiation, allow to expressively evaluate the width of the forbidden band E/sub g/. Besides, the investigation of the PC effect, as it is experimentally Shown, can resolve a thin structure of energy bands. Samples for such measurements should be rather high-resistant (/spl rho//spl ges/ 10/sup 3/...10/sup 4/ Ohm.cm) and photosensitive. Polycrystalline layers of the Pb/sub 3/O/sub 4/ meet these requirements completely. One of the promising non-contact optical methods of studying band structure is the modulation of photoreflectance (PR). Despite of smaller sensitivity of PR (minimal changes of reflectance /spl Delta/R/R=10/sup 4/) in comparison, for example, with electroreflectance, the indicated method allows to determine the change of concentration and the time of their relaxation. We initiated the study with expectation of finding particular characteristics in PR lineshapes, which are related to the local states structure in the forbidden band of the Pb3O/sub 4/ photoelectret layers.