Stable internal polarization in Bismuth Germanium Oxide crystals

The Bismuth Germanium Oxide (BGO) crystals find a wide application in electrooptical devices where (e.g. PROM) the recording mechanism is the generation and separation of electron-hole pairs. Further, the separated electron-hole pairs reduce the voltage across the crystal. In this connection, the study of internal electric fields induced under electret and photoelectret polarization in the crystal is of great importance.The present paper deals with the stable internal polarization induced by the external electric field and light in BGO crystals. The magnitude of polarization (Q) under different conditions of electret creation (for various EpolTpol, Δt1) that permits choosing the optimum conditions for the maximum internal field of E ∼ 4 105 V/cm to be formed in the dark has been measured. The electret creation in the light results both in the rise of the maximum polarization charge value and of the internal field by an order of magnitude (E ∼ 106 V/cn.). Thus, our measurements have shown that the BGO crystal is a pronounced electret and photoelectret material. The internal electric fields appearing in the external field under illumination are of the same order of magnitude as the external field.