BOMBARDMENT INDUCED PHOTOCONDUCTIVITY AND OPTICAL ABSORPTION IN MAGNESIUM OXIDE
Abstract
Measurements of the spectral dependence of the optical absorption of colored MgO crystals revealed several absorption bands (2.1, 3.7, and 4.8 ev) in the visible and UV regions. The bands were superimposed upon a gradually rising tail which extended over the entire spectrum and increased to only about 20 cm (-1) at 200 millimicrons or 6.2 ev, the limit of measurement. A photoconductivity band was found at 1.2 ev. Irradiation of the crystals by 'UV caused an enhancement of the photoconductivity which reached a saturation level independent of the UV intensity; this enhancement is a measure of the density of imperfections in the crystal lattice. The direction of the displacement of the UV-activated region by an electric field indicated that the charge carriers are holes in the valence band. The enhancement of photoconductivity produced by bombardment with Van de Graaff electrons was unstable at room temperature, while that produced by neutron irradiation and the crystals was thermally unstable throughout the spectrum. Neutron irradiation also causes an increase in the level of UV saturation; the increase is stable at room temperature and indicates new lattice defects. The photoconductivity bands present after irradiation corresponded to the optical absorption bands caused by excess Mg. An estimate of the density of lattice defects can be made from the photoconductivity. An energy level model is proposed to explain the photoconductivity bands and the enhancement and saturation effects.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 01, 1952
- Accession Number
- AD0002240
Entities
People
- Harold R. Day