Low Temperature Photoconductivity of F Center in KCl

Transient Photoconductivity of additively colored KCl is studied for excitation in the F , K , L 1 and L 2 bands at low temperatures down to 1.3°K. Electron quantum yield is found near unity in L bands and in high energy tail of K band in the whole temperature range. K band can be divided into two components; K 1 band with low electron yield and K 2 band with unit yield. It is concluded K 2 band corresponds to transition to the conduction band minimum and L bands to the states in the conduction band. Electron yield for K 1 and F bands is studied as a function of temperature and applied electric field. Thermal binding energy of excited state is found the same for K 1 and F states. Field ionization from K 1 state starts at far lower field than from F state. Transport of electrons at low temperature is characterized by non-ohmic behavior above critical field, where electron Schubweg is proportional to E 0.5∼0.7 . The high field behavior can be understood as hot electron phenomena.