Formation of spatial inhomogeneities as a result of heat treatment in silicon doped with zinc

After heat treatment at 450-600 degrees C Si samples doped with Zn in concentration 2*10(16) cm(-3) demonstrate increase of photosensitivity, additional step at 0,6 eV in the photoconductivity spectrum, longtime relaxation and persistent conductivity at low temperatures. All these properties are accompanied by current filamentation in Si(Zn) when tested in gas-discharge image converter. The cause of the effect is redistribution of zinc related centers after heating which results in formation of high resistivity i-type islands embedded in p-type matrix. The potential barriers at the boundaries of the islands separate photoexcited holes and Zn centers in space and interfere with their recombination. That leads to huge increase of lifetime and results in photocurrent growth, persistent conductivity and longterm relaxation. Double acceptor zinc centers are singly ionized in i-type regions and provide additional photoresponse at by greater than or equal to 0,6 eV due to transitions Zn- --> Zn- +h. Annealing of such samples at 800 degrees C restores homogeneity and its original properties.