Fabrication and opto-electrical properties of amorphous (Zn,B)O thin film by pulsed laser deposition

Abstract

Growth of amorphous ZnO by B doping and their opto-electrical properties are reported. The B-doped ZnO (ZnO:B) films were grown by pulsed laser deposition using polycrystalline ZnO:B ceramic targets. Although the solubility limit of B in bulk ZnO polycrystal was ∼4%, 18%-doped ZnO:B showed the shrinkage in the c-axis length. Preferentially (002)-oriented polycrystalline ZnO:B films were grown for the B concentration [B] ¯ 18%; while, amorphous ZnO:B films were obtained for [B] ∼26%. It was found that the density of the amorphous ZnO:B film was smaller by 9% than that of crystalline ZnO (5.61 g•cm-3), which is explained mainly by the incorporation of the light B atoms. The optical bandgap of the ZnO:B films increased with [B] and that of the amorphous ZnO:B film was ∼3.38 eV. The amorphous ZnO:B films have low free electron density of ∼1015 cm-3, suggesting the existence of electron traps. Hall mobility of the amorphous ZnO:B [∼1 cm2(V•s)-1] was smaller than those of the polycrystalline ZnO:B films.