Positron annihilation apectroscopy on colloidal CuIn1-xGaxSe2 semiconductor sanocrystals

Abstract

Simple and low-cost hot-injection method was used to synthesize three samples of colloidal nanocrystals with general chemical formula CuIn1-xGaxSe2 (x=0.0, 0.6 and 0.82). X-ray diffraction (XRD) and transmittance electron microscopy (TEM) have been used to investigate the structural properties of the synthesized nanocrystals and proved their high crystallinity. Positron annihilation lifetime (PAL) and Doppler broadening (DB) techniques were used to give more insights on the structural defects of the grown samples. The results of the positron lifetime measurements indicate that the shortest lifetime component (τ1) with intensity ≳ 97% is greater than the calculated positron bulk lifetime, 235-240 ps. This indicates that the concentrations of the vacancy-type defects for the as-synthesized CuIn1-xGaxSe2 samples are greater than the saturation trapping limit (1018 cm-3). Moreover, results of the PAL measurements and the theoretically calculated positron lifetimes indicate that Cu-Se, In-Se and/or Ga-Se are the dominant vacancy-type defect for all studied range of Ga. Also, the results show that the vacancy-type defect concentrations of samples with Ga content of 0.6 and 0.82 are reduced compared with that for zero-Ga content sample.