Ultrafast Photoexcited-Carrier Behavior Induced by Hydrogen Ion Irradiation of a Cu(In,Ga)Se2 Thin Film in the Terahertz Region

We investigated the effects of H
⁺
ion irradiation on a chalcogenide Cu(In,Ga)Se
₂
(CIGS) thin film as a function of the dose concentration (10
¹⁴
∼ 10
¹⁶
/cm
²
) at 200 keV by using time-resolved THz spectroscopy. The optical conductivity of these films was derived from THz time-domain spectroscopy (THz-TDS) in the THz region. THz emission spectroscopy revealed the emission of a strong-intensity THz pulse from the H
⁺
ion-irradiated CIGS thin film. This is explained by considering the ultrafast behavior of photocarriers, resulting in strong surface band bending induced by the built-in potential with a conversion of the CIGS thin film from
p
- to
n
-type. Finally, we used optical pump THz probe spectroscopy to examine the ultrafast photocarrier dynamics determined by the time of capture at the increased number of surface and bulk defect states. This clearly showed that irradiation with H
⁺
ions could generate a number of defect states while simultaneously pacifying the Cu vacancy defects.