Luminescence properties of pulsed laser deposited CuIn_xGa_1−xSe₂ films

Abstract Pulsed laser deposition (PLD) of CuIn1−xGaxSe2 (CIGS) provides a low cost, single-step process via which stoichiometric, high quality thin films for light harvesting applications can be produced. Little is known about the optical properties of PLD-deposited CIGS and how they compare with the respected properties of the well-studied evaporated or sputtered CIGS films. We report herein a systematic spectroscopic investigation, probing the influence of PLD deposition temperature on the energetics and dynamics of emission from CuIn0.7Ga0.3Se2 films. Variable-temperature steady-state and time-resolved photoluminescence in combination with Gaussian lineshape analysis allow us to unravel the contribution and nature of three main radiative channels, with the high energy one associated with electronic and two lower energy ones with defect levels. The analysis show that the band-edge luminescence grows at the expense of defect emission as PLD temperature increases in the 300 °C–500 °C range. This is further supported by: (i) The dramatic increase of the band-edge recombination lifetime from 30 to 180 ns, (ii) The quenching in the carrier trapping rate from 0.25 ns−1 to 0.09 ns−1 as growth temperature increases. The results correlate well with structural and electrical characterization studies reported previously on PLD-grown CIGS and rationally interpret the improvement in their optoelectronic properties as PLD deposition temperature increases .