Study on annealing of infrared nonlinear optical crystal ZnGeP2

ZnGeP2 crystal is one of the most promising materials for infrared nonlinear optical applications. However, the near-band-edge absorption of native defects degrades the performance of ZGP-OPO device. The single-zone-annealing furnaces were utilized to anneal ZGP samples. The optimal annealing temperature was 600 °C and the optimal annealing atmosphere was ZGP powder vapor. For further annealing effects, the two-zone-annealing method was adopted to anneal ZGP crystals for the first time. The absorption coefficient can be reduced to 0.06 cm−1 at 2 μm and the resistivity can be increased from 5.8×107 Ω cm to 4.1×109 Ω cm. The results indicate that the annealed ZnGeP2 crystals could be used as OPO devices. The mechanism of the two-zone-annealing effects has been briefly discussed in this paper.

► Conventional single-zone-annealing experiments have been carried out to ascertain the optimal annealing condition of ZGP crystals.
► A two-zone-annealing method has been applied to anneal ZGP samples for the first time.
► The mechanism of the two-zone-annealing effects has been briefly discussed.