Investigation Of High Intensity Pulsed TEA-CO₂ Laser-induced Damage On Hg_0.8Cd_0.2Te Wafer

HgCdTe is one of the main materials utilized in infrared detectors. As a key component in varied photoconductive apparatuses, it has been successfully used in fields such as aviations, space flight, military et al. If the high intensity pulse laser irradiates the surface of Hg_0.8Cd_0.2Te wafer, the thermal stresses, evaporation wave and laser supported detonation (LSD) wave exerting on the target surface can damage the wafer. Since the response wavelength of Hg0.8Cd0.2Te is 8¹4 μm, it is expected that the absorptivity of Hg0.8Cd0.2Te materials at 10.6 μm (CO2 laser) is higher than those at other wavelength. This may lead Hg0.8Cd0.2Te material easily to break during the laser irradiation. Therefore, it is important to investigate the damage of Hg0.8Cd0.2Te material by using a high intensity pulse TEA-CO₂ laser. A systematical investigation on the damage of Hg_0.8Cd_0.2Te wafer induced by high intensity pulsed TEA-CO₂ laser has been done. Firstly, the forces on the surface of Hg_0.8Cd_0.2Te wafer induced by the high intensity TEA-CO₂ laser were theoretically deduced. Based on the thermal conduction equations, the maximum thermal stresses acting on the Hg_0.8Cd_0.2Te wafer were analyzed when the high intensity TEA-CO₂ laser irradiated on the surface of the wafer. The stresses of the evaporation wave acting on the Hg_0.8Cd_0.2Te wafer were analyzed based on gas dynamical equations, when the high intensity TEA-CO2 laser irradiated on the surface of the wafer. According to fluid mechanics equations, the stresses of the laser supported absorbed wave acting on the Hg_0.8Cd_0.2Te wafer were studied when the high intensity TEA-CO2 laser irradiated on the surface of the wafer. Contrasted with the above three forces, it can be found that the thermal stress is the biggest force. In addition, the simulations of the temperature distributions, the thermal deformations and the thermal stresses of the Hg_0.8Cd_0.2Te wafer using ANSYS 9.0 have been carried out in this paper too. Based on the simulative results, the damage threshold of Hg_0.8Cd_0.2Te wafer was given. Secondly, this thesis also investigated on the effect of the laser parameters, such as pulse energy, pulse wave shape, pulse width and focus size on the melting time and the damage threshold and obtained that the peak value of the damage threshold for Hg0.8Cd0.2Te wafer was 3.11×10⁶ W/cm². The experimental results were good accordance with the theoretical data. Based on the SEM and optical microscope photograph after the laser irradiation, the reasons caused damage of Hg0.8Cd0.2Te wafer under high intensity pulse laser were obtained. Thermal effect is the primary reason for damage of Hg0.8Cd0.2Te wafer. The melt of Hg0.8Cd0.2Te wafer was originated from the temperature rise of it. The big cracks in the surface of Hg0.8Cd0.2Te wafer were originated from the thermal stress before the wafer`s melt. The small flaws in the surface of Hg0.8Cd0.2Te wafer were originated from the asymmetry thermal expending in the process of solidification. Based on the EDAX analysis data after the laser irradiation, the alterative rules of the element ratio on the surface of the Hg0.8Cd0.2Te wafer were given. The Hg loss on the surface of Hg0.8Cd0.2Te wafer is related to the acting time and temperature, and in laser affected zone and laser unaffected zone the Hg loss induced by the several laser pulses is more than that induced by single laser pulse. Lastly, based on the optical microscope photograph after the laser irradiation, the damage characters and reasons of Hg0.8Cd0.2Te wafer were given by the comparison of laser pulse with different energy, acting numbers and wave shape.