Ablation of CdTe with 100 µs Nd:YAG laser pulses: dependence on target preparation method

Abstract

The results of experimental studies of the ablation of CdTe with a pulsed Nd:YAG laser (wavelength 1064 nm) performed with 100 µs pulses and repetition time of 35 Hz are presented for the pulse energy range from 0.13 to 0.25 J. The main goal is to elucidate the dependence of the ablation process on the target preparation method. The investigation of the vapour stream intensity and chemical composition and their evolution with time are performed with a quadrupole mass spectrometer synchronized with the laser pulses. These studies are performed for three kinds of targets: a target made of CdTe bulk crystal (BC target), a target made of CdTe fine powder pressed under the pressure of 700 atm (PP target), and a target made of loose CdTe powder (N-PP target). The applicability of these targets for obtaining high quality CdTe thin films is determined. The best chemical composition of the vapour stream can be obtained with the BC target. A major drawback of this target is the energetic threshold for ablation with Nd:YAG laser and resulting delay in the ablation process above the threshold. The advantage of powder targets over BC target is the lack of any ablation threshold or delay. Weaker angular dependence of the particle emission (associated with the surface roughness), if confirmed in further experiments, can be the most important advantage of PP and N-PP targets.

Ablation of CdTe with 100μs pulses from Nd:YAG laser: Velocity distribution of emitted particles

“…It is also observed that the theoretical fit to the experimental points is generally good, with the exception of the low velocity side for the 0.28 J pulses. The existence of the ''low velocity tail" for the 0.28 J pulses can be ascribed to the target overheating, which results in the emission of low energy particles of the heat origin [1]. In the case of the 0.28 J pulses we observe, as in the former case, a close similarity between all the distributions, leading to very close values of the most probable velocity.…”

“…The experimental set-up used in this work has been described in a previous work [1]. Hence, here we give only some details necessary to comprehend the TOF experiments.…”

“…The experimental conditions of the ablation process are described in detail in [1]. As in this previous work, in the present experiments three types of the target were used: a target made of CdTe powder poured directly into the holder cup (N-PP target), a pellet made of fine CdTe powder pressed at a pressure of 700 atm (PP target), and a slice cut off from a CdTe bulk crystal (BC target).…”

“…The explanation of the choice of these particular isotopes for studies of the ablation process of CdTe was given in [1]. The measurement results of the TOF velocity distribution for the BC target ablated with 220 mJ laser pulses are shown in Fig.…”

“…Most of the applications need these materials in a thin film form. In a recent paper [1] we concluded that pulsed laser ablation (PLA) of CdTe target with 100 lm pulse of Nd:CdTe laser can be an effective method for the deposition of high quality CdTe thin films. The main goal of that paper was the elucidation of the dependence of the ablation process on target preparation method.…”