Laser‐induced heating of porous Ge layers implanted with Ag⁺ and Cu⁺ ions

Abstract

Porous Ge layers consisting of nanowires were formed by low-energy highdose implantation of monocrystalline c-Ge substrate with Ag + and Cu + ions. The obtained layers were studied by Raman spectroscopy using solid-state and He-Ne exciting lasers with wavelength of 532 and 633 nm, respectively. The crystalline volume fraction and local temperature of porous layers at the surface sites of laser probing were determined. To interpret the change in the shape of the spectra under the action of laser radiation, deconvolution into amorphous and nanocrystalline components was carried out. Analysis of the spectral line shape made it possible to estimate the crystalline and amorphous volume fractions. The quantum confinement model for Ge nanocrystallites

The local crystallization thresholds under laser irradiation of the Cu+‐ion implanted Ge layers with various thicknesses

“…Samples 3 and 4 demonstrated a smaller percentage of the crystalline phase at the least intense excitation. Thus, the assumption expressed in Pavlikov et al [ 7 ] and Sharafutdinova et al [ 8 ] is experimentally confirmed that if the penetration depth of radiation is less than the thickness of the porous layer, then its local heating occurs to temperatures sufficient for recrystallization. This is facilitated by the low thermal conductivity of the PGe layer.…”

“…The intensity of the exciting laser radiation ( ) was increased from a minimum value of 30 to 3000 W/cm 2 . It was demonstrated earlier [ 7,8 ] that initial and final spectra measured at the same spot on the sample surface differ due to change in the proportions of crystalline and amorphous volume fractions in the PGe layers. It was also shown that the implanted PGe layers before laser treatment were completely amorphous, but the action of intense radiation leads to local crystallization.…”

“…[13,14] This makes it possible to subtract from Raman superposition spectra the contribution of the substrate and estimate the fraction of the nanocrystalline phase in PGe layer formed as a result of local crystallization and formation of Ge nanoparticles. The calculation of the crystalline phase fraction was carried out according to the method described in detail in Sharafutdinova et al [8] The dependence of the calculated volume fraction of the nanocrystalline phase on I is shown in Figure 4. It follows from the presented results that samples 1 and 2, which have the smallest thicknesses, have the highest intensity thresholds of local crystallization.…”

“…The calculation of the crystalline phase fraction was carried out according to the method described in detail in Sharafutdinova et al [ 8 ] The dependence of the calculated volume fraction of the nanocrystalline phase on is shown in Figure 4. It follows from the presented results that samples 1 and 2, which have the smallest thicknesses, have the highest intensity thresholds of local crystallization.…”

“…However, for PGe layers where the thickness exceeds the penetration depth of the radiation, local heating and crystallization of the surface occurred. [ 8 ] Such effect was demonstrated for PGe with NW of various size diameter distributions. In order to experimentally confirm the hypothesis suggested in previous works on the dependence of the local crystallization thresholds of PGe layers on the optical penetration depths of probing laser radiation, it was proposed to study PGe layers of different thicknesses when excited by radiation at one wavelength only.…”