Intensity enhancement of Te Raman modes by laser damage in ZnTe epilayers

Abstract

Damage caused by laser irradiation on the surface of ZnTe epilayers was studied by micro-Raman and atomic force microscopy (AFM). ZnTe LO-phonon overtones up to four order and TO + (n − 1)LO zone-center phonons were observed in the resonant micro-Raman spectra at room temperature. Discrepancies in the literature regarding the origin of two features observed at low frequencies around 120 and 140 cm −1 in the Raman spectrum of ZnTe are discussed and resolved. These Raman peaks were not detected by using a low excitation laser power density on a Zn-terminated ZnTe surface; however, with the increase of the laser power density they were found to arise irreversibly. The correspondence of these peaks in a wave number with the strongest Raman peaks of the crystalline tellurium phase and the intensity enhancement behavior with the laser power in a similar way as for CdTe strongly suggests the formation of crystalline tellurium aggregates on the layer surface due to laser irradiation damage. AFM data reveal the occurrence of laser ablation on the ZnTe surface even though the surface temperature of the sample is below the melting point.

Laser irradiation effects on the CdTe/ZnTe quantum dot structure studied by Raman and AFM spectroscopy

“…Summarizing, many authors studied laser-induced effects on II-VI compounds by means of the micro-Raman and AFM techniques. Thus, it has been found that the laser beam of above the bandgap energy causes damage on the surface of the CdTe, 5 ZnTe, 6 and CdZnTe 21 materials. The ablation process of the materials results in the loss of Cd/Zn atoms (photoatomic effect) and consequently the enrichment of Te on the layer surface.…”

“…The main proof for this statement is the presence of two Te modes in the Raman spectra: around 120 cm À1 and 140 cm À1 . The Te-rich region gains in thickness, the heating (owing to the high absorption coefficient of Te) can cause the sublimation and/or migration of Te atoms to cooler zones on the surface (accumulation of material on the pinhole edge 6,21 ). The extent of the laser damage depends on its exposure time and power.…”

“…5 Recently, a significant laser damage was found for ZnTe, CdTe and CdZnTe materials. 5,6 The object of Raman studies in the present paper is CdTe/ZnTe quantum dot structures. The formation of CdTe QDs in ZnTe matrix was confirmed by photoluminescence measurements (PL).…”

“…It was found that the damage is alike to the damage observed in CdTe, ZnTe and CdZnTe crystals/ epilayers. 5,6 Moreover, the temperature of the laser irradiated samples was estimated to be exceeding the melting temperature of ZnTe, which explains laser ablation effect. The analysis performed in present paper might shed light on the origin of the damage in the II-VI compounds, which is still unclear.…”

Terahertz dynamics of lattice vibrations in Au/CdTe plasmonic crystals: Photoinduced segregation of Te and enhancement of optical response

“…Indeed, formation of tellurium under optical illumination is possible in several II-VI telluride semiconductors. It has been observed in CdTe [36], CdZnTe [37,38] and ZnTe [39,40] crystals under continuous wave illumination above the band gap. Recently, excitation of coherent phonons in a segregated layer of Te on ZnTe was induced by illuminating the semiconductor crystal with intense 10 fs optical pulses [41].…”