Indication of Te segregation in laser-irradiated ZnTe observed by in situ coherent-phonon spectroscopy

Abstract

We irradiate a ZnTe single crystal with 10-fs laser pulses at a repetition rate of 80 MHz and investigate its resulting gradual modification by means of coherent-phonon spectroscopy. We observe the emergence of a phonon mode at about 3.6 THz whose amplitude and lifetime grow monotonously with irradiation time. The speed of this process depends sensitively on the pump-pulse duration. Our observations strongly indicate that the emerging phonon mode arises from a Te phase induced by multiphoton absorption of incident laser pulses. A potential application of our findings is laser-machining of microstructures in the bulk of a ZnTe crystal, a highly relevant electrooptic material

Laser induced structural transformation in chalcogenide based superlattices

“…Both modes are blueshifted with respect to Te bulk 17 of about 5 and 2 cm À1 , respectively, due to the Sb 2 Te 3 environment which changes the Te bond length. After exposure of the same sample to higher laser power, the spectrum changes: The Te peaks become more pronounced at 25% illumination until the characteristic double peak turns into a single pronounced mode at 120 cm À1 (see dark cyan curve at 50% laser power), in accordance with similar observation in different Te based compounds, 18 and two additional Te modes at 93 cm À1 and 140 cm À1 are visible. The redshift of these emissions underlines the Te segregation (see the overlap of the peak positions with the Te reference).…”

Ultrafast optical response of the amorphous and crystalline states of the phase change materialGe2Sb2Te5

“…The changes were consistent with the emergence of the modes of elemental Te, indicating that segregation had occurred. Segregation has been observed in other Te-based compounds 18 . An example of such laser-induced changes is shown in Figure 5 and is discussed in more detail in Section VII.…”

Influence of pulse width and detuning on coherent phonon generation

“…Coherent phonons are widely used to study phonon dynamics for a wide variety of materials such as semimetals, [1][2][3][4][5] semiconductors, [6][7][8][9][10][11][12][13] superconductors, [14][15][16][17] and topological insulators, [18][19][20][21] with pump-probe type time-resolved reflectivity measurements. An ultrashort pump pulse coherently excites optical phonons which oscillate in phase and modulate the electric susceptibility.…”