Laser-induced grating spectroscopy of cadmium telluride

Abstract

Laser-induced transient gratings produced by two-photon absorption of picosecond pulses at 1.064 Jim were used to examine the room-temperature nonlinear optical responses of CdTe crystals with different types of conductivity. Pulse-probe degenerate four-wave mixing measurements of grating dynamics on subnanosecond time scales were used to measure the ambipolar diffusion coefficient (Da) of charge carriers in the crystals. The value of Da = 3.0 cm 2 s -1 which was obtained is in very good agreement with theoretical estimates. A long-lived contribution to the signal consistent with a trapped charge photorefractive effect was observed at la:-ge .grati.ng spacings for n-type conductivity, and is tentatively attributed to a l.arger trap denSIty In thIS sample. Measurements of the relative scattering efficiencies of successive diffracted orders in the Raman-Nath regime allowed for calculation of the laser-induced change in the index of refraction, due to the creation of free carriers. The value of ~n = 4 X 10 -4 which was obtained is in good agreement with theoretical estimates. -Polished, 1 Xl XO.l em 3 , n-andp-typesamplesofCdTe were used in this study. The polished surfaces were [111 J faces. Room-temperature absorption spectra were obtained using a Perkin-Elmer Model 330 Spectrophotometer. In the PP and SS experiments, the samples were excited and probed with rp = 30 ps fun width at half maximum (FWHM) Gaussian pulses of the It = 1.064 J-i,m emission of aNd: Y AG 1359

Four- and Two-Wave Mixing in Solids

“…This may be related to the fact, that the total free-carrier distribution in the sample is greater than the Dude model estimate due to additional effects associated with the detailed band structure of the material. Thus, this corroborates the assumption that the signal observed is caused a distribution of free carriers [23].…”

“…The measured value of Da being equal to 2.9 ± 1 cm 2/s is in good agreement with that calculated from the Einstein formula, Da th = 4.3 cm2/s [23].…”

“…(5) with the free-carrier lifetime τFC in place of the decay time. Figure 4 shows the observed decay rates of the DFWM signal of the p-type CdTe sample [23]. The straight line shows the best fit to the data.…”

Dephasing of free carriers and excitons in bulk CdTe

“…The coherent regime is largely unexplored in bulk CdTe. In fact, one implementation of FWM spectroscopy -a transient light-induced grating technique was used quite often to study CdTe with various doping [3][4][5]. However, these experiments were aimed only at determination of incoherent material parametres (ambipolar diffusion coefficients and carrier lifetimes).…”

Photomagnetoelectric effect of high resistivity CdTe

“…As is reported in [1], the room temperature mobility of electrons and holes for these two materials are not so much different, the difference in the diffusion length is mostly due to the difference in the lifetime. The ambipolar diffusion length of about 2 µm, both for p-and n-type CdTe, is reported in laser induced grating spectroscopy [5]. The result, however, is obtained under completely different excitation condition, namely, the laser power density of the order of 10 8 W/cm 2 .…”