Investigation of p‐CdTe and p‐Zn_xCd_1−xTe Single Crystals by ps‐Laser‐Induced Gratings and by Photoluminescence

Abstract

(a), M. PETRAUSKAS (b), V. NETIR~IS (b), G. TAMULAITIS (b), and J. HALFPAP (a) From the measured erasure times of transient gratings created in the volume and on the surface of non-intentionally doped p-type CdTe and Zn,Cdl-,Te (z 5 0.11) single crystals the freecarrier lifetime and the surface recombination velocity a t room temperature are determined, respectively. The erasure time of the surface grating in CdTe i s found to be 130 ps, which is one order smaller than that of the volume grating. A lifetime shortening is observed in mixed crystal. Moreover, using cw-laser excitation the samples are characterized additionally by photoluminescence investigation a t low temperatures to test the quality, to determine the mole fraction, and to identify impurities. The AoX-line observed is interpreted as due t o a single acceptor on Te site.In the mixed crystals at z 2 0.09 the two-mode behaviour of LO-phonons and an u p to now not observed splitting of the AoX-line are found.Aus der Messung der Loschzeiten von im Volumen bzw. auf der Oberflache von undotierten pleitenden CdTe-und Zn,Cdl-,Te (z 5 0,ll)-Einkristallen erzeugten transienten Gittern werden die Lebensdauer der freien Triiger bzw. die Oberflachenrekombinationsgeschwindigkeit bei Raumtemperatur ermittelt. Die Loschzeit des Oberflachengitters in p-CdTe ist um ca. eine GroBenordnung kleiner als die des Volumengitters und betragt 130 ps. I n den Mischkristallen wird eine Verkiirzung der Lebensdauer der freien TrLger heobachtet. Dardberhinaus wird die Photolumineszenz der Proben bei niedrigen Temperaturen und cw-Laser Anregung untersucht, um die Probenqualitiit zu testen, das Mischungsverhaltnis zu bestimmen und Verunreinigungen zu identifizieren. Als Ursache fur die beobachteten AOX-Linien wird ein einfacher Akzeptor auf Te-Platz angenommen. In den Mischkristallen mit r 2 0,09 wird das Zwei-Moden-Verhalten der LO-Phononen und eine bisher nicht bekannte Aufspaltung der AOX-Linie gefunden.

Investigation of nonequilibrium carrier transport in vanadium-doped CdTe and CdZnTe crystals using the time-resolved four-wave mixing technique

“…Previous experimental studies of differently doped CdTe crystals using the picosecond FWM technique are summarized in table 1. The early studies [6][7][8] were carried out at relatively high intensities, when carriers are created by two-step and two-photon absorption, therefore only the bipolar diffusion coefficient D a was determined from the angular dependences of diffraction. The value of D a was found to be slightly smaller than that expected in CdTe, D a = 4.1 cm 2 s −1 .…”

Transient Energy Transfer in ps Two‐Photon Absorption Experiments in CdTe at Room Temperature

“…free-carrier lifetime z,h was neglected because the duration of the diffracted pump pulse zL = 35 ps is very short in comparison with the erasure time z, of the grating of some ns, resulting from free-carrier lifetime z,h and diffusion time zD (l/ze = l/zeh + 1/z, with zD = A2/47?D, = 18ns and z,h = 2.6ns[5]; D, = 13cm2/s[9] at A = 30pm). For the calculation of the maximum values of the refractive and absorptive index changes An(t)…”

“…and y I. RUCKMA", J. KORNACK, J. KOLENDA, and M. PETRAUSKAS Pump-beam-induced change ofthe probe-beam transmittivity AT VS. At calculakd for different pump intensities I,. b ) -values for TPA and FCA, respectively, of CdTe obtained from the fitting of the one-beam transmission experiment (Section 2), a value zeh = 1 5. ns obtained in the DFWM experiment 161, sin2-pulses for probe and pump with zL = 30 and 35 ps, respectively (to take into account the shorter coherence time of 30ps), and a pump-to-probe intensity ratio…”