I • ·1i.tl ';·&" as been showh of the density m modes. One y, according to ave shown that n forced mode - i been observed t in the present ultimately. .,. . I a Tecnologia for 1hys. 13 593-615 (to be published) - 287 82 1-647 1998 J. Supercrit. ohys. 3 201-215 07 - 218 thesis, Imperial stituto Superior Thermophys. 15 Thermophys. 17 Chem. Eng. Data em. Eng. Data 41 Sci. lnstrum. 69 port Properties of ed in Great Britain •• ' I ,• ··- - - ------ - -- High Temperatures- High Pressures, 2001, · m_ -.:1 . 'f 15 ECTP Procee_dings pages 1181 -: 1187 001:10.1068/htwu4n Pulse thermodiffusive processes in semiconductors ··:· .... i'' .; ... .J .. ,:_ .!. ,. _1 ...... .. . ·}" .. Jf-,t1i"# c:;·f{ ,.. ... -:-1 1'7 Yuriy V Drogobitskiy .,, ',: ;-:;;-r' '' Physics Department, Ternopil Pedagogical State University, 2 Krivonosa, PO 282009, Terriopil, Ukraine; fax: +380 3522 0176; email: dao@tu.edu.te.ua Alvaro F Carballo Sanchez, Gerardo Gonzalez de la Cruz, Yuri G Gurevich, Georgiy N Logvinov Departamento de Fisica Centro de lnvestigacion y de Estudios Avanzados del lnstituto Politecnico Nacional, Apartado Postal 14-740, 07000 Mexico, Distrito Federal, Mexico; fax: +525 7477096; email: logvinov@fis.cinvestav.mx Presented at the 15th European Conference on Thermophysical Properties, Wurzburg, Germany, 5- 9 September 1999 Abstract. A one-dimensional problem for the determination of transient electron and phonon temperatures in bounded semiconductors is solved analytically and an exact expression is obtained. The model includes the heating of one of the surfaces of the sample by a rectangular thermal pulse of an arbitrary duration, separate electron and phonon heat boundary conditions, and electron - phonon energy interaction. The characteristic times of the transient processes arc introduced through the electron and phonon thermal diffusion time, '•. P' and electron - phonon energy relaxation time, r,. For nondcgencrate semiconductors, the electron subsystem is described by the essentially nonequilibrium temperature whereas the phonon temperature is equal to the ambient equilibrium temperature. The heat diffusion process is characterised by parameter r. in the case of a thin sample as compared with the electron cooling length, while time '• becomes the characteristic relaxation parameter for long samples. The thermoelectric response is obtained and the analysis is made for the long and short heat pulses. 1 Introduction The creation of high-speed semiconductor devices demands clear understanding of the different dynamic properties of the charge carriers as well as phonons for ultrashort time scales. One of the most effective investigation methods of such properties is the excitation of nonstationary thermal processes in semiconductor samples. These processes can be excited by continuous modulated energy beams or short energy pulses (Othonos 1998; Vargas and Miranda 1988). In most of the experiments, laser radiation is used as the source of the external excitation. Detection of the thermal response of the system in the presence of the applied exter- nal radiation allows us to obtain useful information about different physical parameters of the sample, and in particular, about thermal, relaxation, and optical parameters. In the general case. a detected photothermal signal depends not only on how the heat is transferred along quasiparticle subsystems in the semiconductor, but also on how the energy is distributed between these subsystems. It means that a detected signal depends on different electron and phonon thermal parameters (electron and phonon thermal con- ductivity and diffusivity) and corresponding relaxation times. Of course, it is difficult to extract the contribution of each relaxation process in the response under stationary perturbations in photothermal experiments, but by the use of short thermal pulses it is possible to obtain information about the separate mechanisms of the relaxation phenom- ena. At the present time the technique oflaser pulse generation has reached the femtosecond scale (Othonos 1998), which leads to the possibility of investigating processes with high resolution in solid-state laser spectroscopy.