L Journal of Alloys and Compounds 253–254 (1997) 356–359 Hopping and tunnelling of H(D) in semiconductors a, b b c b b b * G. Cannelli , R. Cantelli , M. Capizzi , F. Cordero , A. Frova , E. Giovine , F. Trequattrini a ` Universita della Calabria, Dipartimento di Fisica, Cosenza, Italy, and INFM b ` Universita di Roma ‘ La Sapienza’, Dipartimento di Fisica, P .le A. Moro 2, 00185, Roma, Italy, and INFM c CNR, Istituto di Acustica ‘ O.M. Corbino’, Via Cassia 1216, 00189 Roma, Italy, and INFM Abstract The dynamics of H and D in p-type Si:B and GaAs:Zn in n-type Si:P and GaAs:Si, have been studied by acoustic spectroscopy measurements in the temperature range 1 K-550 K and at frequencies between 1 and 30 kHz. By combining the data from anelastic relaxation and from the dichroism decay, the relaxation rates of the H–B pair are obtained over 11 decades and there are clear indications of a deviation at low temperature from the classical dependence. However, no conclusions can be drawn at present on the mechanism governing the H(D) transitions. The complete absence of relaxation effects in Si:P may confirm that H occupies backbonding sites in this system. In deuterated GaAs:Zn, a new peak is observed at 20 K. This peak is much broader than a single-time Debye peak, and is due to a species performing unexpectedly high transition rates: more than 15–20 orders of magnitude higher than in all the other semiconductors measured so far. This species has been identified as the D–Zn complex. The analysis of data demonstrates that the nature of the relaxation is strongly quantistic. Measurements on GaAs:Si–D suggest that the energy barrier separating the four D antibonding sites around Si may be rather high. Keywords: Hydrogen (Deuterium)-Semiconductor Systems; H(D) Hopping and Tunnelling; Anelastic Relaxation of the anelastic relaxation data gives the H jumping rate in 1. Introduction an exceptionally wide range (12 orders of magnitude) and 2 1 indicates that a deviation of t ( T ) from the classical law The diffusion coefficient of hydrogen and its isotopes in takes place at low temperature. A fit of the Flynn– semiconductors may be several orders of magnitude lower Stoneham model [3] to the data from the two types of than in metals; nevertheless this light particle can display, experiments was recently accomplished [4] and led the locally, a remarkably high mobility. In boron-doped silicon authors to the conclusion that phonon-assisted incoherent loaded with hydrogen, measurements of infrared absorp- tunnelling for the H motion could take place at low tion [1] and anelastic relaxation (elastic energy loss and temperature. modulus) [2] have shown that H is rather mobile around Direct and unambiguous evidence of quantum tunnelling the substitutional dopant acting as a trapping centre. The in semiconductors was recently reported in an anelastic measurements of Ref. [2] revealed a thermally activated relaxation study of the deuterium dynamics in GaAs doped process due to the H reorientation around B with an with Zn [5]. A relaxation of D occurring at 20 K in the activation energy of W50.22 eV. The pre-exponential kHz range has the highest jumping rate found so far for a factor of the relaxation rate, as derived from the classical hydrogen isotope in a semiconductor and cannot be 21 13 21 Arrhenius law, is t 51.2?10 s , typical of point defect explained in a classical framework. 0 relaxation. The infrared absorption measurements at low This paper reports on the H(D) behaviour in p-type and temperature [2] gave a rather similar value for the activa- n-type doped Si and GaAs. tion energy of the H reorientation around B (W50.19 eV), but the extrapolation of the relaxation rate to infinite 21 10 temperature gave a markedly lower value ( t 59.1?10 0 21 2. Experimental procedure s ), two orders of magnitude slower than that of point defect motion in solids. This observation suggested that The samples were four rectangular bars of 403530.4 under-barrier jumping may take place at low temperature 3 19 2 3 2 1 mm : (i) p-type Si:B with [B]510 cm ; (ii) n-type Si:P for t ( T ). The combination of the infrared absorption and 18 2 3 with [P]55310 cm ; (iii) p-type GaAs:Zn with Ga 19 2 3 * Corresponding author. [Zn]510 cm ; (iv) n-type GaAs:Si with [Si]523 Ga 0925-8388 / 97 / $17.00  1997 Elsevier Science S.A. All rights reserved PII S0925-8388(96)03094-0