Pergamon Solid State Communications, Vol. 98, No. 10, 873-877, 1996 pp. Copyright 0 1996 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0038-1098/96 S12.00 + 00 PI1 SOO38-1098(96)00068-3 QUANTUM DIFFUSION OF DEUTERIUM IN GaAs : Zn G. Cannelli Dipartimento di Fisica, Universita della Calabria, I-87036 Arcavacata di Rende (CS), Italy R. Cantelli Dipartimento di Fisica, Universita di Roma “La Sapienza”, Piazzale Aldo Moro, I-00185 Roma, Italy F. Corder0 Istituto di Acustica “O.M. Corbino”, Consiglio Nazionale delle Ricerche, Via Cassia 1216, I-00189 Roma, Italy E. Giovine, F. Trequattrini, M. Capizzi and A. Frova Dipartimento di Fisica, Universita di Roma “La Sapienza”, Piazzale Aldo Moro, I-00185 Roma, Italy (Received 5 January 1996; accepted 24 January 1996 by E. Molinari) The dynamics of deuterium in GaAs doped with Zn has been investi- gated by anelastic relaxation. The most likely configuration is D trapped by substitutional Zn, although D trapped at a Ga vacancy cannot be excluded. The relaxation of D occurs at about 20 K in the kHz range and has the highest rate found up to now for a hydrogen isotope in a semiconductor. The shape of the curves of the elastic energy loss vs temperature indicates that the nature of the D re- orientation is strongly quantistic. Copyright 0 1996 Elsevier Science Ltd Keywords: A. semiconductors, D. tunnelling, D. acoustic properties. 1. INTRODUCTION THE POSSIBILITY of both coherent or incoherent quantum tunneling of interstitial H is well established in several metals. In some cases, like the O-H pair in Nb, the low energy excitations revealed at low tem- perature by inelastic neutron scattering (INS), specific heat and acoustic experiments can be consistently explained by the two-level system model [l]. The energy levels of the tunnel systems (TS) may be directly probed by the positions of the INS peaks and by the excess specific heat vs temperature, while the acoustic measurements provide information on the transition rates, symmetry and local distortion of the TS. The situation in semiconductors is different. Coherent tunneling states have been proposed to explain some unusual features of optical measure- ments of complexes containing H in Ge and Si [2- 4]. However, those measurements are a rather indirect method for studying the atomic tunneling, as they probe the electron states associated with the TS rather than the TS itself and provide no [2,3] or scarce information [4] on the transition rates of the tunneling particle. Since other types of experiments have not been made, the picture of these tunnel systems is not yet as clear as in the case of metals. Recently, Cheng and Stavola [5]joined their infra- red absorption data with our anelastic relaxation (AR) results [6] on Si:B-H. The jump rate derived from the two experiments, which span 12 orders of magnitude, indicates the influence of quantum tunnel- ing on the reorientation rates of H around B in Si. In fact, at low temperature the H hopping rate starts increasing with respect to the Arrhenius law extra- polated from high temperature. The two sets of data have been interpreted within the Flynn and Stoneham model of thermally assisted incoherent tunneling transitions [7]. In the present work we report a new AR process in deuterium irradiated GaAs : Zn, which not only yields the highest reorientation transition rates found so far for H and its isotopes in a semiconductor, but also 873