L Journal of Alloys and Compounds 310 (2000) 288–291 www.elsevier.com / locate / jallcom Anelastic relaxation in semi-insulating InP a, b c d d b * G. Cannelli , R. Cantelli , F. Cordero , G.M. Guadalupi , B. Molinas , O. Palumbo , b F. Trequattrini a ` Universita della Calabria, Dipartimento di Fisica, Arcavacata di Rende ( CS), I-87036 Cosenza, and INFM, Italy b ` Universita di Roma ‘ La Sapienza’, Dipartimento di Fisica, I-00185 Roma, and INEM, Italy c CNR, Area di Ricerca Roma-Tor Vergata, Istituto di Acustica ‘ O.M. Corbino’, Via Fosso del Cavaliere, I-00 133 Roma, and INFM, Italy d Venezia Tecnologie SpA ( ENI Group), Via delle Industrie 39, I-30175 P . Marghera ( VE), Italy Abstract The elastic energy loss of InP has been measured between 1.9 and 450 K in the frequency range 1 to 16 kHz. In the InP samples displaying the semi-insulating state, obtained either by thermally treating at 9508C the undoped material or by doping with Fe, a well-developed thermally activated relaxation process appears at 300 K. The corresponding peak is described by a single-time Debye 21 14 21 curve with an activation energy E50.67 eV and a pre-exponential factor of the relaxation rate t 53310 s , indicating the presence 0 of a species mobile at room temperature and constituted by atomic complexes. Instead, in the non-semi-insulating InP sample, the peak at 300 K is either absent or masked by the background. The possibility is discussed that the mechanism giving rise to the relaxation peak is due to hydrogen-related defects.  2000 Elsevier Science S.A. All rights reserved. Keywords: Elastic energy loss; Relaxation peak; Hydrogen-related defects 1. Introduction conversion, and many of them hypothesize that the thermal treatment may activate some kinds of deep acceptors in InP is an important material both in microelectronics such a concentration as to compensate the shallow donors and optoelectronics. In its semi-insulating (SI) state, InP is related to impurities or to P vacancies. Among the possible becoming more and more important not only for the deep acceptors the Fe atom, both in Fe doped and in application in high frequency devices but also for optical undoped InP (therefore present at the residual impurity fibre communication systems. SI InP is traditionally ob- level) has been considered. However, also hydrogen-re- tained by doping with Fe; indeed it is widely believed that, lated defects are receiving great attention, since unwanted for the conversion from the n-type conductivity to the high H is always present in III–V materials [5] and may form resistivity state to occur, the electrons supplied to the complexes with native defects and impurities [6–12]. crystal by the unwanted residual impurities (shallow From that illustrated above it results that the physical donors) must be trapped and Fe, which acts as a deep and technological properties of those materials are crucial- acceptor, provides this compensation. However, the ly affected by structural imperfections and impurities, achievement of the SI state by Fe doping may present whose nature is not completely clarified. For this reason, in disadvantages due to the nonuniformity of the electrical the present paper we conducted measurements of the properties along the crystal growth axis caused by Fe complex modulus (elastic energy loss and dynamic segregation [1]. In recent years it was reported that the modulus) in InP:Fe and in undoped semiconducting and semi-insulating state is also reached by thermally treating semi-insulating InP, with the aim of obtaining information undoped InP for several hours or days at about 9008C on the motion parameters of the defect complexes present under phosphorous atmospheres ranging from 1 to tens of in these materials. bars [2–4], but the success of the treatment requires a highly pure starting material [3], and is not guaranteed. Several mechanisms have been proposed for the SI 2. Experiment The thermal treatments (TT) finalized to the conversion *Corresponding author. from the semiconducting to the semi-insulating state were 0925-8388 / 00 / $ – see front matter  2000 Elsevier Science S.A. All rights reserved. PII: S0925-8388(00)01024-0