Positron behaviour in GaSb under pressure N. Bouarissa Physics Department, University of Setif, Setif 19000, Algeria Received 18 November 1998; received in revised form 3 February 1999; accepted 26 May 1999 Abstract The independent particle model was used to compute the pressure effect on positron states in GaSb in the zinc-blende structure. The positron energy levels and wavefunctions at different points of the reciprocal space at normal and under hydrostatic pressure are calculated. An illustrative result of positron thermalization energy and effective band mass shows that the pressure effect manifests by the decrease of both these quantities which tells us that the positron diffuses better under pressure. The positron charge density is reduced under pressure at the interstitial positions and slightly increased at the inter-nuclear spacing. This theoretical estimation is essential for studying positron annihilation in semiconductors under pressure.  1999 Elsevier Science Ltd. All rights reserved. Keywords: GaSb 1. Introduction Semiconductors are understood as solids, the gap of which ranges from a few meV to a few eV. They are essen- tially those crystals whose electronic properties can be described in terms of band structure. The introduction of a new method using diamond anvil cells has given new impetus to the investigation of the elec- tronic states of semiconductors under high pressure. Since the advent of nanodevices, based on compounds semicon- ductors, the understanding, with accuracy, of the behaviour of these materials under an external effect such as pressure is becoming crucial. GaSb with its low band gap is an important material for optoelectronic and electronic devices and is especially suited for lasers operating in the 1.2–3.0 mm wavelength range and for hot-electron transistors [1]. Its electronic structure at normal and under pressure has already been studied both theoretically and experimentally [2–4]. However, more detailed information on the electronic struc- ture and its pressure dependence is essential for a thorough understanding of these devices. This is because the essential properties of semiconductors is their transport mechanisms which are tightly bound to their band gaps. Therefore, the knowledge of this latter and its behaviour under pressure would unable us to predict the overall properties of these materials. A finite tuning could be achieved at some specific pressure. The “pressure tuning” to adjust band gaps can be used to generate, detect or convert electromagnetic radia- tion. The behaviour of positrons in condensed matter has been the subject of intense experimental and theoretical investigation during the last decades, and the use of positrons as a probe of electronic structure has been well documented and reviewed [4–6]. It is well known that the positron interaction in solids has non- destructive character which makes this method very convenient for the study of the electronic and atomic structures of metals and semiconductors [4,7,8], for the understanding of the behaviour of electrons in crystals, for the determination of the shape of the Fermi surfaces [9–11] and for the studies of the basic properties of the electron and positron wavefunctions [12,13] which are necessary for an interpretation of the experimental spec- tra. Theoretical quantities of positron states in solids can be directly compared with accurate experimental data arising, for example, from high-resolution positron life- time spectroscopy, two-dimensional angular correlation (ACPAR) measurements or slow-positron beam experi- ments. Some theoretical attempts have been made to study the pressure dependence of the positron states in Journal of Physics and Chemistry of Solids 61 (2000) 109–114 0022-3697/00/$ - see front matter  1999 Elsevier Science Ltd. All rights reserved. PII: S0022-3697(99)00225-5 www.elsevier.nl/locate/jpcs