Native oxide emerging of the cleavage surface of gallium selenide due to prolonged storage
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CONDUCTOR STRUCTURES, INTERFACES, AND SURFACES
Native Oxide Emerging of the Cleavage Surface of Gallium Selenide Due to Prolonged Storage S. I. Drapaka^, S. V. Gavrylyuka, Z. D. Kovalyuka, and O. S. Lytvynb aFrantsevich
Institute of Materials Science Problems (Chernovtsy Branch), National Academy of Sciences of Ukraine, ul. I. Vilde 5, Chernovtsy, 58001 Ukraine ^e-mail: [email protected] bLashkarev Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, Kiev, 03028 Ukraine Submitted July 24, 2007; accepted for publication September 4, 2007
Abstract—The crystal structure and surface morphology of native oxide emerging on the surface of the (0001) cleavage of undoped and Cd-doped or Dy-doped single crystals of layered GaSe due to prolonged storage in air are studied. The factors that lead to the differences in the outward appearance of oxide films on the surface of undoped (dull surface) and doped samples (transparent films) are analyzed. The results of studies of electrical properties of the 〈gallium selenide〉–〈native oxide〉 systems are reported. It is shown that the films of native oxide on the GaSe surface feature current instability with an N-like current–voltage characteristic. Attention is paid to low values of effective permittivity of native oxide. PACS numbers: 68.35.Ct, 73.40.Kp, 73.40.Cg, 73.40.Qv, 81.65.Mq DOI: 10.1134/S1063782608040088
1. INTRODUCTION Gallium selenide belongs to an extended class of layered semiconductors and is a promising material for various optoelectronic devices (see, for example, [1–4]). The recent increase in interest in GaSe is also associated with its prospects for fabrication of various nanoparticles, including nanotubes [5, 6], and for the use in planar nanotechnologies [7–9]. Therefore, the study of various aspects associated with processes of aging of gallium selenide is a topical problem. The anisotropy of chemical bonds inside and between GaSe layers allows one to obtain an atomically smooth surface with a low density of surface states (1010 cm–2) by cleavage [10]. It is believed that the surface of layered III–VI compounds obtained by cleavage is perfect not only geometrically but also in the sense of inertness to sorption of foreign atoms from atmosphere [11]. However, the work function of charge carriers from the cleavage surface of GaSe depends on the time of holding in air, and for the characteristic time of 5–6 min after cleavage, the work function decreases by ~0.35 eV [12]. It is known that the variation in the work function is associated either with the sorption of oxygen atoms from air or with the formation of the oxide layer on the semiconductor surface [13]. In addition, despite the fact that according to [14–16] even the thermal effect in air at T 400°C does not lead to phase transformations on the GaSe surface, electrical characteristics of the GaSe-based photosensitive structures fabricated by methods excluding the interdiffusion of contacting materials in some cases cannot be interpreted disregarding the thin insulator gap (nativ
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