Sodium-peak splitting in dynamic current-voltage characteristics of convective ion currents in metal-oxide-semiconductor
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CONDUCTOR STRUCTURES, INTERFACES, AND SURFACES
Sodium-Peak Splitting in Dynamic Current–Voltage Characteristics of Convective Ion Currents in Metal–Oxide–Semiconductor Structures S. G. Dmitriev^ and Yu. V. Markin Institute of Radio Engineering and Electronics, Russian Academy of Sciences (Fryazino Branch), pl. Vvedenskogo 1, Fryazino, Moscow oblast, 141120 Russia ^e-mail: [email protected] Submitted March 1, 2007; accepted for publication April 18, 2007
Abstract—The results of simultaneous measurements of dynamic current–voltage and capacitance–voltage characteristics are presented for metal–oxide–semiconductor structures in the temperature range T ≈ 420– 470 K and voltage-sweep rates βV = 0.5–1000 mV/s. The convective currents Icon(V) in oxide are extracted from usual ion currents in the I–V characteristics. In Icon(V) curves, the Na+-ion peaks are split. In addition, an envelope curve is seen in initial portions of “fast” Icon(V) curves with βV 10 mV/s that indicates to the presence of a certain quasi-steady ion-transport mode. A more equilibrium mode at slow rates βV < 1 mV/s manifests itself in the form of stabilization of convective-current peak shapes. The nature of efficient neutralization of the second peaks in the Icon(V) dependences is discussed. PACS numbers: 66.30.Dm, 66.30.Jt, 66.30.Qa, 85.30.De, 85.30.Tv DOI: 10.1134/S1063782608010065
1. INTRODUCTION
their motion is nonequilibrium and complicates the analysis of dynamic I–V characteristics [11]. In practice, the concentration NS is measured at temperatures T ≈ 200°C or lower [2, 7, 13]. In this case, the forward (βV > 0) dynamic I–V characteristics corresponding to the motion of ions from metal to semiconductor are highly asymmetric (and nonequilibrium) [3−5, 10–12] due to (effective) ion traps at metal [4, 5, 10, 11, 14]. For this reason, it is the reverse (βV < 0) dynamic I–V characteristics that are used for measurements [3–5, 13] because the ion peaks in these characteristics acquire a relatively symmetric shape when the sweep rate decreases in the range of βV ≈ 10–100 mV/s. However, as comparison with calculations shows [15], the quasi-equilibrium in the structure can be not yet attained at T ≈ 300°C even for βV < 10 mV/s. Similar investigations at T ≈ 180°C and βV 10 mV/s were performed in [16]. The direct experimental test for equilibrium at T ≈ 200°C shows that it is still incomplete even for βV ≈ 1 mV/s [17] (no data on slower measurements have been reported). The calculations for a film (without semiconductor) [15] indicate that there is a universal quasi-steady mode for ion currents, in which case the current depends only on Vg instead of on βV . This mode manifests itself in the form of the envelope curve at initial portions of the family of dynamic I–V characteristics with different βV . However, the nonlinearity of semiconductor capacitance in the experiment leads to characteristic capaci-
The conventional method of studying mobile ions in silicon MOS (metal–oxide–semiconductor) structures is the method of dynamic current–voltage
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