AC Conductance in Dense Array of the Ge0.7SiO.3 Quantum Dots in Si

• Published in: Low Temperature Physics: Part B (AIP Conference Proceedings Volume 850) 2006-01, Vol.850, p.1530-1531
• Main Authors: Drichko, I L, Diakonov, A M, Smirnov, I Yu, Suslov, A V, Galperin, Y M, Yakimov, A I, Nikiforov, A I
• Format: Article
• Language: English
• ISSN: 0094-243X
• DOI: 10.1063/1.2355286

Complex AC-conductance, AC, in the systems with dense Ge0.7SiO.3 quantum dot (QD) arrays in Si has been determined from simultaneous measurements of attenuation, =(H)-(0), and velocity, V/V(H)[V(H)-V(0)]/V(0), of surface acoustic waves (SAW) with frequencies f = 30-300 MHz as functions of transverse magnetic field H 18 T in the temperature range T = 1-20 K. It has been shown that in the sample with dopant (B) concentration 8.2X1011 cm-2 at temperatures T 4 K the AC conductivity is dominated by hopping between states localized in different QDs. The observed power-law temperature dependence, 1(H=0)~T2.4, and weak frequency dependence, 1(H=0)~0, of the AC conductivity are consistent with predictions of the two-site model for AC hopping conductivity for the case of 0 > > 1, where =2f is the SAW angular frequency and 0 is the typical population relaxation time. At T > 7 K the AC conductivity is due to thermal activation of the carriers (holes) to the mobility edge. In intermediate temperature region 4 < T < 7 K, where AC conductivity is due to a combination of hops between QDs and diffusion on the mobility edge, one succeeded to separate both contributions. Temperature dependence of hopping contribution to the conductivity above T*~4.5 K saturates, evidencing crossover to the regime where 0 < 1. From crossover condition, 0(T*) = 1, the typical value, 0, of the relaxation time has been determined.