Materials Science and Engineering B83 (2001) 145 – 151 Charge retention effect in metal – oxide – semiconductor structure containing Si nanocrystals prepared by ion-beam-assisted electron beam deposition Yong Kim a, *, Kyung Hwa Park a , Won Chel Choi b , Tae Hun Chung a , Hong Jun Bark a , Jae-Yel Yi a , Jaein Jeong c a Department of Physics, Dong -A Uniersity, Hadan -2 -dong, Sahagu, Pusan 604 -714, South Korea b Semiconductor Materials Laboratory, Korea Institute of Science and Technology, PO Box 131, Cheongryang, Seoul 130 -650, South Korea c Sensor and Instrumentation Research Team, Research Institute of Industrial Science & Technology, PO Box 135, Pohang 790 -600, South Korea Received 8 December 2000; accepted 13 January 2001 Abstract An amorphous Si layer prepared by ion-beam-assisted electron beam deposition (IBAED) method is oxidized by a rapid thermal oxidation technique. We observe a nanocrystal band located at about 4 nm from the Si/SiO x interface by cross-sectional transmission electron microscope observation. The metal – oxide – semiconductor (MOS) structure employing the oxide layer with the nanocrystal band exhibits a large capacitance – voltage hysteresis indicative of trapping of electrons/holes. In contrast, a relatively small capacitance – voltage hysteresis is found for the MOS diode prepared by conventional electron beam deposition (EBD) without ion-beam assistance. Such a marked difference shows that the ion-beam irradiation plays an important role in the formation of nuclei, which would grow to nanocrystals during subsequent rapid thermal oxidation process. Interestingly, the MOS prepared by IBAED shows a characteristic capacitance transient behavior, indicative of non-dispersive carrier relaxation. In addition, the charge retention times shows a bias dependence and a maximum of 72 s near the mid-gap voltage. Such a bias-dependent retention time is interpreted in terms of the tunneling of trapped charges in nanocrystals through empty interface states. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Charge retention; Metal-oxide semiconductor; Nanocrystals www.elsevier.com/locate/mseb 1. Introduction Recently, the light-emitting property of Si nanocrys- tals has attracted much attention [1]. This is mainly due to possible applications of nanocrystals to Si-based optoelectronics. Together with the light-emitting prop- erty, nanocrystal could be one of good candidates for a memory island in single electron memory devices (SEMD). Specifically, nanocrystals in a SiO 2 matrix are attractive [2]. Due to the large bandgap and high resistivity of SiO 2 , the tunnel resistance usually exceeds the resistance quantum. This condition is necessary to suppress cotunneling events of electrons through tun- neling barrier. Moreover, small nanocrystals have a sufficient charging energy exceeding the room-tempera- ture thermal energy. Recently, Tiwari et al. [3] have demonstrated room-temperature-operating SEMD em- ploying nanocrystals as memory islands. Their SEMD resembles a floating-gate non-volatile memory. Several SEMDs operating at room temperature have been re- ported, employing a similar device geometry [4–6]. However, the random distribution and size dispersion of nanocrystals are remaining hurdles preventing fur- ther progress of nanocrystal-involved devices. Nanocrystals have been synthesized by several meth- ods including ion implantation [7], co-sputtering [8], and silicon-rich-oxide by chemical vapor deposition [9], etc. However, further research toward the establishment of stable and reliable method compatible with standard * Corresponding author. E-mail address: yongkim@daunet.donga.ac.kr (Y. Kim). 0921-5107/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0921-5107(01)00510-4