MBE-Grown II–VI and Related Nanostructures

Abstract

Nanostructures of II-VI semiconductor materials could potentially offer novel and superior physical (in particular, optoelectronic) properties with respect to their bulk counterparts. Herein, we present our most recent research on several II-VI and related nanostructures grown by molecular beam epitaxy (MBE) technique. These include a ZnSe nanograting. This nanograting structure was realized at the surface of Fe/ZnSe bilayers grown on GaAs(001) substrates by thermal annealing. A model based on an Ewald construction is presented to explain its unusual reflection high-energy electron diffraction (RHEED) patterns. The formation mechanism of this one-dimensional (1D) nanostructure is possibly related to surface energy minimization, together with an Fe-Se exchange interaction and Fe-induced decomposition of several top ZnSe atomic layers during thermal annealing. Another nanostructure investigated was the ZnS Schottky barrier embedded with Fe quantum dots (QDs). Here, a Au/ZnS/Fe-QDs/ZnS/n + -GaAs(100) Schottky barrier structure containing five layers of spherical Fe quantum dots with a diameter of $3 nm was fabricated. Its I-V characteristic measured from 5 K to 295 K displays negative differential resistance (NDR) for temperature £50 K. Staircase-like I-V characteristics were also observed at low temperature in some devices fabricated from this structure. Possible mechanisms that can account for the observed unusual I-V characteristic in this structure are presented. Finally, laterally grown Fe nanowires (NWs) on a ZnS surface were prepared. Under high growth/annealing temperature, two types of Fe NWs with specific orientations can be grown on the ZnS(100) surface. We propose a mean-field model that the torque exerted by type A Fe NWs could effectively turn the two components of type B Fe NWs slightly toward the ZnS [110] direction, leading to the observed misalignment of type B Fe NWs. ZnSe NANOGRATINGRecently, a number of self-assembly techniques have been used in the fabrication of low-dimensional structures such as quantum dots and nanowires. 1,2 These techniques enjoy the advantages of being able to achieve a true nanosize scale of the nanostructures and most importantly large product area by an in situ non-time-consuming fabrication process. In recent years, using state-of-the-art molecular beam epitaxy (MBE) technique, we have been able to study the growth mechanism and/or quantum size effects of several self-assembled nanostructures. 3-5 Herein, we report a novel approach for fabricating a highly aligned nanograting structure on a ZnSe(001) surface by thermal annealing an Fe/ZnSe bilayer grown on a GaAs(001) substrate.In this study, three samples were fabricated on GaAs(001) substrates using a VG V80H MBE system. The substrate of sample I1 was first deoxided at 580°C, and then a thin ZnSe film ($30 nm) was deposited at 250°C using a ZnSe compound effusion

Growth, reaction and nanowire formation of Fe on the ZnS(1 0 0) surface

“…This result is different from the earlier conclusion that type-B nanowires are bcc-Fe [2][3][4]. This could be due to the different experimental conditions, e.g.…”

“…Two types of NWs, with crystal shapes similar to those described in the earlier studies [2][3][4] have been observed together with many other previously unreported crystal shapes. One type labeled as type A NWs in the previous study [2] Other diffraction spots move across the diffraction pattern when the incident electron energy varies (inner spots in figures 3(a) and 3(b)).…”

“…This line of investigation has also been extended to the growth of Fe on wide-band gap semiconductors. It was found that Fe grows on thin epitaxial (1 0 0)-oriented ZnS films on GaP(1 0 0) substrates at temperatures between 350 and 400 °C in the form of nanowires (NWs), using ex situ transmission electron microscopy and electron diffraction [2][3][4]. Recently, magnetic nanowires have been the subject of numerous studies because of their unique physical properties and promising applications in spin-related nanotechnologies such as highdensity magnetic recording, magnetic field sensors, magnetic nanoprobes for spin-polarized microscopy and cell manipulation in biomedical technology [5][6][7][8][9].…”

“…In order to understand the mechanisms that lead to NW growth on ZnS(1 0 0) [2][3][4], we have studied the same system in situ using the laterally resolving surface science technique low energy electron microscopy (LEEM) combined with micro low energy electron diffraction (µLEED) [14,15]. The real-time imaging capability of LEEM allows in situ monitoring of growth dynamics.…”

“…Our investigations of growth were carried out at temperatures in the range 260-400 °C, which covers the range studied previously, but also extends it to lower temperatures. Furthermore, we employed Fe deposition rates here that were about ten times lower than used in previous investigations [2][3][4]. This difference from previous growth conditions was chosen in order to explore growth behavior closer to equilibrium.…”