Recently, a research team led by Prof. ZHAO Jianhua, at the State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, demonstrated their collaborative work with Professor XU Hongqi group at Peking University,on the successful growth of high-quality free-standing two-dimensional single-crystalline InSb nanosheets by molecular-beam epitaxy.
Among all the III-V group semiconductors, InSb is the most desired material system for applications in high-speed, low-power electronics, infrared optoelectronics, spintronics, topological quantum computing, and detection and manipulation of Majorana Fermions owing to its highest electron mobility, narrowest bandgap, smallest eﬀective mass, strong spin-orbit interaction and giant g factor. All these applications require a high degree of InSb growth control on its morphology and especially crystal quality. Unfortunately, because of the largest lattice parameter of InSb in the family of III-V group semiconductors and its intrinsic n-type conductivity, epitaxial growth of InSb layers faces an inevitable diﬃculty in ﬁnding a suitable substrate. Conventionally, buﬀer layers with graded or abrupt composition proﬁle are deposited on lattice mismatched substrates to obtain a layer with a required value of lattice constant. Nevertheless, even when the sophisticated buﬀer-layer engineering is used, the density of dislocations threading to the surface of the buﬀer from its interface with a lattice mismatched substrate is often too high to grow a high crystal quality InSb layer for fabrication of high-performance nano-electronics and quantum devices and for study of novel physical phenomena.
Prof. ZHAO and her collaborators presented a new route of growing high material quality layered InSb structures, in which free-standing InSb nanosheets are epitaxially grown on InAs nanowire stems and thus the process is independent of buffer-layer engineering. The morphology and size of free-standing InSb nanosheets can be controlled in the approach by tailoring the Sb/In beam equivalent pressure ratio and InSb growth time. They demonstrated the growth of free-standing InSb nanosheets with the length and width up to several micrometers and the thickness down to ∼10 nm. High-resolution transmission electron microscope images show that the grown InSb nanosheets are pure zincblende single crystals and have excellent epitaxial relationships with the InAs nanowire stems. The formation of the InSb nanosheets is attributed to a combination of vapor-liquid-solid and lateral growth. Electrical measurements show that the grown InSb nanosheets exhibit an ambipolar behavior and a high electron mobility ~20000 cm2 V-1 s-1. These novel, high material quality, free-standing InSb single-crystalline nanosheets have the great potential not only for applications in highspeed electronics and infrared optoelectronics but also for realization of novel quantum devices for the studies of fundamental physics.
Fig. 1 Diagram of the growth process and SEM images of the InSb nanosheets (upper panel). Diagram and atomic force microscopy image of a typical InSb nanosheet Hall-bar device and transport properties of the InSb nanosheets (lower panel). (Image by Dr. PAN Dong et al.)
Prof. ZHAO Jianhua
Institute of Semiconductors, CAS (http://english.semi.cas.cn/)