Self‐Limiting Synthesis of Ultrathin Ge(110) Single Crystal via Liquid Metal

Abstract

Germanium, the prime applied semiconductor, is widely used in solid‐state electronics and photoelectronics. Unfortunately, since the 3D diamond‐like structure with strong covalent bonds impedes the 2D anisotropic growth, only the examples of ultrathin Ge along the (111) plane have been investigated, much less to the controllable synthesis along another crystal surface. Meanwhile, Ge(111) flakes are limited in semiconductor applications because of their gapless property. Here, ultrathin Ge(110) single crystal is synthesized with semiconductive property via gallium‐associated self‐limiting growth. The obtained ultrathin Ge(110) single crystal exhibits anisotropic honeycomb structure, uniformly incremental lattice, wide tunable direct‐bandgap, blue‐shifted photoluminescence emission, and unique phonon modes, which are consistent with the previous theoretical predictions. It also confirms excellent second harmonic generation and high hole mobility of 724 cm2 V−1 s−1. The realization of ultrathin Ge(110) single crystal will provide an excellent candidate for application in electronics and optoelectronics.

P‐Type 2D Semiconductors for Future Electronics

“…However, only a small range of p‐type 2D semiconductors have been prepared and evaluated in different applications. [ 13 ] Here, as shown in Figure , we build toolkit to summarize potential inorganic p‐type 2D semiconductors and classify them into four categories by elemental composition: single element materials (e.g., Ge, [ 17 ] Se, [ 18 ] Te, [ 19 ] b‐As, [ 20 ] BP [ 10a,b ] ), chalcogenides (e.g., SnS, [ 21 ] GaSe, [ 22 ] MoTe 2 [ 23 ] ), oxides (e.g., h ‐TiO 2 , [ 24 ] Cu 2 O [ 25 ] ), and others (e.g., GeAs, [ 26 ] AsP, [ 11 ] CsSnI 3 [ 27 ] ). The above p‐type members have demonstrated several interesting and important features, such as widely‐tunable bandgaps of 0.3–4.0 eV, ultra‐high hole mobility, mechanical flexibility, and anisotropic electrical conductance, making them attractive for both fundamental studies and practical applications.…”

Wearable Sensors Based on Atomically Thin P‐Type Semiconductors

“…To address this issue, self-limiting CVD synthesis of single crystalline p-type semiconducting Ge (110) was obtained using liquid germanium as the substrate, the hole mobility of which was measured to be 724 cm 2 V −1 s −1 . [73]…”

Facet engineering of ultrathin two-dimensional materials

“…4a. 29 This is because the adsorption energy of Ga atoms on the Ge(110) facet is larger than that of Ge atoms, preventing further deposition of Ge atoms and thus inhibiting the growth along the [110] orientation (Fig. 4b and c).…”

“…Ultrathin two-dimensional (2D) materials are a promising class of nanomaterials with a typical atomic thickness of less than 5 nm and a lateral size greater than 100 nm, or up to several micrometers or even wafer-scale, which are considered one of the best candidates for extending Moore's law. 1,2 Since the successful exfoliation of graphene in 2004, 3 ultrathin 2D materials such as graphene, 4–6 hexagonal boron nitride (h-BN), 7,8 transition metal dichalcogenides (TMDs), 9–12 III–V group semiconductors, 13–15 black phosphorus, 16 MXenes, 17–20 as well as some materials like layered double hydroxides (LDH), 21,22 metal oxides, 23–25 transition metal phosphides (TMPs) 26,27 and elemental materials 28–31 have attracted tremendous interest. Ultrathin 2D materials are generally divided into layered materials and non-layered materials.…”

“…In particular, 2D semiconductor materials with controllable facet orientation can greatly influence the charge transfer/separation process, as well as the electronic structure and bandgap. 29,49,50 The effect of crystal facet engineering on magnetism is mainly reflected in the different atomic numbers in the magnetic center of different facets, which will affect their coordination environment and interaction with other substances. 51–53 Besides, facet-customized epitaxial growth of other 2D materials can be obtained by introducing 2D materials with specific facets as seeds.…”