Important Progress Has Been Made in The Study of Quantum Dot Heteroepitaxy in Semiconductor Research Institutes

Semiconductor Quantum Dot (QD) has become an important material for the construction of a new generation of information devices due to its remarkable quantum limiting effect and adjustable energy level structure, and has important application value in high-performance optoelectronics, single-electron storage and single-photon devices. The preparation of semiconductor quantum dot materials and the new information devices based on them are the hot spots in the frontier research of information technology.

Recently, under the guidance of Wang Zhanguo, academician of the Institute of Semiconductors, Chinese Academy of Sciences, Liu Fengqi and his team have made important progress in the research of quantum dot heteroepitaxy. Using two-dimensional materials as epitaxy substrates, the research team developed a new scheme of van der Waals epitaxy for preparing quantum dot materials (FIG. 1) based on molecular beam epitaxy technology.

Figure 1 Van der Waals epitaxial growth of InSb quantum dots on the surface of MoS2

The two-dimensional material with layered structure has low surface energy because there is no hanging bond on the surface. Therefore, under ultra-high vacuum conditions far from thermal equilibrium, when materials with stable structures such as sphalerite and wurtzite grow on their surfaces, atoms deposited on two-dimensional materials will tend to expose more substrates under the drive of minimum total free energy, and more of their own atoms will be wrapped into the body to reduce surface free energy, so as to achieve the growth of quantum dots. In situ growth monitoring by reflective high energy electron diffraction (RHEED) shows that the van der Waals epitaxial growth of quantum dots is a non-coextensivity mode. Different from the S-K growth mode, the lattice constants of substrate and quantum dot materials are not compatible, thus greatly improving the freedom of the combination of substrate and quantum dot materials, showing universal characteristics. At the same time, the in-plane symmetry of two-dimensional materials can induce the lattice orientation of quantum dot materials. The different surface properties of two-dimensional materials provide new degrees of freedom for the morphology regulation of quantum dots (Figure 2).

FIG. 2 Universality of the van der Waals epitaxial growth method for quantum dots

Based on this scheme, the research team successfully prepared five different kinds of quantum dots on four two-dimensional materials (hBN, FL mica, MoS2, graphene), including four compound semiconductors of group III-V InAs, GaAs, InSb, GaSb and one compound semiconductor of group IV-VI SnTe. There are a total of 20 substrate and quantum dot combinations. The type of quantum dots is limited by the type of molecular beam epitaxy (MBE) source material rather than substrate, which confirms the universality of the epitaxy scheme. The research team completed the van der Waals epitaxy preparation of quantum dots on the wafer scale, showing good size uniformity and distribution uniformity, and can achieve a change of four orders of magnitude in the density of quantum dots over a small substrate temperature range. In addition, by preparing the photodetector, the research team has broadened the response spectrum range of the device and confirmed the efficient transport of interface carriers in 0D/2D mixed-dimensional heterojunctions prepared by van der Waals epitaxy. This epitaxial scheme provides a new platform for the study of mixed-dimensional heterostructures and will help broaden the potential applications of low-dimensional quantum systems.

The results were published in Nature under the title "Epitaxial growth of quantum dots on van der Waals surfaces. Synthesis) (DOI: 10.1038/s44160-024-00562-0). Kaiyao Xin, Lian Li, PhD, and Ziqi Zhou, postdoctoral fellow, are co-first authors of the paper. Fengqi Liu, Shenqiang Zhai, Zhongming Wei, and Can Liu, Associate Professor, Renmin University of China are co-corresponding authors of the paper. Collaborators include Professor Liu Kaihui of Peking University, researcher Zhang Jinchuan of Semiconductor Institute, researcher Liu Junqi and Researcher Deng Huixiong. This work was supported by the National Natural Science Foundation of China, the National Key Research and Development Program, and the Youth Promotion Association of the Chinese Academy of Sciences.