Elsevier

Materials Letters

Volume 178, 1 September 2016, Pages 147-150
Materials Letters

Formation of large-grain crystalline germanium on single layer graphene on insulator by rapid melting growth

https://doi.org/10.1016/j.matlet.2016.05.007Get rights and content

Highlights

  • Crystallization of thermally deposited Ge microstrips on SLG by rapid melting growth.

  • Lateral growth of large grain crystalline Ge was obtained over entire structure.

  • SLG is capable to suppress the spontaneous nucleation in the melting Ge.

  • The interaction of C and Ge atoms at the interface leads to large compressive strain.

  • Innovative breakthrough towards the realization of single-crystalline GOI structure.

Abstract

We demonstrate the crystallization of thermally deposited amorphous germanium (Ge) microstrips on single layer graphene (SLG) by rapid melting growth. Lateral growth of large grain crystalline Ge was successfully obtained over entire microstrip structure. SLG has shown its capability to suppress the spontaneous nucleation in the melting Ge, where no or less intermixing of C and Ge atoms has been detected. The interaction of C atoms from the graphene and Ge atoms at the interface is the possible reason for the observation of large compressive strain generated in the Ge strip grown on SLG. This technique provides an innovative breakthrough towards the realization of single-crystalline Ge-on-insulator (GOI) structure on SLG to facilitate the next-generation ultra-large-scale integrated circuits (ULSIs) with multifunctionalities.

Introduction

As miniaturization of the silicon (Si) transistors becomes increasingly challenging, increased performance can only be achieved by integrating multifunctional materials on Si platform. Recently, the concept of advanced heterogeneous integration on Si platform was proposed by Takagi et al. that will enable the realization of a so-called “More than Moore” technology [1]. Here, the incorporation of germanium (Ge) that possesses higher electron and hole mobilities than that of Si is attractive [2] for not only to enhance the performance of complementary-metal-oxide-semiconductor (CMOS) circuits [3] but also to facilitate the present ultra-large-scale integrated circuits (ULSIs) with various functionalities where Ge can be also used to fabricate various kinds of functional devices, such as optical devices [4], photodetectors [5] and solar batteries [6]. Also the lattice similarity of Ge with the III-V semiconductor, such as GaAs and metallic silicide, such as Fe3Si enables the use of Ge as a buffer layer for the integration of III-V semiconductor and metallic silicide on Si platform [7]. By considering these potential applications, the formation of single-crystalline Ge-on-insulator (GOI) structure needs to be realized on Si substrate. However, the extremely large lattice mismatch between Ge and insulator prevent the direct growth of crystalline Ge on insulator. One of promising technique in growing crystalline GOI structure is to introduce a so-called buffer layer or template layer for the relaxation of lattice mismatch during the crystallization process. Meanwhile, the crystallization of Ge can be achieved by a rapid melting growth [8], [9], [10], [11], [12], [13].

Graphene, a two-dimensional hexagonal network of carbon atoms formed by making strong triangular σ-bonds of the sp2 hybridized orbitals, has been employed as the potential template layer for the growth of various kinds of materials on insulator. It is well documented that graphene has a great potential for novel electronic devices to act as device channel [14], transparent electrode [15], sensing membrane [16] and so forth, because of its extraordinary electrical, thermal, and mechanical properties, including a carrier mobility exceeding 104 cm2/Vs and a thermal conductivity of 103 W/mK [17], [18], [19], [20]. Therefore, with the excellent electrical and thermal characteristics of graphene layers, growing semiconductor nanostructures and thin film on graphene would enable such material system to be exploited in diverse sophisticated device applications such as flexible and transferable electronics.

In recent years, we have shown the growth of several materials such as gallium nitride (GaN) [21], gallium oxide (Ga2O3), zinc oxide (ZnO) [22], [23], [24], [25], [26] and silicon carbide (SiC) [27] on graphene. Recently, we demonstrated for the first time the crystallization of electrodeposited amorphous Ge in (111) orientation on multilayer graphene [28] by rapid melting growth. The induction of lateral growth was achieved since there is a spatial gradient of the solidification temperature originating as a result of the intermixing of C-Ge. In this paper, we present the results of the crystallization of thermally evaporated amorphous Ge on single layer graphene (SLG) with the condition that no or less intermixing of C and Ge is producible during the rapid melting growth.

Section snippets

Experimental details

Fig. 1 shows the schematic of sample structure and fabrication process of Ge on SLG. At first 50 nm thick mirror smooth amorphous Ge thin film was deposited on a chemical vapor deposition (CVD) grown SLG/SiO2/Si(100) substrate (Graphene laboratories Inc., Calverton, NY, USA) using conventional vacuum thermal evaporation technique with a background pressure of 3×10−5 Pa. It is worth noting that the coverage of SLG is around 95% and the properties of CVD grown graphene can be found in ref. [22]. To

Results and discussion

Fig. 2(a) shows the cross-section FESEM micrograph of the as-deposited 50-nm thick Ge layer with a smooth surface and uniform thickness. Based on the EDX spectra (data not shown), the deposited Ge film was found to be highly pure without any excessive contaminants. The random distribution of colors from the EBSD image (data not shown) of the as-deposited Ge layer confirms the crystal structure is amorphous. Fig. 2(b) shows the Nomarski image of microstrips before annealing. It can be seen that

Conclusions

We demonstrate a novel and innovative method to obtain large-grain crystalline GOI structure by introducing SLG as a template layer in order to generate relaxation of large lattice mismatch between Ge and insulator. SLG is sufficient to suppress spontaneous nucleation in melting Ge which leads to the formation of large-grain crystalline Ge microstrip even though in the condition of no or less intermixing of C and Ge atoms. The interaction of C and Ge atoms at Ge/graphene interface is speculated

Acknowledgements

T. Morshed thanks the Malaysia-Japan International Institute of Technology for the scholarship and JASSO for financial support during the research attachment at Sadoh Laboratory, Kyushu University. This work was funded by Universiti Teknologi Malaysia, (GUP-00H82 and GUP-08H02) Malaysia Ministry of Science, Technology and Innovation, (Brain Gain) and the Malaysia Ministry of Education (FRGS-78671).

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