9:30 AM - 11:30 AM
▲ [19a-P6-36] Growth of high quality epitaxial graphene by modified hydrogen annealing
Keywords:Epitaxial graphene, Hydrogen annealing
Epitaxial graphene (EG) on silicon carbide (SiC) is promising for fabrication of graphene field-effect transistors (GFETs) because it can be formed directly on a large size, semi-insulating substrate without any transfer procedures. Among various methods for the betterment of EG, hydrogen (H2) annealing methods have been attracting recent attentions. First, annealing in H2 at high temperatures (>1400 oC) removes the surface polishing damages and causes a uniform array of steps. Second, annealing in H2 at low temperatures (~600 oC) causes a hydrogen intercalation and decouples the buffer layer from the SiC substrate. In this presentation we propose a new H2 annealing method (modified H2 annealing) for the formation of high quality EG. The method consists of (1) low-temperature (LT) annealing in H2 at 500 oC for 5 hours for SiC surface reconstruction and (2) subsequent high-temperature (HT) annealing in Ar/H2 at 1480 oC for the formation of EG. Figure 1(a) shows the AFM image of 4H-SiC(0001) after the procedure (1). A well-ordered surface with a step height of 1.1 nm and a terrace width of 1.5 μm was formed. Using this substrate, graphene was grown in Ar (1420 oC) or in Ar/H2 ambient (1480 oC). The upper images in Figs. 1(b) and 1(c) show the AFM image of the EG grown in Ar and Ar/H2 ambient, respectively. EG grown in Ar ambient shows a minimum-step-bunching (MSB) with a step height of 1.5 nm and a terrace width of 5.0 μm. For EG grown in Ar/H2 ambient, a uniform large-step-bunching (LSB) with high step (~45 nm) and wide terrace (~30 μm) was formed. Moreover, the EG grown under Ar/H2 ambient exhibits a sharper and a higher Raman G’-peak in the spectrum, which indicates formation of high quality graphene. Figure 2 compares the Hall mobility between Ar and Ar/H2 ambient. The EG grown in Ar/H2 ambient shows a higher Hall mobility (2095 cm2/Vs @ n = 1x1012 cm-3) than that grown in Ar ambient (1750 cm2/Vs @ n = 1x1012 cm-3). This improvement is due to the H2-termination of the Si dangling bonds underneath the buffer layer without breakage of the Si-C covalent bond between SiC and the buffer layer, which was confirmed by the appearance of Si-H bond component in X-ray photoelectron spectroscopy (XPS) analysis. This is the first report to form EG by annealing SiC in Ar/H2, which provides a novel, excellent method to fabricate high quality EG to be used in graphene based electronic devices.