## 4 ALD on EG With a Seeding-Layer
### Deposited High-k Metal-Oxide Seed Layers  
As discussed above, the metal to metal-oxide phase transition occurring in the case of the oxidized metal seeding layers can be a source of mobility degradation in EG. To avoid these issues, the deposition of the seed-layer directly on EG from a high-purity oxide source has been also considered.  
As an example, [PERSON] et al. [35] employed 2-3 nm seed layers of SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\) or HfO\({}_{2}\) deposited via nonreactive electron beam physical vapor deposition (EBPVD) at a pressure \(<\)10\({}^{-6}\) Torr. Immediately following the seed-layer evaporation, 8-10 nm of Al\({}_{2}\)O\({}_{3}\) or HfO\({}_{2}\) were deposited by ALD to complete the dielectric stack.  
Figure 7: AFM morphology of Al\({}_{2}\)O\({}_{3}\) thin films grown by ALD at 150 \({}^{\circ}\)C (**a**) and 300 \({}^{\circ}\)C (**b**) on EG/SiC with an oxidized Al seed layer. Morphology of TiO\({}_{2}\) grown by ALD at 120 \({}^{\circ}\)C (**c**) and 250 \({}^{\circ}\)C (**d**) on EG/SiC with an oxidized Ti seed layer. Morphology of Ta\({}_{2}\)O\({}_{5}\) grown by ALD at 150 \({}^{\circ}\)C (**e**) and 300 \({}^{\circ}\)C (**f**) on EG/SiC with an oxidized Ta seed layer. (**g**) Raman spectra of as-grown EG and after ALD deposition of Al\({}_{2}\)O\({}_{3}\), TiO\({}_{2}\) and Ta\({}_{2}\)O\({}_{5}\) with different seed layers. Al\({}_{2}\)O\({}_{3}\) and TiO\({}_{2}\) deposition introduces only a small amount of disorder in EG, whereas Ta\({}_{2}\)O\({}_{5}\) deposition appears to significantly degrade the quality of the underlying EG. Images adapted with permission from Ref. [34], Copyright American Chemical Society 2010.  
Figure 8a shows Raman spectra acquired on as-grown EG samples, after EBPVD oxide deposition and after the complete oxide-seeded ALD process. Minimal changes in the D/G ratio were observed among the different samples, whereas the blue-shift of the G peak after seed-layer and ALD was ascribed to an increase of EG doping.  
Hall effect measurements under high vacuum at 300 K were also carried out on EG prior to and following the metal-oxide seeded ALD in order to evaluate the effect of the deposited dielectrics on carrier transport properties, i.e., the carrier density (n\({}_{\text{s}}\)) and Hall mobility (\(\upmu_{\text{Hall}}\)) [35].  
Figure 8b shows the correlation between \(\upmu_{\text{Hall}}\) and n\({}_{\text{s}}\) measured on as-grown EG, after EBPVD of oxides and the complete oxide-seeded ALD (O-ALD). As-grown EG samples presented \(\upmu_{\text{Hall}}\) values of 700-1100 cm\({}^{2}\)V\({}^{-1}\)s\({}^{-1}\) and n\({}_{\text{s}}\) values of (5-8) \(\times\) 10\({}^{12}\) cm\({}^{-2}\) (n-type), typical of Si-face EG. Figure 8 demonstrates that the high-k seeded dielectrics deposited by PVD and O-ALD resulted in an increase in n\({}_{\text{s}}\) and an increase in \(\upmu_{\text{Hall}}\). Conversely, HfO\({}_{2}\) seeded by a low-k insulator (SiO\({}_{2}\)) resulted in a decrease of \(\upmu_{\text{Hall}}\) and the increase in n\({}_{\text{s}}\). The measured increase of \(\upmu_{\text{Hall}}\) with deposition of high-k seed was attributed to dielectric screening, i.e., a reduction in scattering by remote charged impurities [54]. In particular, HfO\({}_{2}\) seeded O-ALD dielectrics enhance carrier mobility by an estimated 57%-73%, while Al\({}_{2}\)O\({}_{3}\) seeded O-ALD dielectrics increase mobility by 43%-52%.