| AVS 56th International Symposium & Exhibition | |
| Surface Science | Monday Sessions |
| Session SS1+EM-MoA |
| Session: | Semiconductor Surfaces and Interfaces I: Ge and III-V's |
| Presenter: | J.B. Clemens, University of California, San Diego |
| Authors: | J.B. Clemens, University of California, San Diego S.R. Bishop, University of California, San Diego A.C. Kummel, University of California, San Diego |
| Correspondent: | Click to Email |
The formation of a semi-ordered oxide passivation layer between hafnium oxide and In0.53Ga0.47As(001)-(4x2)/c(8x2) and InAs(001)-(4x2)/c(8x2) was studied using scanning tunneling microscopy/spectroscopy (STM/STS), and density functional theory (DFT) calculations. A passivation layer is needed to protect the surface from disruption during bulk amorphous oxide deposition for a high-κ gate insulator. Two methods of forming low coverage of HfO2 were investigated: reactive oxidation of the e-beam deposited Hf metal and e-beam deposition from an HfO2 target. STM results show that Hf atoms must cluster to be reactive to O2. DFT suggests there is a high tendency for Hf to displace substrate atoms, which is undesirable. Direct deposition of the oxide is a better method. At submonolayer coverage, STM has identified individual bonding sites for the HfO2 molecule; the HfO2 forms small structures of mostly monolayer height with a high nucleation density. Density functional theory (DFT) calculations have been employed to assign the bonding structure. The DFT simulations show that for HfO2/InAs(001)-(4x2), the most likely sites are stable by about -4.5 eV and the calculated density of states (DOS) shows no evidence of Fermi level pinning (no mid-gap states). At submonolayer coverage, the HfO2 molecule bonds via group III-oxygen bonds and group V-hafnium bonds. STS measurements of clean InGaAs(001)-(4x2) reveal that the surface has significant band bending, showing p-type character for both n-type and p-type samples. Deposition of > 1 ML of HfO2 is enough to move the Fermi level towards the conduction band for n-type InGaAs(001)-(4x2), as shown in results of STS vs. HfO2 coverage. For p-type material, the Fermi level remains near the valence band after deposition of HfO2. These results are consistent with the Fermi level remaining unpinned. In addition, annealing effects are studied. At temperatures of 300 °C and above, ordered oxide structures are seen in STM which form rows in the [-110] direction. However, lower annealing temperatures of 200 °C and below are preferable for good STS results. Hafnium oxide, evaporated via electron beam deposition, likely creates some O2 and HfO, which may react in an undesirable way with the semiconductor surface. For this reason, a method is also proposed to protect the surface during e-beam deposition via a CO2 protecting layer at low temperature (90 K), which does not appear to perturb the surface.