Comparative Study of Trap Response Inside Conduction Band of GaAs Passivated with High Dielectric Constant Oxides of Y2O3 and HfO2
H. W. Wan1*, T. W. Chang1, K. Y. Lin1, L. B. Young1, J. Kwo2, M. Hong1
1Graduate Institute of Applied Physics and Department of Physics, National Taiwan University, Taipei City, Taiwan
2Department of Physics, National Tsing Hua University, Hsinchu City, Taiwan
* Presenter:H. W. Wan
GaAs is one of the leading candidates to replace Si as the n-channel material for future complementary metal-oxide-semiconductor (CMOS) technology. Therefore, characterization of high-κ/GaAs interface is an urgent issue. Commonly used characterization tools of Terman, conductance, and high-low method can only probe the traps inside GaAs bandgap. With a low conduction band density of states, the traps inside the conduction band may drastically reduce the GaAs based n-MOSFET performance. In this work, we have studied fortunately, frequency dispersions in high-κ/GaAs capacitance-voltage (C-V) measurements at accumulation to characterize and minimize the trap response inside the conduction band of GaAs.
The hetero-structures of high-κ/n-GaAs(001) were grown in our multi-chamber UHV system. Both samples were in-situ capped with ALD-Al₂O₃ 5nm thick to prevent high-κ from moisture absorption. After deposition, Y₂O₃/GaAs and HfO₂/GaAs samples were rapid thermal annealed (RTA) to 900°C. We then fabricated MOS capacitors (MOSCAPs) with e-beam evaporated Ni as gate electrodes and a back ohmic contact of Ti/Au for C-V measurement and border trap analysis.
Figure 1 (a) and (b) show C-Vs of Y₂O₃ and HfO₂ on n-GaAs, respectively, show very small frequency dispersions of 11.97% and 10.38% at accumulation from 500 Hz to 500 kHz were measured for the Y₂O₃/ n-GaAs and HfO₂/n-GaAs, respectively. The small frequency dispersion at depletion region, particularly in the HfO₂/GaAs samples, indicates a smaller Dit. The C-log(F) diagram of both HfO₂ and Y₂O₃ on n-GaAs at accumulation region shows a linear relation, indicating a border-trap dominated condition. A smaller conduction band offset between HfO₂/GaAs (1.51 eV) than Y₂O₃/GaAs (2.2 eV) and a smaller electrons effective mass of HfO₂ (0.11m₀) than Y₂O₃ (0.25m₀) make the electrons easier to tunnel into the traps inside HfO₂. Nevertheless, the superior HfO₂ quality resulted in a smaller frequency dispersion (10.38%) than Y₂O₃ (11.97%), indicating that the excellent quality of HfO₂ has minimized the border trap density.
In this work, using frequency dispersion analysis, the traps response inside the GaAs conduction band has been elucidated. A very small amount of interfacial trap was found inside the conduction band, while a boost of border traps density is observed for both systems. The attainment of low interfacial and border traps density for HfO₂/GaAs is promising for post-Si CMOS technology.

Keywords: border traps, GaAs, high-κ, Y₂O₃ , HfO₂