Comparative study on in situ surface cleaning effect of intrinsic oxide-covering GaAs surface using TMA precursor and Al2O3 buffer layer for HfGdO gate dielectrics

Abstract

In this work, comparative study on the cleaning effect of the intrinsic oxide covering GaAs surface using TMA precursor and Al₂O₃ buffer layer were performed. GaAs substrates were either exposed to the TMA precursor or Al₂O₃ buffer layer was deposited on them under the same cycle prior to the deposition of HfGdO films. The combined results of X-ray photoemission spectroscopy (XPS) analysis and electrical evaluation indicates that the trimethylaluminum (TMA) precursor can effectively remove surface oxides on the GaAs substrate and inhibit oxygen diffusion in a manner similar to the Al₂O₃ buffer layer, thus avoiding the generation of the low-k Al₂O₃ interface layer. Moreover, the reduction in valence band offset and the increase in conduction band offset were obtained through passivated atomic-layer-deposition (ALD) of the TMA precursor. The MOS capacitor with GaAs passivated by 20 cycles TMA ALD showed almost no hysteresis, minimum interface state density (∼1.5 × 10¹² cm⁻² eV⁻¹), greatest band offset (∼2.86 eV), and smaller oxide charge density (∼−2.76 × 10¹³ cm⁻²), which led to the maximum dielectric constant (∼35.9) and the lowest leakage current density (∼1.4 × 10⁻⁵ A cm⁻²). Furthermore, the leakage current density–voltage (J–V) characteristic curves at low temperature determined that the device showed stable and reliable electrical properties.