Arsenic-rich melt effect on threshold voltage scattering for Si-implanted GaAs metal-semiconductor field-effect transistor

The microscopic electrical activation efficiency of implanted Si atoms in undoped, liquid-encapsulated Czochralski-grown GaAs substrates was investigated by means of the threshold voltage (V_th) of implanted metal-semiconductor field-effect transistors as a function of stoichiometry and impurities, especially of carbon as determined by Fourier transform infrared (FT-IR) spectroscopy (≤2.5×10¹⁶ cm ^-3). The V_th scattering, which is related to the electrical activation efficiency dispersion, was small for an As-rich substrate grown from an As-rich melt, whether or not there existed a horizontal 3400-Oe magnetic field. The smallest amplitude of the V_th scattering occurred for the As-rich melt and did not vary with magnetic field. The V _th scattering with magnetic field was independent of carbon concentration (≤2.5×10¹⁶ cm^{- 3}). However, without magnetic field, an effect clearly appeared at low carbon concentration (nearly nondetectable). It seems that the V _th scattering or the electrical activation efficiency dispersion is dominated by the dispersion of stoichiometry, that is, composition, of the GaAs substrate because the electrical activation efficiency depends on the ratio of the Ga vacancy concentration and As vacancy concentration and the magnitude of their concentrations at the annealing temperature for the Si-implanted GaAs substrate. Therefore small V_th scattering means that the dispersion of the composition (Ga and As) is small. The composition dispersion for the most As-rich melt is small because the solidification is controlled by the straight As-rich side solidus line of the Ga:As composition-temperature phase diagram, and thus temperature variations of the GaAs melt in the pyrolytic boron nitride crucible are not as important. Also, there was no correlation between V _th scattering and dislocation density.