Non-alloyed ohmic contacts to n-GaAs using compositionally graded In x Ga1-x As layers grown by molecular beam epitaxy are studied. The carrier concentration reduction in the GaAs buffer layer due to low growth temperature is found to increase overall contact resistance for an n+-InAs/In x Ga1-x As(x=1→0)/GaAs structure. The lowest specific contact resistance (ρ c ) ever reported, 5×10-9 Ω · cm2, is obtained with a 2×1019 cm-3 Si-doped structure grown at 450°C. A similar ρ c value is also obtained when the InAs mole fraction is higher than 0.7. Using WSi as a contact metal, a refractory ohmic contact is realized in which ρ c remains less than 2×10-7 Ω · cm2 under annealing up to 800°C.

No abstract

Oxide defects originating from Czochralski silicon substrates are characterized. It is shown that oxide defect density is significantly large for the oxide thickness range of 20–200 nm. This noteworthy feature is valid for dry oxidation and HCl oxidation alike. It is considered that small defects in the silicon substrate surface layer are introduced into the growing oxides during thermal oxidation and that the small defects in oxides provide conductive paths across the oxides. The origin of the small defects is not known at present. A simple model is proposed in an effort to show the relation between the size and density of the small defects. The oxide thickness dependence data of oxide defect density are characterized in terms of the small-defect behaviors. The relationship between the small-defect size L and the density ρ in the Cz-Si substrates is shown as ρ=ρ0 exp(−L/L0), where ρ0=107 cm−3 and L0=48 nm. In addition, oxide surface etching of thick oxides followed by oxide defect evaluation of the thinned oxides reveals that even thick oxides with seemingly low oxide density contain many small defects. The small defect density in 130 nm oxides is estimated as 120 cm−2.

No abstract

No abstract