A cold-wall rapid thermal processor is used for the wet oxidation of the commensurately grown GexSi1−x layers on Si substrates. The rate of oxidation of the GexSi1−x layer is found to be significantly higher than that of pure Si, and the oxidation rate increases with the increase in the Ge content in GexSi1−x layer. The oxidation rate of GexSi1−x appears to decrease with increasing oxidation time for the time-temperature cycles considered here. Employing high-frequency and quasi-static capacitance-voltage measurements, it is found that a fixed negative oxide charge density in the range of 1011– 1012/cm2 and the interface trap level density (in the mid-gap region) of about 1012/cm2 eV are present. Further, the density of this fixed interface charge at the SiO2/GeSi interface is found to increase with the Ge concentration in the commensurately grown GeSi layers.
The experimental results of the rapid thermal oxidation in the initial oxidation regime of molecular beam epitaxy grown GeSi strained layers are reported. It is shown that the dry oxidation rate of GeSi is the same as that of Si at different temperatures. After a very short initial time (∼10 s), the oxide thickness appears to be a linear function of time, which suggests that the kinetics of oxide growth during dry oxidation is limited by surface reaction controlled mechanisms. Further, the oxidation rate in the thin oxide regime is not affected by the Ge content up to 20% in the GeSi strained layer for dry oxidation. Using secondary-ion mass spectrometry, it is found that Ge is completely rejected out of the SiO2 layer which is formed during oxidation, and a Ge-rich layer is formed at the SiO2/GeSi interface. A significant amount of Ge is found to diffuse into the underlying GeSi layer during the growth of thin oxide films.
The experimental results of a molecular-beam epitaxy grown Si/GeSi p-n heterojunction are reported. It is found that the current flow in these p-n heterojunctions shows a nonideality factor of about 1.5 at room temperature and 2.35 at liquid nitrogen temperature. The nonideal behavior of the Si/GeSi p-n heterojunction is attributed to the charges that are trapped at the heterointerface. Annealing the samples at temperatures higher than the growth temperature results in an increase in the density of defects as well as an increase in the nonideal current. C-V measurements were employed to further investigate the behavior of the charges that are trapped in the interface. From C-V measurements under reverse bias it is found that increasing the annealing time and temperature increases the density of interface traps. In addition, a charge density of about 1012 cm−2 is found to be present at the Si/GeSi interface for the as-grown sample and increases with increasing annealing time and temperature.
A cold-wall rapid thermal processor is used for the oxidation of commensurately grown GexSi1−x layers on Si substrates. It is shown for dry oxidation that the oxidation rate of GeSi is the same as that of Si. The dry oxidationrate of GeSi is independent of Ge concentration (up to 20 % considered in this study) in the GeSi layer. For wet oxidation, however, the rate of oxidation of the GexSi1−x layer is found to be significantly higher than that of pure Si, and the oxidation rate increases with the Ge concentration in GexSi1−x layer. Employing highfrequency and quasistatic Capacitance-Voltage measurements, it is found for a thin oxide that a fixed negative oxide charge density in the range of 1011 – 1012/cm2, and the interface trap level density (in the mid-gap region) of about 1012 /cm2.eV are present. Further, the density of this fixed oxide charge at the SiO2 /GeSi interface is found.to increase with the Ge concentration in the commensurately grown GeSi layers.
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