The chemical etchant composed of hydrofluoric acid, hydrogen peroxide, and acetic acid (HF:H202:CH3COOH) is studied as a selective etchant of SiGe over St. It is found that the solution has a very high selectivity of etching SiGe over St. Etch rates for various GexSil x samples with differing mole fractions of Ge (0.15 -< x -< 0.40) are discussed as well as the stopping behavior of the solution on St. Also discussed is the application of the solution to heterostructure devices, particularly the three terminal resonant tunneling transistor.
Resonant tunneling of holes through an unstrained GeSi well between two strained Si barriers on a relaxed GeSi buffer layer has been observed for the first time. The peak-to-valley ratios of 2.1/1 at 4.2 K and 1.6/1 at 77 K in current-voltage characteristics were attained for light holes. Resonant tunneling from heavy-hole states was also observed at room temperature, as well as 77 and 4.2 K by conductance measurement. The positions of the resonance peaks are in good agreement with the light- and heavy-hole bound states in the quantum well.
B2O3 decomposition by reaction with Si has been studied in situ by Auger electron spectroscopy in a Si molecular beam epitaxy environment as a function of the silicon flux (0<JSi<14.5 Å/min) and the growth temperature (25 °C<Ts<800 °C). Quantitative analysis of Auger signals indicates that oxygen is associated with both SiO2 and B2O3. Below a critical substrate temperature (Ts<500 °C), no reaction occurs between B2O3 and Si. When the substrate temperature is higher than 500 °C, the atomic fraction of Si and B increases while that for SiO2 and B2O3 decreases. The chemical reaction which causes the signal changes is thermally activated, as shown by the dependence of the oxygen on boron concentration ratio, I[O/B], which drops rapidly according to an Arrhenius relation with an activation energy Ea=4.5±1.0 eV. From the experimental results, we propose a model which involves B2O3 reduction by Si to form the (Si-B) and SiO2 phases. SiO2 is then decomposed by Si bombardment on the surface to produce SiO which subsequently desorbs.
The hole transport through the minibands of a GexSi1−x/Si superlattice is observed for the first time. The symmetrically strained, short-period GexSi1−x/Si supperlattice is grown on a Gex/2Si1−x/2 /Si buffer layer. The current-voltage and conductance-voltage characteristics show two peaks which are attributed to the conduction of light holes through the first and second light hole minibands. The light hole miniband energies are estimated by thermionic emission analysis and are in good agreement with the calculated values using effective mass approximation.
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