a b s t r a c t a-Axis-oriented undoped n-BaSi 2 epitaxial films were grown on Si(111) substrates by molecular beam epitaxy, and the crystalline quality and grain boundaries were investigated by means of reflection highenergy electron diffraction, X-ray diffraction, and transmission electron microscopy (TEM). The grain size of the BaSi 2 films was estimated to be approximately 0.1-0.3 mm, and straight grain boundaries (GBs) were observed in the plan-view TEM images. Dark-field TEM images under a two-beam diffraction condition showed that these GBs consist mostly of BaSi 2 {011} planes. The diffusion length of minority carriers in nBaSi 2 was found to be approximately 10 mm by an electron-beam-induced current technique.

No abstract

We have grown 100-nm-thick BaSi2 films on transparent silicon-on-insulator (SOI) substrates using molecular beam epitaxy, for optical absorption measurements. The SOI substrate has a 0.7-µm-thick (111)-oriented Si layer on top of a fused silica substrate. Reflection high-energy electron diffraction and θ–2θ X-ray diffraction patterns showed that a-axis-oriented BaSi2 layers were grown epitaxially. The absorption spectrum of the film measured in a transmission configuration at room temperature revealed that BaSi2 has a large absorption coefficient of 3 ×104 cm-1 at 1.5 eV and an indirect optical absorption edge of 1.34 eV.

Excess-carrier recombination mechanisms in undoped BaSi 2 epitaxial films grown by molecular beam epitaxy on n-type silicon substrates have been studied by the microwave-detected photoconductivity decay measurement. The measured excess-carrier decay is multiexponential, and we divided it into three parts in terms of the decay rate. Measurement with various excitation laser intensities indicates that initial rapid decay is due to Auger recombination, while the second decay mode with approximately constant decay to Shockley-Read-Hall recombination. Slow decay of the third decay mode is attributed to the carrier trapping effect. To analyze Shockley-Read-Hall recombination, the formulae are developed to calculate the effective lifetime (time constant of decay) from average carrier concentration. The measurement on the films with the thickness of 50-600 nm shows that the decay due to Shockley-Read-Hall recombination is the slower in the thicker films, which is consistent with the formulae. By fitting the calculated effective lifetime to experimental ones, the recombination probability is extracted. The recombination probability is found to be positively correlated with the full width at half-maximum of the X-ray rocking curves, suggesting that dislocations are acting as recombination centers. V

a b s t r a c tAn attempt was made to grow BaSi 2 epitaxial films on Si(001) substrates using molecular beam epitaxy. The structure and morphology of the films were investigated using reflection high-energy electron diffraction, X-ray diffraction, electron backscatter diffraction, atomic force microscopy, and transmission electron microscopy. The BaSi 2 film grown was a-axis oriented, despite a large lattice mismatch. The measurements indicated that there are two possible epitaxial relationships of BaSi 2 (100)//Si (001) with BaSi 2 [010]//Si[110] and BaSi 2 [001]//Si[110], due to the fourfold symmetry of Si (001). X-ray reciprocal space mapping revealed that the BaSi 2 film was almost strain-free. Plan-view transmission electron microscopy clarified the grain size and the existence of grain boundaries in the BaSi 2 film.

No abstract

The carrier concentrations and mobilities of impurity (Sb, In, Ga, Al, Ag, and Cu)-doped BaSi 2 films grown by molecular beam epitaxy on highly resistive nor p-Si(111) substrates were measured at room temperature using the van der Pauw technique. Sb-, Ga-and Cu-doped BaSi 2 exhibited n-type conductivity, while In-Al-and Ag-doped BaSi 2 exhibited p-type conductivity. The temperature dependence of resistivity indicated that the carrier transport in Ga-, Al-, Ag-, and Cu-doped BaSi 2 is well explained by both Shklovskii-Efros-type and Mott-type variable range hopping conduction.

We have successfully grown 360-nm-thick undoped n-BaSi 2 epitaxial layers on the n + -BaSi 2 /p + -Si (111) tunnel junction, by molecular beam epitaxy. The external quantum efficiency reached approximately 17.8% at 500 nm under a reverse bias voltage of 4 V at room temperature, the highest value ever reported for semiconducting silicides. The quantum efficiency was compared to 240-nm-thick undoped n-BaSi 2 epitaxial layers on a p-Si(111) substrate.