Tianguo Deng

Impact of Ba to Si deposition rate ratios during molecular beam epitaxy on carrier concentration and spectral response of BaSi2 epitaxial films

Undoped 0.5-μm-thick BaSi2 epitaxial films were grown on Si(111) substrates with various ratios of the Ba deposition rate to the Si deposition rate (RBa/RSi) ranging from 1.0 to 5.1, and their electrical and optical properties were characterized. The photoresponse spectra drastically changed as a function of RBa/RSi, and the quantum efficiency reached a maximum at RBa/RSi = 2.2. Hall measurements and capacitance versus voltage measurements revealed that the electron concentration drastically decreased as RBa/RSi approached 2.2, and the BaSi2 films with RBa/RSi= 2.0, 2.2, and 2.6 exhibited p-type conductivity. The lowest hole concentration of approximately 1 × 1015 cm−3 was obtained for the BaSi2 grown with RBa/RSi = 2.2, which is the lowest value ever reported. First-principles calculations suggest that Si vacancies give rise to localized states within the bandgap of BaSi2 and therefore degrade the minority-carrier properties.

Improving the photoresponse spectra of BaSi2 layers by capping with hydrogenated amorphous Si layers prepared by radio-frequency hydrogen plasma

We studied the surface passivation effect of hydrogenated amorphous silicon (a-Si:H) layers on BaSi2 films. a-Si:H was formed by an electron-beam evaporation of Si, and a supply of atomic hydrogen using radio-frequency plasma. Surface passivation effect was first investigated on a conventional n-Si(111) substrate by capping with 20 nm-thick a-Si:H layers, and next on a 0.5 μm-thick BaSi2 film on Si(111) by molecular beam epitaxy. The internal quantum efficiency distinctly increased by 4 times in a wide wavelength range for sample capped in situ with a 3 nm-thick a-Si:H layer compared to those capped with a pure a-Si layer.We studied the surface passivation effect of hydrogenated amorphous silicon (a-Si:H) layers on BaSi2 films. a-Si:H was formed by an electron-beam evaporation of Si, and a supply of atomic hydrogen using radio-frequency plasma. Surface passivation effect was first investigated on a conventional n-Si(111) substrate by capping with 20 nm-thick a-Si:H layers, and next on a 0.5 μm-thick BaSi2 film on Si(111) by molecular beam epitaxy. The internal quantum efficiency distinctly increased by 4 times in a wide wavelength range for sample capped in situ with a 3 nm-thick a-Si:H layer compared to those capped with a pure a-Si layer.