Simple way of finding Ba to Si deposition rate ratios for high photoresponsivity in BaSi₂ films by Raman spectroscopy

Abstract

Since the photoresponsivity of BaSi2 is sensitive to a Ba-to-Si deposition rate ratio (RBa/RSi), there is a need to determine the optimum value of RBa/RSi. We grew 0.5 μm-thick BaSi2 films with RBa/RSi varied from 1.1−3.6 at 580 °C and 0.4−4.7 and 650 °C. The photoresponsivity reached a maximum at RBa/RSi = 2.2 and 1.2, respectively. Raman spectroscopy revealed that the crystalline quality of BaSi2 became better with decreasing RBa/RSi. However, as RBa/RSi decreased further beyond these values, excess Si precipitated, showing that the optimum value of RBa/RSi should be as small as possible without causing Si precipitates to form.

Three-step growth of highly photoresponsive BaSi2 light absorbing layers with uniform Ba to Si atomic ratios

“…30 The photoresponsivity of BaSi 2 films grown under Si-rich conditions increased with a decrease in R Ba /R Si and reached a maximum at R Ba /R Si = 1.2 when grown at 650°C. 25 This value is approximately three times higher than that previously reported for samples grown at 580°C. In contrast to our prediction, however, the crystalline quality of grown layers degraded.…”

“…44 shows the highest photoresponsivity ever achieved for undoped BaSi 2 films grown by the two-step growth method. 25 Smaller FWHM values in Fig. 5(a) mean higher a-axis orientation of BaSi 2 films.…”

“…We chose sample C among samples A-G because it showed the highest photoresponsivity ever achieved for BaSi 2 films grown by the two-step growth method. 25 Diffraction spots due to c-Si, marked by yellow circles, make a line as shown in Fig. 1(h), which is not parallel to a white broken line joining diffraction spots of BaSi 2 .…”

“…In our previous work, defect characterizations of BaSi 2 films were conducted using deep level transient spectroscopy (DLTS), 23,24 positron annihilation spectroscopy, 25 Raman spectroscopy, 26 and electron paramagnetic resonance, 27 wherein we detected vacancy-type defects, which we regard as Si vacancies (V Si ). First-principles calculations also show that V Si are likely to occur in BaSi 2 14 and that these vacancies give rise to localized states within the bandgap.…”

Operation of BaSi2 homojunction solar cells on p+-Si(111) substrates and the effect of structure parameters on their performance

“…22 In sample D, the n + -BaSi2 layer was set at 150 nm so that photons with long wavelengths around 800 nm would be fully absorbed in the p-BaSi2 light absorber layer. In samples E and F, we employed undoped p-BaSi2 layers with p~10 16 cm -3 instead of B-doped p-BaSi2 layers, 29 The value of α at a wavelength of 800 nm is around 3 × 10 4 cm -1 , meaning that the penetration depth at this wavelength is estimated to be 2/α = 0.66 μm. Therefore, photons with this wavelength are fully absorbed in the 500 nm-thick p-BaSi2 absorber layer.…”