Investigation of defect levels in BaSi₂ epitaxial films by photoluminescence and the effect of atomic hydrogen passivation

Abstract

Photoluminescence (PL) measurements were carried out on 0.5-μm thick BaSi 2 epitaxial films grown on Si(111) substrates with various Ba-to-Si deposition rate ratios (R Ba /R Si ) in the range of 1.7-5.1. The samples were excited from both the frontside (BaSi 2 ) and the backside (Si substrate), at temperatures in the range of 8-50 K. These measurements have highlighted the existence of localized states within the bandgap that result from defects in the BaSi 2 films. The PL intensity is highly dependent on the excitation power, temperature, and R Ba /R Si . Of those studied, the BaSi 2 film at R Ba /R Si =4.0 showed the most intense PL and weak photoresponsivity, whereas the PL intensity was weaker for the other samples. Therefore, we chose this sample for a detailed PL investigation. Based on the results we determined the energy separation between localized states, corresponding to PL peak energies. The difference in PL spectra excited from the BaSi 2 -side and Si-side is attributed to the difference in kinds of defects emitting PL. The photoresponsivity of the BaSi 2 was drastically enhanced by atomic hydrogen passivation, and the PL intensity of the sample decreased accordingly.

Effects of boron and hydrogen doping on the enhancement of photoresponsivity and photoluminescence of BaSi2 epitaxial films

“…Figure 2(a) shows the PL spectrum when the excitation power was P = 240 mW/cm 2 , measured at 9 K. As previously reported in Ref. 21, the BaSi2 film in sample A is defective because its RBa/RSi (4.0) was far away from 2.2. We reproduced well the PL spectrum (black line) by four Gaussian curves (dash-dot lines) as denoted by peaks 1-4 at 0.86, 0.98, 1.04, and 1.12 eV, respectively.…”

“…Undoped-BaSi2 contains point defects which induce localized states within the bandgap. The presence of defects in BaSi2 films and polycrystalline BaSi2 bulks has been examined by photoluminescence (PL), 21,22 deep-level transient spectroscopy, 23,24 and electron paramagnetic resonance. 25 Carrier type, carrier concentration, and photoresponsivity of BaSi2 films are so sensitive to a Ba-to-Si deposition rate ratio (RBa/RSi) during molecular beam epitaxy (MBE) of BaSi2 films.…”

“…The measured PL spectrum (black line) is reproduced well by four Gaussian curves (dash-dot lines) peaking at Peaks 1-4. (b) Excitation power dependence of PLintensity for each peak at 9 K 21.…”

Recent Progress Toward Realization of High‐Efficiency BaSi2 Solar Cells: Thin‐Film Deposition Techniques and Passivation of Defects

“…analyzing the data from photoluminescence, [53,83,84] deep-level transient spectroscopy (DLTS), [85] positron annihilation spectroscopy, [86] and electron paramagnetic resonance [87] measurements. As a result, a scheme of the defect-level positions has been proposed on the basis of radiative defects (Figure 9).…”

Correlation of native defects between epitaxial films and polycrystalline BaSi2 bulks based on photoluminescence spectra

“…Photoluminescence (PL) offers a nondestructive and sensitive tool for defect studies in solar cell materials such as Si. [18][19][20] However, PL reports dealing with single crystalline BaSi2 21 and epitaxial layers 15,22 have been quite limited. In our previous research, 15 PL intensities decreased when the RBa/RSi approached the stoichiometry.…”