Assessing defect-assisted emissions in indirect bandgap BaSi2 by photoluminescence

Journal: Journal of Luminescence (click here for full paper)

Authors: Abdul Rahman Mohmad, Zhihao Xu, Yudai Yamashita, Takashi Suemasu

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Undoped BaSi2 epitaxial layer on Si(111) substrate grown at a Ba-to-Si deposition rate ratio (RBa/RSi) of 0.7,1.2 and 3.7 were studied by power dependent photoluminescence (PL). At 10 K, sample 0.7 and 1.2 showed weak PL spectra while sample 3.7 showed two distinct peaks at high energy side and a broad emission at low energy side. The PL spectra were then deconvoluted using two to four Gaussian curves. The results displayed a non-linear power law suggesting a transition between two limiting power law exponents. Then, power law exponents for cases with shallow and deep levels were calculated and compared to the experiment. It was found that for low RBa/RSi, transition between shallow donor and shallow acceptor dominated the luminescence (PL peak energy of 1.12 eV). Deep donor and deep acceptor started to appear with increasing RBa/RSi and lead to additional transitions with energies of 1.05, 0.976 and 0.878 eV. Analysis carried out suggested that the donor levels may correspond to Si vacancies while deep and shallow acceptors may correspond to Ba antisites and Si interstitials, respectively. We propose that BaSi2 should be grown at low RBa/RSi to avoid the formation of deep donor level and high density of Ba antisites.