| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2014) | |
| Thin Films | Wednesday Sessions |
| Session TF-WeM |
| Session: | Thin Film Synthesis and Characterization II |
| Presenter: | Motoki Takahara, Kyushu University, Japan |
| Authors: | T. Yoshitake, Kyushu University, Japan M. Shaban, Aswan University, Egypt N. Promros, King Mongkut’s Institute of Technology Ladkrabang, Thailand M. Takahara, Kyushu University, Japan T.M. Miostafa, Kyushu University, Japan R. Baba, Kysushu University, Japan |
| Correspondent: | Click to Email |
Semiconducting iron disilicide (β-FeSi2) is a new candidate applicable to near-infrared photoelectronic devices [1-3], because it possesses features such as a direct optical band gap of 0.85 eV above an indirect gap (0.76 eV) and a large absorption coefficient, which is 105 cm-1 at 1.0 eV[4]. Since β-FeSi2 can be epitaxially grown on Si, a heterojunction diode comprising a β-FeSi2 film and singlecrystalline Si substrate is a device that can be briefly formed by employing vapor deposition. For near-infrared light detection in the Si/b-FeSi2 heterojunction diodes, near-infrared light transmitted through the front-side Si substrate can be absorbed in the depletion region of the back-side β-FeSi2 film.
In our previous works, we have progresses researches on p-type Si/n-type β-FeSi2 heterojunction diodes, totally from the epitaxially growth of β-FeSi2 film on Si(111) by sputtering [5] to the evaluation of p-type Si/n-type β-FeSi2 heterojunctions as photodetectors [6,7]. It was confirmed that β-FeSi2 in the heterojunction evidently contributes to the photodetection of near-infrared light from the photoresponse spectrum. In addition, the heterojunction clearly exhibited current due to photogenerated carriers for 1.33 μm light in the I-V curves in comparison with that in the dark. The detectivity at temperatures lower than 100 K reach approximately 2 × 1011 cmHz1/2/W, which is comparable with that of existing near infrared photodiodes comprising PbS and InAs at the same temperature. However, the external quantum efficiency is less than 10 % [6,7].
In this presentation, the progress thus far of our research and recent problems that we are facing and should be solved for the next step will be introduced. A serious problem for the heterojunctions is that a barrier due to a band offset appears in the valence band and it prevents from the flow of photogenerated carriers from the n-type β-FeSi2 layer to the p-type Si layer. The opposite combination, namely n-type Si/p-type b-FeSi2, is structurally ideal because of it has no barriers due to the band offset. In order to form p-type β-FeSi2, the residual carrier density should be reduced for controlling the conduction type. Carbon doping, which might be effective for a reduction in the carrier density, will be introduced.
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