[7a-C13-1~12] 13.2 Exploratory Materials, Physical Properties, Devices

▲ [7a-C13-11] Photoresponse properties of low B-doped p-BaSi₂ on
P⁺ ion-implanted Si (111)

〇Emha Bayu Miftahullatif¹, Takabe Ryota¹, Yachi Suguru¹, Toko Kaoru¹, Suemasu Takashi¹ (1.Univ. of Tsukuba)

Keywords:semiconductor, silicide, solar cell

Semiconducting BaSi₂ has an indirect band gap of approximately 1.3 eV, matching the solar spectrum, and has large absorption coefficients, reaching 3.0´10⁴ cm^-1 at 1.5 eV [1,2]. We have successfully fabricated n-Si/B-doped p-BaSi₂ heterojunction solar cells that achieved a conversion efficiency of 9.9% [3]. In the work mentioned, we used an n-Si(111) substrate with n~10¹⁵ cm^-3, and a 20-nm-thick B-doped p-BaSi₂ layer with hole concentration p = 2.2 × 10¹⁸ cm^-3 [3]. In order to utilize B-doped p-BaSi₂ as an active layer, we need to employ n-Si with higher electron concentration n and low p p-BaSi₂, so that the depletion region stretches toward the p-BaSi₂ layer. However, the rectifying current density versus voltage (J-V) characteristics degraded as we utilized heavily-doped n-Si substrate due to the defects around steps with 3-4 MLs (~1 nm) in height. They were formed during thermal cleaning due to step bunching, confirmed by TEM (Fig. 1). High impurity concentration near the surface is suspected to be one of the origins of this step bunching. In order to reduce this step bunching by maintaining low impurities at the surface, we implant P⁺ ions into the Si substrate to the depth of 50 nm to form heavily-doped n⁺-Si embedding layer. We then formed a low B doped p-BaSi₂ layer and measured the external quantum efficiency (EQE) as well as the J-V characteristics.