2016年第63回応用物理学会春季学術講演会

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一般セッション(口頭講演)

1 応用物理学一般 » 1.4 エネルギー変換・貯蔵・資源・環境

[21a-S322-1~13] 1.4 エネルギー変換・貯蔵・資源・環境

2016年3月21日(月) 09:00 〜 12:30 S322 (南3号館)

佐藤 正志(東海大)、原 一広(九大)

09:45 〜 10:00

[21a-S322-4] Excellent Surface Passivation of Crystalline Silicon by Atomic Layer Deposition AlxMg1-xOy Thin Films

LEE HYUNJU1、Kamioka Takefumi1、Zhang Dongyan1、Iwata Naotaka1、Ohshita Yoshio1 (1.Toyota Technol. Inst.)

キーワード:Silicon solar cell,Surface passivation,aluminum magnesium oxide

In the field of crystalline silicon (c-Si) photovoltaics, trends toward lighter dopant diffusions, thinner substrates, and higher lifetime substrates have placed an increased importance on surface passivation. Recently, AlOx has been intensively studied and enhanced solar cell efficiencies largely by providing excellent passivation on highly and lowly doped p-type silicon surfaces. Meanwhile, to achieve high conversion efficiencies, advanced silicon solar cell architectures such as interdigitated back contact solar cells demand that both the n+ and p+ doped Si surfaces are passivated simultaneously by a single passivation scheme. However, on heavily doped n+ Si surfaces, the AlOx passivation is compromised because the minority carrier (i.e., hole) concentration at the surface is increased by the significant negative fixed charges of the AlOx passivation. Therefore, the absence of significant negative fixed charges and high chemical passivation are expected to be beneficial for the passivation of n+ surfaces. In this study, we focused on a ternary oxide, AlxMg1-xOy (AMO) to make a solution for the passivation of both the n+ and p+ doped Si surfaces because MgOx has not only excellent properties such as high permittivity (κ~9.8), large band gap (7.3 ~7.9 eV), and higher breakdown field (12 MV/cm) but also positive fixed charges on Si surfaces. In addition, magnesium aluminate fabricated by atomic layer deposition is hydrogen-rich and amorphous below 800 ºC. Hence, based on these facts, we have developed ternary AlxMg1-xOy as a new class of passivation materials. From the experiment, we found that a level of surface passivation and interface properties of ternary AlxMg1-xOy thin films can be controlled by varying the Al and Mg precursor cycle ratio during plasma-enhanced atomic layer deposition processes. In addition, we also found that AlxMg1-xOy thin films are superior to pure AlOx thin films for the passivation of c-Si under a given experimental condition. In particular, we can obtain very low Smax of ~5.5 cm/s using AlxMg1-xOy thin films on a p-type Czochralski (Cz) (100) Si wafer after post deposition annealing at 500 ºC in N2. Therefore, we can conclude that ALD with a super-cycle consisted of a number of sub-cycles of AlOx (nAl) and a cycle of MgOx can be applied for effective engineering of physical properties of the ternary AlxMg1-xOy thin films and provide excellent surface passivation on p-type c-Si. During our presentation, we will demonstrate detailed study on the ternary AlxMg1-xOy passivation and discuss its passivation mechanism for c-Si.