Reactive Epitaxial Formation of a Mg-P-Zn Ternary Semiconductor in Mg/Zn3P2 Solar Cells

Ryoji Katsube; Kenji Kazumi; Tomo Tadokoro; Yoshirato Nose

doi:10.1021/acsami.8b11423

Reactive Epitaxial Formation of a Mg-P-Zn Ternary Semiconductor in Mg/Zn₃P₂ Solar Cells

ACS Appl Mater Interfaces. 2018 Oct 24;10(42):36102-36107. doi: 10.1021/acsami.8b11423. Epub 2018 Oct 12.

Authors

Ryoji Katsube¹, Kenji Kazumi¹, Tomo Tadokoro¹, Yoshirato Nose¹

Affiliation

¹ Department of Materials Science and Engineering , Kyoto University , Yoshida-Honmachi , Sakyo-ku, Kyoto 606-8501 , Japan.

PMID: 30260628
DOI: 10.1021/acsami.8b11423

Abstract

Zinc phosphide (Zn₃P₂) has attracted considerable attention as an environmentally benign and earth-abundant photoabsorber for thin-film photovoltaics. It is known that interdiffusion occurs at the Mg/Zn₃P₂ interface, which is a component of the record device, but the micro- and nanoscopic structures of the interface after interdiffusion have been controversial for over three decades. Here, we report on the formation of a Mg-P-Zn ternary semiconductor, Mg(Mg _xZn_{1- x})₂P₂, at the Mg/Zn₃P₂ interface. Interestingly, Mg(Mg _xZn_{1- x})₂P₂ is epitaxially grown on Zn₃P₂ with the orientation relationship of [21̅1̅0](0001)_{Mg(Mg _xZn_{1- x})}||[100](011)_Zn₃P₂ due to interdiffusion. The lattice mismatch of the Mg(Mg _xZn_{1- x})₂P₂ layer on the Zn₃P₂ substrate is less than 0.5%, and this is favorable for carrier transport across the interface. Mg(Mg _xZn_{1- x})₂P₂ is the material suggested as "n-type Mg-doped Zn₃P₂" or "a Mg-P-Zn alloy" in the previous studies. Thus, only the optimization of Mg treatment as conducted in the previous studies is insufficient for the improvement of the cell performance. This work clarified that a suitable microstructure and band structure around Mg(Mg _xZn_{1- x})₂P₂/Zn₃P₂ heterointerface should be established.

Keywords: depletion region; epitaxial growth; interface reaction; magnesium zinc phosphide; photovoltaics; rectifying junction; zinc phosphide.