Defect Formation and Strain Relaxation in graded GaPAs/GaAs, GaNAs/GaAs and GaInNAs/Ge Buffer Systems for high-efficiency Solar Cells

18th Microscopy of Semiconducting Materials Conference

物理学;材料科学

Schöne, J.^1,2 ; Spiecker, E.^1 ; Dimroth, F.^2 ; Bett, A.W.^2 ; Jäger, W.^1

Institute for Materials Science, Christian-Albrechts-University, Kaiserstrasse 2, 24143 Kiel, Germany^1

Fraunhofer Institute for Solar Energy Systems ISE, Heidenhofstrasse 2, 79110 Freiburg, Germany^2

关键词: Alloy compositions;    Characteristic difference;    Compound semiconductors;    Compressive strain;    Defect distribution;    High resolution X ray diffraction;    High-efficiency solar cells;    Metal-organic vapour phase epitaxy;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/471/1/012008/pdf
DOI  :  10.1088/1742-6596/471/1/012008

学科分类：材料科学（综合）

来源: IOP

【 摘 要 】

Transmission electron microscopy of cross-section specimens and high-resolution X-ray diffraction analyses have been applied to investigate the formation of defects and the relaxation of layer strain in step-graded GaPxAs1-xand GaNyAs1-ybuffer layer systems grown by metal-organic vapour phase epitaxy on GaAs (001) substrates with 6° miscut towards (111)A. The investigations have been complemented by characterization of the layer surfaces employing optical microscopy. The comparison of the different buffer concepts reveals characteristic differences in the formation of defects and in the relaxation of tensile layer strain. For GaPAs layers dislocations and microtwins form, releasing the major part of the tensile misfit strain. In contrast, for GaNAs dislocations and microtwins are largely absent, at least in the upper part of the buffer structure, and microcracks are generated. Consequently, during subsequent growth of layers with tensile strain, strain relaxation and defect formation can be effectively hindered by introducing intermediate GaNyAs1-ylayers with concentrations y > 2 % into a GaAs1-xPxbuffer structure [1]. A similar concept can be used for layer systems with compressive strain, however, modified by using layers of differing alloy composition. The use of dilute nitride layers appears to offer a new concept for engineering defect distributions and layer strain in lattice-mismatched compound semiconductor layer structures. Such concepts are of particular interest not only but especially also for applications in high-efficiency III-V solar cells.