Sub-10 μm-Thick Ge Thin Film Fabrication from Bulk-Ge Substrates via a Wet Etching Method

Liming Wang; Ying Zhu; Rui-Tao Wen; Guangrui Xia

doi:10.1021/acsomega.3c07490

Sub-10 μm-Thick Ge Thin Film Fabrication from Bulk-Ge Substrates via a Wet Etching Method

ACS Omega. 2023 Dec 12;8(51):49201-49210. doi: 10.1021/acsomega.3c07490. eCollection 2023 Dec 26.

Authors

Liming Wang¹, Ying Zhu^{1

2}, Rui-Tao Wen², Guangrui Xia¹

Affiliations

¹ Department of Materials Engineering, The University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
² Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, China.

Abstract

Low-defect density Ge thin films are crucial for studying the impact of defect density on the performance limits of Ge-based optical devices (optical detectors, LEDs, and lasers). Ge thinning is also important for Ge-based multijunction solar cells. In this work, Ge wet etching using three acidic H₂O₂ solutions (HF, HCl, and H₂SO₄) was studied in terms of etching rate, surface morphology, and surface roughness. HCl-H₂O₂-H₂O (1:1:5) was demonstrated to wet-etch 535 μm-thick bulk-Ge substrates to 4.1 μm with a corresponding RMS surface roughness of 10 nm, which was the thinnest Ge film from bulk-Ge via a wet etching method to the best of our knowledge. The good quality of pre-etched bulk-Ge was preserved, and the low threading dislocation density of 6000-7000 cm^-2 was maintained after the etching process. This approach provides an inexpensive and convenient way for accurate Ge substrate thinning in applications such as multijunction solar cells and sub-10 μm-thick Ge thin film preparation, which enables future studies of low-defect density Ge-based devices such as photodetectors, LEDs, and lasers.