Large‐Scale Formation of Uniform Porous Ge Nanostructures with Tunable Physical Properties

Abstract

Porous germanium (PGe) nanostructures attract a lot of attention for various emerging applications due to their unique properties. Consequently, there is an increasing need for the development of low‐cost synthesis routes that are compatible with large‐scale production. Bipolar electrochemical etching (BEE) is a widely used solution for producing porous Ge layers. However, the lack of controllable production of large‐scale uniform PGe layers is the limiting factor for mainstream applications. Large‐scale homogeneous PGe layers formation is demonstrated by improving the BEE process. The PGe structures demonstrate excellent homogeneity in thickness and porosity, with a relative variation of below 2% across the 100 mm wafer. Furthermore, this process enables accurate tuning of the PGe's physical properties through variation of the etching parameters. PGe structures with porosity ranging from 40% to 80% and an adjustable thickness, while preserving low surface roughness are demonstrated, giving access to a large variety of PGe nanostructures for a wide range of applications. Ellipsometry and X‐ray reflectivity are employed to measure the porosity and thickness of PGe layers, providing fast and non‐destructive methods of characterization. These findings lay the groundwork for the large‐scale production of high‐quality PGe layers with on‐demand characteristics.

Sustainable Production of Ultrathin Ge Freestanding Membranes

“…The apparent waving of the cleaned surface represents a slight variation in the initial Ge bulk/PGe interface formed during the BEE process, as the bottoms of the pores are not all perfectly aligned. This effect is then partially mitigated directly by the first anodic step of the BEE process during the formation of the new PGe layer [43,48].…”

“…PGe layers were formed using an optimized bipolar electrochemical etching (BEE) process [43] on top of Ge substrates. The p-type gallium (Ga) doped, 100 mm Ge wafers oriented along the (100) axis, with 6 • off-axis miscut towards (111) orientation and resistivity of 8-30 mΩ•cm were used in this study.…”

“…At the end of the process, PGe substrates were rinsed with EtOH (99 wt%), dried under N 2 flow, and subsequently placed into the loading chamber of the growth reactor under a vacuum. Further details on PGe formation can be found in our previous work [43].…”

“…Among them, the porosification lift-off technique has recently received significant attention and development thanks to its potentially high-throughput and cost-effective process [20,25]. This approach involves the formation of a uniform and tunable porous Ge (PGe) layer [43] using electrochemical etching [44][45][46][47], followed by the deposition of a Ge membrane on top of it. The membrane can then be detached from the parent substrate through the weak nanostructured interface, forming a thin Ge FSM.…”

Wafer-scale detachable monocrystalline germanium nanomembranes for the growth of III–V materials and substrate reuse

“…In the present work, we introduce the Porous germanium Efficient Epitaxial LayEr Release (PEELER) process for wafer-scale growth of monocrystalline Ge NMs and their detachment, compatible with Ge substrate reuse. This approach consists of four key steps: (i) wafer-scale porosification by bipolar electrochemical etching (BEE) of Ge wafer, 26 (ii) growth of a monocrystalline Ge NM on porous Ge (PGe), 25 (iii) Ge NM detachment from the substrate, (iv) substrate reconditioning by chemical etching to enable reuse of the substrate for production of multiple Ge NMs. 27 Here, we provide detailed structural investigations of the epitaxial Ge NMs by High-resolution transmission electron microscopy (HRTEM).…”