Selective electrodeposition of indium microstructures on silicon and their conversion into InAs and InSb semiconductors

Abstract

The idea of benefitting from the properties of III-V semiconductors and silicon on the same substrate has been occupying the minds of scientists for several years. Although the principle of III-V integration on a silicon-based platform is simple, it is often challenging to perform due to demanding requirements for sample preparation rising from a mismatch in physical properties between those semiconductor groups (e.g. different lattice constants and thermal expansion coefficients), high cost of device-grade materials formation and their post-processing. In this paper, we demonstrate the deposition of group-III metal and III-V semiconductors in microfabricated template structures on silicon as a strategy for heterogeneous device integration on Si. The metal (indium) is selectively electrodeposited in a 2-electrode galvanostatic configuration with the working electrode (WE) located in each template, resulting in well-defined In structures of high purity. The semiconductors InAs and InSb are obtained by vapour phase diffusion of the corresponding group-V element (As, Sb) into the liquified In confined in the template. We discuss in detail the morphological and structural characterization of the synthesized In, InAs and InSb crystals as well as chemical analysis through scanning electron microscopy (SEM), scanning transmission electron microscopy (TEM/STEM), and energy-dispersive X-ray spectroscopy (EDX). The proposed integration path combines the advantage of the mature top-down lithography technology to define device geometries and employs economic electrodeposition (ED) and vapour phase processes to directly integrate difficult-to-process materials on a silicon platform.

Keywords: Electrodeposition; III-Vs; Integration; Recrystallization; Saturation; TASE.

Fig. 1

Process flow for selective In-based semiconductor integration on Si. a 3D schematic of the template structure. The cavity structure contains inlet holes and a via to the substrate. b Indium is electrodeposited from an electrolyte into the cavity using the via to access the WE and a Pt electrode as CE. c The In-filled template is transferred and heated in a MOCVD reactor for V-element saturation. Here, the liquid In is converted into a crystalline semiconductor, that nucleates from the Si surface. WE working electrode, CE counter electrode

Fig. 2

Top-view SEM images of electrodeposited indium inside 300 nm thick templates. Each template has four inlet openings and one (hidden) seed contact to the wafer. a The straight legs fill uniformly, while gaps can form at recessed corners b. c, d The same structures as in (a, b) after melting and solidification. The spherical particles are artefacts from the template fabrication process

Fig. 3

Cross-sectional images of annealed and recrystallized In structures in templates. a Low resolution cross section of seven devices. b TEM image of a single structure including the seed region. c Corresponding EDX map with indium (red), silicon (green) and oxygen (blue). d, e High-resolution dark field TEM image of In-Si heterointerface and bulk part with collection regions marked with a coloured square in (b)

Fig. 4

Analysis of In electrodeposit saturated with As. a Cross-sectional image of a template filled with InAs. b Close-up of the central part, showing a void in the seed area. c BF TEM overview of an InAs sample and corresponding high-resolution lattice images. d SEM tilted view of an InAs cross where the SiO_x template was removed. e SEM cross-sectional image of a device showing an InAs-In phase separation and large voids. InAs sections are false coloured for better visibility. Red dotted lines in (a–c) mark planar defects in the InAs crystal

Fig. 5

Phase diagram for In-Sb system with the two possible process paths for InSb solidification. Blue arrows indicate the low-temperature process leading to direct InSb nucleation. Light blue arrows depict continued saturation until stoichiometric composition, consuming all In. Pink arrows present the high-temperature path, where InSb crystallization is initiated by cooling of the melt

Fig. 6

Analysis of In electrodeposit saturated with Sb at 480 °C. a Top-view SEM image showing uniform contrast of the InSb cross-structure. b A structure with clogged channels, revealing segments of In (bright) and InSb (darker) intensity. c BF-TEM overview of an InSb sample and corresponding high-resolution lattice images

Fig. 7

Analysis of In electrodeposit saturated with antimony above the InSb melting temperature. a Top-view SEM image showing uniform contrast of the InSb. b Example of a non-uniform sample, revealing segments of In (bright) and InSb (darker) with different contrast. c BF-TEM overview of an InSb sample cross section and corresponding high-resolution lattice images