Nanoscale Gallium Phosphide Epilayers on Sapphire for Low-Loss Visible Nanophotonics

Abstract

Gallium phosphide is a low-loss, high-refractive-index semiconductor considered as a promising material for active and passive components in modern nanophotonics. In this work, we show that nanoscale epitaxial layers of GaP with high optical quality can be formed directly on the transparent sapphire wafers despite the symmetry and lattice constant mismatch. This is achieved using a two-step growth technique through the framework of a domain matching epitaxy mechanism. Direct molecular beam epitaxial growth enables the control of material properties and layer thickness with subnanometer precision and allows us to obtain (111)-oriented epitaxial layers of GaP on high-optical-contrast sapphire wafers without the use of postgrowth layer transfer techniques. The influence of growth conditions on the structural quality of GaP-on-sapphire is revealed using Raman spectroscopy and X-ray diffraction reciprocal space mapping. We study the impact of the growth procedure employing a low-temperature seeding layer on the GaP layer morphology and structural quality. Spectroscopic ellipsometry measurements confirm that both the refractive index and the absorption coefficient of the epitaxial GaP layers are close to those of bulk GaP crystals. We also discuss how the GaP layer morphology and structural quality affect its optical density, drawing special attention to the mechanisms of optical losses. Finally, by nanostructuring the grown layer, we fabricate single GaP nanoantennas and confirm their highly resonant optical response in the visible spectral range, thus confirming the feasibility of the reported technology for various nanophotonic applications.

Revisiting Optical Material Platforms for Efficient Linear and Nonlinear Dielectric Metasurfaces in the Ultraviolet, Visible, and Infrared

“…GaP exhibits high n over the entire visible range and transparency at λ > 540 nm, thereby allowing for alternative optical materials for metasurfaces. , Although GaP exhibits a higher n compared to those of other visibly transparent materials such as TiO 2 and GaN, it has rarely been used for metasurfaces due to difficulties in the growth and deposition of GaP (Figure c.vii). More recently, GaP metalenses have achieved a focusing efficiency of 14.5% at λ = 450 nm using a cost-effective and scalable sputtering process.…”

Broadband Optical Properties of Bi2Se3

“…Hence, even a minor increase in the refractive index has a significant impact on nanophotonics [1]. However, classical high-refractive-index materials (TiO 2 , GaP, Si, and Ge) offer a limited range of available refractive indices, and these typically fall below 4 [2,[6][7][8]. It is thus necessary to search for new optical materials with large optical responses [1].…”

Gallium Phosphide Nanoparticles for Low‐Loss Nanoantennas in Visible Range

“…An alternative material of a nanoantenna operating in a short wavelength range is GaP. It has a moderately high refractive index (n > 3) and a small extinction coefficient at >470 nm (Figure 1a) because of the much larger indirect band gap 2.26 eV (≈550 nm) [12][13][14][15][16][17][18] than that of Si (1.12 eV). For example, the extinction coefficient of GaP at 514 nm is 0.004, which is an order of magnitude smaller than that of Si (0.06).…”

“…However, despite the expected high performance, research on GaP nanoantennas is very scarce. [13,16,19] For example, even the highest symmetry nanoantenna, i.e., a spherical GaP nanoparticle, has not been developed and the antenna performance has not been studied.In this work, we develop colloidal solution of spherical GaP NP nanoantennas operating below 600 nm. We produce spherical GaP NPs by the combination of mechanical milling and a pulsed laser melting in solution process.…”

“…However, despite the expected high performance, research on GaP nanoantennas is very scarce. [13,16,19] For example, even the highest symmetry nanoantenna, i.e., a spherical GaP nanoparticle, has not been developed and the antenna performance has not been studied.…”