Abstract
Due to its high refractive index and low absorption coefficient, gallium phosphide is an ideal material for photonic structures targeted at the visible wavelengths. However, these properties are only realized with high quality epitaxial growth, which limits substrate choice and thus possible photonic applications. In this work, we report the fabrication of single crystal gallium phosphide thin films on transparent glass substrates via transfer bonding. GaP thin films on Si (001) and (112) grown by MOCVD are bonded to glass, and then the growth substrate is removed with a XeF2 vapor etch. The resulting GaP films have surface roughnesses below 1 nm RMS and exhibit room temperature band edge photoluminescence. Magnesium doping yielded p-type films with a carrier density of 1.6 × 1017 cm−3 that exhibited mobilities as high as 16 cm2V−1s−1. Due to their unique optical properties, these films hold much promise for use in advanced optical devices.
Highlights
High index contrast enables strong light confinement due to the change in amplitude of the electric field at an interface between materials of different index[7]
The substrate removal process draws from the well-established epitaxial lift-off technique[17, 18]; here, substrate reuse is not critical, because the substrate is silicon as opposed to expensive GaAs
Reciprocal space maps of films ~ 50 nm thick, below the critical thickness for GaP grown on silicon, show Laue oscillations and film peak widths (36.2 arcseconds) matching the width of the substrate peak (36 arcseconds)
Summary
Hal Emmer[1], Christopher T. Due to its high refractive index and low absorption coefficient, gallium phosphide is an ideal material for photonic structures targeted at the visible wavelengths. We found that substrate removal was necessary to extract enough signal to perform measurements This was expected, since gallium phosphide has a high index of refraction (n ~ 4 near its emission peaks), well matched to the silicon substrate, which absorbs strongly at these wavelengths. Single-crystal GaP (001) films bound to glass with a transparent interlayer were fabricated by a transfer/wafer bond/Si substrate removal process. These films had excellent optical, mechanical, and electronic properties. Due to the distinctive properties of GaP, these films open the door for fabrication of a wide variety of thin film photonic devices
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