Abstract
Silicon photonics has enabled large-scale production of integrated optical devices for a vast array of applications. However, extending its use to nonlinear devices is difficult since silicon does not exhibit an intrinsic second-order nonlinearity. While heterogeneous integration of strongly nonlinear materials is possible, it often requires additional procedures since these materials cannot be directly grown on silicon. On the other hand, CMOS-compatible materials often suffer from weaker nonlinearities, compromising efficiency. A promising alternative to current material platforms is scandium-doped aluminum nitride (Al1−xScxN), which maintains the CMOS compatibility of aluminum nitride (AlN) and has been used in electrical devices for its enhanced piezoelectricity. Here, we observe enhancement in optical second-order susceptibility (χ(2)) in CMOS-compatible Al1−xScxN thin films with varying Sc concentrations. For Al0.64Sc0.36N, the χ(2) component d33 is enhanced to 62.3 ± 5.6 pm/V, which is 12 times stronger than intrinsic AlN and twice as strong as lithium niobate. Increasing the Sc concentration enhances both χ(2) components, but loss increases with a higher Sc concentration as well, with Al0.64Sc0.36N exhibiting 17.2 dB/cm propagation loss at 1550 nm and Al0.80Sc0.20N exhibiting 8.2 dB/cm at 1550 nm. Since other material properties of this alloy are also affected by Sc, tuning the Sc concentration can balance strong nonlinearity, loss, and other factors depending on the needs of specific applications. As such, Al1−xScxN could facilitate low cost development of nonlinear integrated photonic devices.
Highlights
While passive devices have proved useful in guiding light, nonlinear devices are capable of controlling interactions between different light signals in more complex processes,3 widening the capabilities of integrated photonic chips
We report enhanced optical χ(2) of Al1−xScxN thin films based on second harmonic generation (SHG) measurements
We confirmed the quality of our samples, even at a high Sc concentration, by AFM imaging Fig. 1(b) and measuring surface roughness and full-width-half-maximum (FWHM) from x-ray diffraction (XRD) rocking curves Table I
Summary
Integrated photonics is a growing field that manipulates light signals using compact, chip-sized devices. Far-reaching applications range from telecommunication to sensing to optical computing. While passive devices have proved useful in guiding light, nonlinear devices are capable of controlling interactions between different light signals in more complex processes, widening the capabilities of integrated photonic chips. Cascaded χ(2) processes can act as stronger effective χ(3) processes for applications that require higher order nonlinear processes, widening their utility While these processes can be performed with commercial free-space optical components, nonlinear integrated photonic. Other CMOS-compatible materials can be grown directly on silicon or electrical chips, decreasing fabrication cost and complexity. While many devices use lithium niobate (LN) due to its large χ(2), with d33 = 25 pm/V,16 it is not compatible with CMOS processes and cannot be directly grown on silicon platforms. Several solutions include using buffer layers, growing silicon on III–V substrates, and wafer bonding.21 These methods are not always CMOS-compatible and require more complicated fabrication procedures. Unlike many other nonlinear materials, Al1−xScxN is grown at low enough temperatures to be CMOS-compatible and retains a relatively large bandgap. We report enhanced optical χ(2) of Al1−xScxN thin films based on second harmonic generation (SHG) measurements
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