Layered Gallium Monosulfide as Phase‐Change Material for Reconfigurable Nanophotonic Components On‐Chip

Abstract

The demand for information processing at ultrahigh speed with large data transmission capacity is continuously rising. Necessary building blocks for on‐chip photonic integrated circuits (PICs) are reconfigurable integrated low‐loss high‐speed modulators and switches. Phase change materials (PCMs) provide unique opportunities for integration into PICs. Here, the investigation of layered gallium monosulfide (GaS) as a novel low‐loss PCM from infrared to optical frequencies is pioneered, with high index contrast (Δn ≈0.5) at the optical telecommunication band. The GaS bandgap switches from 1.5 ± 0.2 eV for the amorphous state to 2.1 ± 0.1 eV for the crystalline state. It is demonstrated that the reversible GaS amorphous‐to‐crystalline phase transition can be operated thermally and by picosecond green (532 nm) laser irradiation. The design of a reconfigurable integrated optical modulator on‐chip based on Mach‐Zehnder Interferometers (MZI) with the GaS PCM cell deposited on one of the arms for application is presented at the telecommunication wavelength of λ = 1310 nm, where the standard single mode optical fiber exhibits zero chromatic dispersion, and at λ = 1550 nm, where a minimum optical loss of 0.22 dB km−1 is obtained. This opens the route to applications such as reconfigurable modulators, beam steering using phase modulation, and photonic neural networks.

Unveiling Polymorphs and Polytypes of the 2D Layered Semiconducting Gallium Monosulfide

“…Among those, transition DOI: 10.1002/adom.202303002 metal dichalcogenides (TMDs) and their heterostructures have been widely explored. [1,2] Recently, the family of layered post-transition metal chalcogenides (PTMCs), such as indium selenide (InSe [3] In 2 Se 3 ), [4,5] gallium sulfide (GaS), [6][7][8] gallium selenide (GaSe), [9][10][11][12] and gallium telluride (GaTe), [13][14][15] is gaining interest. In particular, the optical band gap of semiconducting PTMCs varies from 1.5 eV to 3.2 eV, filling the gap-space between semiconducting TMDs and 2D insulators such as hexagonal boron nitride (h-BN) and hafnium sulfide (HfS 2 ).…”

“…[16] Specifically, GaS has an optical band gap of 2.5 eV as bulk crystal, that increases up to 3.2 eV for the monolayer. [17] For this reason, it is being exploited in optoelectronic applications including transistors and visible-ultra violet photodetectors, [18][19][20][21][22] photonics, [6] non-linear optics, [23,24] as well as photocatalysis. [8,25] The layered crystalline structure of semiconducting GaS consists of a stacking along the c-axis of covalently bonded tetralayers (TLs) S-Ga-Ga-S, held together by vdW forces, as shown in Figure 1.…”

Stability of Nanometer-Thick Layered Gallium Chalcogenides and Improvements via Hydrogen Passivation

“…GaS has already been integrated in a new generation of UV photodetectors with short time response, − ,, in field effect transitors, and applied to hydrogen evolution catalysis and second harmonic generation . Moreover, very recently, this material has been proposed as phase-change material for reconfigurable on-chip photonic components …”

“… 22 Moreover, very recently, this material has been proposed as phase-change material for reconfigurable on-chip photonic components. 23 …”