# Micro-Transfer-Printing integration of interband cascade lasers on Si

Yannis Billiet, Céline Chevalier, Xavier Letartre, Jean-Louis Leclercq, Pierre Cremillieu, Radoslaw Mazurczyk, Marko Perestjuk, Lamine Ferhat, Christian Grillet, Maëva Fagot, et al.

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Yannis Billiet, Céline Chevalier, Xavier Letartre, Jean-Louis Leclercq, Pierre Cremillieu, et al. Micro-Transfer-Printing integration of interband cascade lasers on Si. Optica Advanced Photonics Congress 2025, Jul 2025, Marseille, France. hal-05355773

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Micro-Transfer-Printing integration of interband cascade lasers on Si

Yannis Billiet*¹,², Céline Chevalier¹, Xavier Letartre¹, Jean-Louis Leclercq¹, Pierre Cremillieu¹, Radoslaw Mazurczyk¹, Marko Perestjuk¹, Lamine Ferhat¹, Christian Grillet¹, Maëva Fagot², Eric Tournié², Maxime Lepage³, Badhise Ben Bakir³, Remi Armand³, Vincent Reboud³, Laurent Cerutti², Christian Seassal¹

1 INL, Ecole Centrale de Lyon, INSA Lyon, CNRS, 69130 Ecully, France

2 IES, Université de Montpellier, CNRS, 34000 Montpellier, France

3 CEA-LETI, Minatec, 38054 Grenoble, France

* yannis.billiet@ec-lyon.fr

**Abstract:** This study presents the technological development for the integration of an Interband Cascade Laser (ICL) source emitting at 4 µm onto a silicon platform, achieved through the Micro-Transfer Printing (µTP) technique.

**1. Introduction**

The generation of optical frequency combs in the mid-infrared (MIR) range, covering wavelengths from 3 to 15 µm, offers interesting prospects for the development of various applications such as spectroscopy, environmental monitoring, medicine, and defense. However, the high cost and complexity of the equipment required to implement these combs currently limits their use to laboratories. Although the demonstration of on-chip frequency combs has recently renewed interest in this technology [1], the size of the devices remains large due to the use of discrete components (notably the pump laser) operating in free space. Therefore, integrating a laser source into an optical circuit, in a material platform where the Kerr effect generates new optical frequencies, would significantly reduce the size and power consumption of frequency comb generation. SiGe is one such promising material platforms due to its transparency window up to 15 µm and supercontinuum generation up to 8.5 µm as another form of a MIR light source has already been demonstrated [2]. We also very recently demonstrated a ring resonator on SiGe with a loaded Q of 236,000 at 4.18 µm wavelength [3].

Interband Cascade Laser (ICLs) are the most promising technology in the 3 to 6 µm wavelength range. These sources, based on interband recombinations in type-II InAs/GaInSb quantum wells arranged in a cascade, significantly reduce power consumption compared to intraband quantum cascade lasers (QCL) [4].

**2. Results**

Among the various approaches for integrating semiconductor laser sources into Si-based photonic platform, the heterogeneous integration of active heterostructures via adhesive bonding (using a BCB layer) or molecular bonding (especially SiO2/SiO2) has reached a mature stage [5]. In this context, the transfer of laser heterostructure coupons by micro-transfer printing (µTP) represents an alternative with unique advantages, including the ability to perform the initial laser fabrication steps on their original substrate. GaSb is a new platform for micro transfer printing, with first results demonstrated over the past two years [6-7]. The challenge lies in identifying a combination of materials with an under-etch sufficiently selective to enable the release of the devices. The technological process developed for the realization of ICLs on Si via µTP is presented in Figure 1.

<figure><img src="image_2.png" /><figcaption>Fig. 1. Developed integration process.</figcaption></figure>

The process consists of preparing coupons with a 6 µm-wide waveguide, including the optical gain region (A-C). The samples are laterally protected and separated from their native substrate through selective chemical underetching (D-E). They are then collected using an elastomer stamp (F) and transferred onto the Si platform coated with a thin layer of adhesive (G). These steps are carried out using a system initially designed for nanoimprint lithography, enabling alignment with a precision better than 1 µm. Finally, electrical contacts are placed laterally using
conventional processes (H). The underetching (step E) and transfer (steps F-G) are the critical stages in this sequence and are the focus of specific development efforts.

<figure><img src="image_3.png" /><figcaption>Fig. 2. SEM image of the coupon before the underetching step (a). SEM profile image of the underetched GaSb/InAsSb heterostructure (b). Optical image of the coupon picked up on the elastomer stamp (c). SEM image of the ICL transferred onto Si, after removal of the encapsulation resist (d).</figcaption></figure>

Underetching, as well as μTP, requires the fabrication of tethers designed to break during the coupon removal step (step F). Figure 2a shows an example of a coupon, laterally supported by tethers, before the underetching step. Figure 2b presents a suspended ICL heterostructure obtained after etching in a citric acid and hydrogen peroxide-based solution. The selectivity proved sufficient to release membranes a few tens of micrometers wide.

The PDMS stamp molding, necessary for picking up the sample (step F), is performed using forced injection to ensure flatness. The stamp is structured to provide greater resilience along the z-axis during the various transfer steps.

The first ICL transfers have been successfully demonstrated on a silicon target coated with a 150 nm layer of Brewer HT10-11 bonding material. A typical device is shown on Fig. 3a. The alignment precision during the transfer process is currently being evaluated.

<figure><img src="image_4.png" /><figcaption>Fig. 3. SEM image of the transferred ICL onto Si after post-process (a). PIV characteristic of the device (b).</figcaption></figure>

The μTP devices were characterized at room temperature. Typical PIV curves (Fig. 3b) demonstrate successful carrier injection in the μTP device and light emission. However, the turn-on voltage and series resistance are high, which precludes laser action with these preliminary devices. Work is in progress to alleviate these issues, as well as to create a better cavity by improving the verticality and smoothness of the facets. The formation of a hybrid cavity with the Si or SiGe platform is also planned. These developments will be presented at the conference.

## Acknowledgment

We acknowledge the support of the Horizon 2020 research and innovation program under the Marie Skłodowska-Curie Actions (Grant No ECLAUSion, 801512) and the International Associated Laboratory in Photonics between France and Australia (LIA ALPhFA). This work was supported by the France 2030 program, managed by the National Research Agency under reference ANR-22-PEEL-0015, as part of the targeted OFCOC project. It also benefited from the Renatech and RENATECH(+) national microfabrication network.

## References

[1] Griffith et al. "Silicon-chip mid-infrared frequency comb generation", Nat. Commun (2015).

[2] Sinobad et al. "Mid-infrared octave spanning supercontinuum generation to 8.5 µm in silicon-geranium waveguides", Optica (2018).

[3] Armand, et al. "Mid-infrared integrated silicon-geranium ring resonator with high Q-factor", APL Photonics 8 (2023).

[4] Tournié, Cerutti. "Mid-Infrared Optoelectronics: Materials, Devices, and Applications", Duxford Cambridge (2020).

[5] Duan et al., "Hybrid III-V on Silicon Lasers for Photonic Integrated Circuits on Silicon," IEEE Quantum Electronics (2014).

[6] Guo et al. "SWIR GaSb Photodiode Integration on Si Photonics through Micro-Transfer-Printing," IEEE Benelux Photonics Chapter: Annual Symposium (2022).

[7] Tuorila et al. "μ-Transfer printing of GaSb-based gain elements for integrated external cavity lasers at 2 µm range," CLEO (2023).