# Direct MBE growth of GaSb on Ge, Ge-on-Si and Ge-on-SiGe-on-Si platforms for integrated mid-infrared photonics

M Silvestre, S Lacaze, A Gilbert, A de Cerdeira Oliveira, D Impelluso, G Isella, J-B Rodriguez, E Tournié

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M Silvestre, S Lacaze, A Gilbert, A de Cerdeira Oliveira, D Impelluso, et al., Direct MBE growth of GaSb on Ge, Ge-on-Si and Ge-on-SiGe-on-Si platforms for integrated mid-infrared photonics. EU-ROMBE 2025, Mar 2025, Saint-Etienne-de-Tinée (06660), France. hal-04992077

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Submitted on 14 Mar 2025

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Distributed under a Creative Commons Attribution 4.0 International License
Direct MBE growth of GaSb on Ge, Ge-on-Si and Ge-on-SiGe-on-Si
platforms for integrated mid-infrared photonics

M. Silvestre,¹,² S. Lacaze,¹ A. Gilbert,¹ A. De Cerdeira Oliveira,³ D. Impelluso,³

G. Isella,³ J-B. Rodriguez,¹ E. Tournié,¹,⁴*

1) IES, University of Montpellier, CNRS, F – 34000 Montpellier, France

2) RIBER SA, F – 95870 Bezons, France

3) L-NESS, Politecnico di Milano Dipartimento di Fisica, I - 22100 Como Italy

4) Institut Universitaire de France (IUF), F-75005 Paris, France

*E-mail: eric.tournie@umontpellier.fr

Monolithically integrated mid-infrared (MIR) photonics is of major interest for free-space communications, bio-sensing, etc. While Si is transparent up to ~7 µm, longer MIR wavelengths require other materials [1]. Ge being transparent up to ~15µm, a variety of photonic integrated circuits (PICs) covering a broad wavelength range from the near-IR to the MIR has recently been developed based on Ge-on-Si and Ge-on-SiGe-on-Si waveguides with various Ge contents and composition profiles [2]. The epitaxial growth of MIR lasers on these PICs is now the missing brick to develop fully integrated active devices.

In this work, we studied the MBE growth of GaSb-based materials on various Ge-based templates grown on silicon wafers by low energy plasma enhanced CVD [3]. Similar to the growth of III-Vs on Si, the main issue is removing anti-phase domains (APDs) delineated by anti-phase boundaries (APBs), a defect detrimental to devices because they create short circuits in lasers [4].

As a preliminary step, we first investigated the growth of GaSb layers on (001) Ge substrates. We will show that the APD burying mechanism previously established for GaSb-on-Si growth, which relies on the substrate surface organization and step-flow growth of GaSb [5], also operates during growth on Ge substrates, but only when they are prepared by UHV annealing in a narrow temperature window.

Next, we studied the growth of GaSb on Ge-on-Si and on Ge-on-SiGe-on-Si relaxed-buffer layers with various Ge-composition profiles. In this case, the cross-hatch pattern on the template surfaces (Fig. 1 c) prevents the proper surface organization prior growth for on axis (001) substrates. However, this effect can be alleviated by using slightly miscut (1°) substrates. By carefully adjusting the surface preparation and GaSb growth conditions, APB-free GaSb layers with a roughness rms as low as 1.0 nm can then be achieved on these templates (Fig. 1 b). Such layers can be used for the direct growth of III-V lasers on germanium-based photonic platforms, and represent a further step in the development of integrated MIR photonics.

Part of this work was sponsored by "France 2030" (Equipex EXTRA, ANR-11-EQPX-0016, Equipex+ HYBAT, ANR-21-ESRE-0026) and the Horizon Europe program (project UNISON, #101128598).

[1] R. Soref, Nat. Photonics 4, 495 (2010), 10.1038/nphoton.2010.171.

[2] D. Marris-Morini, Nanophotonics 7(11), 1781 (2018), 10.1515/nanoph-2018-0113.

[3] G. Isella et al., Solid-State Electron. 48, 1317 (2004), 10.1016/j.sse.2004.01.013.

[4] H. Kroemer, J. Cryst. Growth 81, 193 (1987), 10.1016/0022-0248(87)90391-5.

[5] M. Rio Calvo et al., Adv. Electron. Mater. 8, 2100777 (2022), 10.1002/aelm.202100777.
<figure><img src="image_2.png" /><figcaption>Fig. 1: AFM images of a) 4 µm of Ge template grown on Si with 1° offcut, before GaSb growth. A faint cross-hatch is visible. b) Surface after the growth of 500 nm of GaSb on template a). The surface is APB-free. c) Surface of 1 µm Ge grown on graded SiGe buffer on Si with 1° offcut, before GaSb growth. Surface roughness is due to cross-hatch patterns. d) Surface after the growth of 500 nm of GaSb on template c).</figcaption></figure>