# Controlling position of MOVPE core-shell MQWs on GaN wires

J. Eymery, Vincent Grenier, Akanksha Kapoor, Christophe Durand

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J. Eymery, Vincent Grenier, Akanksha Kapoor, Christophe Durand. Controlling position of MOVPE core-shell MQWs on GaN wires. ICMOVPE XX - The 20th International Conference on Metalorganic Vapor Phase Epitaxy, Jul 2022, Fellbach, Germany. hal-05284099

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Submitted on 26 Sep 2025

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# Controlling position of MOVPE core-shell MQWs on GaN wires

J. Eymery<fnref n="1" />, V. Grenier<fnref n="2" />, A. Kapoor<fnref n="2" />, C. Durand<fnref n="2" />

Developments of new functionalities in semiconductor wires are strongly related to the ability to control their epitaxial relationships with the substrate, but also to position active layers, doped area and contacts. In heterostructures, the longitudinal insertions along wires have been extensively studied using both bottom-up growth and top-down approaches, but the positioning of radial insertions (shells) turned out more difficult to manage due to the non-selective feature of the sidewall growth. In molecular beam epitaxy, flux directionality and shadowing can be used to cover the upper part of dense assemblies or wire sidewalls. The full sidewall covering is obtained for low density wires (i.e., without shadowing effects) by rotating the substrate during the growth. For chemical vapor deposition methods, the gaseous feed provides spontaneously a homogeneous covering of the sidewalls and, consequently, bottom-up approaches are mainly used to structure or position the shells. Several solutions involving complementary technological steps have been proposed to solve this problem by metal-organic vapor phase epitaxy (MOVPE): for instance, holes in thick selective growth layers have to guide the wire growth before depositing InGaN/GaN core-shell multiple quantum wells (MQW) [1] and III-V materials on Si [2,3]. Alternatively, a dielectric layer can be deposited to cover the full length of the wire and protect the sidewall facets, and then etched locally to get back to a free surface on which the core-shell structure is grown [4]. All these methods often involve *ex situ* technological process developments and may induce parasitic surface contaminations between the wire core and the shell.

This talk will enlighten the mechanisms involved in the use of silane for wire MOVPE growth to control MQW positioning [5]. Its first basic role promotes the longitudinal growth rate still to get ultra-long wires (> 250 µm). Then we will discuss method allowing a partial covering of the shell around the wire [5,6] that will be demonstrated with the realization of several devices (visible & UV emitters, detectors, photovoltaics... [5-10]). The basic idea is to form an *in situ* selective-growth layer around the bottom part of a wire during its growth and then to continue the wire growth without this layer. This is done by stopping the silane flow and by consuming the reactor residue to keep on the wire growth. Then a change of growth conditions, closer to usual planar growth, allows the sidewall deposition only at the top part of the wire where there is no effective selective growth layer. This method will be illustrated with the spontaneous MOVPE growth of non-catalyzed GaN wires where silane can form SiNₓ [11]. The existence of a threshold in silane concentration for complete growth selectivity is demonstrated, and its impact on the growth mechanism and device realization will be discussed, in particular the possibility to manage growth on partially covered SiNₓ portions. It will be illustrated by the growth of InGaN/GaN MQWs along different lengths at the top of GaN wires and the generality of this approach will be also demonstrated by AlGaN/GaN MQWs shells [12]. This last case evidences a lower selectivity of the SiNₓ layer for the Al-based MQWs than for the In- ones. A detailed structural and optical characterization will be discussed to explain the applications for wire nanodevices.

## References:

[1] R S.D. Hersee et al., *Electronics Letters* **75**, U24 (2009).

[2] C.P.T. Svensson et al., *Nanotechnology* **19**, 305201 (2008).

[3] K. E. Moselund et al., *Device Lett.* **33**, 1453 (2012).

[4] L. E. Fröberg et al., *IEEE Elec. Device Letters* **29**, 981 (2008).

[5] J. Eymery, D. Salomon, X. Chen and C. Durand, World Patent No. 2,012,136,665, Oct. 11 (2012).

[6] R. Koester et al., *Nano Lett.* **11**, 4839 (2011).

[7] S. Salomon et al., *Nanotechnology* **25**, 375502-8 (2014).

[8] N. Guan et al., *ACS Photonics* **3**, 597 (2016).

[9] H. Zhang et al., *ACS Appl. Mat. & Interf.* **8**, 26198 (2016).

[10] A. Messanvi et al., *ACS App. Mat. & Interf.* **7**, 21898 (2015). A. Kapoor et al., *ACS Applied Materials & Interfaces* **12** 19092 (2020).

[11] D. Salomon et al., *Nano Lett.* **17**, 946 (2017).

[12] V. Grenier et al., *ACS Applied Materials & Interfaces* **12** 4407 (2020) 4407 & ACS Crystal Growth & Design **21** 6504 (2021).

<footnote n="1">¹Univ. Grenoble Alpes, CEA, IRIG, MEM, NRS, 38000 Grenoble Cedex, France</footnote>

<footnote n="2">²Univ. Grenoble Alpes, CEA, IRIG, PHELIQS, NPSC, 38000 Grenoble Cedex, France</footnote>
<figure><img src="image_2.png" /></figure>

<figure><img src="image_3.png" /><figcaption>**Fig 1** 45°-tilted scanning electron microscopy view of a typical self-catalysed and self-organized MOVPE growth of N-polar GaN single-crystal wires on c-plane sapphire substrate.</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>**Fig 2** Measurements of the GaN wire length l and diameter as a function of the growth time t. The dotted line shows the fit of the l(t) with the Ruth and Hirth model [V. Ruth et al, *Jour. Chem. Phys.* **41**, 3139 (1964)].</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>**Fig 3** SEM image of the growth of 5 x InGaN/GaN MQWs on GaN wires illustrating positioning. The inset shows a µPL measurement at 10K and a cross-section transmission electron microscopy view. Schematic view of radial and longitudinal MQWs.</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>**Fig. 4** Three core-shell MQW systems grown around GaN microwires emitting in the visible and UV range. TEM images in cross-section views and photoluminescence at 5K for the three MQW systems (InGaN/GaN, GaN/InAlN, GaN/AlGaN).</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>**Fig. 5** (left) 30° tilted SEM image of an assembly of as-grown GaN wires on c-sapphire substrate. (right) single core-shell GaN/AlGaN wire (see MQW) at the top of the wire.</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>**Fig. 6** TEM image of a core-shell GaN/AlGaN wire at the top and bottom (see Fig. 5). Influence of SiNx selective growth layer.</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>**Fig. 7** Examples of applications using the SiNx passivation and GaN wires. From left-top to right-bottom: flexible emitters (here blue), coupled emission-detection wires, photovoltaics, capacitive flexible sensors using long wires.</figcaption></figure>