The use of van der Waals substrates, in which the epitaxial growth is achieved through weak dipolar interactions, can result in a significant relaxation of the epilayer strain, facilitating at the same time layer detachment.
Here, we study the case of GaN layers grown on graphene and muscovite mica. Morphology, surface potential and strain relaxation of GaN are addressed. In the case of graphene, we show it experiences interesting transformations during the growth of GaN, resulting in the intercalation of metal atoms below the graphene layer. In the case of mica, we find that part of the strain accumulated in the GaN layer relaxes by the formation of three-dimensional structures in the shape of telephone cord buckles, straight blisters or by more complex arrangements. Their characteristics are studied in relation to the initial compressive strain and the elastic parameters of the materials.
Superconducting nanowire single photon detectors stand today as the best technology, due to their near-unity detection efficiency, low dark count rates, and low timing jitter. In this work, we demonstrate the improvement of the superconducting properties of NbN thin films on 8” silicon-on-insulator wafers by using an ultra-thin (10-15 nm) sputtered AlN buffer layer. The higher crystalline quality of NbN, leads to an increase of the superconducting critical temperature up to 10 K for 9-nm-thick NbN films. The material was validated for single photon detection using a fiber-coupled vertical SNSPD with half-cavity architecture. This results opens the way for the development of CMOS compatible waveguide-integrated detectors. The implementation of such guided devices is a keystone for the development of a fully integrated quantum photonics platform able to generate, manipulate and detect a large number of photonic qubits for secure communications and quantum computing applications.
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