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Flexible electronics and mechanically bendable devices based on Group III-N semiconductor materials are emerging; however, there are several challenges in manufacturing, such as cost reduction, device stability and flexibility, and device-performance improvement. To overcome these limitations, it is necessary to replace the brittle and expensive semiconductor wafers with single-crystalline flexible templates for a new-bandgap semiconductor platform. The substrates in the new concept of semiconductor materials have a hybrid structure consisting of a single-crystalline III-N thin film on a flexible metal tape substrate which provides a convenient and scalable roll-to-roll deposition process. We present a detailed study of a unique and simple direct epitaxial growth technique for crystallinity transformation to deliver single-crystalline GaN thin film with highly oriented grains along both a -axis and c -axis directions on a flexible and polycrystalline copper tape. A 2-dimensional (2D) graphene having the same atomic configuration as the (0001) basal plane of wurtzite structure is employed as a seed layer which plays a key role in following the III-N epitaxy growth. The DC reactive magnetron sputtering method is then applied to deposit an AlN layer under optimized conditions to achieve preferred-orientation growth. Finally, single-crystalline GaN layers (∼1 μm) are epitaxially grown using metal organic chemical vapor deposition (MOCVD) on the biaxially-textured buffer layer. The flexible single-crystalline GaN film obtained using this method provides a new way for a wide-bandgap semiconductor platform pursuing flexible, high-performance, and versatile device technology. 

We report on growth of 100-nm single-phase wurtzite BAlN layers with B contents up to 7.2% by MOCVD, which can be potentially applied to deep UV DBRs for VCSELs. 

A top-illuminated deep-ultraviolet Al_0.6Ga_0.4N p-i-n avalanche photodiode (APD) structure was designed and grown by metalorganic chemical vapor deposition on an AlN bulk substrate and on two different quality AlN/sapphire templates, and APDs were fabricated and tested. The APD devices with a circular diameter of 20  μm have demonstrated a distinctive reverse-bias breakdown behavior. The reverse breakdown voltage of the APDs is approximately −140 V, which corresponds to a breakdown electric field of 6–6.2 MV/cm for the Al_0.6Ga_0.4N material as estimated by Silvaco TCAD simulation. The APDs grown on the AlN bulk substrate show the lowest leakage current density of <1 × 10⁻⁸ A/cm²(at low reverse bias) compared to that of the devices grown on the AlN templates. From the photocurrent measurement, a maximum gain (current limited) of 1.2 × 10⁴is calculated. The average temperature coefficients of the breakdown voltage are negative for APD devices fabricated from both the AlN bulk substrate and the AlN templates, but these data show that the coefficient is the least negative for the APD devices grown on the low-dislocation-density AlN bulk substrate.