Nonpolar m-plane GaN films have been grown by metalorganic vapor-phase epitaxy on patterned a-plane sapphire substrates (diameter: 3 in.) without dielectric masks made of materials such as SiO 2 . The m-plane GaN layer had a smooth and transparent surface over the entire area of the substrate. Furthermore, the epitaxial relationships between the m-plane GaN film and the patterned a-plane sapphire substrate were as follows: ½0001 GaN k ½0001 Sapphire and ½11 20 GaN k ½10 10 Sapphire . The full width at half maximum values of the X-ray rocking curves for ( 1010) GaN along ½11 20 GaN and ½0001 GaN were found to be 396 and 565 arcsec, respectively.

The fabrication of a blue m-plane GaInN light emitting diode (LED) grown on an m-plane GaN layer grown on a 3-in. patterned sapphire substrate is reported. The output power of the LED was approximately 3 mW at the wavelength of 461 nm, a driving current of 20 mA, and a forward voltage of 3.5 V. This is the first report of nonpolar or semipolar blue LEDs grown on hetero-substrates with milliwatt scale output power.

We reduced the operating voltage of AlGaN homojunction tunnel junction (TJ) deep-ultraviolet (UV) light-emitting diodes (LEDs) by two approaches: the suppression of carbon incorporation and the doping of a high concentration of silicon in an n + -AlGaN layer. The AlGaN homojunction TJ deep-UV LEDs had a significantly reduced forward voltage upon suppressing the incorporation of carbon in the n + -AlGaN layer. The suppression of electron compensation by carbon in nitrogen sites and the doping of a high concentration of silicon in an n + -AlGaN layer are important for reducing the operating voltage of AlGaN homojunction TJ deep-UV LEDs.

AlGaN-based ultraviolet light-emitting diodes (UV-LEDs) are key components for the inactivation of viruses. Highly efficient and high-power UV-LEDs, capable of inactivating viruses in a short time, are in demand. For this purpose, the growth technologies of n-type AlGaN contact layers were developed from two points of view: first, to decrease the resistivity of n-type Al0.62Ga0.38N by minimizing the electron compensation, resulting in electronic degeneracy with metallic conduction; second, to improve the light emission uniformity in AlGaN multiquantum wells (MQWs) by controlling the morphology of the underlying n-type AlGaN layer to inhibit macrostep formation. A UV-LED module emitting at 275 nm was demonstrated with the developed growth technology, and illuminated with an irradiation power of 2.6 mW cm−2 on SARS-CoV-2 samples. Over 99.999 % of viruses were inactivated within 5 s owing to the high power of this module.

We demonstrated the structural optimization of AlGaN tunnel junction (TJ) deep-ultraviolet light emitting diodes by changing the thickness and impurity concentrations of p+-type and n+-type AlGaN constituting the TJ. By decreasing the total thickness of the TJ to 23 nm, the operating voltage reached a minimum of 8.8 V at 63 A/cm2. Further decrease in TJ thickness markedly increases the operating voltage. This finding implies that the depletion layer width becomes greater than the TJ thickness if it is smaller than 12 nm. Therefore, we conclude that the TJ thickness must be greater than the depletion layer width.