We fabricated InGaN LEDs prepared on β-Ga<sub>2</sub>O<sub>3</sub> (201) single-crystal substrates. The substrates were produced by
using the edge-defined film-fed growth (EFG) method. A Si-doped GaN epitaxial layer was grown on an electrically
conductive β-Ga<sub>2</sub>O<sub>3</sub> (201) substrate by metal organic chemical vapor deposition (MOCVD). The full-width at half
maximum (FWHM) of (0002) and (101 1) X-ray rocking curves (XRCs) of the Si-doped GaN layer were 220 arcsec and
223 arcsec, respectively. The dark spot density measured by cathode luminescence (CL) was approximately 1.5×10<sup>8</sup> cm<sup>-2</sup>.
The crystalline quality was equal to that of GaN layer on sapphire. We fabricated a vertical LED in the p-side down
configuration. The peak wavelength was approximately 450 nm. The p-contact metal area was 300 ×300 μm<sup>2</sup>. The light
output power did not saturate at 1000 A/cm<sup>2</sup>. This device characteristic indicates the great potential of Ga<sub>2</sub>O<sub>3</sub> for use in
A key component of the OCT technique is the light source with widely spectrum. Extremely broadband 1.0 μm
semiconductor light sources are fabricated with two kinds of device structures of multiplexing emitting layer. The
measured spectra of the fabricated device with "longitudinal bandgap modulated structure" show that the full-width at half-maximum spectral width could be as large as 156 nm. The wavelength swept sources which contain a fabricated device with "asymmetric dual emitting layers structure" have a center wavelength of 1.06 μm, wavelength range of 90 nm, scanning rate of 2kHz.