Broadband Emission of Photoluminescence from Type‐II Quantum Wells Applied to Superluminescent Diodes

In this study, InGaAs/GaAsSb Type‐II quantum wells (QWs) are investigated as promising broadband light sources for optical coherence tomography (OCT). OCT requires a wide spectral width for high axial resolution within the 700–1400 nm biological window. However, current superluminescent diodes (SLDs) using conventional materials have wavelength limitations. The GaAs‐based Type‐II QWs are promising for the 1.0–1.4 µm range, enabling wavelengths beyond 1.3 µm on GaAs substrates. Three QW structures (Type‐I, Type‐II W‐shaped, Type‐II) are fabricated on GaAs substrates via metal–organic vapor‐phase epitaxy (MOVPE), and their photoluminescence (PL) spectra are measured. Type‐II QWs consistently exhibit the widest broadband PL spectrum. Notably, the 5 nm well width Type‐II QW shows the broadest average PL full width at half maximum (FWHM), possibly because of narrower conduction‐band quantum level spacing. The SLD fabricated with 5 nm well width InGaAs/GaAsSb Type‐II QW as the active layer has a significant broadband electroluminescence (EL) spectrum. A maximum EL spectrum FWHM of approximately 180 nm is observed. This surpasses that of conventional Type‐I QW SLDs, highlighting InGaAs/GaAsSb Type‐II QWs on GaAs substrates as highly promising OCT broadband light sources.