Luminescence mechanism of InGaAs self-fit well-cluster composite structure with super-wide spectra

This paper reports an InGaAs/GaAs well-cluster composite(WCC) quantum structure, which has shown great advantages in the development of new types of lasers with super-wide spectra. The spectral bandwidth is broadened to 6-fold broader than that of a classic InGaAs quantum well under the same carrier density. However, the luminescence mechanism of InGaAs/GaAs WCC structure is still unclear because of the self-fit distribution of indium contents and hybrid strain types in In_xGa_1-xAs material. In this paper, the gain spectra and energy band structure containing both compressive and tensile strain states are obtained to reveal the super-wide spectra with dual peaks in transverse electric (TE) and transverse magnetic (TM) polarization modes. The super-wide spectrum with a bimodal feature is attributed to all emissions from normal In_0.17Ga_0.83As region and indium-deficient In_xGa_1-xAs regions caused by the self-fit migration of indium atoms. The band offsets of heavy holes and light holes in normal and indium-deficient In_xGa_1-xAs regions are determined by calculating the peak space of TE and TM spectra. In addition, the thickness fluctuation and hybrid strain distribution in the asymmetrical WCC structure are also obtained by comparing the intensity of dual peaks. The significance of this result is that it not only reveals the energy band characteristics and luminescence mechanism but also determines the critical thickness of indium atom self-fit migration. The result is significant to greatly enhance the performance of InGaAs-based WCC tunable lasers in extending spectral tuning range.