Growth and properties of InGaN/GaN quantum wells and blue light emitting diodes by metal–organic chemical vapour deposition

The effects of the indium flow rate on the properties of InGaN/GaN quantum wells have been investigated by using atomic force microscopy, photoluminescence (PL), transmission electron microscopy and high-resolution x-ray diffraction. The high-indium content In_xGa_1−x N/GaN (x > 0.3) quantum wells used in this study were grown on c-plane sapphire by using metal–organic chemical vapour deposition. The indium flow rate in the quantum well layers was varied while keeping other growth parameters fixed. With increasing indium flow rate, the indium solid composition in the well layers increases and the magnitudes of the indium spatial fluctuations increase. However, the defects increase and the quantum well structure degrades. As a result, the PL peak position was redshifted and the intensity was reduced. The transmission electron microscopy images show that the quantum-dot-like regions are clear for In_xGa_1−x N/GaN (x = 0.35). Temperature- and excitation-power-dependent photoluminescence spectra support the results of transmission electron microscopy measurements. In addition, the electroluminescence spectra of the light emitting diode shows that the dominant mechanism in InGaN/GaN quantum wells is a localized effect in the quantum-dot-like regions. The V-defects originate at threading dislocations and the inversion domain boundary due to higher misfit strain with increasing indium flow rate.