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Variation with Al alloy composition in AlGaN • For bulk AlGaN the bandgap variation is accurately reflected in the PL spectrum, however it is not true for AlGaN/GaN heterostructures where due to the strong electric field there is a red shift. So Al composition calculated from PL peak position is NOT totally accurate Slide # 1 PL spectra of Quantum Wells n=3 n=2 n=1 n En * 2 m LZ 2 n=1 n=2 n=3 2 , n 1, 2, 3... • The e1-h1 transition is most probable and observed with highest intensity • At higher temperature other transitions are also observed • All peaks are red-shifted at higher temperatures Slide # 2 PL spectrum for non-polar QW • With increasing well width – The intensity increases due to increased confinement – The peak position shifts to lower energy due to reduction in quantum size effect (QSE) i.e. splitting of energy levels in a QW Slide # 3 – The full width at half maximum (FWHM) also decreases Polar (Nitride) QW PL spectrum Electron and hole wave-functions for non-polar material Electron and hole wave-functions for polar material due to built-in electric field • With increase in well thickness – Intensity decreases due to reduced overlap of the electron and hole wavefunctions due to polarization – Energy decreases due to Quantum Confined Stark Effect (QCSE) or reduction in transition energy gap due to electric field Slide # 4