1. Slide # 1 PL spectra of Quantum Wells The e1-h1 transition is most probable and observed with highest intensity At higher temperature higher levels can be populated, and e2-h2 transition can also be seen n = 1 n = 2 n = 3 n = 2 n = 1

2. 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 –The full width at half maximum (FWHM)  also decreases

3. Slide # 3 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 due to quantum confined stark effect (QCSE) –Energy decreases due to quantum size effect (QSE), and by lowering of energy gap between the energy states

4. Slide # 4 PL as indicator of material quality Better quality of epilayer means higher intensity and narrower FWHM Also true for quantum wells where the interface fluctuations controls the FWHM of PL peaks AlGaN epilayers grown on superlattice (SL) buffered GaN layers produces the best quality

5. Slide # 5 Summary of Photoluminescence Information on bandgap and hence material composition (peak position). Direct or indirect bandgap (from intensity) Information on dopant density and their energy levels (FWHM and peak position) Information on the quality of material, both substrate and epitaxial layers (poor quality material has more states giving rise to non-radiative recombination, or radiative recombination at a different wavelength) Information on material properties such as phonon energies, effective mass, and dielectric constant (from spectra of the hydrogenic model of the impurities) Information on the energy levels of quantum wells, their interface roughness, alloy disorder, and built-in electric field (from the peak position, FWHM, and the variation of lineshape with width of the QWs)