Selective photoluminescence spectroscopy of shallow levels in wide band gap semiconductors

We present an overview of recent selective photoluminescence (PL) experimen ts on shallow levels in ZnSe and GaN. Through two electron transitions (TET ) and electronic Raman scattering (ERS) investigations on solid phase recry stallized bulk ZnSe doped with Al, Cl and In, the spectroscopic properties of donor impurities are re-examined. It is shown that the donor spectra pre viously attributed to Al and Cl are in fact due to common residual impuriti es. The Al-donor excited states are detected up to n = 6 allowing a very ac curate determination of its ionization energy. We show that the central cel l correction of Al is vanishing leading to a new evaluation of the Rydberg which is discussed in view of the last experimental determinations of the d ielectric constant and electron effective mass. The neutral-donor bound-exc itons have been studied in n-type wurtzite GaN homoepitaxial layers and het eroepitaxial layers deposited on sapphire or SiC substrates. It is demonstr ated that the existence of strain distributions in heterostructures induces original resonant effects on selective photoluminescence spectra allowing to identify the bound exciton excited states on a large domain of tensile a nd compressive strains and in particular near the A and B valence band cros sing. Finally, the donors are investigated by TET and ERS spectroscopy. (C) 2001 Elsevier Science B.V. All rights reserved.