IDENTIFICATION OF THE 1.19-EV LUMINESCENCE IN HEXAGONAL GAN

We report on optical investigations of a near-infrared luminescence ba nd in hexagonal GaN with a single zero-phonon line (ZPL) at 1.1934 eV. It is attributed to the spin-forbidden internal d-d transition (1)E(D )-(3)A(2)(F) of a defect with a d(2) electronic configuration. This as signment is based on the observed Zeeman splittings, which agree with the ground and excited states being threefold and twofold degenerate, respectively. This interpretation is supported by the observed small f ull width at half maximum (FWHM) of the ZPL, the weak phonon sideband, and the weak temperature dependence of the luminescence band. With in creasing temperature, the ZPL shifts towards lower energies but mainta ins its FWHM of about 200 mu eV up to 60 K. The observed luminescence lifetime of 65 mu s indicates a strong mixing of the (1)E(D) with the T-3(2)(F) multiplet at slightly higher energies by spin-orbit interact ion. Photoluminescence excitation spectra show intracenter absorption into the higher excited T-3(1) states at 1.62 and 2.8 eV in n-type sam ples, proving the defect to be in the luminescent charge state in n-ty pe material. Thus, we propose Ti2+ as the luminescence center responsi ble for the 1.19-eV transition. Implications for the band offset betwe en GaN and GaAs are discussed.