Giant shifts of photoluminescence bands in GaN

Unusually large shifts of photoluminescence (PL) bands with excitation intensity or with temperature are sometimes observed in GaN. In particular, the ultraviolet luminescence band with a maximum at 3.28 eV is attributed to transitions from the conduction band (or shallow donors) to the shallow MgGa acceptor. In semi-insulating GaN samples doped with Mg, enormous redshift (up to 0.6 eV) and broadening of this PL band can be observed with variation of temperature or excitation intensity. A similar behavior of PL was observed in semi-insulating GaN doped with Zn. The blue band with a maximum at 2.9 eV in GaN:Zn is attributed to electron transitions from the conduction band or from shallow donors to the ZnGa acceptor level located at 0.4 eV above the valence band. In conductive n-type GaN, this PL band redshifts by only 7 meV with decreasing excitation intensity by five orders of magnitude, and the shift is explained with the donor–acceptor pair model. However, in semi-insulating GaN:Zn samples, a gradual shift by up to 0.8 eV with decreasing excitation intensity has been observed. Finally, the yellow luminescence band shifts by not more than 7 meV in high-quality, undoped GaN samples, while a redshift by more than 0.1 eV can be observed in GaN heavily doped with Si. The giant shifts are attributed to the presence of electric fields in high-resistivity or heavily doped n-type GaN.Unusually large shifts of photoluminescence (PL) bands with excitation intensity or with temperature are sometimes observed in GaN. In particular, the ultraviolet luminescence band with a maximum at 3.28 eV is attributed to transitions from the conduction band (or shallow donors) to the shallow MgGa acceptor. In semi-insulating GaN samples doped with Mg, enormous redshift (up to 0.6 eV) and broadening of this PL band can be observed with variation of temperature or excitation intensity. A similar behavior of PL was observed in semi-insulating GaN doped with Zn. The blue band with a maximum at 2.9 eV in GaN:Zn is attributed to electron transitions from the conduction band or from shallow donors to the ZnGa acceptor level located at 0.4 eV above the valence band. In conductive n-type GaN, this PL band redshifts by only 7 meV with decreasing excitation intensity by five orders of magnitude, and the shift is explained with the donor–acceptor pair model. However, in semi-insulating GaN:Zn samples, a gradual sh...