Assignment of deep levels causing yellow luminescence in GaN

Abstract

The deep levels in GaN associated with yellow luminescence transitions have been investigated using photoluminescence, Hall measurements, and deep level transient spectroscopy (DLTS). Hall measurements on Si-doped GaN show the presence of donor levels at ∼18, ∼35, and ∼70 meV, which are respectively associated with the Si shallow donors, O impurities, and the nitrogen vacancies (VN). DLTS measurements, on the other hand, reveal trap levels at Ec−0.1 eV, Ec−(0.2–0.24) eV, and Ev+0.87 eV. The trap level at Ec−0.1 eV obtained from DLTS can be correlated to the 70 meV deep donor (VN) obtained from Hall measurements. The deep donor band at Ec−(0.2–0.24) eV is attributed to the ON related defect complex decorated along dislocation sites while the hole level at Ev+0.87 eV is attributed to the Ga vacancy (VGa). Thermal annealing at 750 °C in nitrogen ambient results in reduction of yellow luminescence, which could be due to decrease in the concentration of VN and ON-related defect complexes. From these observations, we propose that yellow luminescence in GaN arises from the transitions from the Ec−(0.2–0.24) eV levels to the deep level at Ev+0.87 eV.