Deep level related yellow luminescence in p-type GaN grown by MBE on (0001) sapphire

Abstract

Yellow luminescence (YL) has been studied in GaN:Mg doped with Mg concentrations ranging from 1019 to 1021 cm-3 by spectral CL (T=K) and TEM and explained by suggesting that a different mechanism could be responsible for the YL in p-type GaN with respect to that acting in n-type GaN.Transitions at 2.2, 2.8, 3.27, 3.21, and 3.44 eV were found. In addition to the wurtzite phase, TEM showed a different amount of the cubic phase in the samples. Nano tubes with a density of 3×109 cm−2 were also observed by approaching the layer/substrate interface. Besides this, coherent inclusions were found with a diameter in the nm range and a volume fraction of about 1%.The 2.8 eV transition was correlated to a deep level at 600 meV below the conduction band (CB) due to MgGa-VN complexes. The 3.27 eV emission was ascribed to a shallow acceptor at about 170-190 meV above the valence band (VB) due to MgGa.The 2.2 eV yellow band, not present in low doped samples, increased by increasing the Mg concentration. It was ascribed to a transition between a deep donor level at 0.8-1.1 eV below the CB edge due to NGa and the shallow acceptor due to MgGa. This assumption was checked by studying the role of C in Mg compensation. CL spectra from a sample with high C content showed transitions between a C-related 200 meV shallow donor and a deep donor level at about 0.9-1.1 eV below the CB due to a NGa-VN complex. In our hypothesis this should induce a decrease of the integrated intensity in both the 2.2 and 2.8 eV bands, as actually shown by CL investigations.

Green luminescence in Mg-doped GaN

“…The YL band with a maximum at 2.2-2.3 eV is sometimes observed in Mg-doped GaN [4,[36][37][38][39]. We clearly distinguish this band from the GL2 band with a maximum at 2.35 eV studied in the current work.…”

“…Note that the authors of Ref. [4] attributed the YL band to transitions from the deep N Ga donor to the shallow Mg Ga acceptor, although, in our opinion, the arguments of such an attribution are not convincing.…”

“…They predicted that the full width at half maximum (FWHM) of the V N -related luminescence band at low temperature, W (0), is 0.33 eV. These data were compared with the YL band observed by Salviati et al [4] in Mg-doped GaN [ ω max ≈ 2.2 eV, W (0) 0.4 eV]. Note that the authors of Ref.…”

First-Principles Calculations of Luminescence Spectrum Line Shapes for Defects in Semiconductors: The Example of GaN and ZnO

“…Nitrogen vacancies have low formation energies in p-type GaN, and they have been suggested [24] as a cause of the YL in p-GaN observed in Ref. [25]. The calculated luminescence lineshape for the transition…”

Large Negative Thermal Quenching and Broadening Lineshape Analysis of Acceptor-Associated Yellow Luminescence in Si-Doped GaN

“…12−14 In addition, the observation of YL in heavily Mg-doped p-type GaN indicated that the radiative transition between the deep donor and the Mg Ga shallow acceptor could be another possible mechanism causing YL. 15 Temperature dependence of YL intensity usually shows a normal thermal quenching behavior with a high characteristic temperature (over which YL intensity decreases rapidly) of around 450 K, caused by the thermal emission of holes from YL deep acceptors (hereafter simply denoted as YL acceptors) to the valence band. 16−19 Despite sample dependence, YL intensity was often observed to slightly attenuate from the moderate temperature in the range of 50−110 K to the room temperature in most cases.…”