Two different behavior patterns of photoluminescence depending on Mg doping rate in p-type GaN epilayers

Abstract

Mg-doped p-type GaN epilayers grown by metalorganic chemical vapor deposition exhibit two different types of photoluminescence (PL) characteristics depending on Mg doping rate; the existence of critical Mg concentration is found where both electrical and optical characteristics show an abrupt change in their behavior. In samples with relatively low Mg concentration, a band edge emission, a peak associated with shallow donor-acceptor pair recombination, and a 2.8 eV blue band emission appear in the PL spectrum. Intensities of all three PL peaks decrease with increasing annealing temperature; the blue band quenches most rapidly. In contrast, in samples grown with high ratio of Mg/Ga flow rate, only a strong blue emission band is observed and the intensity of the blue band increases with the annealing temperature suggesting a different origin from the blue band of lightly doped samples. From the annealing temperature dependence of the blue band intensity, we speculate that the emission mechanism of the blue band in relatively lightly Mg-doped GaN epilayers involves Mg-related deep level complexes such as substitutional/interstitial Mg-related complexes. On the other hand, a model involving a formation of pyramidal defects and the presence of Mg-rich inclusions which modifies the dominant optical transition can be a possible explanation for the origin of the blue band in heavily doped ones.

Influence of carrier gas H 2 flow rate on quality of p-type GaN epilayer grown and annealed at lower temperatures

“…[15][16][17] It is reported that a thermal annealing can make H atoms change into various states, and the concentration for each state is determined by the thermal equilibrium and affected by annealing temperature. [18] The improvement of p-type quality means that the H + concentration in p-type layer decreases with annealing temperature increasing in our experiment. With the increase of annealing temperature, more and more Mg acceptors are activated by thermal annealing.…”

“…In the annealing process, the H atom can change into various states and in these states of the H atom the H − can combine and change the donors' state. [18] The effect of annealing on the compensation donors also relates to the H state changing in the annealing process, but more work needs to be done to confirm this point.…”

Optical and structural characterization of blue-emitting Mg2+- and Zn2+-doped GaN nanoparticles

“…Similar blue emission has been observed and well-studied for Mg 2+ -and Zn 2+ -doped GaN in films. [29][30][31] These peaks are attributed to donor-acceptor pair recombination, preferentially from the conduction band to the shallow acceptor states (ca. 0.5 eV above the valence band) created by the incorporation of Mg 2+ or Zn 2+ .…”

InN, latest development and a review of the band-gap controversy

“…For epitaxial GaAs bandedge luminescence is also quenched with oxygen doping to 10 18 cm −3 in favour of near mid-gap deep level trap-related PL peaks [120]. For GaN, heavy Mg doping also results in the quenching of band-edge luminescence in favour of a blue luminescence band possibly related to deep level acceptor states [121], while for epitaxial CdTe deep level emissions with 14 meV FWHM have been observed (much sharper than any of the InN emissions observed to date) but only for samples greater than 3 µm in thickness [122]. Again no band-edge luminescence was observed.…”