Increase in luminescence efficiency of GaPN layers by thermal annealing

Abstract

The effect of rapid thermal annealing (RTA) on the luminescence properties of GaPN layers was investigated. GaPN layers were grown on GaP and Si substrates. The luminescence properties were evaluated by cathodeluminescence and low-temperature photoluminescence. It was found that the luminescence intensity was increased and the peak photon energy was shifted to the high-energy side in all samples after RTA. The luminescence intensity of the GaPN layers was increased with increasing the annealing temperature. It was also found that high-temperature RTA can be applied to the GaPN layer grown on the Si substrate with a thin Si cap layer rather than the GaPN layer on the GaP substrate. It was estimated that high-temperature RTA reduces the spatial fluctuation of nitrogen compositions and the density of defects attributed to nitrogen atoms. . Thus, GaPN has attracted much attention as a novel material, because GaPN with the nitrogen composition of about 2% is latticematched to Si. Moreover, relatively strong photoluminescence (PL) and electroluminescence have been observed [2,3]. We have realized a dislocation-free GaPN layer, which was lattice-matched to Si, grown on Si substrates with a thin GaP buffer layer [4,5]. Additionally, the PL was observed at room temperature (RT). However, the PL intensity was decreased with increasing the nitrogen composition as reported in previous papers [2,6]. The decrease in the PL intensity implies that the GaPN layer contains a large number of nonradiative recombination centers and/or deep-levels. These defects could be generated due to a large miscibility gap and fluctuations of nitrogen compositions in the GaPN layer. It is needed to improve the crystalline quality of GaPN layer.Thus, we have investigated the effect of rapid thermal annealing (RTA) on the luminescence properties of the GaPN layer grown on a GaP substrate (GaPN/GaP) and a Si substrate (GaPN/Si), respectively.

Growth and characterization of GaPN by OMVPE

“…In case of OMVPE-grown sample, integrated PL intensity became about 20 times strong by the annealing. The improvement of PL intensity is observed for MBE-grown samples [7], but the effect is much larger in OMVPE grown samples than the MBE grown one. PL peak shape and the peak energy of the OMVPE-grown sample did not change by the annealing, which is quite different from the results of MBE-samples, i.e., PL intensity at lower energy tail decreased by the annealing, and higher energy side became strong.…”

“…For the MBE grown samples, the effects of post growth annealing on PL properties are believed a reduction of spatial fluctuation of nitrogen compositions and the density of defects attributed to nitrogen atoms, and the blue-shift could be caused by the improvement of the uniformity of the nitrogen compositions and the increase in injected carriers due to the decrease in defects [7]. The small blue-shift observed in OMVPE sample suggests that the spatial fluctuation of nitrogen compositions is smaller than the MBE samples.…”

“…In order to see the difference between OMVPEand MBE-grown samples, PL properties of OMVPEgrown samples were compared with that of MBE-grown sample. The growth conditions for MBE grown samples were described in previous paper [7]. Fig.…”

Carbon doping for p‐type GaP and GaPN in molecular beam epitaxy using carbon tetrabromide source

“…However, the same tendency has not been seen in carbon doped GaPN. Second, the annealing process at 900 °C for 1 min does not influence on n h and μ h , although it has been reported that the same annealing process significantly improves crystallinity and intensifies photoluminescence in undoped and Mg-doped ptype GaPN epilayers [10,11]. Figure 4 shows PL spectra of GaP and GaPN measured at 10 K. Both in GaP and GaPN, the carbon incorporation reduces the PL intensity without peak shift, and the peak intensity decreases with the increase of n h .…”

“…Prior to the growth of C-doped GaP and GaPN layers, a 100-nm-thick undoped GaP buffer layer was deposited. A rapid thermal annealing (RTA) at 900 ºC for 60 s under a flow of N 2 gas was performed for carbon doped samples, as it has been reported that the same RTA process is significantly effective in improving crystallinity and intensifying PL in undoped and Mg-doped p-type GaPN films [5].…”