No abstract

Ammonothermal GaN samples with the concentration of free electrons of 1018 and 1019 cm−3 were annealed in a wide range of temperatures (Tann = 300–1400 °C) under atmospheric N2 pressure and under ultra-high N2 pressure conditions to avoid the GaN decomposition. Photoluminescence (PL) studies reveal the YL2 band with a maximum at 2.3 eV before annealing and two new PL bands after annealing at Tann > 600 °C: the OL3 band with a maximum at 2.1 eV and the RL4 band with a maximum at 1.6–1.7 eV. The ammonothermal GaN samples have high concentrations of complexes containing gallium vacancy (VGa), hydrogen, and oxygen. The first-principles calculations suggest that the VGa-3Hi complex is the origin of the YL2 band, while the VGa-3ON complex is responsible for the RL4 band.

No abstract

No abstract

photoluminescence (pL) was used to estimate the concentration of carbon in Gan grown by hydride vapor phase epitaxy (HVPE). The PL data were compared with profiles of the impurities obtained from secondary ion mass spectrometry (SiMS) measurements. comparison of pL and SiMS data has revealed that apparently high concentrations of C and O at depths up to 1 µm in SIMS profiles do not represent depth distributions of these species in the Gan matrix but are rather caused by post-growth surface contamination and knocking-in impurity species from the surface. in particular, pL analysis supplemented by reactive ion etching up to the depth of 400 nm indicates that the concentration of carbon in nitrogen sites is below 2-5 × 10 15 cm −3 at any depth of Gan samples grown by HVpe. We demonstrate that pL is a very sensitive and reliable tool to determine the concentrations of impurities in the Gan matrix.GaN is a key material in modern solid-state lighting technology. The investigation and identification of point defects in GaN is very important, with immediate technology relevance to longer lifetime of light-emitting devices. Photoluminescence (PL) is a powerful tool for investigation of point defects in GaN 1 . Only few point defects in unintentionally doped GaN are well understood and reliably identified. One of them is the C N defect with the −/0 and 0/ + thermodynamic transition levels at 0.916 eV and ~0.3 eV, respectively, above the valence band 2-5 . This defect is responsible for the yellow luminescence (YL1) band with a maximum at 2.2 eV and zero phonon line (ZPL) at 2.59 eV in n-type GaN. Transitions via the 0/ + level of this defect can be observed as the blue luminescence (BL C ) band with a maximum at 3.3 eV at high excitation intensity 4 . The YL1 band is commonly observed in n-type GaN layers grown by metalorganic chemical vapor deposition (MOCVD), where the concentration of unintentionally introduced carbon is usually in the range of 10 16 -10 18 cm −3 , depending on growth conditions 6,7 . Undoped or Si-doped GaN samples grown by hydride vapor phase epitaxy (HVPE) contain much less carbon (10 15 -10 16 cm −3 ) 8-11 , yet still the YL1 band may be strong in these samples due to high hole-capture cross-section for the C N defects 12 .We have recently demonstrated 12 that PL can be used for determination of concentrations of defects responsible for PL bands. However, the concentrations of impurities found from PL were inconsistent with the concentrations found from secondary-ion mass spectrometry (SIMS) analysis in that study. Comparison of these two techniques is complicated by the following ambiguity. SIMS measurements provide depth profiles of impurity concentrations regardless of positions of impurity species (lattice sites or precipitations), whereas PL signal, excited with above-bandgap light, is collected from impurity atoms at lattice sites in the near-surface region (roughly, top 0.4 µm layer in GaN). The problem is that close to the surface, where PL is collected, very high concentrations of carbon an...