Search

Photoluminescence (PL) from GaN substrates fabricated by the ammonothermal growth method was studied in a wide range of temperatures and excitation intensities, both with steady-state and time-resolved PL techniques. Three defect-related PL bands were detected: the ultraviolet luminescence band with the zero-phonon line at 3.27 eV, the Zn-related BL1 band with a maximum at 2.9 eV, and the yellow luminescence band (labeled YL2) with a maximum at 2.3 eV. The YL2 band belongs to an unknown defect and is different from the CN-related YL1 band. Its maximum blueshifts by 0.06 eV with increasing excitation intensity and redshifts by more than 0.1 eV with a time delay after a laser pulse. The YL2 band is preliminarily attributed to a defect complex containing the gallium vacancy. [ABSTRACT FROM AUTHOR]

• Round shape of seeds allowed to crystallize GaN without cracks at the edges. • 60 µm/day growth rate in ammonothermal crystallization is presented. • Etch pit density in laterally-grown GaN was of the order of 102 cm−2. • Stress Induced Polarization Effect (SIPE) was visible in Am-GaN crystals. Progress in basic ammonothermal gallium nitride crystallization is reported. In order to prevent the appearance of cracks in growing GaN a new shape of native seeds is proposed. Crystallization results on irregular (old) and round (new) shapes are compared in terms of growth rate and structural quality. The new type of seeds allowed to grow crystals twice as fast without losing the very high structural quality. Etch pit density in the new-grown material is examined and compared to that in the seeds. Material deposited in vertical <000–1> and lateral <11–20> directions is analyzed. In the latter case the etch pit density is as low as 102 cm−2. An influence of growth process parameters and crystal growth configuration on the structural quality of crystallized GaN is discussed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract Recent progress in ammonothermal technology of bulk GaN growth in basic environment is presented and discussed in this paper. This method enables growth of two-inch in diameter crystals of outstanding structural properties, with radius of curvature above tens of meters and low threading dislocation density of the order of 5 × 104 cm−2. Crystals with different types of conductivity, n-type with free electron concentration up to 1019 cm−3, p-type with free hole concentration of 1016 cm−3, and semi-insulating with resistivity exceeding 1011 Ω cm, can be obtained. Ammonothermal GaN of various electrical properties is described in terms of point defects present in the material. Potential applications of high-quality GaN substrates are also briefly shown. [ABSTRACT FROM AUTHOR]