Defects in Single Crystalline Ammonothermal Gallium Nitride

Abstract

Native bulk gallium nitride (GaN) has emerged as an alternative for sapphire and silicon as a substrate material for III‐N devices. While quasi‐bulk GaN substrates are currently commercially available, single crystal GaN substrates are considered essential for future high performance light emitters and power devices. The ammonothermal method is currently considered one of the most feasible methods to grow large truly bulk crystals of GaN at low cost and high structural quality. High crystalline quality GaN substrates sliced from ammonothermally grown crystals have been demonstrated and utilized in homoepitaxy for III‐N devices. However, despite the high crystalline quality the properties of as‐grown ammonothermal GaN crystals and substrates are affected by the presence of impurities and other defects that hinder their use for device applications. Here, the main developments of ammonothermal growth of GaN and the effects of impurities, native point defects, and dislocations on the material properties are summarized. Additionally, measurement techniques that enable the evaluation of point defect concentration and low dislocation density distribution over a large area on bulk GaN substrates are reviewed.

Ammonothermal Synthesis of Nitrides: Recent Developments and Future Perspectives

“…Suihkonen et al studied and reviewed the formation and concentration of defects in ammonothermal GaN. [79,80] Impurities can be mainly ascribed to oxygen originating from nutrient and mineralizer,a sw ell as transition metals from autoclavem aterials. Galliumv acancies and inclusions of hydrogen were also detected in both ammonobasic and -acidic grown crystalsr esultingi ni ncreased subband-gap absorption.…”

“…Galliumv acancies and inclusions of hydrogen were also detected in both ammonobasic and -acidic grown crystalsr esultingi ni ncreased subband-gap absorption. [80][81][82] These point defects strongly affect electronic and opticalp roperties of GaN andc ause lattice strain, which can even lead to cracking of the wafers. Transition element impurities are strongly reduced using liner systems or capsules, whereas oxygen gettersc an be employed to lower the oxygen concentration in GaN crystals.…”

“…Suihkonen et al. studied and reviewed the formation and concentration of defects in ammonothermal GaN . Impurities can be mainly ascribed to oxygen originating from nutrient and mineralizer, as well as transition metals from autoclave materials.…”

Spectroscopy of defects in neutron irradiated ammono-thermal GaN by combining photoionization, photoluminescence and positron annihilation techniques

“…The pristine and neutron-irradiated AT GaN samples were examined at room temperature (RT), using a digital positron lifetime spectrometer with a Gaussian time resolution of 250 ps. Two identical pristine samples were sandwiched together with the 22 Na μCi positron source foiled in 1.5 μm thick aluminium. To have the PAS spectrum, the positron lifetime records of 10 6 positron annihilation (PA) events were collected.…”

“…By manipulating the ratio between the dopant density and the concentration of radiation defects, it is possible to increase the radiation resistance of the sensors. In this work, the evolution of the pulsed photoionization (PPIS), scintillation (pulsed photoluminescence -PPL) and positron annihilation (PAS) [22][23][24][25] spectroscopy means have been combined to reveal the prevailing defects of different species and scintillation efficiency with neutron irradiation fluence. The contactless PPIS is beneficial in discovery of photoactive centres.…”