InN crystals with hexagonal shapes were grown from InCl 3 and KNH 2 in supercritical ammonia at around 280 MPa. For a successful crystal growth a molar ratio of the chloride to the amide of 1:3 was applied, thus providing an essentially ammononeutral milieu. The obtained InN crystals vary in size and aspect ratio depending on the applied furnace temperature: at 663 K hexagonal platelets up to 2 μm in diameter, as well as rods with lengths of 4 μm and diameters of 1 μm were obtained; at 773 K rods grew up to 2.5 μm in length. By combining both temperature programs, with a 10 h annealing step at both temperatures, we were able to increase the crystal size up to 5.2 μm in length and 0.4 μm in diameter.
Reactions
of Ga or GaN with RbNH2 or CsNH2 under ammonothermal
conditions result in liquids representing intermediate
compounds in the ammonobasic GaN crystal growth. These liquids are
fully miscible with liquid ammonia at room temperature and under autogenous
pressure, and may eventually solidify to amorphous solids. The Cs-containing
liquid initially contains an equilibrium mixture of tetraamidogallate
ions [Ga(NH2)4]− and a dinuclear
complex [(H2N)3Ga(μNH)Ga(NH2)3]2–. Oxygen impurities induce the
formation of a μ-O-bridged dinuclear complex [(H2N)3GaOGa(NH2)3]2–. Mononuclear tetraamidogallate ions are the dominating species directly
after synthesis, but the equilibrium shifts gradually toward the imido
complex when ammonia is removed, and eventually a second condensation
step to [(H2N)2Ga(μ-NH)2Ga(NH2)2]2
– occurs. Addition
of excess liquid ammonia under ambient conditions causes quantitative
conversion of the dinuclear species to [Ga(NH2)4]−. The [Ga(NH2)4]− ions are also the only observable gallium-containing species in
saturated solutions of the solid intermediates Li[Ga(NH2)4] and Na2[Ga(NH2)4]NH2 in liquid ammonia at room temperature and autogenous pressure.
The
electronic structure and band gap of InN synthesized by the
ammonothermal method are studied by synchrotron-based soft X-ray absorption
spectroscopy (XAS), emission spectroscopy (XES), X-ray excited optical
luminescence (XEOL) spectroscopy, and density functional theory (DFT).
The measured N K-edge XAS and XES spectra and XEOL spectra are used
to estimate the band gap of InN, and it is found to be 1.7 ±
0.2 eV for both independent measurements, which is close to the initially
reported values in the range of 1.89–2.10 eV for polycrystalline
InN and about twice the value recently obtained for single crystalline
thin films between 0.70 and 1.0 eV. The possible origin of the measured
increased band gap is discussed in terms of the presence of oxygen
impurities and other impurity phases. Oxygen K-edge XES and XAS measurements
are performed and reveal the presence of oxygen impurities. To gain
insight into the structure of InN in the presence of oxygen impurities,
we perform DFT calculations for hypothetical Wurtzite-type InO0.5N0.5 and InO0.0625N0.9375 and the known c-In2O3 and find that the measured
O K-edge spectra of the samples agree well with InO0.0625N0.9375. The XEOL measurements also confirm the presence
of oxygen impurities, which are caused by substituting nitrogen atoms
with oxygen atoms, and the impurity phase of In2O3 in the samples.
Ammonothermally grown GaN crystals are highly demanded as superior substrates for manufacturing high-performance blue and white LEDs. Ba or Ba(NH 2 ) 2 can act as effective mineralizers under ammonothermal conditions (523 K, 110-150 MPa) and lead to the formation of barium bis(tetramidogallate), Ba[Ga(NH 2 ) 4 ] 2 , a new intermediate in h-GaN synthesis, which was obtained in three solid forms. Single crystals of all three modifications were characterized by X-ray diffraction [a]
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.