Indium nitride and gallium nitride grown from the melt at subatmospheric pressures

The wide-band-gap, group III nitride semiconductors (Al,Ga,In)N are a promising system for visible/near-UV optoelectronic devices. Despite significant technological advances, improvement in material quality is required. Moreover, pure InN has received little attention due to unavailability of high quality crystals, and uncertainty on the fundamental properties of InN exist in the literature.; In this work, bulk, polycrystalline gallium nitride and indium nitride were synthesized without a substrate by saturating gallium or indium metal with atomic nitrogen from both ECR and ball plasma microwave sources. The results show that atomic nitrogen is an attractive alternative to high pressure N₂ for the synthesis of the bulk nitrides.; The GaN and InN crystals were confirmed to be wurtzitic by x-ray and electron diffraction. Weak yellow-band photoluminescence intensity and near-band-edge linewidths of 4 meV for some GaN crystals indicated high optical quality. The high crystalline quality of the InN crystals allowed for the most precise measurement of the lattice parameters currently possible: a = 3.5366 Å, c = 5.7009 Å. Raman spectra of InN were taken from both randomly oriented polycrystals and groups of oriented, faceted platelets. Phonon modes were assigned as $ETO1=445cm-1,ATO1=472cm-1,E22=448cm-1,$ and $ALO1=558cm-1$, and previous disagreement in the literature is explained. The $E22$ and $ALO1$ linewidths of were 2.5 and 19 cm−1 are the narrowest ever reported. The measured TO phonon frequencies and lattice parameters were compared to those calculated from first principles and excellent agreement was found.; Preliminary experiments on the growth of GaN from Ga/In alloys were performed. Addition of inert, soluble third elements to the Ga/N melt depresses the liquidus temperature, which is equivalent to increasing the solubility of GaN at constant temperature.; Upon introduction of an (0001) sapphire substrate into the melt, oriented thin films of the solid nitride formed on the substrate. The mechanism of this growth is not yet known, but may involve transport of the metal as a liquid film and subsequent reaction with atomic nitrogen. Single crystal films of GaN with a thickness of >10 μm and a growth rate of >50 μm/hr were obtained.