The structural properties of the group III-nitrides including AlN, Ga_1-xMn_xN, GaN:Cu, and InN were investigated by Raman spectroscopy. Absorption and photoluminescence (PL) spectroscopy were utilized to study the optical properties in these materials.

The analysis of physical vapor transport (PVT) grown bulk AlN single crystals showed that oxygen, carbon, silicon, and boron as the major impurities in the bulk AlN. The Raman analysis revealed high crystalline quality and well oriented AlN single crystals with minimum strain. The static dielectric constant of AlN along c-axis and perpendicular to c-axis were found to be 8.72 and 8.41, respectively. The absorption coefficient of AlN single crystals were assessed from deep UV to the FIR spectral range. The absorption and photoluminescence analysis indicate that the oxygen-related impurities in the AlN single crystals may not be the dominant defect in AlN, suggesting that nitrogen vacancies, and/or C, B, and Si contribute significantly to the observed optical properties of bulk AlN crystals.

In situ Cu-doped GaN epilayers with Cu concentration in the range of 2x10¹⁶ cm^-3 - 5x10¹⁷ cm^-3, grown on sapphire substrate by metal organic chemical vapor deposition (MOCVD)., were investigated by Raman spectroscopy and PL. The Raman spectra revealed high crystalline GaN:Cu layers with minimal damage to the hexagonal lattice structure due to the Cu incorporation. A strong Cu related emission band at 2.4 eV was observed and assigned to Cu induced optical transitions between deep Cu states and shallow residual donor states. Compensation of Cu acceptor states by residual donor like hydrogen and poor activation probability of deep of Cu states are believed to be responsible for the semi-insulating electrical conductivity.

Ferromagnetic Ga_1-xMn_xN epilayers, grown by MOCVD with Mn concentration from x = 0 to x = 1.5, were optically investigated by Raman, PL, and transmission spectroscopy.  The Raman studies revealed Mn-related Raman peaks at 300 cm^-1, 609 cm^-1, and 669 cm^-1.  A broad absorption band centered at 1.5 eV has been assigned to Mn related electronic transitions in Ga_1-xMn_xN. The PL emission band centered at 3.0 eV has been assigned to the Mn-related defects states.

The structural properties of InN layers, grown by high pressure-CVD with different free carrier concentrations, were analyzed by Raman spectroscopy. The Raman results show that the InN layers have high crystalline quality, similar to those InN layers grown by MBE..  The free carries in layers were calculated by using Lindhard-Mermin dielectric function taking into account finite wave vectors, for various scattering processes including, forbidden Frohlich (IIF), deformational potential associated with allowed electro-optic (DP-EO), and charge density fluctuation (CDF) mechanisms.  The experimental Raman spectra are well described by the DP-EO scattering mechanism.  The free carrier concentrations in the layers are in the range of low 10¹⁹ cm^-3 up to 10²⁰ cm^-3.  The origin of the high free carrier concentrations in the layers is related to In to nitrogen stoichiometry variations in the layers.