Boron nitride (BN) materials have unique properties, which has led to interest in them in the last few years. The deformation of boron nitride materials including hexagonal boron nitride, boron nitride nanosheets (BNNSs) and boron nitride nanotubes have been studied by Raman spectroscopy. Both mechanical and liquid exfoliations were employed to obtain boron nitride nanostructures. Boron nitride glass composites were synthesised and prepared in thin films to be deformed by bending test in-situ Raman spectroscopy. Hexagonal boron nitride in the form of an individual flake and as flakes dispersed in glass matrices has been deformed and Raman measurement shows its response to strain. The shift rates were, -4.2 cm-1/%, -6.5 cm-1/% for exfoliated h-BN flake with thick and thin regions and -7.0 cm-1/%, -2.8 cm-1/% for the h-BN flakes in the h-BN/ glass (I) and glass (II) composites. Boron nitride nanosheets (BNNSs) shows a G band Raman peak at 1367.5 cm-1, and the deformation process of BNNSs/ glass composites gives a shift rate of -7.65 cm-1/% for G band. Boron nitride nanotubes (BNNTs) have a Raman peak with position at 1368 cm-1, and their deformation individually and in composites gives Raman band shift rates of -25.7 cm-1/% and -23.6 cm-1/%. Glass matrices shows compressive stresses on boron nitride fillers and this was found as an upshift in the frequencies of G band peak of boron nitride materials. Grüneisen parameters of boron nitride (BN) were used to calculate the residual strains in glass matrices of BNNSs nanocomposites as well as to estimate the band shift rates which found to be in agreement with the experimental shift rate of bulk BN and BNNTs.

In the course of these investigations altogether 18 different compounds have been synthesized and their chemical, structural and physical properties were characterized (XRD, XANES, IR, Raman spectrum, magnetic susceptibility, electrical resistivity, low temperature and TG/DTA). Up to now only nitridonickelates and nitridocuprates were known to exhibit exclusively low oxidation states of the transition metals between 0 and +2. In this work it has been presented that also nitridocobaltates belong to this group. We have proved that “Ca3CoIIIN3” do not exist and the real chemical formula can be regarded as Ca5[CoIN2]2. In the thesis another seven new nitridocobaltates(I) have been described, these add to four already known structures. Among novel phases only Ba9Ca[Co2N3]3 may indicate higher valency state for cobalt with the [Co2N3]5- complexes. The XANES data supporting CoII state by comparison with other compounds possess this oxidation state. The crystal structure of Ba9Ca[Co2N3]3 is related to the perovskite type structure. The remarkable structural features of Sr2[CoN2]0.72[CN2]0.28 ≈ Sr6[CoN2]2[CN2] nitridocobaltates [CoIN2]5- ions partially substituted by carbodiimides [N=C=N]2- ions. Up to now in the crystal structure no indications for a homogeneity range could be observed. Both crystal structures of (Sr6N)[CoN2][CN2]2 and Sr6[CoN2]2[CN2] encompass nitridocobaltate [CoN2]5- and carbodiimide [N=C=N]2- ions. In the structures distorted rocksalt motif based on Sr-N partial structure can be distinguished. Up to now in the system AE-Fe-N-(C) only four crystal structures were reported and in the thesis three new were refined Sr8[FeIIIN3]2[FeIIN2], Sr3[FeN3] and (Sr6N)[FeN2][CN2]2 and their physical properties were characterized. The system AE-Mn-N-(C) via this work was extended by Sr8[MnN3]3 and Sr4[MnN3][CN2]. Up to date the only nitridometalate containing different transition elements is Ba[Ni1-xCuxN]. In this work one more mixed nitridometalate has been described Sr8[MnIIIN3]2[FeIIN2]. The crystal structure of Sr4[MnN3][CN2] revealed some weak diffuse scattering lines. The general formula of Sr4[MnN3][CN2] can be written as Sr4[Mn0.96N2.90][C0.96N2] to emphasize possible homogeneity range. Any explanation of the phenomena and establishment of possible homogeneity range are still a challenge. The structures of Sr8[MIIIN3]2[FeIIN2] (M = Mn, Fe) are related to Sr8[MnIVN3]2[MnIIIN3]. All these compounds are first mixed-valency compounds for respective systems and exhibit close relation to crystal structures of Sr3[MN3] (M = Mn, Fe). From the XANES data alike behaviour of all structures containing Mn was observed. Due to some possible degree of Mn/Fe mixing in the crystal structure of Sr8[MIIIN3]2[FeIIN2] the chemical formula might be written as Sr8[MnN3]2-x[FeN3]x[FeN2]. This needs to be investigate in details. Up to now in the literature the only crystallographic data of nitridometalates contain [NCN]2- ions include two compounds. In this work four novel nitridometalate carbodiimides and cyanamides Sr4[MnN3][CN2], (Sr6N)[MN2][CN2]2 (M = Co, Fe) and Sr6[CoN2]2[CN2] have been synthesized. Predominant magnetic properties in the investigated nitridometalates are connected to some antiferromagnetic M-M interactions supported by AFM ordering. The electrical resistivity often shows at some semi-conducting character of these compounds. XANES spectroscopy provided many useful data about valency states of the transition elements, coordination environment around absorbing atoms and electronic structure. The influence of different parameters on the transition metals K-edges was studied in details. IR and Raman give general data about [NCN]2- ions.

The popularity of III-nitride materials has taken up the semiconductor industry to newer applications because of their remarkable properties. In addition to having a direct and wide band gap of 3.4 eV, a very fascinating property of GaN is the band gap tuning from 0.7 to 6.2 eV by alloying with Al or In. The most common orientation to grow optoelectronic devices out of these materials are the polar c-plane which are strongly affected by the intrinsic spontaneous and piezoelectric polarization fields. Devices grown in no polar orientation such as (1 0 –1 0) m-plane or (1 1 –2 0) a-plane have no polarization in the growth direction and are receiving a lot of focus due to enhanced behaviour. The first part of this thesis deals with the development of non-polar epimGaN films of usable quality, on an m-plane sapphire by plasma assisted molecular beam epitaxy. Growth conditions such as growth temperature and Ga/N flux ratio were tuned to obtain a reasonably good crystalline quality film. MSM photodetectors were fabricated from (1 0 -1 0) m-GaN, (1 1 -2 0) a-GaN and semipolar (1 1 -2 2) GaN films and were compared with the polar (0 0 0 2) c-GaN epilayer. Later part of the thesis investigated (1 0 -1 0) InN/ (1 0 -1 0) GaN heterostructures. Further, we could successfully grow single composition nonpolar a-plane InxGa1-xN epilayers on (1 1 -2 0) GaN / (1 -1 0 2) sapphire substrate. This thesis focuses on the growth and characterisation of nonpolar GaN, InxGa1-xN and InN by plasma assisted molecular beam epitaxy and on their photodetection potential. Chapter 1 explains the motivation of this thesis work with an introduction to the III-nitride material and the choice of the substrate made. Polarization effect in the polar, nonpolar and semipolar oriented growth is discussed. Fabrication of semiconductor photodetectors and its principle is explained in details. Chapter 2 discusses the various experimental tools used for the growth and characterisation of the film. Molecular beam epitaxy technique is elaborately explained along with details of the calibration for the BEP of various effusion cells along with growth temperature at the substrate. Chapter 3 discusses the consequence of nitridation on bare m-sapphire substrate. Impact of nitridation step prior to the growth of GaN film over (1 0 -1 0) m-sapphire substrate was also studied. The films grown on the nitridated surface resulted in a nonpolar (1 0 -1 0) orientation while without nitridation caused a semipolar (1 1 -2 2) orientation. Room temperature photoluminescence study showed that nonpolar GaN films have higher value of compressive strain as compared to semipolar GaN films, which was further confirmed by room temperature Raman spectroscopy. The room temperature UV photodetection of both films was investigated by measuring the I-V characteristics under UV light illumination. UV photodetectors fabricated on nonpolar GaN showed better characteristics, including higher external quantum efficiency, compared to photodetectors fabricated on semipolar GaN. Chapter 4 focuses on the optimization and characterisation of nonpolar (1 0 -1 0) m-GaN on m-sapphire by molecular beam epitaxy. A brief introduction to the challenges in growing a pure single phase nonpolar (1 0 -1 0) GaN on (1 0 -1 0) sapphire without any other semipolar GaN growth is followed by our results achieving the same. Effect of the growth temperature and Ga/N ratio on the structural and optical properties of m-GaN epilayers was studied and the best condition was obtained for the growth temperature of 7600C and nitrogen flow of 1 sccm. Strain in the film was quantitatively measured using Raman spectroscopy and qualitatively analyzed by RSM. Au/ nonpolar GaN schottky diode was fabricated and temperature dependent I-V characteristics showed rectifying nature. Chapter 5 demonstrates the growth of (1 0 -1 0) m-InN / (1 0 -1 0) m-GaN / (1 0 -1 0) m-sapphire substrate. Nonpolar InN layer was grown at growth temperature ranging from 3900C to 440C to obtain a good quality film at 4000C. An in-plane relationship was established for the hetrostructures using phi-scan and a perfect alignment was found for the epilayers. RSM images on the asymmetric plane revealed highly strained layers. InN band gap was found to be around 0.8 eV from absorption spectra. The valance band offset value is calculated to be 0.93 eV for nonpolar m-plane InN/GaN heterojunctions. The heterojunctions form in the type-I straddling configuration with a conduction band offsets of 1.82 eV. Chapter 6 focuses on the optimization of nonpolar (1 1 -2 0) a-GaN on (1 -1 0 2) r-sapphire by molecular beam epitaxy. Effect of the growth temperature and Ga/N ratio on the structural and optical properties of a-GaN epilayers was studied and the best condition was obtained for the growth temperature of 7600C and nitrogen flow of 1 sccm. An in-plane orientation relationship is found to be [0 0 0 1] GaN || [-1 1 0 1] sapphire and [-1 1 0 0] GaN || [1 1 -2 0] sapphire for nonpolar GaN on r-sapphire substrate. Strain in the film was quantitatively measured using Raman spectroscopy and qualitatively analyzed by RSM. UV photo response of a-GaN film was measured after fabricating an MSM structure over the film with Au. EQE of the photodetectors fabricated in the (0 0 0 2) polar and (1 1 -2 0) nonpolar growth directions were compared in terms of responsively, nonpolar a-GaN showed the best sensitivity at the cost of comparatively slow response time. Chapter 7 demonstrates the growth of non-polar (1 1 -2 0) a-plane InGaN epilayers on a-plane (1 1 -2 0) GaN/ (1 -1 0 2) r-plane sapphire substrate using PAMBE. The high resolution X-ray diffraction (HRXRD) studies confirmed the orientation of the films and the compositions to be In0.19Ga0.81N, In0.21Ga0.79N and In0.23Ga0.77N. The compositions of the films were controlled by the growth parameters such as growth temperature and indium flux. Effect of variation of Indium composition on the strain of the epilayers was analyzed from the asymmetric RSM images. Further, we report the growth of self-assembled non-polar high indium clusters of In0.55Ga0.45N over non-polar (1 1 -2 0) a-plane In0.17Ga0.83N epilayer grown on a-plane (1 1 -2 0) GaN / (1 -1 0 2) r-plane sapphire substrate. The structure hence grown when investigated for photo-detecting properties, showed sensitivity to both infrared and ultraviolet radiations due to the different composition of InGaN region. Chapter 8 concludes with the summary of present investigations and the scope for future work.

In the course of these investigations altogether 18 different compounds have been synthesized and their chemical, structural and physical properties were characterized (XRD, XANES, IR, Raman spectrum, magnetic susceptibility, electrical resistivity, low temperature and TG/DTA). Up to now only nitridonickelates and nitridocuprates were known to exhibit exclusively low oxidation states of the transition metals between 0 and +2. In this work it has been presented that also nitridocobaltates belong to this group. We have proved that “Ca3CoIIIN3” do not exist and the real chemical formula can be regarded as Ca5[CoIN2]2. In the thesis another seven new nitridocobaltates(I) have been described, these add to four already known structures. Among novel phases only Ba9Ca[Co2N3]3 may indicate higher valency state for cobalt with the [Co2N3]5- complexes. The XANES data supporting CoII state by comparison with other compounds possess this oxidation state. The crystal structure of Ba9Ca[Co2N3]3 is related to the perovskite type structure. The remarkable structural features of Sr2[CoN2]0.72[CN2]0.28 ≈ Sr6[CoN2]2[CN2] nitridocobaltates [CoIN2]5- ions partially substituted by carbodiimides [N=C=N]2- ions. Up to now in the crystal structure no indications for a homogeneity range could be observed. Both crystal structures of (Sr6N)[CoN2][CN2]2 and Sr6[CoN2]2[CN2] encompass nitridocobaltate [CoN2]5- and carbodiimide [N=C=N]2- ions. In the structures distorted rocksalt motif based on Sr-N partial structure can be distinguished. Up to now in the system AE-Fe-N-(C) only four crystal structures were reported and in the thesis three new were refined Sr8[FeIIIN3]2[FeIIN2], Sr3[FeN3] and (Sr6N)[FeN2][CN2]2 and their physical properties were characterized. The system AE-Mn-N-(C) via this work was extended by Sr8[MnN3]3 and Sr4[MnN3][CN2]. Up to date the only nitridometalate containing different transition elements is Ba[Ni1-xCuxN]. In this work one more mixed nitridometalate has been described Sr8[MnIIIN3]2[FeIIN2]. The crystal structure of Sr4[MnN3][CN2] revealed some weak diffuse scattering lines. The general formula of Sr4[MnN3][CN2] can be written as Sr4[Mn0.96N2.90][C0.96N2] to emphasize possible homogeneity range. Any explanation of the phenomena and establishment of possible homogeneity range are still a challenge. The structures of Sr8[MIIIN3]2[FeIIN2] (M = Mn, Fe) are related to Sr8[MnIVN3]2[MnIIIN3]. All these compounds are first mixed-valency compounds for respective systems and exhibit close relation to crystal structures of Sr3[MN3] (M = Mn, Fe). From the XANES data alike behaviour of all structures containing Mn was observed. Due to some possible degree of Mn/Fe mixing in the crystal structure of Sr8[MIIIN3]2[FeIIN2] the chemical formula might be written as Sr8[MnN3]2-x[FeN3]x[FeN2]. This needs to be investigate in details. Up to now in the literature the only crystallographic data of nitridometalates contain [NCN]2- ions include two compounds. In this work four novel nitridometalate carbodiimides and cyanamides Sr4[MnN3][CN2], (Sr6N)[MN2][CN2]2 (M = Co, Fe) and Sr6[CoN2]2[CN2] have been synthesized. Predominant magnetic properties in the investigated nitridometalates are connected to some antiferromagnetic M-M interactions supported by AFM ordering. The electrical resistivity often shows at some semi-conducting character of these compounds. XANES spectroscopy provided many useful data about valency states of the transition elements, coordination environment around absorbing atoms and electronic structure. The influence of different parameters on the transition metals K-edges was studied in details. IR and Raman give general data about [NCN]2- ions.