GaN on Si plays an important role in the integration and promotion of GaN-based wide-gap materials with Si-based integrated circuits (IC) technology. A series of GaN film materials were grown on Si (111) substrate using a unique plasma assistant molecular beam epitaxy (PA-MBE) technology and investigated using multiple characterization techniques of Nomarski microscopy (NM), high-resolution X-ray diffraction (HR-XRD), variable angular spectroscopic ellipsometry (VASE), Raman scattering, photoluminescence (PL), and synchrotron radiation (SR) near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. NM confirmed crack-free wurtzite (w-) GaN thin films in a large range of 180–1500 nm. XRD identified the w- single crystalline structure for these GaN films with the orientation along the c-axis in the normal growth direction. An optimized 700 °C growth temperature, plus other corresponding parameters, was obtained for the PA-MBE growth of GaN on Si, exhibiting strong PL emission, narrow/strong Raman phonon modes, XRD w-GaN peaks, and high crystalline perfection. VASE studies identified this set of MBE-grown GaN/Si as having very low Urbach energy of about 18 meV. UV (325 nm)-excited Raman spectra of GaN/Si samples exhibited the GaN E₂(low) and E₂(high) phonon modes clearly without Raman features from the Si substrate, overcoming the difficulties from visible (532 nm) Raman measurements with strong Si Raman features overwhelming the GaN signals. The combined UV excitation Raman–PL spectra revealed multiple LO phonons spread over the GaN fundamental band edge emission PL band due to the outgoing resonance effect. Calculation of the UV Raman spectra determined the carrier concentrations with excellent values. Angular-dependent NEXAFS on Ga K-edge revealed the significant anisotropy of the conduction band of w-GaN and identified the NEXAFS resonances corresponding to different final states in the hexagonal GaN films on Si. Comparative GaN material properties are investigated in depth.

A series of indium nitride (InN) thin films have been grown on sapphire substrates by molecular beam epitaxy (MBE) technology under different growth conditions of temperature and plasma power. Their structural, surface, and optical properties are studied by a variety of techniques of scanning electron microscopy, Hall effect, x-ray diffraction, photoluminescence (PL), Raman scattering, x-ray photoelectron spectroscopy (XPS), synchrotron radiation x-ray absorption near edge structure (XANES), and so on. The lower carrier concentration in InN can be obtained with a higher MBE growth temperature and a lower plasma power. As the plasma power increases, the PL peak energy is observed to shift toward the higher energy side and the Raman E2 (high) and A1 (LO) modes are shifted to the lower frequency. The residual compressive strain in epitaxial InN is relaxed. The lower plasma power and the higher growth temperature are preferred for the MBE growth of high-quality InN films. The influencing factors on the InN PL peak and band gap Eg have been revealed. It is evidenced that the InN PL peak and Eg can be shifted from high down to ∼0.65 eV with the carrier concentration down to low E19 cm−3 and the plasma power down to ∼80 W. Both the XPS and N K-edge XANES revealed the antisite defect of N on the In site, NIn. The XANES In L-edge measurements on the In L3-edge of InN films with various carrier concentrations has indicated the fourfold InN intermediate crystal structures. These obtained results are significant and useful to deepen the understanding and promote further investigation in InN and III-N materials.

MgZnO possesses a tunable bandgap and can be prepared at relatively low temperatures, making it suitable for developing optoelectronic devices. Mg_xZn_1−xO (x~0.1) films were grown on sapphire by metal–organic vapor phase epitaxy under different substrate-growth temperatures T_s of 350–650 °C and studied by multiple characterization technologies like X-ray diffraction (XRD), spectroscopic ellipsometry (SE), Raman scattering, extended X-ray absorption fine structure (EXAFS), and first-principle calculations. The effects of T_s on the optical, structural, and surface properties of the Mg_0.1Zn_0.9O films were studied penetratively. An XRD peak of nearly 35° was produced from Mg_0.1Zn_0.9O (0002) diffraction, while a weak peak of ~36.5° indicated MgO phase separation. SE measurements and analysis determined the energy bandgaps in the 3.29–3.91 eV range, obeying a monotonically decreasing law with increasing T_s. The theoretical bandgap of 3.347 eV, consistent with the SE-reported value, demonstrated the reliability of the SE measurement. Temperature-dependent UV-excitation Raman scattering revealed 1LO phonon splitting and temperature dependency. Zn-O and Zn-Zn atomic bonding lengths were deduced from EXAFS. It was revealed that the surface Mg amount increased with the increase in T_s. These comprehensive studies provide valuable references for Mg_0.1Zn_0.9O and other advanced materials.