In this thesis, we study a series of Si-doped GaN thin films and nanodots. These samples are growth on c-face sapphire substrate by Molecular Beam Epitaxy. In Si-doped GaN thin film growth, different Si cell temperature are used to control the dopant concentration. Van der Pauw hall measurement is used to measure the carrier concentrations and the mobilities. As increase Si cell temperature, the carrier concentration and the mobility increase. The maximum carrier concentration is 8 ¡Ñ 1019 cm-3, and the maximum mobility is 194 cm2/V-s. As increasing the Si dopant concentration, the near band edge photoluminescence emission peak intensity increases, but the full width at half maximum broaden from 47 meV to 117 meV. In Raman measurement result, with the increasing of Si dopant concentration, the E2(high) mode shifts from 569.4 cm-1 to 567.9 cm-1. The A1(LO) mode disappears gradually. In the nanodot growth, the AFM images show that the nanodots size become large as increasing the growth time. The nanodots size is change from 1.2 nm to 5.6 nm high and 40 nm to 110 nm wide, but the density of the nanodots decreases from 1.9 ¡Ñ 1010 cm-2 to 6 ¡Ñ 109 cm-2 at 15 sec and 90 sec growth, respectively. According to the AFM image of the nanodots surface morphology, the nanodots growth mode should be the Stranski-Krastanow mode.

Ultrafast time-resolved pump-probe (TRPP) apparatus has been applied to study the carrier dynamics of Si-doped InN thin films grown buffer by molecular beam expitaxy with and without a low-temperature growth GaN buffer layer. The peak of the PL has been found to increase from 0.7 to 0.8 eV with the back ground density. The total decay rates as a function of the delay time were obtained by the density-dependent TRPP peak intensity and the time-resolved TRPP signals. The total decay rates were interpreted as the sum of radiative and nonradiative recombination. The Shockley-Read-Hall decay rate derived from the TRPP signal at low photoexccitation density was found to increase with the doping density. At low concentration, the Auger recombination is not effective. The dominant recombination mechanism at room temperature is the Shockely-Read-Hall recombination.

In this thesis, we study a series of Si doped InN films. These samples are grown on sapphire (0001) by molecular beam epitaxy (MBE). We have doped Si in InN films successfully. In this experiment, we control Si cell temperature to change carrier concentration of samples during InN film growth. The carrier concentration and mobility are explored by van der Pauw Hall measurement. As carrier concentration increases, mobility decreases. Carrier concentration changes with Si cell temperature from 6.16x1018 cm-3 to 1.19x1020 cm-3. Photoluminescence (PL) emission peak energy shows blue shift when carrier concentration increases, but the intensity decreases and full width at half maximum (FWHM) broadens. The PL peak of InN film with 1.19x1020 cm-3 split into two peaks 0.74 eV and 0.89 eV. In Raman spectra, Raman modes position and FWHM do not change with carrier concentration. In temperature dependence PL, the dependence of PL spectra shows decrease when carrier concentration increases. In power dependence PL, the PL emission peak energy of InN films with 6.16x1018 cm-3 and 8.50x1018 cm-3 show blue shift, while the PL peaks of InN films with 1.43x1019 cm-3 and 2.27x1019 cm-3 show no significant move. The fitting of power density vs. intensity is linear for all samples, but all slope of them are less than 1 expect for InN film with 1.43x1019 cm-3.