S. Guermazi

Porous silicon as an intermediate buffer layer for GaN growth on (100) Si

We report preliminary results on the growth of GaN on (100) Si substrate using porous silicon (PS) as an intermediate buffer layer. The growth was in situ monitored by laser beam reflectivity. Analysis of the evolution of the reflectivity signal indicates a change from relatively flat surface to rough one as the growth temperature (Tg) is increased. At a temperature of about 1050°C, the growth rate is very low and the reflected signal intensity is constant. When the growth temperature is varied, no drastic change of the porosity of the intermediate layer was detected. Scanning electron microscope (SEM) observations of the GaN/SP/Si structure revealed a good surface coverage at 500°C. When Tg increases, the structure morphology changes to columnar like structure at 600°C, and well-developed little crystallites with no preferential orientation appear at 800°C. These observations agree well with the X-ray diffraction (XRD) analysis. A preferential hexagonal growth is obtained at low growth temperature, while cubic phase begin to appear at elevated temperatures.

Cathodoluminescence and depth profiling studies of unintentionally doped GaN films grown by MOVPE

GaN layers are grown by metalorganic vapor phase epitaxy at 1050 °C on porous silicon and (111) oriented silicon substrates. AlN buffer layers of about 100 nm thickness were previously deposited on Si substrates. The effect of substrates on optical properties is revealed by Cathodoluminescence measurements (CL), recorded at room temperature and liquid nitrogen temperature. Various excitonic transitions are depicted. Spectral features associated with F°X energy around 3.4 eV and bound excitons (D°X and A°X in the range 3.29–3.35 eV) related to wurtzite GaN excitons are observed. Yellow band is located around 2.15 eV. CL depth profiling is also investigated at various e-beam energies (3–25 keV). The low-energy electron beam irradiation reveals an inhomogeneous distribution of point defects in depth, and high non-radiative recombination beyond a threshold energy. Good agreement between our experimental data and literature is obtained. Moreover, CL investigations prove that growth of GaN on (111) oriented Si substrate improve the crystalline quality of the layer.

Theoretical and Experiment Study of Cathodoluminescence of GaN

In this work, we report the theoretical and experimental results of cathodoluminescence (CL) from GaN layers with thickness (1–3) micron grown at 800 °C by MOVPE on silicon substrate. The CL measurements were performed in a digital scanning electron microscope DSM 960 at room temperature. The CL spectra recorded at room temperature (RT) show the main UV peak at 3.42 eV of the fundamental transition and a broad yellow band at 2.2 eV attributed the intrinsic defects and extrinsic dopants and impurities. The simulation of the CL excitation and intensity is developed using consistent 2‐D model based on the electron beam energy dissipation and taking into account the effects of carrier diffusion, internal absorption and the recombination processes in GaN. Then, we have investigated the evolution of the CL intensity from GaN as a function the electron beam energy in the range Eo = (5–20) keV. A comparative study between experimental and simulated CL spectra at room temperature is presented.