A. Bousetta

Formation of carbon nitride films on Si(100) substrates by electron cyclotron resonance plasma assisted vapor deposition

We report the growth of thin carbon nitride films on Si(100) substrates at temperatures in the range of 100–700 °C using electron‐beam evaporation of graphite assisted with electron cyclotron resonance (ECR) plasma generated nitrogen species. The effect of the substrate temperature, and the nitrogen flow on the composition ratio C/N, and the C—N bonding were investigated using Fourier transform infrared spectroscopy (FTIR), x‐ray photoelectron spectroscopy (XPS), Rutherford backscattering spectroscopy (RBS), and Raman spectroscopy. The FTIR spectra show that the films produced exhibit a very high visible to infrared transmittance (0.85–0.95). These spectra were dominated by amine group (NH2) with the presence of C‐N stretching modes. From both RBS and XPS, the nitrogen concentration in the film was calculated and was found in the range of 24%–48%, depending on the nitrogen partial pressure in the ECR source. Raman spectrum of the high nitrogen content thin film shows a well resolved peak at 1275 cm−1 sugg...

Physical properties of thin carbon nitride films deposited by electron cyclotron resonance assisted vapor deposition

Electron cyclotron resonance (ECR) plasma‐assisted vapor deposition has been used to grow thin carbon nitride films on Si(100) and sapphire substrates. The composition, structure, and optical properties of the films were investigated by x‐ray photoelectron spectroscopy (XPS), Rutherford backscattering (RBS), Raman, and optical absorption spectroscopies. The effect of varying the nitrogen gas flow, at constant substrate temperature and carbon deposition rate, on the C/N composition ratio and the CxNy crystal structure was investigated. From both RBS and XPS, the nitrogen concentration in the film was found to be in the range of 20%–48% and varied directly with the nitrogen partial pressure in the ECR source. In CN films with low nitrogen content, the Raman spectra showed no evidence of CN bonding and were characteristic of graphitic carbon. In contrast, the Raman spectra of high nitrogen content thin films show a wide peak at 1291 cm−1, suggesting the formation of a CxNy phase with predominately sp3 bondin...

Electrical properties of boron nitride thin films grown by neutralized nitrogen ion assisted vapor deposition

Boron nitride (BN) thin films (containing mixed cBN/hBN phase) have been deposited on Si(100) substrates using neutralized nitrogen beam and electron beam evaporation of boron. All as‐deposited BN films were p type with a room‐temperature carrier concentration in the range of 5×1016 to 1×1017 cm−3. The Mg‐doped BN films showed carrier concentrations in the range of 1.2×1018 cm−3 to 5.2×1018 cm−3 when the Mg cell temperature was varied from 250 to 500 °C. The films were analyzed for both majority elements (B and N) and dopant/impurity (Si, Mg, Fe, etc.) incorporation using secondary ion mass spectroscopy and mass spectroscopy of recoiled ions (MRSI). MRSI is shown to be superior for dopant characterization of boron nitride thin films.

Growth of cubic boron nitride on Si(100) by neutralized nitrogen ion bombardment

Highly cubic phase and stoichiometric boron nitride films were deposited on Si(100) substrates using a neutralized nitrogen beam and electron beam evaporation of boron. High intensity, focused, and low‐energy neutralized nitrogen beam was supplied using a newly developed neutralizer atomic beam ion source (NABS) adapted to a Kaufman‐type ion source. The films were grown at substrate temperatures in the range 400–500 °C and a boron evaporation rate of 0.2 A/s. Infrared transmittance spectra of the films showed that a highly cubic phase (80%) was obtained in the area of the focused beam. These films were compared to those obtained using similar conditions but with the NABS disconnected from the ion source, and it was found that the cubic phase content decreases drastically (10%). The results show that the NABS was the determining factor in enhancing the formation of the cubic boron nitride films. Furthermore, the addition of Ar to N, which is reported to increase the momentum transfer and promote the format...

The investigation of GaN growth on silicon and sapphire using in-situ time-of-flight low energy ion scattering and RHEED

In-situ time-of-flight low energy ion scattering (TOF-LEIS) and reflection high energy electron diffraction (RHEED) is used effectively to monitor surface structure, major elements, and impurities during substrate annealing, nitridation and thin film growth of GaN on Si and Al 2 O 3 substrates by electron-cyclotron-resonance (ECR) assisted MBE. During the annealing process of silicon, a combination of time-of-flight direct recoil spectroscopy (TOF-DRS) and mass spectroscopy of recoiled ions (MSRI) was used to monitor the desorption of surface contaminants such as H, C, and O. A change from a 1 x 1 RHEED pattern of oxygen-covered Si(001) to a 1 x 2 + 2 x 1 RHEED pattern, evidence of a clean Si(001) substrate, was observed. For the case of Al 2 O 3 (0001), a 1 x 1 RHEED pattern of the hexagonal structure was seen when all major contaminants were removed, as indicated by MSRI. The nitridation of a clean Al 2 O 3 surface was followed by RHEED and the formation of an AlN overlayer was confirmed by MSRI. A 1 x 1 RHEED pattern was observed after GaN thin film growth on sapphire, indicating a good crystalline structure. Si nitridation and subsequent deposition of columnar GaN on Si, resulted in an amorphous RHEED pattern. MSRI spectra showed the presence of Si in addition to Ga and N. When nitridation of Si was avoided the resulting GaN film was polycrystalline as observed by RHEED and complete coverage occurred, evidenced by the absence of Si in the MSRI spectra. The results show that a combination of RHEED and TOF-LEIS permit real-time optimization of substrate preparation and thin film growth parameters.

Investigation of GaN deposition on Si, Al2O3, and GaAs using in situ mass spectroscopy of recoiled ions and reflection high‐energy electron diffraction

In situ mass spectroscopy of recoiled ions (MSRI) and reflection high‐energy electron diffraction (RHEED) are used to monitor the surface structure, and the near surface layer composition during the pre‐growth preparation step and the deposition of GaN thin films on Si (001), Al2O3 (0001), and GaAs (001) substrates by electron‐cyclotron‐resonance (ECR)‐assisted molecular beam epitaxy. Due to the high lattice mismatch between GaN thin films and these substrates, the initial nucleation step is found to be critical on the resulting thin film properties. Nitridation of the clean Al2O3 (0001) and GaAs(001) surface is observed by RHEED, and the formation of an AlN/GaN overlayer is confirmed by MSRI. During GaN deposition on Si, Al2O3, and GaAs, MSRI and RHEED are used to follow the growth mode and coverage. If a RHEED pattern from the nucleating GaN overlayer has a cubic or wurtzitic symmetry and the MSRI spectra—which is sensitive to the first few monolayers—shows the presence of Ga and N, only then the growth is layer by layer. Scanning electron microscopy micrographs also show a smooth and continuous surface. If an amorphous RHEED pattern is observed and the presence of the Si (Al, O in the case of Al2O3 and As in the case of GaAs) signal is detected in addition to Ga and N, the growth is columnar. In conclusion, we show that RHEED and MSRI form a powerful combination of thin film surface characterization tools ideally suited for real‐time optimization of substrate preparation and thin film growth parameters for the nitride materials system.

The nitridation of GaAs and GaN deposition on GaAs examined by in situ time-of-flight low energy ion scattering and RHEED

Abstract The growth of GaN on traditional zincblende III–V semiconductors such as GaAs is important technologically. Due to the high lattice mismatch between GaAs and III–V nitrides, the use of a buffer layer is always required. This can be achieved through either a low temperature buffer, a strained superlattice, or nitridation of GaAs surfaces by electron cyclotron resonance (ECR) bombardment. While this last process was shown to improve the electrical and optical properties of the nitride thin films, no detailed investigation of the nitridation process has been reported. In this work, in situ time-of-flight low energy ion scattering (TOF-LEIS) and reflection high energy electron diffraction (RHEED) are used to monitor surface structure, major elements, and impurities during the nitridation of GaAs as a function of time, temperature, and ECR power.