Nanodiamond formation by hot-filament chemical vapor deposition on carbon ions bombarded Si

Nanocrystalline diamond films were grown by a two-step process on Si(1 0 0) substrate, which was first pretreated by pure carbon ions bombardment. The bombarded Si substrate was then transformed into a hot-filament chemical vapor deposition (HFCVD) system for further growth. Using the usual CH4/H-3 feed gas ratio for micro crystalline diamond growth, nanodiamond crystallites were obtained. The diamond nucleation density is comparable to that obtained by biasing the substrate. The uniformly distributed lattice damage is proposed to be responsible for the formation of the nanodiamond. (C) 2002 Elsevier Science B.V. All rights reserved.

Parasitic reaction and its effect on the growth rate of AlN by metalorganic chemical vapor deposition

The Al composition of metalorganic chemical vapor deposition (MOCVD)-grown AlGaN alloy layers is found to be greatly influenced by the parasitic reaction between ammonia (NH3) and trimethylaluminum (TMAI). The growth process of AlN is carefully investigated by monitoring the in situ optical reflection. The abnormal dependencies of growth rate on growth temperature, reactor pressure, and flux of NH3 are observed and can be well explained by the effect of parasitic reaction. The increase of growth rate with increasing flux of TMAI is found to depend on the growth temperature and reactor pressure due to the presence of parasitic effect. A relatively low growth temperature and a reduced reactor pressure are suggested for the effective decrease of parasitic reaction during the MOCVD growth of AlN and probably lead to a more effective incorporation of Al into the AlGaN layers. (c) 2005 Elsevier B.V. All rights reserved.

Effects of annealing treatment on the formation of CO2 in ZnO thin films grown by metal-organic chemical vapor deposition

Post-growth annealing was carried out on ZnO thin films grown by metal-organic chemical vapor deposition (MOCVD). The grain size of ZnO thin film increases monotonically with annealing temperature. The ZnO thin films were preferential to c-axis oriented after annealing as confirmed by Xray diffraction (XRD) measurements. Fourier transformation infrared transmission measurements showed that ZnO films grown at low temperature contains CO2 molecules after post-growth annealing. A two-step reaction process has been proposed to explain the formation mechanism of CO2, which indicates the possible chemical reaction processes during the metal-organic chemical vapor deposition of ZnO films.

Normal incidence p-i-n Ge heterojunction photodiodes on Si substrate grown by ultrahigh vacuum chemical vapor deposition

We report on normal incidence p-i-n heterojunction photodiodes operating in the near-infrared region and realized in pure germanium on planar silicon substrate. The diodes were fabricated by ultrahigh vacuum chemical vapor deposition at 600 degrees C without thermal annealing and allowing the integration with standard silicon processes. Due to the 0.14% residual tensile strain generated by the thermal expansion mismatch between Ge and Si, an efficiency enhancement of nearly 3-fold at 1.55 mu m and the absorption edge shifting to longer wavelength of about 40 nm are achieved in the epitaxial Ge films. The diode with a responsivity of 0.23 A/W at 1.55 mu m wavelength and a bulk dark current density of 10 mA/cm(2) is demonstrated. These diodes with high performances and full compatibility with the CMOS processes enable monolithically integrating microphotonics and microelectronics on the same chip.

Metalorganic chemical vapor deposition of GaNAs alloys using different Ga precursors

The GaNAs alloys have been grown by metalorganic chemical vapor deposition (MOCVD) using dimethylhydrazine (DMHv) as the nitrogen precursor, triethylgallium (TEGa) and trimethylgallium (TMGa) as the gallium precursors, respectively. Both symmetric (004) and asymmetric (1 1 5) high-resolution X-ray diffraction (HRXRD) were used to determine the nitrogen content in GaNAs layers. Secondary ion mass spectrometry (SIMS) was used to obtain the impurity content. T e influence of different Ga precursors on GaNAs quality has been investigated. Phase separation is observed in the < 1 1 5 > direction when using TMGa as the Ga precursor but not observed when using TEGa. This phenomenon should originate from the parasitic reaction between the Ga and N precursors. Furthermore. samples grown with TEGa have better quality and less impurity contamination than those with TMGa. Nitrogen content of 5.742% has been achieved using TEGa and no phase separation observed in the sample. (C) 2002 Elsevier Science B.V. All rights reserved.

Blue-yellow ZnO homostructural light-emitting diode realized by metalorganic chemical vapor deposition technique

We report on the realization of ZnO homojunction light-emitting diodes (LEDs) fabricated by metalorganic chemical vapor deposition on (0001) ZnO bulk substrate. The p-type ZnO epilayer was formed by nitrogen incorporation using N2O gas as oxidizing and doping sources. Distinct electroluminescence (EL) emissions in the blue and yellow regions were observed at room temperature by the naked eye under forward bias. The EL peak energy coincided with the photoluminescence peak energy of the ZnO epilayer, suggesting that the EL emissions emerge from the ZnO epilayer. In addition, the current-voltage and light output-voltage characteristics of ZnO homojunction LEDs have also been studied. (c) 2006 American Institute of Physics.

Structural and optical properties of a-plane ZnO thin films synthesized on γ-LiAlO2 (302) substrates by low pressure metal-organic chemical vapor deposition

Nonpolar a-plane (1120) ZnO thin films have been fabricated on gamma-LiAlO2 (302) substrates via the low-pressure metal-organic chemical vapor deposition. An obvious intensity variation of the E-2 mode in the Raman spectra indicates that there exhibits in-plane optical anisotropy in the a-plane ZnO thin films. Highly-oriented uniform grains of rectangular shape can be seen from the atomic force microscopy images, which mean that the lateral growth rate of the thin films is also anisotropic. It is demonstrated experimentally that a buffer layer deposited at a low temperature (200 degrees C) can improve the structural and optical properties of the epilayer to a large extent. (c) 2007 Elsevier B.V. All rights reserved.

Characterization of m-plane ZnO thin film on gamma-LiAlO2 (100) substrate by metal-organic chemical vapor deposition

Non-polar (1 (1) over bar 00)m-plane ZnO thin film has been prepared on gamma-LiAlO2 (100)substrate via the low pressure metal organic chemical vapor deposition. Obvious intensity variation of the E-2 mode in the polarized Raman spectra and the absorption edge shift in the polarized optical transmission spectra indicate that the m-plane film exhibits optical anisotropy, which have applications in certain optical devices, such as the UV modulator and polarization-dependent beam switch. From the atomic force microscopy images, highly-oriented uniform-sized grains of rectangular shape were observed. (c) 2008 Elsevier B.V. All rights reserved.

Structural and optical properties of Al1-xInxN epilayers on GaN template grown by metalorganic chemical vapor deposition

This paper reports that Al1-xInxN epilayers were grown on GaN template by metalorganic chemical vapor deposition with an In content of 7%-20%. X-ray diffraction results indicate that all these Al1-xInxN epilayers have a relatively low density of threading dislocations. Rutherford backscattering/channeling measurements provide the exact compositional information and show that a gradual variation in composition of the Al1-xInxN epilayer happens along the growth direction. The experimental results of optical reflection clearly show the bandgap energies of Al1-xInxN epilayers. A bowing parameter of 6.5 eV is obtained from the compositional dependence of the energy gap. The cathodoluminescence peak energy of the Al1-xInxN epilayer is much lower than its bandgap, indicating a relatively large Stokes shift in the Al1-xInxN sample.

Impact of thickness of GaN buffer layer on properties of AlN/GaN distributed Bragg reflectors grown by metalorganic chemical vapor deposition

We studied the impact of the thickness of GaN buffer layer on the properties of distributed Bragg reflector (DBR) grown by metalorganic chemical vapor deposition (MOCVD). The samples were characterized by using metallographic microscope, transmission electron microscope (TEM), atomic force microscopy (AFM), X-ray diffractometer (XRD) and spectrophotometer. The results show that the thickness of the GaN buffer layer can significantly affect the properties of the DBR structure and there is an optimal thickness of the GaN buffer layer. This work would be helpful for the growth of high quality DBR structures.

Photoluminescence properties of tensile-strained GaAsP/GaInP single quantum wells grown by metal organic chemical vapor deposition

Tensile-strained GaAsP/GaInP single quantum well (QW) laser diode (I-D) structures have been grown by low-pressure metal organic chemical vapor deposition (LP-MOCVD) and related photoluminescence (PL) properties have been investigated in detail. The samples have the same well thickness of 16 nm but different P compositions in a GaAsP QW. Two peaks in room temperature (RT) PL spectra are observed for samples with a composition larger than 0.10. Temperature and excitation-power-dependent PL spectra have been measured for a sample with it P composition of 0.15. It is found that the two peaks have a 35 meV energy separation independent of temperature and only the low-energy peak exists below 85 K. Additionally, both peak intensities exhibit a monotonous increase as excitation power increases. Analyses indicate that the two peaks arise from the intrinsic-exciton recombination mechanisms of electron-heavy hole (e-hh) and electron-light hole (e-hh). A theoretical calculation based oil model-solid theory, taking, into account the spin-orbit splitting energy, shows good agreement with our experimental results. The temperature dependence of PL intensity ratio is well explained using the spontaneous emission theory for e-hh and e-hh transitions. front which the ratio can be characterized mainly by the energy separation between the fill and Ill states.

The influence of low-temperature Ge seed layer on growth of high-quality Ge epilayer on Si(100) by ultrahigh vacuum chemical vapor deposition

High-quality Ge epilayer on Si(1 0 0) substrate with an inserted low-temperature Ge seed layer and a thin Si0.77Ge0.23 layer was grown by ultrahigh vacuum chemical vapor deposition. The epitaxial Ge layer with surface root-mean-square roughness of 0.7 nm and threading dislocation density of 5 x 10(5) cm(-2) was obtained. The influence of low temperature Ge seed layer on the quality of Ge epilayer was investigated. We demonstrated that the relatively higher temperature (350 degrees C) for the growth of Ge seed layer significantly improved the crystal quality and the Hall hole mobility of the Ge epilayer. (C) 2008 Elsevier B.V. All rights reserved.

High rate deposition of microcrystalline silicon films by high-pressure radio frequency plasma enhanced chemical vapor deposition (PECVD)

Hydrogenated microcrystalline silicon (mu c-Si:H) thin films were prepared by high-pressure radio-frequency (13.56 MHz) plasma enhanced chemical vapor deposition (rf-PECVD) with a screened plasma. The deposition rate and crystallinity varying with the deposition pressure, rf power, hydrogen dilution ratio and electrodes distance were systematically studied. By optimizing the deposition parameters the device quality mu c-Si:H films have been achieved with a high deposition rate of 7.8 angstrom/s at a high pressure. The V-oc of 560 mV and the FF of 0.70 have been achieved for a single-junction mu c-Si:H p-i-n solar cell at a deposition rate of 7.8 angstrom/s.