Microstructure of the silicon film prepared near the phase transition regime from amorphous to nanocrystalline

A kind of hydrogenated diphasic silicon films has been prepared by a new regime of plasma enhanced chemical vapor deposition (PECVD) near the phase transition regime from amorphous to nanocrystalline. The microstructural properties of the films have been investigated by the micro-Raman and Fourier transformed Infrared (FT-IR) spectra and atom force microscopy (AFM). The obtained Raman spectra show not only the existence of nanoscaled crystallites, but also a notable improvement in the medium-range order of the diphasic films. For the FT-IR spectra of this kind of films, it notes that there is a blueshift in the Si-H stretching mode and a redshift in the Si-H wagging mode in respect to that of typical amorphous silicon film. We discussed the reasons responsible for these phenomena by means of the phase transition, which lead to the formation of a diatomic hydrogen complex, H-2* and their congeries.

Strong red light emission from silicon nanocrystals embedded in SIO2 matrix

In this study, silicon nanocrystals embedded in SiO2 matrix were formed by conventional plasma enhanced chemical vapor deposition (PECVD) followed by high temperature annealing. The formation of silicon nanocrystals (nc-Si), their optical and micro-structural properties were studied using various experimental techniques, including Fourier transform infrared spectroscopy, micro-Raman spectra, high resolution transmission electron microscopy and x-ray photoelectron spectroscopy. Very strong red light emission from silicon nanocrystals at room temperature (RT) was observed. It was found that there is a strong correlation between the PL intensity and the substrate temperature, the oxygen content and the annealing temperature. When the substrate temperature decreases from 250degreesC to RT, the PL intensity increases by two orders of magnitude.

MOCVD growth of cubic GaN: Materials and devices

Many impressive progresses have been made recently on the growth of cubic-phase GaN by MBE and MOCVD. In this paper, some of our recent progress will be reviewed, including the growth of high quality cubic InGaN films, InGaN/GaN heterostructure blue and green LEDs. Cubic-phase GaN films were grown on GaAs (100) substrates by MOCVD. Growth conditions were optimized to obtain pure cubic phase GaN films up to a thickness of 4 mum. An anomalous compressive strain was found in the as-grown GaN films in spite of a smaller lattice constant for GaN compared with that of GaAs substrates. The photoluminescence FWHM of high quality InGaN epilayers was less than 100 meV The InGaN/GaN heterostructure blue LED has intense electroluminescence with a FWHM of 20 nm.

In situ annealing during the growth of relaxed SiGe

In this paper, a graded Si1-xGex buffer and thereafter the Si0.8Ge0.2 uniform layer were grown at a little lower temperature to keep the surface smooth, which will provide the gliding dislocations a wider channel and less low energy nucleation sites on the surface. Therefore, the dislocation density may be reduced. However, the motion of the existing threading dislocations cannot retain equilibrium at lower temperature, strain will accumulate and be in favor of the nucleation of dislocation. In situ annealing was used to reduce the residual strain in the sample during the low-temperature growth of SiGe. A fully relaxed Si0.8Ge0.2 layer was obtained with the surface dislocation density of 3x10(5)cm(-2).

Indium-doping enhanced two-dimensional-electron-gas performance in AlGaN/GaN heterostructures

Indium (In)-doping was applied in GaN layers during growth of AlGaN/GaN heterostructure with unintentionally doped or modulation Si-doped AlGaN layers. It was found that In-doping was effective in improving electron sheet density of two-dimensional-electron-gas (2DEG) in the heterostructures. Furthermore, In-doping also improved mobility in heterostructures with Si modulation-doped in AlGaN layers. The possible reasons were discussed. X-ray diffraction (XRD) and wet chemical etching revealed that crystalline quality of GaN was improved by In-doping. It was proposed that In-doping modified growth kinetics of GaN.

The influence of oxygen content on photoluminescence from Er-doped SiOx

SiOx films with oxygen concentrations ranging 13-46 at.% were deposited by plasma enhanced chemical vapor deposition (PECVD) technique using: pure SiH4 and N2O mixture. Erbium was then implanted at an energy of 500 KeV with dose of 2x10(15) ions/cm(2). The samples were subsequently annealed in N-2 for 20 sec at temperatures of (300-950 degrees C). Room temperature (RT) photo-luminescence (PL) data were collected by Fourier Transform Infrared Spectroscopy (FTIS) with an argon laser at a wavelength of 514.5 nm and an output power from 5 to 2500 mw. The intense room-temperature luminescence was observed around 1.54 mu m. The luminescence intensity increases by 2 orders of magnitude as compared with that of Er-doped Czochralski (CZ) Si. We found that the Er3+ luminescence depends strongly on the SiOx microstructure. Our experiment also showed that the silicon grain radius decreased with increasing oxygen content and finally formed micro-crystalline silicon or nano-crystalline silicon. As a result, these silicon small particles could facilitate the energy transfer to Er3+ and thus enhanced the photoluminescence intensity.

High quality hydrogenated amorphous silicon films with significantly improved stability

High quality hydrogenated amorphous silicon (a-Si:H) films have been prepared by a simple "uninterrupted growth/annealing" plasma enhanced chemical vapor deposition (PECVD) technique, combined with a subtle boron-compensated doping. These a-Si:H films possess a high photosensitivity over 10(6), and exhibit no degradation in photoconductivity and a low light-induced defect density after prolonged illumination. The central idea is to control the growth conditions adjacent to the critical point of phase transition from amorphous to crystalline state, and yet to locate the Fermi level close to the midgap. Our results show that the improved stability and photosensitivity of a-Si:H films prepared by this method can be mainly attributed to the formation of a more robust network structure and reduction in the precursors density of light-induced metastable defects.

High temperature operation of 650nm AlGaInP quantum well laser diodes grown by LP-MOCVD

Low threshold current and high temperature operation of 650nm AlGaInP quantum well laser diodes grown by low pressure metal organic chemical vapor deposition (LP-MOCVD) are reported in this paper. 650nm laser diodes with threshold current as low as 22-24mA at room temperature, and the operating temperature over 90 degrees C at CW output power 5 mW were achieved in this study. These lasers are stable during 72 hours burn in under 5mW at 90 degrees C.

High performance 1.55 mu m InGaAsP/InP strained layer quantum well laser diodes fabricated by MOCVD overgrowth method

High performance uncooled 1.55 mu m InGaAsP/InP strained layer quantum well (SL-QW) lasers grown by low pressure metal organic chemical vapor deposition (LP-MOCVD) were reported in this paper. Whole MOCVD over growth method were applied in this work. The threshold currents of 5mA and the highest lasing temperature of 122 degrees C were obtained.

The study of single mode 650nm AlGaInP quantum well laser diodes for DVD

Single mode 650nm AlGaInP quantum well laser diodes grown by low pressure metal organic chemical vapor deposition (LP-MOCVD) was reported in this paper. Selected buried rigewaveguid were applied for single mode operation especially for DVD use. The operating temperature over 90 degree at CW output power 5 mW was achieved.

The diphasic nc-Si/a-Si : H thin film with improved medium-range order

A series of silicon film samples were prepared by plasma enhanced chemical vapor deposition (PECVD) near the threshold from amorphous to nanocrystalline state by adjusting the plasma parameters and properly increasing the reactions between the hydrogen plasma and the growing surface. The microstucture of the films was studied by micro-Raman and Fourier transform infrared (FTIR) spectroscopy. The influences of the hydrogen dilution ratio of silane (R-H = [H-2]/[SiH4]) and the substrate temperature (T-s) on the microstructural and photoelectronic properties of silicon films were investigated in detail. With the increase of RH from 10 to 100, a notable improvement in the medium-range order (MRO) of the films was observed, and then the phase transition from amorphous to nanocrystalline phase occurred, which lead to the formation of diatomic hydrogen complex, H-2* and their congeries. With the increase of T-s from 150 to 275 degreesC, both the short-range order and the medium range order of the silicon films are obviously improved. The photoconductivity spectra and the light induced changes of the films show that the diphasic nc-Si/a-Si:H films with fine medium-range order present a broader light spectral response range in the longer wavelength and a lower degradation upon illumination than conventional a-Si:H films. (C) 2004 Elsevier B.V. All rights reserved.

Influence of heated catalyzer on thermal distribution of substrate in HWCVD system

Based on Stefan-Boltzman and Lambert theorems, the radiation energy distribution on substrate (REDS) from catalyzer with parallel filament geometry has been simulated by variation of filament and system layout in hot-wire chemical vapor deposition. The REDS uniformity is sensitive to the distance between filament and substrate d(f-s) when d(f-s) less than or equal to 4 cm. As d(f-s) > 4 cm, the REDS uniformity is independent of d(f-s) and is mainly determined by filament number and filament separation. Two-dimensional calculation shows that the REDS uniformity is limited by temperature decay at filament edges. The simulation data are in good agreement with experiments. (C) 2003 Elsevier Science B.V. All rights reserved.

Type-II SiGe/Si MQWS (multi-quantum wells) and self-organized Ge/Si islands grown by UHV/CVD system

Type-II SiGe/Si MQWs (Multi-Quantum Wells) and Self-Organized Ge/Si Islands were successfully grown by a homemade ultra-high vacuum/chemical vapor deposition (UHV/CVD) system. Growth characteristics and PL (photoluminescence) spectra at different temperature were measured. It demonstrated that some accumulation of carriers in the islands results in the increase of the integrated PL intensity of island-related at a certain temperature range.

Heteroepitaxial growth and annealing of gamma-Al2O3 thin films on silicon

The gamma-Al2O3 films were grown on Si (100) substrates using the sources of TMA (Al (CH3)(3)) and O-2 by very low-pressure chemical vapor deposition (VLP-CVD). It has been found that the gamma-Al2O3 film has a mirror-like surface and the RMS was about 2.5nm. And the orientation relationship was gamma-Al2O3(100)/Si(100). The thickness uniformity of gamma-Al2O3 films for 2-inch epi-wafer was less than 5%. The X-ray diffraction (XRD) and reflection high-energy electron diffraction (RHEED) results show that the crystalline quality of the film was improved after the film was annealed at 1000degreesC in O-2 atmosphere. The high-frequency C-V and leakage current of Al/gamma-Al2O3/Si capacitor were also measured to verify the annealing effect of the film. The results show that the dielectric constant increased from 4 to 7 and the breakdown voltage for 65-nm-thick gamma-Al2O3 film on silicon increases from 17V to 53V.

Study on optical band gap of boron-doped nc-Si : H film

The optical band gap (E-g) of the boron (B)-doped hydrogenated nano-crystalline silicon (nc-Si:H) films fabricated using plasma enhanced chemical vapor deposition (PECVD) was investigated in this work. The transmittance of the films were measured by spectrophotometric and the E-g was evaluated utilizing three different relations for comparison, namely: alphahnu=C(hnu-E-g)(3), alphahnu=B-0(hnu-E-g)(2), alphahnu=C-0(hnu-E-g)(2). Result showed that E-g decreases with the increasing of Boron doping ratio, hydrogen concentration, and substrate's temperature (T-s), respectively. E-g raises up with rf power density (P-d) from 0.45W.cm(-2) to 0.60w.cm(-2) and then drops to the end. These can be explained for E-g decreases with disorder in the films.