Influence of the deposition parameters on the microstructure and opto-electrical properties of hydrogenated nanocrystalline silicon films by HW-CVD

Hydrogenated nanocrystalline silicon (nc-Si:H) films were prepared at high deposition rates (> 13 Å/s) from pure silane without hydrogen dilution by hot wire deposition method by varying filament-to-substrate distance (d_s-f). In this study we have systematically and carefully investigated the effect of filament-to-substrate distance on structural, optical and electrical properties of the Si:H films. A variety of characterization techniques, including Raman spectroscopy, low angle X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Atomic Force Microscopy (AFM), Field Emission Scanning Electron Microscopy (FE-SEM), UV-Visible-NIR spectroscopy and electrical dark and photoconductivity measurement were used to characterize these films. Films deposited at d_s-f > 5 cm are amorphous while those deposited at d_s-f < 5 cm are biphasic; a crystalline phase and an amorphous phase with nano-sized crystallites embedded in it. Low angle X-ray diffraction analysis showed that the crystallites in the films have preferential orientation along (111) directions. Decrease in d_s-f, the crystallinity and crystalline size increases whereas hydrogen bonding shifts from mono-hydride (SiH) to di-hydride (SiH₂) and poly-hydride (SiH₂)_n complexes. The band gaps of nc-Si:H films (~ 1.9-2.0 eV) are high compared to the a-Si:H films, while hydrogen content remains < 10 at.%. We attribute the high band gap to the quantum size effect. A correlation between electrical and structural properties has been established. Finally, from the present study it has been concluded that the filament-to-substrate distance is a key process parameter to induce the crystallinity in the films by hot wire method. The ease of depositing films with variable crystallite size and its volume fraction, and tunable band gap is useful for fabrication of tandem/micro-morph solar cells.     

Electrical and optical properties of titanium nitride coatings prepared by atmospheric pressure chemical vapor deposition

In order to examine the possibility for TiN coatings to be low-E, TiN coatings were deposited on the glass substrates by atmospheric pressure chemical vapor deposition using titanium tetrachloride (TiCl₄) and ammonia (NH₃) as precursors. X-ray diffraction, sheet resistance measurement, optical transmittance spectroscopy and infrared reflectance spectroscopy were carried out to determine the relationships between the preparation parameters and the microstructure, electrical and optical properties of the coatings. The results showed that the concentration of crystals increased with increasing the substrate temperature and the flow of TiCl₄, resulting in a decrease of the electrical resistivity. The optical transmittance of TiN thin films was strongly dependent on the gas flow and the substrate temperature. Under optimum conditions, continuous polycrystalline TiN coatings with FCC structure were obtained with an electrical conductivity around 34.5 Ω/□, an optical transmittance around 50% in the visible range, and an infrared reflectance higher than 50% above 3000 nm. This indicates that TiN coated glasses may be possible candidates for high IR reflectance windows.     

Effect of N2/CH4 flow ratio on microstructure and composition of hydrogenated carbon nitride films prepared by a dual DC-RF plasma system

Hydrogenated carbon nitride (a-CN:H) films were deposited on n-type (1 0 0) silicon substrates making use of direct current radio frequency plasma enhanced chemical vapor deposition (DC-RF-PECVD), using a gas mixture of CH₄ and N₂ as the source gas in range of N₂/CH₄ flow ratio from 1/3 to 3/1 (sccm). The deposition rate, composition and bonding structure of the a-CN:H films were characterized by means of X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectrometry (FTIR). The mechanical properties of the deposited films were evaluated using nano-indentation test. It was found that the parameter for the DC-RF-PECVD process had significant effects on the growth rate, structure and properties of the deposited films. The deposition rate of the films decreased clearly, while the N/C ratio in the films increased with increasing N₂/CH₄ flow ratio. CN radicals were remarkably formed in the deposited films at different N₂/CH₄ flow ratio, and their contents are related to the nitrogen concentrations in the deposited films. Moreover, the hardness and Young’s modulus of the a-CN:H films sharply increased at first with increasing N₂/CH₄ flow ratio, then dramatically decreased with further increase of the N₂/CH₄ flow ratio, and the a-CN:H film deposited at 1/1 had the maximum hardness and Young’s modulus. In addition, the structural transformation from sp³-like to sp²-like carbon-nitrogen network in the deposited films also was revealed.     

Microstructure of hydrogenated silicon carbide thin films prepared by chemical vapour deposition techniques

We present the results of investigations on a variety of stoichiometric μc-SiC:H films deposited by Hot-Wire- and Plasma-Enhanced Chemical Vapour Deposition using monomethylsilane diluted in hydrogen as precursor gas. Infrared spectroscopy, grazing incidence X-ray diffraction, and Transmission Electron Microscopy were applied and compared to separate the contributions from the different structure phases of the material. It is shown that an evaluation of the crystalline volume fraction from the infrared absorption lineshape of the Si–C stretching mode is not possible, although stated in the literature. A correlation of this lineshape with the material strain is proposed. Moreover, a variation in strain, grain size, and structural defects is found depending on the deposition conditions, but a mixture of an amorphous and a crystalline phase could not unambiguously be identified.     

Correlation between nitrogen incorporation and structural modification of hydrogenated carbon nitride films

The growth and microstructure of hydrogenated carbon nitride a-CN_x:H (0 ? x ? 0.10) films deposited by PECVD have been studied. Upon the analysis of FTIR spectra, Raman spectra and XPS, it is concluded that π doping could take place even at a very low percentage of nitrogen, which favors the formation of sp² carbon clusters. The C 1s peak shifts toward higher binding energy while the N 1s peak remains constant as the nitrogen content in the film increases, which can be considered as a result of the chemical shifts on charge transfer due to the strong electronegativity of the N atom. 3D profile measurements show that there were a great number of particles formed when nitrogen is incorporated in to the films and the particles coalescence when the nitrogen content increases due to enhanced surface diffusion. The stress of the films converts from compressive to tensile stress gradually with increased N content. The elimination of grain boundaries and annihilation of excess vacancies, due to columnar structure increasing by diffusion leads to volume shrinkage of the film, thus causing tensile stress. These analyses were fairly consistent to help understand the effects of nitrogen in hydrogenated carbon films.     

Dielectric properties of Zr-Sn-Ti-O thin films prepared by pulsed laser deposition

Zr_0.26Sn_0.23Ti_0.51O₂ (ZSTO) films with a dielectric constant of about 40 have been prepared directly on silicon substrates by pulsed laser deposition at 600 °C. TEM observation showed that the as-deposited films are amorphous. Differential thermal analysis showed that the ZSTO films crystallize at about 620 °C. Capacitance-voltage (C-V) characteristics of metal-oxide-semiconductor (MOS) composed of Pt/ZSTO/Si prepared at different deposition temperature have been measured. The EOT of the MOS structures with the same ZSTO physical thickness increased slightly when the deposition temperature increased. The EOT is about 4.2 nm for the 40 nm ZSTO deposited at 600 °C. The leakage current characteristics of ZSTO films for the as deposited, post-annealed in oxygen ambient and post-annealed in nitrogen ambient by rapid thermal annealing have been studied comparatively. The films post-annealed in nitrogen ambient have the lowest leakage current and the as-deposited films have the largest leakage current characteristics. It is proposed that amorphous Zr-Sn-Ti oxide stabilized at 600 °C is a potential dielectric material for dynamic random access memory and high k dielectric gate applications.     

Properties of hydrogenated amorphous silicon prepared by chemical vapor deposition

Properties of hydrogenated amorphous silicon (a-Si:H) prepared by chemical vapor deposition (CVD) are reported and compared to corresponding properties of glow discharge a-Si:H. The CVD material was produced from mixtures of silane, disilane, trisilane and higher polysilanes in hydrogen carrier gas at one atmosphere total pressure, at substrate temperatures from 420 to 530 °C. The photovoltaic properties of our present CVD a-Si:H are somewhat inferior to those of the best glow discharge a-Si:H. However, as discussed below, there are some indications that higher quality CVD a-Si:H may be possible.     

Photocatalytic TiO2 films prepared by chemical vapor deposition at atmosphere pressure

Nanometer semiconductor titanium dioxide thin films have excellent properties of photocatalysitic degeneration. The glass coated TiO₂ films is called self-cleaning glass. In this paper, chemical vapor deposition (CVD) method is employed to deposit TiO₂ films on glass. The effect of spacing between nozzle and glass and the effect of substrate temperature on deposition rate are studied. The crystalline structure at different deposition temperatures is analyzed by XRD and anatase was found. And the microstructure of the TiO₂ films is also determined by SEM. It shows that the size of crystal grain increases with the temperature.     

Characterization of hydrogenated amorphous silicon thin films prepared by magnetron sputtering

Magnetron sputtered hydrogenated amorphous silicon (a-Si:H) thin films have been characterized. Hydrogen (H₂) with argon (Ar) was introduced into the sputtering chamber to create the plasma. A sudden increase in the deposition rate occurred when the hydrogen was added. The maximum hydrogen content of 16 atomic percent (at.%) was achieved and a bandgap of about 2.07 eV was determined from the spectral investigations of the hydrogenated films. The effect of radio frequency (RF) power on the deposition rate, as well as on the hydrogen content was investigated. To change the hydrogen content in the films, the hydrogen flow rate was varied while keeping the argon flow rate constant. The hydrogen content in the films increased with increasing hydrogen flow rate up to the maximum content of 16 at.% and then decreased for further increases in hydrogen flow.     

Effect of heat treatment on phase transformation of aluminum nitride ultrafine powder prepared by chemical vapor deposition

Ultrafine aluminum nitride (AlN) powders were obtained by chemical vapor deposition via AlCl₃–NH₃–N₂ system operated at various temperatures and at a same 200 cm³/min flow rate of NH₃ and N₂, respectively. It has been shown that when the reaction temperature of AlCl₃ and NH₃ was above 600°C, then crystalline AlN powder can be formed; whereas, amorphous AlN was obtained with NH₄Cl if reacted in a lower-temperature zone of the reaction chamber. The amorphous AlN powder was heat treated at 1400°C under NH₃ and N₂ atmosphere for 2 h, then the crystalline phases of the obtained powder belong to a single phase of AlN; a mixture of AlN and Al₂O₃ and only AlON, respectively. On the other hand, if crystalline AlN powder is heat treated at 1400°C under N₂ atmosphere for 2 h, the crystalline phases were composed of the major phase of AlN and a minor phase of Al₂O₃. The morphology, particle size and agglomerate size of the AlN powder were strongly dependent on the heat-treatment temperature. The particle size of AlN powder increases from 28.1 to 45.0 nm, as the heat treatment temperature increases from 800 to 1400°C.     

X-ray photoelectron spectroscopy studies on the bonding properties of oxygenated amorphous carbon nitride thin films synthesized by pulsed laser deposition at different substrate temperatures

Oxygenated amorphous carbon nitride thin films (a-CN_xO_y) were deposited by pulsed laser deposition of camphoric carbon (CC) target at various substrate temperatures (ST). The influence of ST on the bonding properties of a-CN_xO_y films was investigated. The nitrogen to carbon (N/C) atomic ratio and oxygen to carbon (O/C) atomic ratio, bonding state and microstructure of the deposited a-CN_xO_y films were characterized by X-ray photoelectron spectroscopy (XPS) and been confirmed using standard measurement techniques. The bonding states between the C and N, and C and O in the deposited films are found significantly influenced by the ST during deposition process. The N/C and O/C atomic ratio of the a-CN_xO_y films reached the maximum value at 400 °C. The XPS C 1s shows the bonding state of a-CN_xO_y films changes from diamond-like tetrahedral (sp³) carbon and carbon (C–C) bonding to graphite-like trihedral (sp²) CC bonding with the increase of ST. While, the XPS N 1s shows the sp³ C–N bonds increases with higher rates compared with sp² CN bonds up to 400 °C, after which it decreases with higher ST. The C–N bonding of C–N, CN and CN were observed in the deposited a-CN_xO_y films.     

1H-1,2,3-triazole,a promising precursor for chemical vapor deposition of hydrogenated carbon nitride

Well-crystallized hydrogenated carbon nitride thin films have been prepared by microwave plasma enhanced chemical vapor deposition (MWPECVD). 1H-1,2,3-triazole+N₂ and Si (1 0 0) were used as precursor and substrate, respectively. Substrate temperature during the deposition was recorded to be 850 °C. The synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photo-electron spectroscopy (XPS) analyses. The plasma compositions were checked by optical emission spectroscopy (OES). XRD observation strongly suggests that the films contain polycrystalline carbon nitride with graphitic structure of (1 0 0), (0 0 2), (2 0 0) and (0 0 4). XPS peak quantification reveals that the atomic ratio of the materials C:N:O:Si is 32:41:18:9. X-ray photo-electron peak deconvolution shows that the most dominant peak of C (1s) and N (1s) narrow scans correspond to sp² hybrid structure of C₃N₄. These observations indicate that 1H-1,2,3-triazole favors the formation of hydrogenated carbon nitride with graphitic phase by CVD method and thus is in good agreement with XRD results. SEM of surface and OES of plasma also support the formation of polycrystalline carbon nitride films from 1H-1,2,3-triazole+N₂ by CVD.     

Nanoindentation investigation of amorphous hydrogenated carbon thin films deposited by ECR-MPCVD

Nanomechanical properties of amorphous hydrogenated carbon thin films are performed by nanoindentation technique. The amorphous hydrogenated carbon films are produced on silicon substrate by electron cyclotron resonance microwave plasma chemical vapor deposition (ECR-MPCVD). The effect of negative bias voltage on amorphous hydrogenated carbon films is examined by Raman spectroscopy and the results showed that the intensity ratio of D-peak to G-peak (I_D/I_G) of amorphous hydrogenated carbon films at various bias voltages, increased as the bias voltage increased. The results also showed that Young’s modulus and hardness also increased as the bias voltage increased. In addition, Young’s modulus and hardness both decreased as the indentation depth increased.     

Structure,properties and gas sensing effect of SnSe2 films prepared by pulsed laser deposition method

Amorphous SnSe₂ films were prepared by pulsed laser deposition (PLD) from solid polycrystalline targets. The atomic scale structure has been revealed by X-ray diffraction. Hardness and electrical properties were measured. Strong gas sensing properties have been evidenced for the first time in heat treated films.     

Optical and electrical properties of chlorinated and hydrogenated amorphous silicon prepared by glow discharge

Chlorinated and hydrogenated amorphous silicon films were prepared by glow discharge of a SiCl₄/H₂ mixture. Infrared spectra of these films show that, in addition to the hydrogen induced bands, two new modes appear at 545 cm^?1 (SiCl stretching) and 500 cm^?1 (Si TO modes induced by chlorine). Observation of the 545 cm^?1 band proves that chlorine is able to act as a dangling bond terminator in an amorphous silicon matrix. A good agreement is found between the total amount of chlorine determined by electron microprobe analysis and the value estimated from the integrated strength of the SiCl stretching mode. The relatively high value of the optical band gap (1.80 eV) of our material containing only 5 at.% bonded hydrogen shows that chlorine plays a major role in the optical gap value. Electrical conductivity, photoconductivity and luminescence properties are qualitatively similar to that of a: SiH films.     

Formation of hydrogenated amorphous carbon films containing fullerene-like structures

Hydrogenated amorphous carbon films containing fullerene-like structures were obtained by magnetron sputtering of a titanium target in methane and argon atmosphere. The microstructure of the film was investigated by transmission electron microscopy and Raman spectra. Additionally, the three stage model proposed by Ferrari and Robertson was used to explain the formation process of fullerene-like structures. The results show that titanium target was covered by a hydrocarbon layer, and the new-produced hydrocarbon layer on titanium target rather than the titanium surface was sputtered during deposition. The product of the sputtering can serve as ‘seeds’ for the formation of fullerene-like structures. These ‘seeds’ or nuclei are proposed to be open graphene structures, at the effect of ions bombardment, more defects are introduced and the curved structure arises due to incorporation of odd member rings into the graphene sheets, which resulted in the formation of curved planes with small radii of curvature and closed fullerene-like structure.     

Optical band gap of zinc nitride films prepared by reactive rf magnetron sputtering

Polycrystalline Zn₃N₂ films are prepared on Si and quartz glass substrates by RF magnetron sputtering at room temperature. The structural and optical properties are studied by X‐ray diffraction and double beam spectrophotometer, respectively. X‐ray diffraction indicates that the Zn₃N₂ films deposited on Si and quartz glass substrates both have a preferred orientation in (321) and (442), also are cubic in structure with the lattice constant a=0.9847 and 0.9783 nm, respectively. The absorption coefficients as well as the film thickness are calculated from the transmission spectra, and their dependence on photon energy is examined to determine the optical band gap. Zn₃N₂ is determined to be an indirect‐gap semiconductor with the band gap of 2.11(2) eV. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrical properties of PbxSn1‐xS thin films prepared by hot wall deposition method

The Pb_xSn_1‐xS (x = 0 – 0.25) thin films were prepared on glass substrates by hot wall vacuum deposition. The films were polycrystalline monophase in nature and had orthorhombic crystal structure. The thickness of the films was about 2‐3 μm. The temperature dependences of the conductivity were measured in the temperature range from 150 to 420 K. The films revealed p‐type of conductivity. The Seebeck coefficient and conductivity values of the films was in the range of α = 6 – 360 μV/K and σ = 4.8×10^‐5 – 1.5×10^‐2 Ω^‐1·cm^‐1, respectively, at room temperature depending on concentration of the lead in the films. The lead atoms created the substitution defects Pb_Sn in the crystal lattice of the Pb_xSn_1‐xS. These defects formed the donor energy levels in the band gap. The activation energy of the films increased in the range ΔE_a = 0.121 – 0.283 eV with increasing of the lead concentration. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)