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• B-doped diamond-like C film grown by (CH 4 +Ar+B 2 H 6) plasma at 3.55 Pa, 450 °C and −40 V bias. • With B doping, I D /I G increased, while both I Dia /I D and I Dia /I G reduced in Raman data. • Optimized film attained ∼3.02 ×10−5 s cm−1 conductivity, 3.35 eV band gap and 50 % sp 3 content. • At minute doping XRD peak of diamond 〈111〉 plane evolved with a minor rise in band gap. The main objective of this work was the preparation and optimization of boron-doped diamond-like carbon (DLC) films having a good crystalline structure, and electronic and optical properties, at an extremely low deposition pressure and relatively low growth temperature, by varying the flow rates of precursor gases (CH 4 , B 2 H 6, and Ar) in the plasma controlled at 800 W of RF power. Planar inductively coupled plasma-enhanced chemical vapour deposition technique was used to enable deposition at ∼5.33 Pa and 450 °C, at a constant negative substrate bias of -40 V. The flow rate of the dopant gas (B 2 H 6) was changed to obtain a set of samples, while the precursor gas (CH 4) flow rate was kept fixed. The doped sample, prepared with B 2 H 6 /CH 4 ratio (r) = 1 %, was found to possess a maximum I D /I G (intensity ratio of the D peak with the G peak) of ∼0.819 and a minimum I Dia /I G ratio (relative intensity of the Diamond peak to the G peak) of ∼1.149. A high sp3 content of ∼50 % was revealed from the X-ray photoelectron spectroscopy analysis and the transmission electron microscopy images also indicated the presence of prominent 〈111〉, 〈220〉, and 〈311〉 crystallographic planes. The B-doped DLC film possessed enhanced electrical conductivity (σ RT) of ∼3.02 ×10−5 S cm−1 relative to the intrinsic DLC films, a corresponding minimum of activation energy (ΔE H) (as calculated in the above room-temperature regime) of ∼170 meV, an optical band gap (E g) of ∼3.35 eV, and the root mean square roughness of ∼48.12 nm. [ABSTRACT FROM AUTHOR]

Optical, structural, and electrical characterizations of the Si:H network have been performed during its changes occurred by the increasing H2 dilution to the SiH4 ensemble in hot-wire chemical vapor deposition (HWCVD). A rapid structural transformation from a mostly amorphous phase to comprehensive micro/nanocrystallinity was attained at a relatively low H2 dilution, even at a low substrate temperature, because of the associated abundance of atomic H in HWCVD. However, elevated H2 dilution induces enormous polyhydrogenation and formation of lesser dense network full of voids, mostly around the tiny micro/nanocrystallites. This highly defective grain boundary zone provides high density of electronic trapping centers and contributes significantly to the transport of carriers. The overall electrical transport in the amorphous-micro-nano-crystalline heterogeneous Si:H network has been accounted in the framework of a three-phase model comprised of amorphous and crystalline (micro- and nano-) components while the grain boundary being the third phase, separately contributing to a potential energy barrier in between. The three-phase model to the electrical phenomena of nanocrystalline structures convincingly explains the dual activation energies arising in the electrical conduction with distinguishably different temperature dependent behaviors from that occurs in the conventional amorphous matrix. [ABSTRACT FROM AUTHOR]

Systematic investigation on the optoelectronic and structural changes occurring in the p –nc-Si network due to the inclusion of oxygen into the initial crystalline-like matrix has been done. The incorporation of O into the Si network occurs via the Si–O–Si bond which is effectively responsible for the widening of optical band gap. B incorporation takes place via the B–Si bonds as well as the B–O bonds which increases at enhanced CO 2 dilution to the plasma. The continuously increased intensity of (SiH 2 ) n wagging and Si-H 2 bending mode in p –nc-SiO x films indicates poly-hydrogenation as inherent to the increasing oxygen alloying of the network. Two stage activation energies across around 340 K in the temperature dependent dark conductivity identify prominent two phase structure of the p –nc-SiO x material, the Si-ncs being embedded within amorphous p –SiO x matrix. The p –nc-SiO x film grown by typical 13.56 MHz PE-CVD at a low growth temperature ∼170 °C and optimized with a convincingly good combination of the electrical conductivity (σ D ∼6.8 × 10 −2 S cm −1 ), optical band gap (E g ∼1.91 eV) and volume fraction (X C ∼54%) of the Si crystallinity containing C H <6 at% and C O < 1 at%, emerges highly competent for effective utilization in the window layer of nc-Si p – i – n solar cells with superstrate configuration. [ABSTRACT FROM AUTHOR]

Using low-pressure planar inductively coupled plasma CVD at 87% H 2 -dilution to the SiH 4 plasma, nc-Si:H films are prepared that possess preferential growth along 〈2 2 0〉 crystallographic orientation with I 220 / I 111 > 1.2, bonded H-content of ∼5.5 at.%, a low microstructure factor of ∼0.56, along with a reasonably high σ D ∼ 5.2 × 10 −4 S cm −1 , Δ E ∼ 143 meV and σ Ph ∼ 1.4 × 10 −3 S cm −1 . The growth of the nc-Si:H network has been optimized to a moderately high nanocrystallinity (∼68%), with an average grain size of ∼8 nm. The overall network comprises a significant fraction of ultra-nanocrystalline component, X unc / X nc ∼ 0.47, which are dominantly inhabited by the thermodynamically preferred 〈2 2 0〉 crystallographic orientation that provides convenient electrical transport perpendicular to the film surface and subsequently could facilitate photovoltaic performance. The cross-sectional view of the fracture surface demonstrates columnar structures, closely correlated to the favored growth of the nanocrystallites along 〈2 2 0〉 crystallographic orientation that retains direction perpendicular to the substrate surface. The underlying phenomena could be demonstrated as a consequence of preferential growth induced by high atomic H density present in the planar inductively coupled SiH 4 plasma obtained via much lower H 2 -dilution compared to that realized in conventional capacitively coupled plasma-CVD. The nc-Si:H films with precise material properties as well as the allied low-pressure ICP-CVD growth process could be of significant use in further progress of nc-Si solar cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • Single-step growth of DLC films with nanocrystal phase on glass substrate, without diamond powder pre-treatment. • Inductively coupled low-pressure high electron-density (CH 4 + Ar) plasma used for the film deposition. • Optimum DLC film obtained at –40 V dc substrate-bias, 450 °C, 900 W rf power and 25 sccm CH 4 flow. • DLC film showed [I D /I G ] min ∼0.61 with [I Dia /I D ] max ∼1.09 in Raman and ~64% of sp3 bonds in XPS data. • DLC film exhibited wide optical band gap ∼3.71 eV and 〈1 1 1〉 nanocrystal facets in the network. Working at relatively low-temperature and low-pressure, the development and optimization of diamond-like carbon (DLC) films with significant nanodiamond components on inexpensive glass substrates, without conventional pre-treatment by diamond powders, is the main objective of the present work. Using the most familiar CH 4 -precursors diluted by Ar in a high-density plasma triggered at high rf power (900 W) in a planar inductively-coupled plasma chemical vapour deposition (ICP-CVD) system, DLC thin-films are prepared via optimization in the flow rate of the precursor gas at 30 mTorr (∼4 Pa) pressure and 450 °C substrate temperature and, further by applying negative dc-bias to the substrates. The optimized samples obtained with negative substrate-bias possess good crystalline properties. From Raman results, the most crystalline sample is obtained with characteristic minimum I D /I G ratio reduced from 0.75 to 0.61, maximum I Dia /I D enhanced from 0.94 to 1.09, and the sp3 hybridized C C bonds increased from 44% to ∼64% at a substrate-bias of –40 V. The residual stress, and the optical band gap were calculated from Raman analysis. The optimized DLC film exhibits a high optical band gap (3.71 eV) as calculated from Tauc's plot analysis of the UV–Vis data. The well-identified 〈1 1 1〉 crystallographic planes in the TEM micrograph demonstrate a significant fraction of nanocrystalline diamond component in the optimum DLC film. [ABSTRACT FROM AUTHOR]

Thin film nano-diamonds have been synthesised using CH4/H2mixture by micro-wave plasma enhanced CVD (MW-PECVD) at a substrate temperature as low as 250°C. These are found to be spherically shaped, homogeneously distributed on the film surface (size ∼100 nm) and are related to ball-like or ballas-like nano-diamonds. With the increment of temperature from 200°C to 250°C, these spherical structures are found to form in increasing number density, but the same could not be grown with the variation of power and pressure. However, the bulk material is found to improve in crystallinity with the increment of pressure and highly polycrystalline nano-diamonds (111), along with Graphitic [(100), (004)] inclusions, have been grown using a gas pressure of 70 Torr and 500 W of MW power. The preliminary results on FE-SEM, Raman and HR-TEM studies are discussed here. Further developments of the material and characterisation are in progress. [ABSTRACT FROM AUTHOR]

Highlights: [•] Si films of ~86% nanocrystallinity prepared by ICP-CVD at 300°C. [•] 〈220〉 Crystallographic orientation is favored at higher grain size. [•] Photoluminescence blue shift demonstrated on lowering in grain size around 4–5nm. [ABSTRACT FROM AUTHOR]

Abstract: Application of appropriate dc bias to the substrate has been identified as one of the efficient parameters, beyond the mostly used classical ones, in controlling the growth of nanocrystalline silicon (nC-Si:H) network by plasma CVD of SiH4. The present communication demonstrates that applying negative dc substrate bias at the moderate level the overall nanocrystallinity in the material be enhanced significantly. The nC-Si:H film of ∼70% crystalline volume fraction along with a high σD ∼3.1×10–4 Scm–1 and Eσ ∼191meV has been obtained at a low substrate temperature of 200°C and with a growth rate of ∼8nm/min from only 1sccm of the feed gas SiH4, using −75V dc substrate bias and He as the diluent to the plasma. Besides the extent of crystallinity, the average grain size (ρ) has been demonstrated to be controllable within nano-dimensions, 1< ρ<10nm, by tuning negative dc substrate bias during plasma processing. The present report comprehensively elaborates the effect of applied negative dc substrate bias on the growth morphology of the nC-Si:H thin films from He-diluted SiH4 plasma, in view of controlling nanocrystallization at low substrate temperature by RF-PCVD, while controlled transmission of energy to the growing surface obtained from metastable and ionic helium (He* and He+) bombardment has been deemed instrumental. [Copyright &y& Elsevier]

Abstract: Effect of H2-dilution to the SiH4 plasma, R(H2), on the microcrystallization of Si:H network at a low substrate temperature (180°C) has been studied by using hot-wire CVD. Structural characterization of the films has been performed by micro-Raman, ellipsometry, infrared absorption and X-ray diffraction studies. A dramatic structural transformation from amorphous to microcrystalline phase has been identified at an H2-dilution beyond 92.0%, induced by high atomic H density in the plasma. A virtual saturation in overall crystallinity has been attained for H2-dilution in the range 92.75⩽R(H2) (%)⩽93.75, contributing crystalline volume fraction changing between 60% and 64%, the average crystalline grain size varying between 150 and 200Å and bonded hydrogen content maintaining between 3.3 and 2.6at%. A crystalline volume fraction of 86.6% was obtained along with a low bonded H-content of 1.76at% at R(H2)=98.0%. However, at such extremely high H2-dilution, overall crystallization is hindered due to enormous polyhydrogenation and formation of lesser dense network full of voids. Hence, microcrystallization in Si-network can be easily obtained in HWCVD, at a relatively low hydrogen dilution and low substrate temperature, without compromising much with the deposition rate arising out of those two stringent factors affecting in the conventional technique; and thereby, enhancing the technological acceptability of the deposition process presently dealt with. [Copyright &y& Elsevier]

In view of obtaining a Si:H network at the onset of microcrystallinity at a high deposition rate, we have adopted an intelligent approach to find out a tricky plasma condition in radio frequency (rf) plasma-enhanced chemical vapor deposition that provides a better control on growth introducing retarded microcrystallization. The deposition parameter includes a combination of high electrical power applied to the (SiH4+H2)-plasma and high gas pressure in the reaction chamber. High rf power increases the number density of film-forming precursors as well as atomic H density in the plasma, which helps to increase the film deposition rate and to promote microcrystallinity, respectively. In addition, high pressure helps not only to increase the film-growth rate by producing a dense plasma but also retards the microcrystallization process by increasing significantly the gas phase collision frequency and consequently reducing the effective reactivity of atomic H on the surface of a fast-growing Si:H network. A combination of high-power and high-pressure plasma conditions provides a reasonably wide range of H2 dilution to work with and better control in producing a Si:H network at the onset of microcrystallinity, while increasing the film-growth rate. [ABSTRACT FROM AUTHOR]

In view of using doped nanocrystalline Si (nc-Si) as the emitter layer in nc-Si/crystalline-Si heterojunction solar cells, a very thin (≤ 50 nm) emitter layer with high conductivity and superior crystallinity is optimum. In the present work, p -nc-Si:H thin film prepared in inductively coupled plasma chemical vapor deposition, without using additional H 2 -dilution in [SiH 4 + B 2 H 6 (1% in H 2)]-plasma, retains conductivity ~10−1 S cm−1 and crystallinity ~68% at a low thickness (t) ~50 nm. The charge carrier transport through the heavily doped nc-Si network demonstrates reverse Meyer–Neldel characteristics for t ≥ 50 nm. However, with reduction to t < 50 nm, the evolution of the ultra-nanocrystalline dominated amorphous network, accompanied by accumulation of Si–H–Si platelet-like components in the grain boundary, leads to a drastic reduction in conductivity to 10−4 S cm−1. In this context, the post-deposition and short-time hydrogen plasma treatment (PSHPT) on the as-deposited ultra-thin (t ~30 nm) film becomes instrumental in substantially enhancing the crystallinity from 40% to 69% and increasing conductivity by two orders of magnitude to 10−2 S cm−1. The network modification by PSHPT proceeds via transformation of the surface and sub-surface weak bonds and is significant for the ultra-thin film compared to the thick film, due to retaining a superior surface-to-bulk ratio. [Display omitted] • Preparation of highly conducting p -nc-Si thin film at a low thickness using ICP-CVD. • Maintaining adequate crystallinity in the p -nc-Si thin film at thickness ~50 nm. • A drastic fall in conductivity and crystallinity in ultra-thin film of thickness ~30 nm. • Improvement in conductivity and crystallinity by post-deposition H 2 -plasma treatment. • H 2 -plasma treatment on emitter layer improves heterojunction solar cell characteristics. [ABSTRACT FROM AUTHOR]

A comprehensive analysis on the electrical transport phenomena prevailing in undoped nc-Si/a-SiNx:H thin films prepared by inductively coupled plasma chemical vapor deposition and its correlation with the specific inhomogeneous structure, consisting of a mixture of different phases involving charge transfer by tunneling and thermionic emission or a connected network of aggregates of such components, has been made for deeper understanding in order to facilitate and improve the device applicability of the material. The nc-Si/a-SiNx:H films exhibit a thermally activated electrical transport above room temperature. Multi-phonon hopping (MPH), following σ∝Ty, occurs below room temperature, involving higher number of acoustic phonons in less crystalline network at higher nitrogenation. In less nitrogenated network, the MPH conduction continues up to the lowest temperature because of less localization of charge carriers within larger size of the nanocrystallites. Mott variable range hopping (Mott-VRH), following ln(σ) ∝ T-¼, is in effect below a certain temperature for highly nitrogenated network. The nature of variations of Mott parameter, T*, hopping activation energy, Wh, optimum hopping distance, rh, and the estimated density of states at the Fermi level, N(EF), identify the increased degree of disorder in the film attributing enhanced amorphous concentration at higher nitrogenation. The transition from MPH to Mott-VRH occurring at higher temperature at relatively higher nitrogenation has been interpreted as the freezing out of the acoustic phonons associated with lower grain size with higher number density at comparatively higher temperature, considering the phonon wavelength approximately of the size of nanocrystallites. The present intrinsic nc-Si/a-SiNx:H material containing nanocrystallites of average size ∼12-2 nm and number density ∼1011-1012 cm-2 providing a significantly wide range of optical band gap, Eg ∼ 1.80-2.75 eV with associated very high electrical conductivity, σD ∼ 10-2-10-6 S cm-1 along with high carrier concentration, ne ∼ 1014-1011 cm-3 and electron mobility, μe ∼ 246-105 cm2 V-1 s-1, seems to be the superior, concerning issues related to usability in device fabrication, among typical wide optical gap silicon dielectric materials available in the literature, e.g., silicon carbide, silicon oxide, and amorphous silicon films with nc-Si inclusions; while being the only comprehensive report on nanocrystalline silicon nitride (nc-Si/a-SiNx:H) thin films, in particular. [ABSTRACT FROM AUTHOR]

A Ge top layer of thickness ∼ 1. 2 μ m was grown on the top Si of a silicon-on-insulator (SOI) wafer by plasma-enhanced chemical vapor deposition (PECVD) technique followed by rapid thermal annealing (RTA) makes this a GeSOI wafer. The top active Ge layer on RTA recrystallizes into a compact layer of Ge nanocrystals with lattice constants close to those of the Ge single crystal enabling device fabrication and a partially suspended Ge microline photodetector was fabricated that can show adequate photo gain. It was established through simulation that the partial suspension of the microline is necessary to isolate the microlines from the bulk of the wafer which inhibits carrier recombination by the underlying oxide layer. • A Ge top layer on SOI wafer has been grown using PECVD technique. • The defects incorporated during deposition have been restored by RTA at 600°C. • Raman spectroscopy, XTEM, GIXRD study reveals the quality of top Ge layer. • Grown Ge layer was found to be adequate for fabricating a photodetector. • Necessity of partial suspension was established by COMSOL simulation. [ABSTRACT FROM AUTHOR]