We analyze properties of ultra-thin SiO2 + very thin SiOx double layer structure formed on high-doped n-type Si (100) wafers using FTIR, X-ray reflectivity and AFM methods. The observed absorption band around 1230 cm−1 is attributed to the longitudinal optical mode of SiOx precipitates incorporated in silicon matrix. In particular, the corresponding peak positions indicate that there are precipitates of SiOx with x >1.8. The absorption band around 1070 cm−1 is attributed to the Si–O–Si stretching bond. This position is characteristic for stoichiometric SiO2. From the results it can be concluded that differently shaped particles co-exist in the samples. This assumption is supported by the oxide density measurements performed by FTIR and X-ray reflectivity. We determined density of oxide layers, roughness of corresponding interfaces, and surface roughness by the X-ray reflectivity. The obtained values were compared with those determined by FTIR and AFM. Additionally, we present the results of multifractal analysis on a complete set of six samples.

In our previous publications [1, 2 and 3], spreading resistance probe (SRP) measurements for quality control of metal induced lateral crystallization (MILC) of amorphous silicon (a-Si) were studied, and the mechanism of nickel diffusion was simulated using technology computer-aided design (TCAD) modeling.

Now, we continue to present the explanation of experimental results by modeling with the Synopsys TCAD package, whereby models for resistivity vs. grain size in implanted recrystallized silicon layers are implemented and compared with experiments.

Findings show that the SRP method can be used for the characterization of the MILC process of amorphous silicon and that a comparison of experimental and calculated data allows both a turn from qualitative to quantitative analysis of recrystallized silicon film and an estimate of grain size. It has been found that grain size depends on location in the MILC region and on the time and temperature of recrystallization.

We have observed the growth of defects caused by optical illumination in liquid nitrogen. We kept the sample in liquid nitrogen over one year. After one year and half the ESR signal reached ∼1018 cm−3 with no evidence of saturation. After that, we step-wise annealed isochronal the sample up to room temperature, where two thirds of original defects were annealed out. After room temperature, the sample was annealing isothermally around 300 K for several months. At this temperature, the defects slowly anneal. After a hundred of hours at 295K, the defect density decreased 10x from its original value at 77K.

We fabricated PMOS SPC-Si TFTs which show better current uniformity than ELA poly-Si TFTs and superior stability compare to a-Si:H TFT on a glass substrate employing alternating magnetic field crystallization. However the leakage current of SPC-Si TFT was rather high for circuit element of AMOLED display due to many grain boundaries which could be electron hole generation centers. We applied off-state bias annealing of VGS=5V, VDS=−20V in order to suppress the leakage current of SPC-Si TFT. When the off-state bias annealing was applied on the SPC-Si TFT, the electron carriers were trapped in the gate insulator by high gate-drain voltage (25V). The trapped electron carriers could reduce the gate-drain field, so that the leakage current of SPC-Si TFT was reduced after off-state bias annealing. We applied AC-bias stress on the gate node of SPC-Si TFT for 20,000 seconds in order to verify that the leakage current of SPC-Si TFT could be remained low at actual AMOLED display circuit after off-state bias annealing. The suppressed leakage current was not altered after AC-bias stress. The off-state bias annealed SPC-Si TFT could be used as pixel element of high quality AMOLED display.

Hydrogenated amorphous silicon films containing silicon nanocrystalline inclusions (a/nc-Si:H) that have been n-type doped have been synthesized using a dual-plasma co-deposition system. We report the structural and electronic properties of n-type doped a/nc-Si:H as a function of phosphine doping level and nanocrystalline concentration. The volume fraction of nanocrystals in the doped a/nc-Si:H thin films is measured using Raman spectroscopy, and the hydrogen binding configurations are characterized using infra-red absorption spectroscopy. In undoped a/nc-Si:H, the inclusion of low and moderate nanocrystalline concentrations results in an increase in the dark conductivity, compared to a-Si:H films grown without nanocrystalline inclusions. In contrast, the addition of even a low concentration of silicon nanoparticles in doped a/nc-Si:H thin films leads to a decrease in the dark conductivity and photoconductivity, compared to pure a-Si:H films.

Vertical stacking of transistors is a promising technology which can realize compact and high-speed integrated circuits (ICs) with a short interconnect delay and increased functionality. Two layers of low-temperature fabricated single-grain thin-film transistors (SG TFTs) have been monolithically integrated. NMOS mobilities are 565 and 393 cm2/Vs and pMOS mobilities are 159 and 141 cm2/Vs, for the top and bottom layers respectively. A three-dimensional (3D) inverter has also been fabricated, with one transistor on the bottom layer and the other on the top layer. The inverters showed an output voltage swing of 0 to 5 V with a switching voltage of around 2 V.

Silicon-germanium (Si1−x Gex :H) thin films have been prepared by plasma enhanced chemical vapor deposition of SiH4 and GeH4 and measured during growth using real time spectroscopic ellipsometry. A two-layer virtual interface analysis has been applied to study the structural evolution of Si:H films prepared in multistep processes utilizing alternating intermediate and low H2-dilution material layers, which have been designed to produce predominately amorphous films with a controlled distribution of microcrystalline particles. The compositional evolution of alloy-graded a-Si1−x Gex :H has been studied as well using similar methods. In each case, depth profiles of microcrystalline content, f μc , or Ge content, x, have been extracted. Additionally, real time spectroscopic ellipsometry has been used to monitor post-deposition exposure of a-Si:H, a-Si1−xGex:H, and a-Ge:H films to a hydrogen plasma in situ in order to determine sub-surface amorphous film modification similar to that which would occur when a highly H2-diluted layer is deposited on a layer prepared with lower dilution. These analyses provide guidance for enhanced performance of Si:H based solar cells, through controlled bandgap grading using compositionally graded amorphous binary alloys (a-Si1−xGex :H) or the incorporation of controlled fractions of microcrystallites into bulk amorphous i-layer materials, and by providing a fundamental understanding of the modification of component layers during the deposition of subsequent layers in multilayer stacks.

A novel crystallization method for silicon based thin film transistor (TFT) is proposed for the fabrication of high performance large size flat panel displays. In spite of using almost the same TFT fabrication process as that of hydrogenated amorphous silicon (a-Si:H) TFT, the proposed metal capped laser thermal annealing method realizes the formation of uniform and dense micro crystalline silicon (μc-Si), and provides mobility of 3.1 cm2/V•s, threshold voltage (ΔVth) of 2.3 V, and sub threshold slope (S) of 0.93 V/decade. Moreover, proposed stacked n+ amorphous silicon structure realizes extremely low off-current maintaining high on-current. As the reliability of TFT, a threshold voltage sift (ΔVth) under the high current bias stress test (BTS) condition was investigated, and realized the assumed ΔVth of +1.77 V after 100,000 hours stress of 10 μA and 50°C. This value is 2 orders smaller than that of a-Si:H TFT and only three times larger than that of low temperature poly silicon (LTPS) TFT.

We believe that our μc-Si TFT technology is the suitable solution for the high quality, large size flat panel display mass-production.

We report on SiO2 film formation using Polysilazane precursor treated with remote oxygen plasma and high-pressure H2O vapor heating. Polysilazane precursor films with a thickness of 130 nm were formed on silicon substrates by spin coating method. They were annealed at 350°C in remote oxygen plasma at a pressure of 2.0×10−2 Pa and a 13.56×106 Hz radio frequency power of 300 W for 3h followed by 1.3×106-Pa-H2O vapor heating at 260°C for 3 h. Polysilazane precursor films were entirely oxidized by high-pressure H2O vapor heat treatment, and the density of Si-N bonding and Si-H bonding in Polysilazane precursor films were effectively dissociated by the combination of high-pressure H2O vapor heat treatment with remote oxygen plasma treatment. While MOS(Metal-Oxide-semiconductor) capacitors fabricated only by high-pressure H2O vapor heat treatment had a high specific dielectric constant of 6.1, a fixed oxide charge density of 1.3×1012 cm−2 and a density of interface trap of 5.4×1011 cm−2eV−1, the remote oxygen plasma treatment followed by high-pressure H2O vapor heat treatment allowed us to reduce them to 4.1 and 1.6×1011 cm−2, 4.2×1010 cm−2eV−1, respectively.

An important issue for the massive implementation of thin silicon technology in photovoltaic is the use of plastic substrates, which allow the use of roll-to-roll deposition systems and planar monolithic interconnection between the cells. However, the use of plastic substrates require a fully low temperature process; especially critical in the deposition of the thin amorphous (a-Si:H) or nanocrystalline (nc-Si:H) layers. Hot-Wire Chemical Vapour Deposition (HW-CVD) technique has demonstrated to be a good alternative to deposit quality thin films at low temperature. In this paper we focus our study on very thin (50 nm) n- and p-doped nc-Si:H films deposited at low substrate temperature around 100°C. We have observed that, in this low temperature deposition conditions, the promotion of an a Si:H incubation layer leads to a poor doping efficiency and poor electrical properties of the films. Hence, in addition to the optimization of the deposition conditions, we deposited doped layers by cyclically varying the hydrogen dilution (CVH) during deposition process. This CVH method promotes a layer-by-layer growth and inhibits the formation of the incubation layer. Several doped nc-Si:H layers have been deposited with and without this CVH method. The structural, electrical and optical properties of these films and advantage of CVH in improving the device quality of the thin doped layers are reported.

A multiplexer is a device that combines two or more signals onto a single output without losing their specificity. In this paper we present results on the use of multilayered a-SiC:H heterostructures either as wavelength-division multiplexing or demultiplexing device (WDM). The WDM is a glass/ITO/a-SiC:H (p-i-n)/ a-SiC:H(-p) /Si:H(-i)/SiC:H (-n)/ITO double heterostructure which faces the modulated light incoming together from different beams, each one with a specific wavelength and period. By reading out, at different applied bias, the photocurrent generated by all the incoming optical carriers, the information is multiplexed or demultiplexed and can be transmitted and recovered again. The devices were characterized through spectral response measurements, under different electrical bias and frequencies. Results show that in the multiplexing mode the output signal is balanced by the wavelength of each incoming optical carrier and modulated by their frequencies. In the demultiplexing mode the photocurrent is controlled by the applied voltage and optical bias allowing to regain the transmitted information. An electrical model is presented to explain the device operation.

Improved light-trapping is a major route to improving solar cell efficiencies. We design a combination of a 2-dimensional photonic crystal and a one-dimensional distributed Bragg reflector as the back reflector for a-Si:H solar cells. This configuration avoids inherent losses associated with textured back-reflectors. The photonic crystals are composed of ITO and can easily serve as a conducting back contact. We have optimized the geometry of the photonic crystal to maximize absorption using rigorous scattering matrix simulations. The photonic crystal provides strong diffraction of red and near-IR wavelengths within the absorber layer and can enhance the absorption by more than a factor of 10 relative to the case without the photonic crystal. The optical path length with the photonic crystal can improve over the limit for a random roughened scattering surface.

In this paper, we report on low noise, high fill factor amorphous silicon (a-Si:H) image sensor structures for indirect radiography. Two types of the sensor arrays comprising n-i-p photodiodes and m-i-s photosensors have been fabricated. The device prototypes contain 100 × 100 pixels, with a pixel pitch of 139 μm. The active-matrix addressing is provided by low off-current TFTs. The sensors are vertically integrated onto the TFT-backplane, by implementing a 3-μm-thick low-k interlayer dielectric. This dielectric layer serves to reduce the data line capacitance and to planarize underlying topography. The detector was designed for reduced data-line resistance and parasitic coupling. Details of the device design and fabrication, along with sensor performance characteristics, are presented and discussed.

Intrinsic hydrogenated amorphous silicon (a-Si:H) films can yield in outstanding electronic surface passivation of crystalline silicon (c-Si) wafers as utilized in the HIT (heterojunction with intrinsic thin layer) solar cells. We have studied the correlation between the passivation quality and the interface nature between thin amorphous layers and an underlying c-Si substrate for understanding the passivation mechanism. We found that a thin (∼5nm) intrinsic layer is inhomogeneous along the growth direction with the presence of a hydrogen rich layer at the interface and that completely amorphous films result in better passivation quality and device performance than an epitaxial layer. Post annealing improves carrier lifetime for the amorphous layer, whereas the annealing is detrimental for the epitaxial layer. We have also found that the passivation quality of intrinsic a Si:H(i) film deteriorates severely by the presence of a boron-doped a-Si:H(p+) overlayer due to Si-H rupture in the a-Si:H(i) film. Finally, for a passivation layer in the hetero-junction structure, a-Si1−xOx will be demonstrated in comparison with a-Si:H.

Electrical techniques based on capacitance and conductance measurements are powerful tools for interface characterization in semiconductor heterostructures. We here detail their application to the study of the heterointerface formed between hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si). The main parameters governing the device applications are the conduction and valence band mismatch, and the density of interface states. The presence of a high interface states density can be revealed by capacitance versus temperature and frequency measurements. For very high quality interfaces that are required for instance to reach high conversion efficiencies in solar cells, the usual measurements performed in the dark and at zero or reverse bias are not sensitive enough. We show that the sensivity to interface states can be enhanced by using capacitance measurements under illumination and at a forward bias close or equal to the open-circuit voltage. In this case, the measured capacitance is determined by the diffusion of free carriers in c-Si and limited by recombination at the interface. Regarding the determination of band offsets, the method using a plot of the inverse square capacitance as a function of bias to determine the intercept of the extrapolated linear region is shown to lead to errors even in the absence of any interface charge. This is due to the presence of a strong inversion layer in c-Si at the interface, the effect of which has been ignored so far in the literature. The presence of this strong inversion layer is evidenced from planar conductance measurements on (n) a-Si:H/(p) c-Si structures. We emphasize that these measurements are very sensitive to details of the band structure profile. In particular, it is shown that the temperature dependence of the sheet electron density allows the determination of the conduction band offset between a-Si:H and c-Si with a good precision. We find 0.15 ± 0.04 eV.

The as-deposited passivation quality of amorphous silicon films on crystalline silicon surfaces is dependent on deposition conditions and resulting hydrogen bonding structure. However the initial surface passivation can be significantly improved by low temperature post-deposition anneal. For example an improvement in effective lifetime from 780 μsec as-deposited to 2080 μsec post-anneal is reported in the present work. This work probes the hydrogen bonding environment using monolayer resolution Brewster angle transmission Fourier transform infrared spectroscopy of 100 Å thick films. It is found that there is significant restructuring at the a-Si:H / c-Si interface upon annealing and a gain of mono-hydride bonding at the c-Si surface is detected. Calculations show an additional 3.56 − 4.50 × 1014 cm−2 mono-hydride bonding at c-Si surface due to annealing. The estimation of the surface hydride oscillator strength in transmission mode is reported for the first time to be 7.2 × 10−18 cm on Si (100) surface and 7.5 × 10−18 cm on Si (111).

This paper presents the mechanical characterization of both elastic and fracture properties of thin silicon films from the load-deflection response of membranes, also known as the bulge test. Properties extracted include the plane-strain modulus, prestress, fracture strength and Weibull modulus. Diaphragms made of low-temperature, hydrogenated amorphous and nanocrystalline silicon films (a-Si:H and nc-Si:H, respectively) deposited by plasma enhanced chemical vapor deposition (PECVD) and, for comparison, membranes composed of high-temperature polycrystalline silicon (poly-Si) deposited by low pressure chemical vapor deposition (LPCVD) have been fabricated and characterized. The structures are bulged until failure occurs. From the stress profiles in the diaphragms at fracture, the brittle material strength is analyzed using Weibull statistics. The bulge setup is fully automated for the sequential measurement of several membranes on a substrate realizing the high-throughput acquisition of data under well controlled conditions. A comprehensive study of the mechanical properties of low-temperature silicon films as a function of deposition parameters, namely substrate temperature, RF power, hydrogen dilution and doping, is presented.

Nanocrystals embedded in an oxide matrix have been fabricated by annealing SiGeO films deposited by LPCVD. The composition of the oxide layers and its evolution after annealing as well as the presence and nature of nanocrystals in the films have been studied by several experimental techniques. The results are analyzed and discussed in terms of the main deposition parameters and the annealing temperature.

The influence of the crystalline volume fraction of hydrogenated microcrystalline silicon (mc-Si:H) on the performance of thin-film transistors (TFTs) processed at temperatures below 180 °C was investigated. TFTs employing mc-Si:H channel material prepared near the transition to amorphous growth exhibit the highest electron charge carrier mobilities exceeding 50 cm2/Vs. The influence of the crystalline volume fraction of the intrinsic mc-Si:H material on the transistor parameters like the charge carrier mobility and the contact resistance will be discussed.

An examination of the noise of polycrystalline silicon thin film transistors, in the context of flat panel x-ray imager development, is reported. The study was conducted in the spirit of exploring how the 1/f, shot and thermal noise components of poly-Si TFTs, determined from current noise power spectral density measurements, as well as through calculation, can be used to assist in the development of imagers incorporating pixel amplification circuits based on such transistors.