This work deals with the study of the role of the film thickness and composition on the color selectivity of the collecting spectrum of glass/ZnO:Ga/p-a-Si1-xCx:H/ a-Si1-xCx:H /a-Si:H/n-a-Si:H/Al photoelectronic detectors produced in a single chamber plasma enhanced chemical vapor deposition (PECVD) system. The cross contaminations were minimized by a rotate-cover substrate holder system. The devices can detect the blue illumination at small reverse bias and detect red illumination at large reverse bias. The role of the process parameters, especially the thickness of the p-type and intrinsic a-Si1-xCx:H, and the intrinsic a-Si:H layers on the device performances were studied in detail aiming to achieve a better detectivity.

One-dimensional silicon nanowire structures have been successfully made by using the proximity and accumulation effects of electron-beam (e-beam) lithography. Wire structures are fabricated in a thin poly silicon layer on a silicon substrate with a 400 nm buried SiO2. Measurements of the current-voltage characteristics at various temperatures from 4 K up to 300 K show significant nonlinearities and single-electron effect behavior. The blockade size is significantly affected by thermal effects, oscillations of the blockade, and the conductivity dependence on the gate potential.

Experimental results on thin films of the new material GexC1-x, deposited by a unique dual plasma hollow cathode sputtering technique are presented. The mostimportant contribution of this work is that it shows that by using non-equilibrium growth conditions resulting from the hollow cathode technique, one can grow Group IV materials which cannot otherwise be grown using normal CVD or MBE processes. The sputtering is accomplished by igniting a dc plasma in the Ar and H2 gases which are fed through Ge and C nozzles.

The GeC films are grown on etched Si (100), on Si with the native oxide and on glass. The films grown on glass were quite disordered, but the films grown on both types of Si substrates were very ordered in nature. This order has been characterized using Xray diffraction (XRD) and Raman spectroscopy.

Films with as much as 8% C have been deposited. In order to produce useful GexC1-x films, the C must bond to the Ge at lattice sites. Evidence of this desired GeC bond has been seen using Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy, and XRD.

We have investigated the low-temperature epitaxial growth of thin silicon films by hotwire chemical vapor deposition (HWCVD). Using reflection high energy electron diffraction (RHEED) and transmission electron microscopy (TEM), we have found conditions for epitaxial growth at low temperatures achieving twinned epitaxial growth up to 6.8 μm on Si(100) substrates at a substrate temperature of 230°C. This opens the possibility of growing high quality films on low cost substrates. The H2:SiH4 dilution ratio was set to 50:1 for all growths. Consistent with previous results, the epitaxial thickness is found to decrease with an increase in the substrate temperature.

The crystal growth of SiC films on (100) Si and thermally oxidized Si (SiO2/Si) substrates by hot-mesh chemical vapor deposition (HMCVD) using monomethylsilane as a source gas was investigated. A mesh structure of hot tungsten (W) wire was used as a catalyzer. At substrate temperatures above 750°C and at a mesh temperature of 1600°C, 3C-SiC crystal was epitaxially grown on (100) Si substrates. From the X-ray rocking curve spectra of the (311) peak, SiC was also epitaxially grown in the substrate plane. On the basis of the X-ray diffraction (XRD) measurements, on the other hand, the growth of (100)-oriented 3C-SiC films on SiO2/Si substrates was determined to be achieved at substrate temperatures of 750-800°C, while polycrystalline SiC films, at substrate temperatures above 850°C. From the dependence of growth rate on substrate temperature and W-mesh temperature, the growth mechanism of SiC crystal by HMCVD was discussed.

We report highest quality Ge epilayers on nanoscale patterned Si structures. 100% Ge films of 10 μm are deposited using chemical vapor deposition. The quality of Ge layers was examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution x-ray diffraction (HRXRD) measurements. The defect density was evaluated using etch pit density measurements. We have obtained lowest dislocation density (5×105 cm-2) Ge films on the nanopatterned Si structures. The full width half maximum peaks of the reciprocal space maps of Ge epilayers on the nanopatterned Si showed 93 arc sec. We were able to get rid of the crosshatch pattern on the Ge surface grown on the nanopatterned Si. We also showed that there is a significant improvement of the quality of the Ge epilayers in the nanopatterned Si compared to an unpatterned Si. We observed nearly three-order magnitude decrease in the dislocation density in the patterned compared to the unpatterned structures. The Ge epilayer in the patterned Si has a dislocation density of 5×105 cm-2 as compared to 6×108 cm-2 for unpatterned Si.

The morphology of Si1-Y GeY:H films in the range of Y=0.23 to 0.9 has been studied by AFM. The films were deposited by Low Frequency (LF) PE CVD at substrate temperature Ts=300 C and discharge frequency f=110 kHz from silane+germane mixture with and without, Ar and H2 dilution. The films were deposited on silicon and glass substrates. AFM images were taken and analyzed for 2x2 μm2 area. All the images demonstrated “grain” like structure, which was characterized by the height distribution function F(H) average roughness <H>, standard height deviation Rq, lateral correlation length Lc, area distribution function F(s), mean grain area <s>, diameter distribution function F(d), and mean grain diameter <d>. The roughness <H> of the films monotonically increases with Y for all dilutions, but more significantly in the films deposited without dilution. Lc continuously grows with Y in the films deposited without dilution, while more complex behavior of Lc(Y) is observed in the films deposited with H- or Ar dilution. The sharpness of F(H) characterized by curtosis γ depends on dilution, and the sharpest F(H) are for the films deposited with Ar ( γ=5.30,Y=0.23) and without dilution (γ=4.3, Y=0.45). Isothermal annealing caused an increase of <H>, Lc in the films deposited with H- and Ar dilutions, while in the films prepared without dilution the behavior was more complex, depending on the substrates. After the annealing a significant sharpening of the height distributions, F(H), was observed in the films deposited with H dilution or without dilution.

This paper presents the fabrication and characterization of electrolyte-gate (EG) hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs). In these devices, the metal gate is replaced by a Pt electrode immersed in an electrolyte. The source-drain current of these devices is modulated by the voltage applied through the Pt electrode. Device characteristics are compared with structurally equivalent top-gate a-Si:H TFTs. The EG devices show higher mobility and smaller subthreshold slope than their counterparts with metal gate and work in a narrower voltage range. EG-TFTs show chemical sensitivity, illustrated by a voltage shift in the transfer curve as a consequence of pH variation. The sensitivity of the devices to pH is different depending on whether the top layer in contact with the electrolyte is SiO2 or SiNx.

The Saddle-Field Glow Discharge PECVD system emulates RF-like excitation using a semi-transparent anode and a DC power supply. It has been used to deposit high quality amorphous and microcrystalline hydrogenated silicon thin films in the past. The growth of microcrystalline material is particularly sensitive to the conditions under which it is produced. Significant levels of microcrystallinity are only produced under conditions of higher pressure and electrical isolation of the substrate surface from the grounded substrate holder. We present results of a study on the relationship between substrate electrical potential and microcrystalline growth, as quantified by Raman scattering spectroscopy, at growth pressures near the minimum required for microcrystalline growth.

This paper presents and discusses the results of measuring IR reflection and ellipsometric parameters, optical microscopy and AFM the mixed phase of amorphous Si:Y films with microcrystalline inclusions. These films were obtained by electron-beam evaporation of siliconyttrium alloys with different Y concentration (5-30 %) at two substrate temperatures (370 and 620 °C).

An experimental scheme for validating the cause of the hysteresis phenomenon in hydrogenated amorphous silicon thin film transistor (a-Si:H TFT) is reported. The different gate starting voltage to the desired gate voltage has been considered to prove an effect of filling an acceptor-like or donor-like state in the interface. The integration time of the semiconductor parameter analyzer (HP4156B) has also been controlled to investigate the effect between the detrapping rate and hysteresis. The experimental results show that the previous data voltage in the (n-1)th frame affects the OLED current in the (n)th frame.

Over the past few years we have been developing a scientific basis for amorphous silicon-based integrated photonics technology. Waveguides using hydrogen-implanted, optically-smooth, hot-wire-deposited films have been prepared and demonstrated, and structures were characterized by Raman spectroscopy of the implanted and the non-implanted regions of the waveguide samples. The analysis is consistent with greater disorder in the film structure induced through implantation. More recently, materials prepared by femtosecond laser ablation of silicon powder have been characterized by Raman spectroscopy indicating a structure having both amorphous and crystalline components. As amorphous silicon photonics continues to evolve, the patterning of materials of differing crystallinity may become an issue of interest.

Ag/ZnO back reflectors (BR) on specular stainless steel substrates are optimized for hydrogenated amorphous silicon germanium alloy (a-SiGe:H) and nanocrystalline silicon (nc-Si:H) solar cells. The BRs are deposited using a sputtering method. The texture of the Ag and ZnO layers is controlled by deposition parameters as well as chemical etching with diluted HCl. The surface morphology is investigated by atomic force microscopy. The scattered light intensity from a He-Ne laser, which illuminates the sample surface perpendicularly, is measured at different angles. Finally, a-SiGe:H and nc-Si:H solar cells are deposited on the BR substrates prepared under various conditions. For a-SiGe:H bottom cells, the improved BR with large micro-features leads to an enhanced open-circuit voltage. For the nc-Si:H solar cells, large micro-features on the improved BR eliminate interference fringes otherwise observed in the quantum efficiency measurement and result in high short circuit current density. The result is consistent with an enhanced scattered light intensity. Hence, the cell performance was improved. We also deposited a-Si:H/a-SiGe:H/nc-Si:H triple-junction cells on the optimized BR and achieved a high initial active-area efficiency of 14.6%.

We demonstrate that metastable changes or instabilities in the dark conductivity of microcrystalline silicon upon heat treatment and ambient conditions, which have been reported in the literature, are accompanied by changes in the photoconductivity or the majority-carrier mobility-lifetime product. The minority-carrier mobility-lifetime product and sub-gap absorption appear to be much less affected by different heat treatment procedures and ambient conditions. The observations can be related to Fermi-level induced change in defect occupancy by which the effective density of recombination centres is reduced for electrons but remains the same for holes. Minority carrier properties seem to be better suited as an indicator for sample quality and for comparison of microcrystalline silicon samples from different laboratories.

High intensity electron field emissions were obtained from SiC/Si heterostructures formed by high temperature carbon implantation into silicon and subsequently etching of the top silicon layer. Implantation processes were performed at 700 °C with a dose of 3.0 to 8.0 x 1017 ions/cm2. Post-implantation annealing in argon at 1250 °C for 5h was done for partial samples. β-SiC precipitates were easily formed and embedded in silicon at the interface of SiC/Si heterostructures during high temperature carbon implantation for all samples. The densely distributed small protrusions led to efficient electron emission. Implantation dose scarcely impacted the electron emission characteristics when it reached to a definite value. After annealing, the density of protrusions at the interface of SiC/Si heterostructures became smaller since β-SiC precipitates were grown into larger sizes, which caused to a relatively inefficient electron emission.

Light-emission from silicon based on quantum confinement in nanoscale structures has sparked intense research into this field ever since its discovery about 15 years ago. The lack of a simple high-yield synthesis approach for luminescent silicon nanocrystals has so far hampered their widespread application in such diverse areas as opto-electronics, solid-state lighting for general illumination, and fluorescent agents for biological applications. In this paper we discuss a nonthermal plasma process for the synthesis of luminescent silicon nanocrystals. The particle size is mainly controlled by the residence time in the plasma region. The system is capable of producing several tens of milligrams of luminescent powder per hour.

Preliminary results are presented on the kinetics of fast states at 25°C created by 1 sun illumination in protocrystalline hydrogen diluted a-Si:H films. The results are for the bulk properties of the a-Si:H films which was confirmed by the similarity of results obtained on corresponding intrinsic layers in p-i-n solar cells. It is found that the kinetics exhibit two regimes. The first regime is in the form of a delay before the onset of an A·log(t) time dependence indicative of a dispersive process. Despite the unexpected effect of a dependence of this first regime on the degradation/annealing history of the samples, it was possible to characterize the highly reproducible logarithmic dependences for different illumination times as well as in the presence of different carrier generation/recombination rates. It is found that for the degradation times studied, the annealing kinetics associated with the second regime are independent of the 1 sun illumination time but are dependent on the recombination introduced by illuminations as low as ∼0-5 of 1 sun. These fast states are located close to midgap, similar to the position of dangling bond defects. The results presented raise interesting questions that still need to be answered about the nature and origin of the fast defects in order to assess their contribution to the long term degradation and the overall stability a-Si:H materials.

Thin hydrogenated amorphous silicon (a-Si:H) layers deposited by hot-wire chemical vapor deposition (HWCVD) are studied for use as the emitter in silicon heterojunction (SHJ) solar cells on p-type crystalline silicon wafers. Low interface recombination velocity and high open-circuit voltage are achieved by a low substrate temperature (<150°C) intrinsic a-Si:H deposition which ensures immediate amorphous silicon deposition. This is followed by deposition of n-type a-Si:H at a higher temperature (>200°C) which improves dopant activation and other properties. A prolonged atomic H pretreatment to clean the c-Si surface is actually detrimental because it creates additional defects in the c-Si lattice. However, a brief H pretreatment is beneficial and may render the intrinsic interlayer unnecessary. The n-type a-Si:H thickness must be limited to ~5 nm to minimize current loss, because the phosphorous doped a-Si:H layer has significant absorption in the usable solar spectrum. Using the optimized a-Si:H emitter, we obtain efficiency of nearly 17% on planar float-zone (FZ) silicon and 15% on planar Czochralski (CZ) silicon substrates with aluminum back-surface-field (Al-BSF) and contacts.

This paper presents a brief review of the research that began in the early '80s, continued through the '90s, and produced a “standard model” for the optical absorption edge of amorphous silicon. The research began as a response to the invention of a-Si:H solar cells by Carlson and Wronski at RCA laboratories in 1976, and the subsequent worldwide interest in the optical characterization of a-Si:H thin films. The immediate need was soon met, but the research continued as an effort to understand the physics of the optical absorption edge in a-Si:H, as well as to understand the differences between, and similarities to, the indirect optical absorption edge of c-Si. In this paper, we highlight the successes of this standard model, and briefly cover its experimental and theoretical development over the last 25 years. We summarize its current status, and suggest some experimental and theoretical opportunities for, and challenges to, what may now be called a standard model for the optical absorption edge of both a-Si:H and a-Ge:H.

In this paper, we present the results of ion shower implantation to adjust threshold voltages on ELC (excimer laser crystallized) poly silicon thin film transistors. We observed that the threshold voltages of poly Si TFT strongly depended on the shower implantation dose, not the shower implantation energy for the 500 Å-thick active silicon layer. The threshold voltages for the reference, dose 5×1011 cm-2, and 1×1012 cm-2 cases were 0.30V, 1.25V, and 2.04V, respectively. We conclude that the threshold voltage can be appropriately adjusted by tuning the dose of the counter doping shower implant and its DIBL can still be suppressed to within an acceptable level.