Silicon suboxide (SiOx1 0<x<2) thin films have been investigated by means of photoluminescence, FTIR and photothermal deflection spectroscopy. Results showed that as the oxygen content in the films increases, the temperature dependence of PL intensity (Ipl) becomes weaker, and the PL peak position (Ep) shifts to the visible with decreasing intensity predominantly due to a decrease in the absorption coefficient. After sequential rapid thermal annealing from 500 to 100°C, Ep shifts simply to low photon energy. However, Ip1 of high oxygen content films first increases with increasing annealing temperature (TRTA), then decreases when TRTA>800°C, in contrast to low oxygen content films whose Ip1 monotonically decreases with TRTA and disappears above 700°C. The results are interpreted in terms of inhomogeneity in the as-deposited films, phase segregation upon annealing, and quantum confinement.

We have measured the dependence of the holes mobility-lifetime product on temperature under various light intensities in intrinsic a-Si:H. We find that this product exhibits thermal quenching which is accompanied by a superlinear light intensity dependence. Numerical calculations that we have carried out show that these results can be accounted for within the framework of the conventional recombination model. However, to yield such an agreement the capture coefficients for both charge carriers at the tail states must be smaller than the corresponding coefficients for the dangling bonds. Thus the sensitizing nature of the tail states is revealed.

Trivalent erbium (Er3+) presents a characteristic intra 4f optical transition 4I13/2 → 4I15/2 at 1.54 μm when incorporated in several solid hosts. Hydrogenated amorphous silicon (a-Si:H) is a good candidate as a host for applications in optical communications and photonic integration. We have studied Er3+ photo and electroluminescence in a-Si:H prepared by co-sputtering from a silicon target partially covered with metallic erbium chunks. Since the presence of oxygen impurities enhances the luminescence intensity, we studied the influence of oxygen added to the sputtering gas on the material properties. We found that oxygen reduces the erbium incorporation into the films. We obtained samples presenting 1.54 μm photoluminescence as deposited for a wide range of erbium concentrations. Maximum room-temperature photoluminescence efficiency is obtained for samples that contain ∼ 1% [O]/[Si] concentrations. The temperature quenching is small, mainly due to the temperature dependence of the luminescence lifetime.

Room temperature electroluminescence at 1.54 νm was observed in reverse biased Si/a-Si:Er:O:H/Al structures.

Infrared PL from νc-Si and nc-Si thin films is a potential spectroscopic tool for sensitive diagnostics of structure and defects. Bhat et al. have shown that the dominant PL band found in νc-Si centered at 0.9 eV cannot be assigned to the amorphous phase, as the energeticaly similar defect band found in a-Si:H (i.e., at 0.9 eV) shows a different temperature dependence and is much broader (i.e., FWHM of 0.15 eV compared to 0.35 eV) [1]. Recently, Carius et al. have observed a gradual lower energy shift of the 0.9 eV PL down to 0.82 eV for nc-Si as the plasma deposition excitation frequency is increased with a corresponding decrease in FWHM from 0.15 0.12 eV, respectively [2]. However, a lower energy shift in optical absorption was not observed, nor did they look for a correlation with the variation of any other physical property. Here, we report a broader range of energy variation for PL from our ECR-PECVD deposited nc-Si films accompanied with an energy shift in optical absorption and variation in dark conductivity and crystallite size. It has been argued that this PL peak in question could arise from the radiative transitions between bandtail states as in the case of ∼1.3 eV PL in a-Si:H or it may be associated with structural defects [2,3]. Our observations support both possibilities.

Cumulative thermal annealing (TA) changes the photoluminescence (PL) intensity in erbium-doped a-Si:H films prepared using DC magnetron sputtering of a composite Er-Si target at substrate temperature 200°C. The intensity of erbium-related 1.54 νm PL at 77 K is enhanced about 50 times after TA at 300°C for 15 min in nitrogen atmosphere. No erbium-related PL is observed after TA at T≤500°C. The TA process is discussed in terms of a model of partial structural rearrangement in an a-Si(Er):H amorphous network.

The aim of this work is to present an analytical model able to interpret the role of the thin collecting resistive layer on the static performances exhibited by 2D amorphous silicon hydrogenated pin thin film position sensitive detectors. In addition, experimental results concerning the device linearity and spatial resolution are presented and checked against the predicted values of the analytical model proposed.

In this paper we present the characterization of an ATCD three color detector used in the charge integration regime, as necessary in large area matrices. In particular, we present linearity measurements of mesa insulated devices and characterization of the self-bias process occurring in the transient read-out of stacked structures. A new system architecture is introduced which considers interlaced row charge restore, and separates the charge restore process from the charge sampling process in order to reach self-bias within a short frame time.

The importance of micro-crystalline silicon (μc-Si:H) for the photo-conducting dipole antenna application is investigated in this paper. The structural and optical properties of gc-Si:H films prepared by plasma enhanced chemical vapor deposition are studied with Raman spectra, scanning electron microscope, and ellipsometer measurements. The influence of grain size and defects on the opto-electronic characteristics of the photo-conducting dipole antenna is discussed. A sample of the antenna fabricated in our clean room laboratory is reported.

We present first results on the performance of flat dynamic x-ray detectors (FDXD) based on arrays of amorphous silicon thin film transistors (TFT) with charge storage capacitances and lead oxide as x-ray photoconductor. In order to increase the “active area” of every pixel, the layout of the array has been made in a multilevel arrangement, where the charge collecting electrode is separated from the underlying electronics by a thick insulating layer. This allows for a geometrical overlap of the pixel electrodes and TFTs. PbO has been chosen as the x-ray sensing material due to its very high x-ray sensitivity. The relevant detector properties of evaporated PbO layers are described along with results obtained on first FDXD devices with PbO.

Image sensors in TFA (Thin Film on ASIC) technology have been successfully fabricated and tested. This paper provides a survey of TFA research results so far and outlines future perspectives. The properties of different a-Si:H b/w and color thin film detectors are evaluated, including spectral sensitivity, dark current, temperature influence and transient behavior. Furthermore several TFA prototypes and emerging concepts are presented, ranging from a simple one-transistor cell design to a locally autoadaptive sensor.

Changes of several orders of magnitude in the low field conductivity of hydrogenated amorphous silicon alloy metal-semiconductor-metal MSM devices can be obtained by current stressing. This feature is suitable for memory applications, since the device can be programmed from an unstressed state to a stressed state with a ratio greater than 104. The change in conductivity is attributed to the creation of a large concentration of silicon dangling bond states during current stressing which form a defect band with a low activation energy for current transport. In this paper, we consider the use of current induced conductivity in hydrogenated amorphous silicon nitride (a-SiNx:H) multi-layer structures and show that, in principle, highly complex three dimensional circuits could be made. In particular, the potential of this approach is illustrated by using a simple MSMSM device with two silicon rich silicon nitride layers. An array with lxi0 elements has been fabricated and programmed to store 28 bits of binary information with three outputs per input.

We report on the first monolithic, amorphous-silicon-based, photovoltaic-powered electrochromic window coating. The coating employs a wide bandgap a-Sil-xCx:H n-i-p photovoltaic (PV) cell as a semitransparent power supply, and a LiyWO3/LiAlF4/V205 electrochromic (EC) device as an optical-transmittance modulator. The EC device is deposited directly on top of a PV device that coats a glass substrate.

The a-Sil-xCx:H PV cell has a Tauc gap of 2.2 eV and a transmittance of 60 to 80% over a large portion of the visible light spectrum. We reduced the thickness of the device to about 600 Å while maintaining a 1-sun open-circuit voltage of 0.9 V and short-circuit current of 2 mA/cm2.

Our prototype 16 cm2 PV/EC device modulates the transmittance by more than 60% over a large portion of the visible spectrum. The coloring and bleaching times of the electrochromic device are approximately 1 minute under normal operating conditions (±1 volt).

Application of amorphous silicon/crystalline silicon heterojunctions formed by RF sputter deposition and plasma enhanced chemical vapor deposition to the fabrication of nuclear radiation detectors is described. The performance of these heterojunctions as blocking contacts on highresisitivity p-type and n-type single crystal silicon and on lithium-ion compensated silicon (Si(Li)), which are commonly used in silicon detector fabrication, is presented. It is shown that an aluminum/amorphous-silicon contact on Si(Li) x-ray detectors results in about a factor of two reduction in the background counts when compared to a normal gold barrier contact.

Previously it was shown that high quality wide gap hydrogenated amorphous silicon material could be prepared by a layer-by-layer technique involving hydrogen chemical annealing. Using this wide gap material, high electric field, n-i-p diode devices were fabricated. Reverse bias dark current was suppressed by optimization of the n-layer doping level (250ppm) and the thickness (2000Å). Working vidicon type device were prepared, tested, and optimized by further reduction in the high reverse bias leakage current. Vidicon devices showed very promising performance; however, at the present stage of development some point defects were observable at the highest reverse bias voltages probed (∼-6×105 V/cm).

The achievement of large size displays and the capability of high throughput low temperature laser re-crystallised polysilicon TFTs to provide complex circuitry has opened up new market opportunities, such as the “system on panel” architecture, where the circuitry necessary for the operation of an interactive portable computer is to be fabricated on the display substrate. In the development of polysilicon technology for these applications, device physics and modelling are expected to play a major role as they have done in the case of single crystal silicon. However, polysilicon TFTs present a much higher level of complexity than single crystal devices, due to the presence of grain boundaries and associated defects which drastically affect the electrical properties. For the first time, a polysilicon TFT parameter extractor has been developed based on data from capacitance (C-V) and conductance (I-V) measurements. The method yields the flat band voltage, the front interface state density and the bulk density-of-states (DOS) for the entire range. The method is applied to laser re-crystallised polysilicon TFTs and verified via comparison with 2-D simulation. It is found that this technique allows a much higher degree of accuracy than other methods published so far.

The conduction band ΔEc and valance band ΔEv, off-sets at interfaces are critical parameters for device simulation. With the transport simulation code AMPS we demonstrate the possibility of using an analysis of the far forward I-V characteristics versus temperature for i- layer /n+ or i-layer /p+ hetero structures to obtain ΔEc or AE., respectively. For example, if one wants to extract AE, from experimental data for the interface a-Si/uc n+ Si interface, we show this can be done using a metal/intrinsic a-Si:H/uc n+ Si structure. With proper choice of the metal, the hole barrier height at the metal can be made large enough that the far forward current is only carried by electrons. We have found that, with the proper choice of structure thickness this far forward current can be controlled by ΔEc and not by space charge limited current. Unlike the work of Arnold et al [1], we have found that the choice of structure thickness is critical. In this case of an a-Si/uc n+ structure this far forward current is actually controlled by ΔEC+ΔVn where ΔVn is the activation energy in the n+ uc-Si layer. Since ΔVn can typically be ∼ 0.05eV in uc-Si, we see that ΔEc is essentially controlling this far forward current. To demonstrate the approach for the case of an a-Si/uc n+ Si interface we consider different i-layer thicknesses.

The growth of hydrogenated amorphous silicon films is often explained by the arrival of SiHx radicals on the substrate and the subsequent cross-linking reactions leading to an homogeneous material which can be described by a continuous random network. Here we summarize our recent Work on a new class of silicon thin films produced under plasma conditions where silicon clusters and radicals contribute to the deposition. The main aspects are: i) silicon clusters with sizes of the order of 1-5 nm are easily formed in silane plasmas; ii) these silicon clusters can contribute to the deposition and lead to the formation of films with medium-range order (“polymorphous silicon”); iii) despite their heterogeneity, the films have improved transport properties and stability with respect to a-Si:H. The excellent transport properties are confirmed by the achievement of stable single junction p-i-n solar cells with efficiencies close to 10 %.

We investigated the transport and recombination behavior of pin solar cells based on micro- crystalline silicon (μc-Si:H). A comparison of experimental and simulated data of the dark I/V- curves, the I/V-behavior under AM1.5 illumination as well as the quantum efficiency reveals an enhanced defect density in μc-Si:H compared to c-Si which could be located as defect rich grain boundaries around the crystallites. Further, in case there is amorphous phase in the material, the distribution of a-Si:H around the crystallites is unlikely, since the electronic transport properties are disturbed, whereas an arrangement in the shape of extended areas does not affect the transport behavior significantly due to occurrence of percolation.

In order to study the observed frequency variation of small-signal admittance of forward- biased amorphous silicon (a-Si:H) p-i-n diodes, we performed time-resolved measurements of currents induced by application of a small voltage step superimposed on a constant DC bias. The small amplitude ensures a linear behavior of the system under study. The transient current response includes all the details necessary to explain the stationary response to small sine-wave excitation. Details are obtained through a Fourier transform of the transient current. The real and imaginary parts of the resulting complex current are related to the capacitance and conductance spectra. This approach can explain phenomena taking place in the stationary regime such as negative capacitance values measured at low frequencies.

In the frequency domain, measured capacitances do show negative values, as well as a clear dependence on the applied forward bias voltage. Namely, higher voltages extend the region in which the phenomenon occurs to higher frequencies of the probe signal. In the time domain, all measured transient currents exhibit common features such as an initial decay after the displacement current and, for higher DC biases, a gradual increase. A physical explanation of the current transient is proposed which accounts for the dependence on applied DC bias. A mathematical model is used to show how a delayed increase in the current leads to a modulation of the capacitance and conductance in the frequency domain, the two being related to each other. This finally allows the comprehension of the observed frequency domain behavior.

Using numerical simulator, the operational principle of two-terminal a-Si:H based three-color detectors with the multi-layer multi-bandgap PIN or PIIiN structure is investigated. Two different approaches, which lead to bias-controlled three-color detection, are described and evaluated in terms of spectral response, rejection ratio, color suppression, illumination intensity and bias-light. For both PIIN and PIIN structure, bias-light dependence and intensity dependence is investigated. Numerical simulation results showed strong negative correlation between color separation and bias-light sensitivity. The importance of the transparent conducting oxide for the three-color detection limits is demonstrated.