Modeling and realization of a high-gain homojunction a-Si:H bulkbarrier phototransistor

We report an extensive analysis of amorphous silicon bulk-barrier phototransistors. Starting from a new analytical model for the device, we take into account the peculiarity of the material and, in particular, of the p-doped base, which we find to critically affect device operation. We demonstrate the possibility of obtaining lightly p-doped material suitable for high-gain devices, and we use the equilibrium model of defects in amorphous silicon as a guideline for our work. Finally, measurements on a number of high-gain devices verify our theoretical predictions     

Transient behavior of adjustable threshold a-Si:H/a-SiC:Hthree-color detector

In this paper, we investigate the transient behavior of a-Si:H/a-SiC:H adjustable-threshold three-color detectors (ATCDs) for applications in bidimensional large area image sensors. Red, green, and blue color sensing in the charge integration regime is demonstrated, and the transient mechanisms of charge and discharge of the equivalent capacitance are discussed by means of load curve diagrams. The possibility of driving 2-D arrays of ATCDs is discussed by means of a test circuit simulating the row select TFT and the data line capacitance by discrete components. Readout times on the microsecond timescale and saturation times three orders of magnitude greater have been obtained under 0.1 mW/cm² illumination, resulting in the possibility of scanning 1000 rows. Finally, an equivalent circuit is introduced and solved by AIM-SPICE, and simulations of the static and dynamic behavior are presented     

掺硼a-SiC:H/a-Si:H异质结的硼扩散(英文)

The diffusion of impurities in a p-i-n solar cell is one of causes for the degradation of energy conversion efficiency. However, few reports on the study of the illumination dependence of the boron diffusion in B-doped a-SiC:H/a-Si:H heterojunction have been seen so far. In this work, the B depth profiles in B-doped a-SiC:H/a-Si:H hetero junctions after illumination and annealing have been measured by nuclear reaction analysis; from the change of B profiles, we estimate the diffusion coefficient of B in a-Si:H.Diffusion of electrically activated B atoms is investigated and a simple discussion for the results obtained is presented as well.     

a-Si:H,a-SiC:H和a-SiN:H合金系统中g值的理论计算(英文)

The g-values of the ESR signals caused by dangling bonds in a-Si:H, a-SiC:H and a-SiN:H alloy systems have been calculated for a cluster by using the CNDO method, and compared with the observed g-values. The detailed formula for the calculation of g-values was derived from the formula of A.J.Stone. It is found that the g-values for dangling bonds on Si atoms are affected by the surrounding C or N atoms in a-SiC:H or a-SiN: H alloy systems and the calculated results are in good accordance with the observed ones. Some usefull discussions have also been made.     

Performance of a high-resolution contact-type linear image sensorwith a-Si:H/a-SiC:H heterojunction photodiodes

A 400 DPI (dots-per-inch) contact-type linear image sensor with a scanning speed of 2 ms/line using amorphous silicon photodiodes and poly-Si thin-film transistor drivers has been developed. The characteristics of the heterojunction photodiodes are discussed, and the results of sensor performance tests are examined in terms of output signal uniformity, photoresponse lag, spectral response, gray scale, and the reliability of the 400 DPI image sensor     

Device analysis for a-Si:H thin-film transistors with organicpassivation layer

Two dimensional device analysis has been performed to explain the experimental drain current-gate voltage (I_D-V_GS) characteristics of hydrogenated amorphous silicon thin-film transistors with various passivation layers. The shift of the I_D-V_GS curve in the negative direction and the increase of S-factor (the inverse of subthreshold slope in logarithmic I_D-V_GS curve) can be explained well by introducing positive fixed charges and defect states in the back interface region. It was found that the positive fixed charge and the defect density of a-Si:H TFT with an organic passivation layer are higher than those of conventional a-Si:H TFT with a silicon-nitride (SiN_x) passivation layer. The simulation shows that the front and back interfaces interact and this explains why the passivation affects the device performance such as V_th and S-factor in a-Si:H TFTs     

High mobility tri-layer a-Si:H thin-film transistors with ultrathinactive layer

We show that hydrogenated amorphous silicon thin-film transistors (a-Si:H TFT's) with active layer thickness of 13 nm perform better for display applications than devices with thicker 50-nm active layers. A direct comparison of a-Si:H TFT's fabricated using an i-stopper TFT structure shows that ultrathin active layers significantly improve the device characteristics. For a 5-μm channel length TFT, the linear region (V_DS=0.1 V) and saturation region mobilities increase from 0.4 cm²/V·s and 0.7 cm²/V·s for a 50-nm thick active layer a-Si:H device to 0.7 cm²/V·s and 1.2 cm²/V·s for a 13-nm thick active layer a-Si:H layer device fabricated with otherwise identical geometry and processing     

Optimization of Al/a-SiC:H optical sensor device by means of thermal annealing

The optimization of optoelectronic properties of Al/a-SiC:H Schottky diodes grown as Al/a-SiC:H/c-Si(n) structures is studied by means of thermal annealing of a-SiC:H thin films. According to the spectral response of the Schottky diodes the measured quantum efficiency, η_measured, increases with increasing annealing temperature (400–600 °C), whereas η_measured decreases for T_a>600 °C. For T_a=600 °C, optimum material quality of a-SiC:H films is achieved and the spectral response of the Al/a-SiC:H/c-S(n) structures present very high and almost constant values (η_measured80%) for the whole range of wavelengths from 500 up to 850 nm. These results show that our Al/a-SiC:H/c-S(n) structures can be very attractive as optical sensors. Diffusion length calculations as well as the mobility by lifetime product (μτ)_p of the minority carriers (holes) of a-SiC:H films present a dependence on T_a similar to that of the measured quantum efficiency. Finally, the quantum efficiency of films processed with T_a=675 °C is found to increase when the Al/a-SiC:H/c-S(n) structures are exposed to hydrogen, a result that could be promising for the construction of a hydrogen detection sensor.     

a-SiC/c-Si异质结太阳能电池中a-SiC:H薄膜的设计分析

通过应用Scharfetter-Gummel解法数值求解Poisson方程,对热平衡p (a-SiC:H）/n(c-Si）异质结太阳能电池进行计算机数值模拟分析。给出了p (a-SiC:H）膜厚及其p型掺杂浓度设计,还讨论了p (a-SiC:H)/n(c-Si）异质结太阳能电池稳定性。     

An a-SiGe:H phototransistor integrated with a Pd film on glasssubstrate for hydrogen monitoring

A novel a-SiGe:H optoelectronic hydrogen gas sensing device has been developed. The optoelectronic gas sensing device integrated a high optical gain a-SiGe:H optical sensor with a sputtered palladium (Pd) film on a glass substrate. Through the mechanism of the Pd film's transmitted optical power modulated with the H₂ concentration in atmosphere, the device can be operated at room temperature with a wider range (50 ppm to 133000 ppm) and faster response, in comparison to a conventional Pd catalytic type H₂ sensors, thus providing a good candidate for hydrogen monitoring     

An a-Si:H photoconductive sensor with a gate electrode

A hydrogenated amorphous silicon photoconductive sensor with a gate electrode is developed for a matrix-driven linear image sensor array. The photoresponse time for this new sensor is about 1/3 of that for a conventional photoconductive sensor. A new dynamic model is proposed to analyze the photoresponse characteristics for this sensor. The minimum photoresponse time predicted by the calculation is about 2 ms. This value is markedly short compared with that for a conventional photoconductive sensor (about 5 ms)     

A high-resolution staggered-configuration CCD imager overlaid with an a-Si:H photoconductive layer

A high resolution "two-level" CCD imager was overlaid with an a-SiC: H (intrinsic)/a-Si: H (intrinsic)/a-SiC:H (p-type) photo-conversion layer. This device has 400 (horizontal:H) × 500 (vertical:V) pixels, in which 385(H) × 490(V) pixels are effective. The image area is 8.8 mm (H) × 6.5 mm (V), which corresponds to ⅔-in optical format. The high-resolution feature has been realized by staggered configuration pixel layout and novel interline transfer CCD scanner, which can read out two horizontal rows simultaneously. A horizontal limiting resolution of 500 TV lines, which is twice the conventional horizontal 400-pixel-number CCD, has been obtained without increasing the pixel packing density.     

Optoelectronic characteristics of a-SiC:H-based P-I-N thin-filmlight-emitting diodes with low-resistance and high-reflectance N+-a-SiCGe:H layer

The graded-gap a-SiC:H-based p-i-n thin-film light-emitting diodes (TFLEDs) with an additional low-resistance and high-reflectance n⁺ -a-SiCGe:H layer were proposed and fabricated on indium-tin-oxide (ITO)-coated glass substrate in this paper. For a finished TFLED, a brightness of 720 cd/m² could be obtained at an injection current density of 600 mA/cm², and its EL (electroluminescence) threshold voltage was lowered to 8.6 V. In addition, the effects of reflectance and resistance of a-SiCGe:H film on the performance of TFLED were discussed. The optimum rapid thermal annealing (RTA) conditions for fabrication of TFLED after metallization were also studied and employed to improve the optoelectronic characteristics of TFLED     

掺杂B(CH)3的P型a-SiC:H层及a-Si:H电池的P/I界面研究

研究了衬底温度、反应气体流量等工艺条件对掺杂B(CH3)3(TMB)的P型氢化非晶硅碳(a-SiC:H)窗口材料性能的影响,获得了电导率达到8.97×10-7 S/cm、光学带隙大于2.0 eV的P型a-SiC:H窗口材料.研究了单结电池P型a-SiC:H窗口层的CH4流量与P、I层制备温度三者间的匹配关系.结果表明,随着衬底温度的提高,需要更多的CH4流量以增大P型窗口层的带隙Eg和电池的短路电流密度Jsc;沉积系统中,P型窗口层的温度比本征吸收层高25～50 ℃时,电池性能较好.研究了3种类型的P/I缓冲层对单结电池性能的影响.大量实验表明,不掺B的C缓冲层适合于低温和小CH4流量情况使用;掺B的C缓冲层 不掺B的C缓冲层适合于高温和大CH4流量情况使用;采用不掺B的C缓冲层的电池光稳定性高于采用B、C渐变缓冲层的电池.研究还表明,采用新型TMB作为P型窗口层掺杂剂的电池比传统采用B2H6作为P型窗口层掺杂剂的电池转换效率提高约1.0%.     

An accurate CAD model for the ambipolar a-Si: H TFT

The ambipolar output drain current versus drain voltage characteristics of hydrogenated amorphous silicon thin-film transistors are modeled by a method intended for use in computer-aided design programs. An accurate model has been developed that uses a modified experimental sheet conductivity curve to predict the output drain characteristics over many orders of magnitude of the drain current in both the n-channel and p-channel modes of operation. Analytical expressions for the drain current are developed.     

Influence of deposition pressure on p-type a-Si:H window layer doped by trimethylboron for a-Si:H superstrate solar cell in plasma enhanced chemical vapor deposition

Wide bandgap (E_g) p-type window layer is very important for silicon based thin film solar cell to obtain high performance, especially high open-circuit voltage (V_OC). In this work, the influence of the deposition pressure on the properties of p-type a-Si:H window layer doped by trimethylboron (TMB) in plasma enhanced chemical vapor deposition (PECVD) was investigated systematically by transmission, Raman, and Fourier transform infrared (FTIR) spectroscopies. As a result, high performance hydrogenated amorphous silicon (a-Si:H) p–i–n superstrate solar cell with V_OC up to 927 mV was successfully achieved on Asahi Type-U SnO₂:F coated glass. In this case, excellent wide bandgap p-type a-Si:H window layer was fabricated under a mild deposition condition, including a low hydrogen dilution ratio (H₂/SiH₄) of 20, a relatively high deposition temperature of 220 °C, which was also adopted for the i-layer and n-layer deposition, and a moderate deposition pressure of about 160 Pa. We think it is the compromise between wide E_g and good microstructure quality of the p-layer that brings about the good solar cell performance. Such p-type window layer will be very helpful for the fabrication of a-Si:H solar cell, especially of the cell finished in a single PECVD chamber, due to its mild deposition condition.     

Operating principles and performance of a novel a-Si:H p-i-n-based X-ray detector for medical image applications

This work develops a novel hydrogenated amorphous silicon (a-Si:H) p-i-n photodiode-based X-ray detector aimed at medical image applications. The new detector consists of an a-Si:H p-i-n photodiode and a stacked dielectric layer, deposited on the p-layer (n-i-p-SiN/sub x/) or the n-layer (p-i-n-SiN/sub x/) of the p-i-n photodiode, as the main charge storage element. This detector operates as a capacitor and is connected in parallel to a reverse-biased p-i-n photodiode during the detection cycle to accumulate photon-converted charges. The junction capacitance (C/sub j/) of the p-i-n diode was enhanced by this stacked dielectric layer without reducing the active area of the detector. The design of the charge storage capacity and the photon-charge transfer efficiency can be optimized separately for various applications. Moreover, the linearity, dynamic range of operation, and data retention capacity of the detector were found to be markedly improved by the enlarged capacitance in the detector. The operating principles and performance of this novel device are discussed, and the corresponding control sequence of the switch of the device array is also addressed. The experimental results proved that this novel structure is valid and can be applied to construct effectively a two-dimensional detection array, offering considerable advantages of the novel device in X-ray medical image applications.     

异质结硅太阳能电池a—Si：H薄膜的研究

通过应用Scharfetter-Gummel数值求解Poisson方程，对热平衡态P^ （a-Si:H)/n(c-Si)异质结太阳能电池进行计算机数值模拟分析。结果指出，采用更薄P^ (a-Si：H）薄膜设计能有效增强光生载流子的传输与收集，从而提高a-Si/c-Si异质结太阳能电池的性能。同时，还讨论了P^ (a-Si:h)薄膜中P型掺杂浓度对光生载流了传输与收集的影响。高强茺光照射下模拟，计算表明，a-Si/c-Si异质结结构太阳能电池具有较高光稳定性。