Amorphous Silicon Germanium Thin Films Research Articles

Ultralow thermal conductivity of amorphous silicon–germanium thin films for alloy and disorder scattering determined by 3ω method and nanoindentation

Abstract The ultralow thermal conductivity (1.3 W/(m∙K)) of amorphous silicon–germanium films for alloy and disorder scattering was investigated using the 3ω method and nanoindentation. The films exhibited the lowest phonon mean free path (MFP) of 0.5 nm compared to that of amorphous silicon (1.1 nm) and germanium (0.9 nm) films, owing to alloy scattering in the silicon–germanium films. Based on Matthiessen’s rule, the phonon MFPs of the amorphous silicon–germanium films contributing to alloy and disorder scattering were calculated to be 1.0 nm for both. Therefore, alloy and disorder scattering contribute equally to the reduction in the phonon MFP.

N-type amorphous silicon-germanium thin films with embedded nanocrystals as a novel thermoelectric material of elevated ZT

The state-of-art thermoelectric (TE) materials with high efficiency (i.e., ZT ~ 1) at room temperature require meeting essential features, such as being environmentally friendly (i.e., avoiding the use of rare and toxic elements), cheap to produce, and high ZT. However, the enhancement of ZT has always been a challenge because the Seebeck coefficient, electrical conductivity, thermal conductivity, and absolute temperature are interdependent. In this work, we report the fabrication of amorphous silicon-germanium (a-SiGe) thin films deposited by low-frequency plasma-enhanced chemical vapor deposition (LF-PECVD) with embedded nanocrystals that have a ZT of 2.61 at room temperature. The above is achieved by enhancing the thermoelectric power factor and, simultaneously, keeping the lowest thermal conductivity; both are in concordance with the phonon-glass electron-crystal (PGEC) approach. The power factor enhancement is accomplished by increasing the electrical conductivity through N-type doping and an annealing process at 500 °C to which thin films were subjected to improve their transport properties while avoiding crystallization. Therefore, the room-temperature electrical conductivity increased two orders of magnitude from 1.11E-01 up to 42.79 S/cm. In addition, the growth of nanocrystals (5–15 nm) embedded into the amorphous matrix contribute to the transport of charge carriers. The measured thickness and Seebeck coefficient of thin films were 200 nm and −1.038 mV/K, respectively. On the other side, the lowest thermal conductivity is reached because the material’s amorphous phase is kept despite the applied post-deposition thermal annealing. The experimental value for thermal conductivity was 0.53 W/m·K, almost half of the minimum thermal conductivity proposed by Slack. In summary, the structural characterization (developed by X-ray diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy) shows that a-SiGe material not only has an amorphous phase despite the applied thermal annealing, but it also possesses nanocrystals, which is demonstrated by transmission electron microscopy in high-resolution mode. Therefore, the a-SiGe material obtained in this research is proposed as a novel and potential thermoelectric material because it has optimized TE properties and meets desirable features, such as being inexpensive, non-hazardous, and environmentally friendly for energy harvesting applications.

Short-circuit current density and fill factor improvement by optimizing In2O3:H and metal back reflector layers for p-i-n a-SiGe:H thin film solar cells

In this work, high efficiency p-i-n structure hydrogenated amorphous silicon germanium (a-SiGe:H) thin film solar cells were prepared via optimizing hydrogenated indium oxide In2O3:H (IOH) and silver/chromium/aluminum (Ag/Cr/Al) back reflector (BR) layers. Layer wise films including Al, Ag/Cr/Al and IOH/Ag/Cr/Al BR materials were fabricated into solar cells for improving short-circuit current density (Jsc) and fill factor (FF) which in turn enhanced output solar cell performance. Low resistivity, low carrier density and high mobility of IOH layers have been investigated with different water partial pressure ( $${\text{P}}_{{{\text{H}}_{ 2} {\text{O}}}}$$ ). Jsc was enhanced by 13.4% with IOH/Ag/Cr/Al BR structure due to their excellent optoelectronic properties compared to the initial solar cells with Al only. The spectral response of external quantum efficiency at long wavelengths of 550–900 nm was enhanced significantly by adding Ag and Cr with Al as composite electrode. A massive gain in Jsc of 1.13 mA/cm2 was further improved by using optimal $${\text{P}}_{{{\text{H}}_{ 2} {\text{O}}}}$$ with IOH compared to the one without this layer. High efficiency of 9.27% for a-SiGe:H solar cell was successfully fabricated with a high Jsc of 18.40 ± 0.03 mA/cm2 and FF of 69.48%.

Biocompatibility and surface properties of hydrogenated amorphous silicon-germanium thin films prepared by LF-PECVD

We studied the surface morphology and biocompatibility of hydrogenated amorphous silicon-germanium (a-Si1-xGex:H) thin films prepared by Low Frequency Plasma Enhanced Chemical Vapor Deposition (LF-PECVD). These films were deposited on a Corning 2947 glass substrate having a thickness of 3 μm, the electrical performance showed a decreased electrical resistance for low regime voltage. The root mean square (RMS) surface roughness of the films was measured by atomic force microscopy (AFM) in a non-contact mode. A biocompatibility tests was carried out using primary cultures of dorsal root ganglion (DRG) of Wistar rats. The DRG neurons were incubated for 18 hours on a-Si1-xGex:H thin films, and subsequent electrophysiological recording was performed. These neurons displayed typical ionic currents, including a fast-inward current at the beginning of voltage clamp pulse (Na+ current) and ensuing outward currents (K+ current). In current clamp experiments, depolarizing current pulse injection caused typical action potential discharge of the neurons. These results confirmed the feasibility of using a-Si1-xGex:H thin films as a biocompatible material.

Double p-SiOx layers to improve the efficiency of p–i–n a-SiGe:H thin film solar cells

In this work, p–i–n hydrogenated amorphous silicon germanium (a-SiGe:H) thin film solar cells were fabricated by using double p-type silicon oxide (p-SiOx) layers, and the power conversion efficiency (PCE) was increased from 7.79 to 9.10%. The optoelectronic properties and functions of p-SiOx layer in a-SiGe:H cells were measured and discussed. A window layer (~ 20 nm) was deposited and characterized to determine the optimal single p-SiOx layer parameters. After that, an ultra-thin contact layer (~ 4 nm) of p-SiOx was deposited in front of the window layer. Through comparative analyses between single and double p-SiOx layers, the performance of the device has greatly improved in open-circuit voltage (Voc), fill factor (FF) and short-circuit current density (Jsc). The optimization of interface contact between top transparent conductive oxide (TCO) and p-layer effectively improves the device efficiency. Finally, a-SiGe:H solar cell with high Voc = 750 mV, FF = 68.36% and Jsc = 17.75 mA/cm2 were fabricated successfully. A high efficiency of 9.10% has been achieved by double p-SiOx layers for a-SiGe:H thin film solar cell.

The Electrical Characterization of Hydrogenated Amorphous Silicon Germanium Film Used in Un-Cooled Micro-Bolometer

In this paper, the deposition and the electrical characterization of hydrogenated amorphous silicon germanium (a-SixGey:H) thin films were performed by plasma enhanced chemical vapour deposition (PECVD) at low temperature with different flow ratios of SiH4/GeH4. The temperature coefficient of resistance (TCR) and temperature dependence of conductivity were measured to study the influence of deposition parameter. The resistance uniformity were also investigated. The result showed that the film presented high TCR values of around 3.5%K-1and moderate conductivity value of 1.47×10-3(Ω•cm)-1respectively at room temperature, while the non-uniformity below 5% which indicated the high resistance uniformity in films.

Role of a-Si:H buffer layer at the p/i interface and band gap profiling of the absorption layer on enhancing cell parameters in hydrogenated amorphous silicon germanium solar cells

Separate influences of a hydrogenated amorphous silicon (a-Si:H) buffer layer at the p/i interface and staircase band gap profiling of entire absorption layer on cell parameters, such as open-circuit voltage (Voc), short-circuit current density (Jsc) and fill factor (FF), of hydrogenated amorphous silicon germanium (a-SiGe:H) thin film solar cells are discussed. An added thin a-Si:H buffer layer at the p/i interface can mainly improve Voc and Jsc while the staircase band gap profiling can enhance FF. Consequently, a combination of the buffer layer and band gap profiling can lead to significantly enhance Voc, Jsc and especially FF. A significant performance-improvement of the a-SiGe:H solar cell from 8.3% up to 9.8% was recorded by this combination. Role of the buffer layer and band gap profiling process was examined by empirical results and simulations.

Transparent conductive Hf-doped In2O3 thin films by RF sputtering technique at low temperature annealing

Hf-doped In2O3 transparent conductive polycrystalline films (IHFO) were grown at a low substrate temperature by radio frequency magnetron sputtering for the applications of silicon-based solar cell. The effect of argon flow rate on the electrical and optical properties of the films was investigated. Low temperature thermal treatment improved IHFO films properties, with the optimal Hall mobility of 79.6cm2/Vs and resistivity of 3.76×10−4Ωcm. The average transmittance of the 807nm thick IHFO films in the range of 300–1500nm was above 83%. The carrier density was utilized to evaluate the plasma wavelength of IHFO conducting film which was 1.8μm. The optimized IHFO film was then applied to amorphous silicon germanium thin film solar cells as the contacting layer. Compared to the cell without such a layer, the efficiency was higher by 0.35%.

Improvement of hydrogenated amorphous silicon germanium thin film solar cells by different p-type contact layer

In this study, we report an appreciably increased efficiency from 6% up to 9.1% of hydrogenated amorphous silicon germanium (a-SiGe:H) thin film solar cells by using a combination of different p-doped window layers, such as boron doped hydrogenated amorphous silicon (p-a-Si:H), amorphous silicon oxide (p-a-SiOx:H), microcrystalline silicon (p-µc-Si:H), and microcrystalline silicon oxide (p-µc-SiOx:H). Optoelectronic properties and the role of these p-layers in the enhancement of a-SiGe:H cell efficiency were also examined and discussed. An improvement of 1.62mA/cm2 in the short-circuit current density (Jsc) is attributed to the higher band gap of p-type silicon oxide layers. In addition, an increase in open-circuit voltage (Voc) by 150mV and fill factor (FF) by 6.93% is ascribed to significantly improved front TCO/p-layer interface contact.

Properties of a-SiGe Thin Films on Glass by Co-Sputtering for Photovoltaic Absorber Application.

Non-hydrogenated amorphous Silicon-Germanium (a-SiGe) thin films were deposited at two different base pressures by RF magnetron co-sputtering. Moreover, an ex-situ thermal annealing was carried out to investigate the material properties to be suitable as the bottom cell of multi-junction solar cells. Compositional study of the films using EDX showed Ge-rich thin films with 75 atomic% of Ge. XRD reflection study implied that all samples were entirely amorphous in nature. However, a significant improvement of morphology possibly due to low base pressure was observed while thermal annealing caused peening and reduction of surface inhomogeneity in both as-sputtered films. UV-VIS-IR analysis confirmed the FESEM results. The highest transmittance was observed in the as-deposited sample grown at 4 x 10(-5) Torr, which however reduced after thermal annealing. Tauc's model was implied for band gap determination and band gap energy as low as 1.07 eV was found in the annealed sample grown at lower base pressure (4 x 10(-6) Torr). Electrical properties of films were investigated by Hall effect measurement system and results found the reduction of resistivity with the same trend of optical band gap energy.

Fabrication of amorphous silicon–germanium thin film solar cell toward broadening long wavelength response

The morphous silicon germanium (a-SiGe) thin films are fabricated in a radio frequency plasma enhanced chemical vapor deposition system. This paper summarizes our recent works on how to make a suitable a-SiGe solar cell to enhance the light absorption in the long wavelength region. Up to now, a single junction p-i-n a-SiGe solar cell with an initial efficiency of 9.06% is obtained. The long wavelength response in QE is broadened to 950 nm. The QE reaches about 26.63% at 800 nm wavelength.

Role of thermal annealing on SiGe thin films fabricated by PECVD

Amorphous Silicon Germanium (a-SiGe) thin films of 500nm thickness are deposited on silicon substrates using Plasma Enhanced Chemical Vapour Deposition (PECVD). To obtain polycrystalline nature of films, thermal annealing is done at various temperature (450–600°C) and time (1–10h). The surface morphology of the pre- and post-annealed films is investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The crystallographic structure of the film is obtained by X-ray diffraction method. Raman spectroscopy is carried out to quantify the Ge concentration and the degree of strain relaxation in the film. Nano-indentation is performed to obtain the mechanical properties of the film. It is found that annealing reduces the surface roughness of the film and increases the Ge concentration in the film. The grain size of the film increases with increase in annealing temperature. The grain size is found to decrease with increase in annealing time up to 5h and then increased. The results show that 550°C for 5h is the critical annealing condition for variation of structural and mechanical properties of the film. Recrystallization starts at this condition and results in finer grains. An increase in hardness value of 7–8GPa has been observed. Grain growth occurs above this critical annealing condition and degrades the mechanical properties of the film. The strain in the film is only relaxed to about 55% even for 10h of annealing at 600°C. Transmission Electron Microscopy (TEM) observations show that the strain relaxation occurs by forming misfit dislocations and these dislocations are confined to the SiGe/Si interface.

Optimization of hydrogenated amorphous silicon germanium thin films and solar cells deposited by hot wire chemical vapor deposition

This work studies hydrogenated amorphous silicon germanium films, deposited by hot wire chemical vapor deposition, to be used as low band gap absorber material in thin film solar cells. Material properties, such as the bonding configurations, the ambipolar diffusion length and the optical band gap, were examined as a function of the substrate temperature and germanium content. Our best materials were incorporated in single junction solar cells with high long-wavelength response and a tandem solar cell with an efficiency of 10.42%.

Effect of gradually increasing germane flow rate during the deposition on the performance of a-SiGe:H solar cell

In this paper, we fabricated a hydrogenated amorphous silicon-germanium ( a - SiGe : H ) thin film solar cell with gradually increasing GeH 4 flow rate in order to absorb long wavelength of solar spectrum without stacked structures such as tandem or triple junctions. The thin film solar cell with the a - SiGe : H in its intrinsic layer deposited using 13.56 MHz radical-assisted/plasma-enhanced chemical vapor deposition (RA/PECVD) was characterized according to several conditions of gradually varying GeH 4 flow rate. Under AM 1.5 G conditions, open-circuit voltage (V OC ), short-circuit current density (J SC ), fill factor and efficiency have been investigated. Also, external quantum efficiency (EQE) was measured. As a result, the best value of V OC , J SC and fill factor were 0.42 V, 24.16 mA/cm2 and 0.52, respectively. Efficiency of the solar cell was up to 5.3%, and EQE in the wavelength range of 400–800 nm occupied most of photon absorption.

Optimization design of hydrogenated amorphous silicon germanium thin film solar cell with graded band gap profile

The simulation program AMPS-1D (analysis of microelectronic and photonic structures) employed to simulate and compare the performances of hydrogenated amorphous silicon germanium (a-SiGe:H) thin film solar cell with and without band gap grading at a radiation of AM1.5G (100 mW/cm2) and room temperature by introducing energy band engineering. The simulation results show that the efficiency of the solar cell with band gap grading is 0.477% higher than that without band gap grading due to the higher open circuit voltage (Voc) and better fill factor (FF). Subsequently, a-SiGe:H thin film solar cells with three different window layers such as hydrogenated amorphous silicon (a-Si:H), hydrogenated amorphous silicon carbide (a-SiC:H) and hydrogenated nanocrystalline silicon (nc-Si:H) are simulated, respectively. The numeric calculation results indicate that the fermi level EF of the a-SiGe:H thin film solar cell crosses the valence band when nc-Si:H window layer is employed in the simulation. This will improve the conductivity and the open circuit voltage of the solar cell. In addition, the electric field at front contact interface is reduced due to the lower contact barrier height. This may be more beneficial to the carrier collection by front contact. On the other hand, thanks to the wider band-gap difference between the window layer and the intrinsic layer, a potential barrier is built at the valence-band p/i interface due to the band offset. This will hinder the hole migration and collection. Thus, an nc-Si:H buffer layer, which can relax the valence-band offset and be more beneficial to the carrier migration and collection, is introduced at p/i interface. Finally, the optimum conversion efficiency of the a-SiGe:H thin film solar cell with graded band gap is achieved to be 9.104%.

The investigation of ZnO:Al2O3/metal composite back reflectors in amorphous silicon germanium thin film solar cells

Different aluminum-doped ZnO (AZO)/metal composite thin films, including AZO/Ag/Al, AZO/Ag/nickel—chromium alloy (NiCr), and AZO/Ag/NiCr/Al, are utilized as the back reflectors of p—i—n amorphous silicon germanium thin film solar cells. NiCr is used as diffusion barrier layer between Ag and Al to prevent mutual diffusion, which increases the short circuit current density of solar cell. NiCr and NiCr/Al layers are used as protective layers of Ag layer against oxidation and sulfurization, the higher efficiency of solar cell is achieved. The experimental results show that the performance of a-SiGe solar cell with AZO/Ag/NiCr/Al back reflector is best. The initial conversion efficiency is achieved to be 8.05%.

Investigation of nanocrystallization of a-Si1 − xGex:H thin films diluted with argon in the PECVD system

The structural evolution and nanocrystallization of hydrogenated amorphous silicon germanium (a-Si1−xGex:H) thin films deposited by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) through decomposition of silane and germane diluted with argon gas have been investigated by atomic force microscopy (AFM), X-ray diffraction (XRD), Raman and Fourier transform infrared (FTIR) spectroscopy, respectively. The results show that argon dilution gas plays a significant role in the growth of nanocrystalline grains in a-Si1−xGex:H thin films. It is observed that the nanocrystalline grains have been developed in amorphous network when the argon dilution ratio is about 4, a relatively low ratio compared to hydrogen dilution. Moreover, the surface roughness, nano-grain size, crystalline volume fraction and hydrogen content of the thin films increase with the rise of argon dilution ratio. Besides, the electrical and optical properties of the samples with different argon dilution ratios have been also measured. Finally, the effect of germanium content on the nanocrystallization of the thin films with fixed argon dilution ratio has been studied. It is found that the a-Si1−xGex:H thin films with high germanium content are prone to nanocrystallization.

Improved aluminum-doped ZnO/metal back reflector for p-i-n amorphous silicon germanium thin film solar cells

Different aluminum-doped ZnO (AZO)/metal composite films, including AZO/Al, AZO/Ag/Al and AZO/Ag/NiCr/Al, were utilized as the back reflectors for p-i-n hydrogenated amorphous silicon germanium (a-SiGe:H) thin film solar cells. It was found that AZO/Al had a better performance than single Al electrode and the thickness of AZO film could strongly affect the short-circuit current density (Jsc) of the solar cells. However, AZO/Ag/Al, which was expected to improve the back reflectance further, gave out a bad effect, due to the inter diffusion of Ag and Al. While a nickel–chromium (NiCr) film was inserted between Ag and Al as a diffusion barrier, the highest Jsc was achieved. So AZO/Ag/NiCr/Al could be utilized as an improved AZO/metal back reflector for p-i-n a-SiGe:H solar cells.

Modification to the performance of hydrogenated amorphous silicon germanium thin film solar cell

摘要 采用射频等离子体增强化学气相沉积技术, 研究了非晶硅锗薄膜太阳电池. 针对非晶硅锗薄膜材料的本身特性, 通过调控硅锗合金中硅锗的比例, 实现了对硅锗薄膜太阳电池中开路电压和短路电流密度的分别控制. 借助于本征层硅锗材料帯隙梯度的设计, 获得了可有效用于多结叠层电池中的非晶硅锗电池. 关键词: 非晶硅锗薄膜太阳电池 / 短路电流密度 / 开路电压 / 带隙梯度 Abstract In this paper, we study hydrogenated amorphous silicon germanium thin film solar cells prepared by the radio frequency plasma-enhanced chemical vapor deposition. In the light of the inherent characteristics of hydrogenated amorphous silicon germanium material, the modulation of the germanium/silicon ratio in silicon germanium alloys can separately control open circuit voltage (Voc) and short circuit current density (Jsc) of a-SiGe:H thin film solar cells. By the structural design of band gap profiling in the amorphous silicon germanium intrinsic layer, hydrogenated amorphous silicon germanium thin film solar cells, which can be used efficiently as the component cell of multi-junction solar cells, are obtained. Keywords: hydrogenated amorphous silicon germanium solar cell / short circuit current density / open circuit voltage / band gap profiling 作者及机构信息 刘伯飞, 白立沙, 魏长春, 孙建, 侯国付, 赵颖, 张晓丹 1. 南开大学光电子薄膜器件与技术研究所, 光电子薄膜器件与技术天津市重点实验室, 光电信息技术科学教育部重点实验室, 天津 300071 基金项目: 国家重点基础研究计划(批准号: 2011CBA00706, 2011CBA00707)、国家高技术研究发展计划(批准号: 2013AA050302)、天津市科技支撑项目(批准号: 12ZCZDGX03600)、天津市重大科技支撑计划(批准号: 11TXSYGX22100)和高等学校博士学科点专项科研基金(批准号: 20120031110039)资助的课题. Authors and contacts Liu Bo-Fei, Bai Li-Sha, Wei Chang-Chun, Sun Jian, Hou Guo-Fu, Zhao Ying, Zhang Xiao-Dan 1. Key Laboratory of Photoelectronic Thin Film Devices and Technology, Key Laboratory of Opto-Electronic Information Science and Technology Minsitry of Education, Institute of Photo Electronics Thin Film Devices and Technology, Nankai University, Tianjin 300071, China Funds: Project supported by the National Basic Research Program of China (Grant Nos. 2011CBA00706, 2011CBA00707), the National High Technology Research and Development Program of China (Grant No. 2013AA050302), the Science and Technology Support Program of Tianjin, China (Grant No. 12ZCZDGX03600), the Major Science and Technology Support Project of Tianjin, China (Grant No. 11TXSYGX22100), and the Specialized Research Fund for the Doctor Program of Higher Education of China (Grant No. 20120031110039). 参考文献 [1] Mackenzie K D, Eggert J R, Leopold D J, Li Y M, Lin S, Paul W 1985 Phys. Rev. B 31 2198 [2] Yan B, Yue G, Sivec L, Yang J, Guha S, Jiang C 2011 Appl. Phys. Lett. 99 113512 [3] Zhang X D, Zheng X X, Wang G H, Xu S Z, Yue Q, Lin Q, Wei C C, Sun J, Zhang D K, Xiong S Z, Geng X H, Zhao Y 2010 Acta Phys. Sin. 59 8231 (in Chinese) [张晓丹, 郑新霞, 王光红, 许盛之, 岳强, 林泉, 魏长春, 孙建, 张德坤, 熊绍珍, 耿新华, 赵颖 2010 物理学报 59 8231] [4] Zheng X X, Zhang X D, Yang S S, Wang G H, Xu S Z, Wei C C, Sun J, Geng X H, Xiong S Z, Zhao Y 2011 Acta Phys. Sin. 60 068801 (in Chinese) [郑新霞, 张晓丹, 杨素素, 王光红, 许盛之, 魏长春, 孙建, 耿新华, 熊绍珍, 赵颖 2011 物理学报 60 068801] [5] Zhang X D, Zheng X X, Xu S Z, Lin Q, Wei C C, Sun J, Geng X H, Zhao Y 2011 Chin. Phys. B 20 108801 [6] Han X Y, Hou G F, Zhang X D, Wei C C, Li G J, Zhang D K, Chen X L, Sun J, Zhang J J, Zhao Y, Geng X H 2009 Chin. Phys. B 18 3563 [7] Crandall R S 1983 J. Appl. Phys. 54 7176 [8] Matsuda A, Koyama M, Ikuchi N, Imanishi Y, Tanaka K 1986 J. Appl. Phys. 25 54 [9] Mahan A H, Menna P, Tsu R 1987 Appl. Phys. Lett. 51 1167 [10] Banerjee A, Xu X, Yang J, Guha S 1995 Appl. Phys. Lett. 67 2975 [11] Zimmer J, Stiebig H, Wagner H 1998 J. Appl. Phys. 84 611 施引文献

디스플레이 패널에 집적이 가능한 적외선 포토센서

This paper presents a study of an integrated infrared (IR) photo sensor for display application. We fabricated hydrogenated amorphous silicon thin film transistor (a-Si:H TFT) and hydrogenated amorphous silicon germanium thin film transistor (a-SiGe:H TFT) which were bottom gate structure. We investigated the dependence of a-SiGe:H TFT characteristics on incident wavelengths. We proposed photo sensor which responded to wavelengths of IR region. Proposed pixel circuit of photo sensor was consists of switch TFT and photo TFT, and one capacitor. We developed integrated photo sensor circuit and investigated the performance of the proposed sensor circuit according to the input wavelengths. The developed photo sensor circuit with a- SiGe:H TFT was suitable for IR.