厚薄膜材料与器件 第四章新型半导体薄膜材料及器件.ppt

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,第四章 新型半导体薄膜材料及器件,新型半导体薄膜材料以非晶硅、微晶硅及多晶硅薄膜为代表，在发光、存储、传感、显示、能源等领域有广泛的用途。,新型半导体薄膜器件正向高效率、长寿命、低价格、高集成等方向发展。,新型半导体薄膜器件的发展以微电子学微基础。,第一节 硅基非晶态半导体薄膜,非晶硅（,amorphous silicon,）,简称,a-Si,，,是当前非晶半导体材料及器件研究的重点和核心。,其可用作大面积、高效率太阳能电池材料，大屏幕液晶显示器和平面显示器，,a-Si,传感器和摄像管，非晶电致发光器件等对非晶半导体的研究不仅在新材料、新器件和新工艺方面具有重要意义，而且对进一步认识固体理论中的许多问题也会产生深远影响。,特点,结构上，非晶半导体的组成原子排列呈长程无序状态，但原子间的键合力十分类似于晶体，即其结构上表现为长程无序、短程有序。因而在能带结构上是定域化的，,即电子的迁移率变得十分小，室温下电阻率很高,。,可通过改变组分,实现物性的连续变化,，包括密度、相变温度、电导率、禁带宽度等。,在热力学上处于亚稳态，在一定条件下可转变为晶态。,材料结构、电学及光学性质都十分灵敏地依赖于制备条件与制备方法，因而性能重复性较差。,物理性能各向同性，无周期性结构约束。,容易形成大面积均一性好的薄膜。,a-Si,中一般存在大量氢，常称氢化非晶硅，,(a-,Si:H,),Study by Fluctuation electron microscopy,Qualitative picture of variance of the diffracted intensity from:,(a)a completely random collection of atoms and(b)a sample consisting of randomly oriented ordered clusters.(a)is small and shows little dependence on the imaging conditions.(b)is large,and varies significantly with the imaging conditions.,Density of states as a function of energy for a-Si and a-,Si:H,非晶硅在微电子硅材料中所占比例,非晶硅结构,制备方法,非晶态半导体薄膜制备的技术关键在于避免材料的成核和晶化。通常采用快速冷却的方式。,不同的材料成核和结晶的能力不同，其制备的冷却速率也不一样。,易于实现高冷却速率的制备方法主要有：,真空蒸发沉积法、辉光放电化学气相沉积法、溅射沉积法、热丝化学气相沉积法、微波回旋共振化学气相沉积,等。,SiH,4,的分解过程,辉光放电分解,要使,SiH,4,气体和稀释气体,H,2,分解，需要一定的能量：,H,2,H+H,SiH,4,Si,2H,2,SiH,4,SiH,H,2,H,SiH,4,e(,高速,)SiH,4,*,e(,低速,),SiH,4,*,Si,*,2H,2,4.6eV,4.4eV,5.9eV,Schematic concept for the dissociation processes of SiH,4,and H,2,molecules to a variety of chemical species in the plasma through their electronic-excited states.,生长机理,生成,a-,Si:H,薄膜的主要反应是：,SiH,(,气,),H(,气,),Si(,固,),H,2,(,气,),其次，可能出现的反应有：,SiH,(,气,),SiH,(,固,),SiH,(,气,),H(,气,),SiH,2,(,固,),氢一方面是形成,a-,Si:H,薄膜的重要反应物，同时其又可能破坏反应生成表面，存在：,Si(,固,),H(,气,),SiH,(,气,),这将消除薄膜表面上弱的,Si,Si,键，重新建立起较稳定的,Si,Si,键合。,生长设备,ECR-CVD system,The“hot wire”deposition system,which shows great promise for producing amorphous silicon PV devices,薄膜的表面形貌,AFM images of a-Si film at different H concentrations in the process gas,(a)0%;(b)20%and(c)49%.These films were prepared by 2 ECR plasma sputtering at room temperature,on quartz.Thickness of films was 500 nm.,性能,Some properties of a-,Si:H,and a-,SiGe:H,a-Si,薄膜的应用,DEVICE,PRODUCTS,Photovoltaic,cell,Photovoltaic modules,Calculators,watches,battery chargers,etc,Photoreceptor,Electrophotography,LED printers,Photoconductor,Colour sensors,light sensors,etc.,Image sensor,Contact-type image sensors,electronic white boards.,Solar control layer,Heat-reflecting float glass.,Thin-film field-effect transistor,Displays,television,logic circuits for image sensors.,High-voltage thin-film transistor,Printers.,太阳能电池,太阳能电池薄膜制式调查,太阳能电池 工作原理,p-i-n amorphous silicon solar cell,i,层为本征层，是核心部分，是光生载流子的产生区。,Band diagram of a-,SiGe:H,TCO：Transparent electrode IL：Insulation film SUS：Stainless steel substrate,太阳能电池结构,PIN,光电二极管,The,pin,diode structure,Cartoon illustrating the principal parameters used in modeling,photocarriers,in semiconductors.,bandedge,level energies,E,C,and,E,V,bandgap,E,G,interband,photocarrier,generation,G,electron and hole,mobilities,e,and,h,and densities,n,and,p,and electronhole recombination,R,.,a-Si p-i-n diode I-V curve under different illumination intensities,PIN,光电二极管的应用,PIN,光电二极管的应用领域很广，主要用作：,通讯用光电探测器、光接收器；,各种通信设备收发天线的高频功率开关切换和,RF,领域的高速开关；,各种家电遥控器的接收管,(,红外波段,),、,UHF,频带小信号开关、收音机,BC,频带到1000MHZ,之间电流控制可变衰减器等。,可见光,/,红外探测器,The device behaves like a back-to-back diode.,The applied voltage forward biases one diode and reverse biases the other one.,The visible spectrum of the impinging light is absorbed by the amorphous layers and only the long-wavelength region of the spectrum radiation reaches the c-Si junction.,Then the measured current is due to the carriers,photogenerated,in the p-doped crystalline material,where they move by diffusion.,On the other side,when the amorphous p-i-n diode is reversely biased the measured current is due to the carriers photo-generated in the a-,SiH,intrinsic layer where they move by drift.Short-wavelength light is then detected.,Sensors and Actuators A 88(2001)139-145,Uncooled,IR focal plane array,a 320 x 240 pixel array with a pitch of 45,m.,a single stage thermoelectric temperature stabilizer,integrated into a miniaturized package.,Material:Resistive,amorphous silicon,.,A histogram plot of the sensitivity of a component polarized with 3 Volts,The mean value of the sensitivity is about 9,6 mV/K with a,nonuniformity,(standard deviation/mean value)of 1.5%.,Thermographs,在液晶显示器中的应用,ITO Electrode,（,a,）,AMLCD,截面；（,b,）,AMLCD,显示元结构,在,TFT,元件的应用,a-Si TFT,元件制备工艺流程,A researcher works on a commercial lithography machine,which is a microcircuit manufacturing device.,a-,Si:H,TFTs,液晶显示器截面结构示意图,第二节 多晶硅和微晶硅薄膜,尽管,a-,Si:H,薄膜在光学方面有很大的优点，但在电学性质方面因载流子的迁移率低，极大地限制其应用。因而发展氢化微晶硅（,c-Si:H,）,和多晶硅（,poly-,Si:H,）,薄膜是很必要的。,微晶硅和多晶硅具有很多优良性质，可在低温下大面积生长，容易进行掺杂，可制作欧姆接触层，具有较高的电导率，等等。,c-Si:H,薄膜的生长方法,基于高氢气稀释比、高功率密度的,PECVD,技术；,用氢等离子体退火处理,a-,Si:H,薄膜；,电子回旋共振等离子体沉积技术；,热丝或催化,CVD,沉积技术。,Schematic cross-section of,a hot-wire deposition chamber,at Utrecht University.It basically contains a substrate holder,a shutter,a hot-wire assembly,a gas inlet and a pump port.The substrate holder is optionally heated using the external heater.,热丝,CVD,c-Si:H,薄膜生长机理,Si,(,固体,),SiH,4,SiH,x,SiH,n,扩散,粒子,H,H,e,SiH,4,SiH,4,Si,m,H,等离子体,1,2,c-Si:H,从,a-,Si:H,相中成核相,Schematic diagram of solid phase crystallization of amorphous silicon by thin film heater.,多晶硅电镜照片,晶界模型,多晶硅的应用,太阳能电池,Thin Solid Films 451452(2004)455465,太阳能电池,IV-characteristics of a solar cell,Solar Energy Materials&Solar Cells 81(2004)141,Thin-film transistors,（,TFTs,）,top-gate(TG),TFTs,(TEM image),Linear transfer characteristics of,TFTs,with PECVD a-,SiN:H,gate insulator,Linear transfer characteristics of a TG TFT with HWCVD poly-Si layer,思考题,非晶硅材料有哪些主要特点？,分析非晶硅薄膜的生长机理。,非晶硅薄膜主要应用于哪些元器件中？,多晶硅与非晶硅的主要区别是什么？,