The document discusses digital strategies for museums and cultural heritage institutions. It provides examples of different types of narratives that can be told including biographical, fictional, fragmented, and thematic. Museums should tell stories to engage audiences, provide experiential and pedagogical value, and build networks. Digital technologies can help make participation, connectivity, computation, interactivity, and immersion possible. The document suggests museums can tell stories using their collections, audiences, processes, places and spaces. It then tasks participants with building a narrative around artifacts from the EMMA museum considering its available assets and constraints like copyright.
This document describes a weekly networking event in New York for journalism students and professionals. The event will provide opportunities to meet employers in the field, practice pitching skills, and explore areas of journalistic interest. It will take place every Wednesday from 7-9pm in Manhattan at no cost to members. The event organizers aim to carefully select guests and pair each participant with a professional journalist. The goal is to help young journalists build connections and get noticed in the competitive field.
Katalog trotec-xl63-videoprobe-system-videoendoscopy-tridinamika, jual videoprobe xl63 trotec, beli, info harga, spesifikasi dan review.
Dapatkan informasi lengkap tentang produk trotec di
www.tridinamika.com
untuk informasi dan pemesanan hubungi
sales@tridinamika.com
This document lists four holidays: Tree Planting Day, National Day which celebrates the founding of the Communist Party of China, Armed Forces Day, and Christmas.
El documento habla brevemente sobre la vida y obra del poeta francés Charles Perrault (1628-1703). Menciona que Perrault nació en París y trabajó como funcionario real, y que es más conocido por haber escrito cuentos de hadas populares como Caperucita Roja y Cenicienta.
The document discusses digital strategies for museums and cultural heritage institutions. It provides examples of different types of narratives that can be told including biographical, fictional, fragmented, and thematic. Museums should tell stories to engage audiences, provide experiential and pedagogical value, and build networks. Digital technologies can help make participation, connectivity, computation, interactivity, and immersion possible. The document suggests museums can tell stories using their collections, audiences, processes, places and spaces. It then tasks participants with building a narrative around artifacts from the EMMA museum considering its available assets and constraints like copyright.
This document describes a weekly networking event in New York for journalism students and professionals. The event will provide opportunities to meet employers in the field, practice pitching skills, and explore areas of journalistic interest. It will take place every Wednesday from 7-9pm in Manhattan at no cost to members. The event organizers aim to carefully select guests and pair each participant with a professional journalist. The goal is to help young journalists build connections and get noticed in the competitive field.
Katalog trotec-xl63-videoprobe-system-videoendoscopy-tridinamika, jual videoprobe xl63 trotec, beli, info harga, spesifikasi dan review.
Dapatkan informasi lengkap tentang produk trotec di
www.tridinamika.com
untuk informasi dan pemesanan hubungi
sales@tridinamika.com
This document lists four holidays: Tree Planting Day, National Day which celebrates the founding of the Communist Party of China, Armed Forces Day, and Christmas.
El documento habla brevemente sobre la vida y obra del poeta francés Charles Perrault (1628-1703). Menciona que Perrault nació en París y trabajó como funcionario real, y que es más conocido por haber escrito cuentos de hadas populares como Caperucita Roja y Cenicienta.
EVALUATION OF SO2 AND NOX OFFSET RATIOS TO ACCOUNT FOR SECONDARY PM2.5 FORMATIONSergio A. Guerra
On January 4, 2012, the EPA committed to engage in rulemaking to evaluate updates to the Guideline on Air Quality Models (AppendixWof 40 CFR 51) and, as appropriate, incorporate new analytical techniques or models for secondary PM2.5. As a result, the National Association of Clean Air Agencies (NACAA) developed a screening method involving offset ratios to account for
secondary PM2.5 formation. This method can be used to evaluate total (direct and indirect) PM2.5 impacts for permitting purposes. Therefore, the evaluation of this method is important to determine its viability for widespread use.
- The document outlines modifications made to rules regarding pay fixation for government employees in Kerala who receive promotions.
- The modifications dispense with refixing pay in the promoted post based on changes to pay in the lower post. Promotees can now choose the date their pay is fixed in the new post.
- Examples are provided to illustrate how pay will be fixed for promotions to posts with minimum pay above or below 20,700 rupees under the new rules.
This short document promotes creating presentations using Haiku Deck on SlideShare. It encourages the reader to get started making their own Haiku Deck presentation by simply clicking the "GET STARTED" button provided. In just one sentence, it pitches presentation creation using Haiku Deck on SlideShare.
Advanced Modeling Techniques for Permit Modeling - Turning challenges into o...Sergio A. Guerra
Advance modeling techniques can be used in AERMOD to refine the inputs that are entered in the model to get more accurate results. This presentation covers:
-AERMOD’s Temporal Mismatch Limitation
-Building Downwash Limitations in BPIP/PRIME
-Advanced Modeling Techniques to Overcome these Limitations
Solutions include:
Equivalent Building Dimensions (EBD)
Emission Variability Processor (EMVAP)
Updated ambient ratio method (ARM2)
Pairing AERMOD values with the 50th % background concentrations in cumulative analyses.
Effects of Wind Direction on VOC Concentrations in Southeast KansasSergio A. Guerra
Twenty-four-hour whole-air samples were collected in evacuated stainless steel canisters and analyzed for volatile organic compounds (VOC) at selected sites in southeast Kansas from March 1999 to October 2000. The purpose was to assess the influence on air quality of four industrial facilities that burn hazardous waste located in the communities of Coffeyville, Chanute, Independence and Fredonia. Fifteen of the VOC analytes were found at concentrations above the detection limit and above levels observed in the blanks. Data were analyzed to investigate whether sampling site and date had a significant effect on VOC concentration. Results indicate that site and/or date were significant factors for many of the VOCs. To further investigate the temporal factor, sampling days were divided into four classifications based on wind direction: predominantly north winds, predominantly south winds, calm/variable winds and
other winds. Results from statistical analyses show that wind direction was a significant factor for benzene, toluene, o-xylene, naphthalene, and carbon tetrachloride. Data from upwind and downwind samples were analyzed for the four cities of interest in the study area, to investigate the effect of the four targeted sources on VOC concentrations. Results from Fredonia showed higher concentrations of toluene, ethyl benzene, styrene, methyl chloride, and trichloroethylene in the upwind samples, although none of the results were statistically significant. Chanute also showed higher concentrations of the same compounds and m,p-xylene in the upwind samples; results were significant at the 0.05 level for toluene, ethylbenzene, and xylene. These results indicate that sources other than those targeted in the sampling network may be contributing to
the VOC levels. Results from Independence showed higher concentrations of ethylebenzene and styrene in the downwind samples; results were statistically significant. These results indicate that the source targeted in the sampling network may be contributing to the VOC levels at those sampling sites.
Universal Design for Learning (UDL) is a framework for teaching that uses flexible approaches to accommodate learner differences. It focuses on providing multiple means of representation, action and expression, and engagement to benefit the greatest number of students regardless of ability. The goal of UDL is to reduce barriers in instruction and make material accessible to all students through creativity and flexibility so that all students can find learning rewarding.
This document provides an overview of Hispanic culture and history. It discusses that Hispanic culture encompasses many Spanish-speaking countries and regions. It outlines the various forms of government and economies in countries like Spain, Cuba, Central America, and South America. The document also provides a timeline of major historical events and discusses traditions, values, and learning and communication styles of Hispanic students. It notes how these cultural factors can influence academic achievement and language development.
The document discusses collecting feedback on a teaser trailer for an urban drama film from two sources: 1) An online survey of 66 respondents aged 16-24 about aspects of urban dramas like characters, music, and stereotypes. Respondents preferred accurate stereotypes and fast-paced grime music. 2) YouTube comments on a draft trailer which provided positive feedback on its urban drama feel, effects, and locations but said the abrupt ending lacked climax. The feedback was used to change the ending shot and trim overly long staged shots.
Agilent Technologies
The premier measurement company -- advancing electronics, communications, life sciences and chemical analysis
Agilent Technologies Inc adalah perusahaan pengukuran utama dunia dan pemimpin teknologi dalam elektronik dan komunikasi. 20.500 karyawan perusahaan melayani pelanggan di lebih dari 100 negara. Sebagai perusahaan pengukuran utama dunia, Agilent menawarkan jangkauan luas solusi pengukuran inovatif di industri. Perusahaan empat bisnis – Analisis Kimia, Biologi, Diagnostik dan Genomics, dan Elektronik Pengukuran – menyediakan pelanggan dengan produk dan layanan yang membuat perbedaan nyata dalam kehidupan orang-orang di mana-mana. Dan di Agilent Laboratorium Penelitian, kita melakukan penelitian yang mengantisipasi kebutuhan pelanggan dan menghasilkan terobosan bahwa pertumbuhan listrik.
Asal Negara : U.S.A
Jenis Industri :
Automotive/Transportation, Communications and Networking Systems or Equipment , Computers and Peripherals , Consumer Electronics & Appliances , Aerospace/Defense/Government , Electronic Instrumentation or Test , Medical Devices & Systems , Semiconductor Design & Manufacturing , Academia , Energy , Application & Technologies: Advanced Technology , Components , Design Tools (EDA) , Manufacturing , Software/Hardware Development , Test & Measurement
Kategori Produk :
Oscilloscopes , Spectrum Analyzers (Signal Analyzers) , Network Analyzer , Handheld Oscilloscopes, Analyzers, Meters , Logic Analyzers , Protocol Analyzers and Exercisers , EMI/EMC, Phase Noise, Physical Layer Test Systems ,Bit Error Ratio Test (BERT) Solutions , Digital Multimeters (DMM) , Power Meters & Power Sensors , Frequency Counter Products , Noise Figure Analyzers & Noise Sources , LCR Meter & Impedance Measurement Products , Digitizers , DC Power Analyzers , Dynamic Signal Analyzers, Materials Measurement , Parameter & Device Analyzers, Curve Tracer
Untuk pemesanan dan informasi hubungi :
Tridinamika - Test and Measurement
www.tridinamika.com
email to : sales@tridinamika.com
EVALUATION OF SO2 AND NOX OFFSET RATIOS TO ACCOUNT FOR SECONDARY PM2.5 FORMATIONSergio A. Guerra
On January 4, 2012, the EPA committed to engage in rulemaking to evaluate updates to the Guideline on Air Quality Models (AppendixWof 40 CFR 51) and, as appropriate, incorporate new analytical techniques or models for secondary PM2.5. As a result, the National Association of Clean Air Agencies (NACAA) developed a screening method involving offset ratios to account for
secondary PM2.5 formation. This method can be used to evaluate total (direct and indirect) PM2.5 impacts for permitting purposes. Therefore, the evaluation of this method is important to determine its viability for widespread use.
- The document outlines modifications made to rules regarding pay fixation for government employees in Kerala who receive promotions.
- The modifications dispense with refixing pay in the promoted post based on changes to pay in the lower post. Promotees can now choose the date their pay is fixed in the new post.
- Examples are provided to illustrate how pay will be fixed for promotions to posts with minimum pay above or below 20,700 rupees under the new rules.
This short document promotes creating presentations using Haiku Deck on SlideShare. It encourages the reader to get started making their own Haiku Deck presentation by simply clicking the "GET STARTED" button provided. In just one sentence, it pitches presentation creation using Haiku Deck on SlideShare.
Advanced Modeling Techniques for Permit Modeling - Turning challenges into o...Sergio A. Guerra
Advance modeling techniques can be used in AERMOD to refine the inputs that are entered in the model to get more accurate results. This presentation covers:
-AERMOD’s Temporal Mismatch Limitation
-Building Downwash Limitations in BPIP/PRIME
-Advanced Modeling Techniques to Overcome these Limitations
Solutions include:
Equivalent Building Dimensions (EBD)
Emission Variability Processor (EMVAP)
Updated ambient ratio method (ARM2)
Pairing AERMOD values with the 50th % background concentrations in cumulative analyses.
Effects of Wind Direction on VOC Concentrations in Southeast KansasSergio A. Guerra
Twenty-four-hour whole-air samples were collected in evacuated stainless steel canisters and analyzed for volatile organic compounds (VOC) at selected sites in southeast Kansas from March 1999 to October 2000. The purpose was to assess the influence on air quality of four industrial facilities that burn hazardous waste located in the communities of Coffeyville, Chanute, Independence and Fredonia. Fifteen of the VOC analytes were found at concentrations above the detection limit and above levels observed in the blanks. Data were analyzed to investigate whether sampling site and date had a significant effect on VOC concentration. Results indicate that site and/or date were significant factors for many of the VOCs. To further investigate the temporal factor, sampling days were divided into four classifications based on wind direction: predominantly north winds, predominantly south winds, calm/variable winds and
other winds. Results from statistical analyses show that wind direction was a significant factor for benzene, toluene, o-xylene, naphthalene, and carbon tetrachloride. Data from upwind and downwind samples were analyzed for the four cities of interest in the study area, to investigate the effect of the four targeted sources on VOC concentrations. Results from Fredonia showed higher concentrations of toluene, ethyl benzene, styrene, methyl chloride, and trichloroethylene in the upwind samples, although none of the results were statistically significant. Chanute also showed higher concentrations of the same compounds and m,p-xylene in the upwind samples; results were significant at the 0.05 level for toluene, ethylbenzene, and xylene. These results indicate that sources other than those targeted in the sampling network may be contributing to
the VOC levels. Results from Independence showed higher concentrations of ethylebenzene and styrene in the downwind samples; results were statistically significant. These results indicate that the source targeted in the sampling network may be contributing to the VOC levels at those sampling sites.
Universal Design for Learning (UDL) is a framework for teaching that uses flexible approaches to accommodate learner differences. It focuses on providing multiple means of representation, action and expression, and engagement to benefit the greatest number of students regardless of ability. The goal of UDL is to reduce barriers in instruction and make material accessible to all students through creativity and flexibility so that all students can find learning rewarding.
This document provides an overview of Hispanic culture and history. It discusses that Hispanic culture encompasses many Spanish-speaking countries and regions. It outlines the various forms of government and economies in countries like Spain, Cuba, Central America, and South America. The document also provides a timeline of major historical events and discusses traditions, values, and learning and communication styles of Hispanic students. It notes how these cultural factors can influence academic achievement and language development.
The document discusses collecting feedback on a teaser trailer for an urban drama film from two sources: 1) An online survey of 66 respondents aged 16-24 about aspects of urban dramas like characters, music, and stereotypes. Respondents preferred accurate stereotypes and fast-paced grime music. 2) YouTube comments on a draft trailer which provided positive feedback on its urban drama feel, effects, and locations but said the abrupt ending lacked climax. The feedback was used to change the ending shot and trim overly long staged shots.
Agilent Technologies
The premier measurement company -- advancing electronics, communications, life sciences and chemical analysis
Agilent Technologies Inc adalah perusahaan pengukuran utama dunia dan pemimpin teknologi dalam elektronik dan komunikasi. 20.500 karyawan perusahaan melayani pelanggan di lebih dari 100 negara. Sebagai perusahaan pengukuran utama dunia, Agilent menawarkan jangkauan luas solusi pengukuran inovatif di industri. Perusahaan empat bisnis – Analisis Kimia, Biologi, Diagnostik dan Genomics, dan Elektronik Pengukuran – menyediakan pelanggan dengan produk dan layanan yang membuat perbedaan nyata dalam kehidupan orang-orang di mana-mana. Dan di Agilent Laboratorium Penelitian, kita melakukan penelitian yang mengantisipasi kebutuhan pelanggan dan menghasilkan terobosan bahwa pertumbuhan listrik.
Asal Negara : U.S.A
Jenis Industri :
Automotive/Transportation, Communications and Networking Systems or Equipment , Computers and Peripherals , Consumer Electronics & Appliances , Aerospace/Defense/Government , Electronic Instrumentation or Test , Medical Devices & Systems , Semiconductor Design & Manufacturing , Academia , Energy , Application & Technologies: Advanced Technology , Components , Design Tools (EDA) , Manufacturing , Software/Hardware Development , Test & Measurement
Kategori Produk :
Oscilloscopes , Spectrum Analyzers (Signal Analyzers) , Network Analyzer , Handheld Oscilloscopes, Analyzers, Meters , Logic Analyzers , Protocol Analyzers and Exercisers , EMI/EMC, Phase Noise, Physical Layer Test Systems ,Bit Error Ratio Test (BERT) Solutions , Digital Multimeters (DMM) , Power Meters & Power Sensors , Frequency Counter Products , Noise Figure Analyzers & Noise Sources , LCR Meter & Impedance Measurement Products , Digitizers , DC Power Analyzers , Dynamic Signal Analyzers, Materials Measurement , Parameter & Device Analyzers, Curve Tracer
Untuk pemesanan dan informasi hubungi :
Tridinamika - Test and Measurement
www.tridinamika.com
email to : sales@tridinamika.com
2. HoHai University
Dissertation for the Bachelor Degree in Science
Analysis of the Influence to J-V Characteristics of InGaN
Solar Cell from Induced Polarization and Phase Separation
Candidate
Supervisor
Academic Degree Applied for
Specialty
Affiliation
Date of Defense
Degree-Conferring-Institution
Zhao Shiyang
Zhang Kaixiao
Bachelor of Science
Applied Physics
Department of Physics
June, 2012
HoHai University
2012 June
China Nanjing
6. Abstract
II
Abstract
Energy crisis is one of the top problems which always puzzling people from all
around the world. With the importance of new energy and renewable sources of
energy increasing, using solar energy has drawn much more attention than ever before.
Among them, the research to solar cell transfer efficiency becomes an important
problem which many scholars wish to study. The bandgap of InN has been revised
from 1.89eV to around 0.7eV, according to a research in 2002. This change foretell a
truth that we can make the bandgap of InxGa1-xN, a ternary alloy, be continuously
varied from 3.4eV (GaN) to 0.7eV (InN) by changing the compositions of indium.
Thus, the corresponding wavelength of absorption spectrum has been extended from
ultraviolet (365nm) to infrared (1770nm), covering almost the whole solar spectrum.
Therefore, we can adjust the bandgap of material through changing the compositions
of indium. In addition, InGaN has high absorption, high mechanical strength and
some other outstanding properties. It is very certain that the research towards InGaN
must be one of hottest question which people want to study within solar cell area in
the near future, owing to the deficient research at the moment.
The intention of this paper is to offer a theoretical foundation for preparation and
improvement of InGaN solar cells. I have simulate single-junction InGaN solar cells
and what influence has been made by induced polarization and phase separation by
using the analysis of microelectronic and photonic structures (wxAMPS). The main
study contents of this dissertation include the following respects:
The thesis addresses the significance of this topic by studying the background of
solar cell. The thesis also make a detailed introduction about the development of solar
cell and the main role of this article, InGaN, a newly developing material. This essay
introduces the characteristics and applications of the semiconductor. Moreover, this
essay makes further explanations and illustrations to some important parameters of
semiconductor, for instance, forbidden bandgap and density of carriers. After bring in
some main parameters of solar cell, this thesis mentions some advantages and
disadvantages of InGaN material. By reading related documents, this essay offers
7. Abstract
III
some reasons about why phase separation and induced polarization happened and how
it happened. What is more, this essay makes some explanations about the effects with
academic analysis and build up a simple model at the same time, as preparations for
later work. The thesis uses the knowledge and conclusion that already known to us to
get certain parameters that needed in my simulation. The thesis uses wxAMPS
software to simulate In0.65Ga0.35N solar cells under phase separation and induced
polarization, respectively. The thesis figures out what are the different in J-V
characteristic between the ideal condition and under special conditions and supply a
reference for improving the function of solar cells.
Key words: InGaN; wxAMPS software; solar cell; J-V characteristic; phase
separation; induced polarization
18. 河海大学本科毕业论文
8
2.1.3 禁带宽度
电子在真空中所能得到的能量值基本是连续的,但在晶体中的情况就可能截
然不同了。孤立原子中电子的能级是彼此分离的,当几个原子比较紧密地集合在
一起时,原来的能级就形成了允许的能量带,如图 2-2。当原子像在晶体中那样
有秩序地排列时,彼此之间存在一个平衡的原子间距。图 a 和图 b 分别表示原子
的两种情况。图 a 表示的是在原子平衡间距 d 处,晶体具有被禁带所隔开的电子
允带。图 b 表示的为在不同晶体材料的平衡间距 d 处,能带互相重叠,实际上得
到一个连续的允带。
图 2-2 大量相同原子集合成晶体时孤立原子中分离电子允许能级如何分裂成允带的示意图
(a)在晶体中原子的特征间隔 d 处存在着一些被禁带隔开的电子允许能带
(b)在 d 处最上面的能带发生重叠
2.1.4 电子和空穴
电子和空穴的双层停车场模型是比较经典的一种简单易懂的阐述方式。停车
场的第一层(底层)代表了价带,第二层(顶层)代表了导带。当代表电子的汽车全
部停在底层时,不论是一层的汽车还是二层的空位(即电子和空穴)都无法移动,
也就无法产生所谓的流量(即电流)。但当底层有汽车从一层移动到二层之后(应
该类似于电子被激发的过程)无论是上层的电子还是底层的空位都可以有移动的
可能性。下层虽然实质是汽车在移动,但某种意义上来讲可以把它看做是空位的
转移(即空穴的移动)。因此整个停车场的流量是楼上汽车加楼下空位移动的和
(即半导体内的电流可以看作是导带中的电子和价带中的空穴运动的总和)。如
下图 2-3 所示。
19. 河海大学本科毕业论文
9
图 2-3 用“停车场”简单类比半导体中导电过程
(a)不能移动 (b)上下层都可以移动
2.1.5 允许态的能量密度
单位体积半导体中,在禁带的能量范围内其态密度显然为零,而在允带内就
不是零,这就引出了有关究竟有多少电子状态分布在允带内的问题。
答案可以相当简单地或得,至少对于靠近允带边缘的能量是如此。在允带边
缘,可将载流子看成类似于自由载流子。对于靠近导带边(在无各向异性的情况
下)的能量 E,单位体积、单位能量的允许状态数 N(E)由下式得出:
2/1
3/2*
)(
28
)( 3 c
e
EE
h
m
EN
)12(
其中,h 是普朗克常数。对于靠近价带边的能量,存在类似的表达式。
2.1.6 电子和空穴的密度
知道了允许状态的密度(2-1 式)和这些状态的占有几率,就可以计算电子和
空穴的实际能量分布。由于费米-狄拉克分布函数的性质,导带中的大多数电子
和价带中的空穴都聚集在带边附近,每个带中的总数可通过积分求得。单位体积
晶体中,在导带内的电子数 n 由下式得出,即:
max
)()(
c
c
E
E
dEENEfn )22(
经过一系列简化、估计、改变积分变量等工作可得到:
)/()(2
3
2
*
)
2
(2 kTEEe cF
e
h
kTm
n
)32(
21. 河海大学本科毕业论文
11
Ⅲ族杂质时,这些杂质容易把多余的空穴让给价带,相当于从价带接受电子,故
被称为“受主”。
2.2 InGaN 太阳能电池
2.2.1 III 族氮化物的发展
III 族氮化物的发展要一直追溯到二十世纪初,世界上第一块 GaN 化合物半
导体由 Fichter 在 1910 年生长出来,而第一块 InN 化合物半导体则是由 Johnson
在 1932 年生长出的。在 III 族氮化物的生长中,蓝宝石被作为广泛使用的基底,
但是由于存在着晶格的不匹配,生长出来的薄膜质量较差。1969 年,Maruska
等人报道了利用氢化物气相外延法(HVPE)生长出 GaN,这才使得对 GaN 的研究
有了新的突破。1971 年,Manasevi 和 Erdmann 第一次用有机金属化学气相沉积法
(MOCVD)生长出了 GaN,而 MOCVD 也成为了现在生长外延薄膜层中最常用的
方法。
到了 80 年代,终于迎来了两个突破性的变化。一个是 1983 年 Yoshida 等人
在 500℃低温下引入 GaN 作为缓冲层来减小蓝宝石和 GaN 间的晶格失配,生长
出了高质量 GaN。另一个是 1989 年,Amano 等人利用低能量电子束辐射生长了
掺杂 Mg 的 GaN。这些划时代的突破促进了 III 族氮化物的研究。尽管已经在 GaN
和低 In 组分的 InGaN 材料的研究上取得了显著成就,但是高 In 组分 InGaN 的
晶体质量相比于低 In 组分 InGaN 薄膜较差,因此要实现高质量的 InN 和高 In 组
分的 InGaN 仍然是不小的难题。
在所有的 III 族氮化物半导体中,InN 的电子迁移率和饱和速度都是最高的。
2003 年,H. Lu 等人用分子束外延法(MBE)生长了迁移率最高的 InN。传统半导
体的晶体结构是金刚石和闪锌矿等立方对称结构。而 III 族氮化物半导体存在纤
锌矿结构和闪锌矿两种结构,其中纤锌矿结构是稳定态。纤锌矿结构中,氮原子
形成一个六角密堆积结构。沿着 c 轴方向的 InN 晶体结构,可以看作是一系列
InANAInBNBInANAInBNB„„的六角堆积原子的层状结构。而闪锌矿结构是由
一系列 InANAInBNBInCNCInANA„„堆积而成的
[28]
。图 2-4 表示的是 III 族氮
化物的六角纤锌矿晶格结构。由于 III 族氮化物缺少一个沿 c 轴的对称中心,这
就产生了诸多特别的特性,如压电、热释电以及非线性光学等性质,这些性质对
27. 河海大学本科毕业论文
17
2.4.2 太阳能电池的结构及工作原理
太阳能发电有两种方式,一种是光一热一电转换方式,另一种是光一电直接
转换方式。其中,光一电直接转换方式是利用光电效应,将太阳辐射能直接转换
成电能,光一电转换的基本装置就是太阳能电池。换言之,太阳能电池是通过光
电效应或者光生伏打效应直接把光能转化成电能的半导体器件,其基本结构是一
个 PN 结。所谓光生伏打效应即当物体受到光照时,物体内的电荷分布状态发生
变化而产生电动势和电流的一种效应。太阳电池的主要参数包括开路电压、短路
电流、填充因子和光电转换效率,若使太阳电池具有高的效率,前三者的乘积必
须最大
[30]
。如果在晶体硅中掺人能够俘获电子的硼、铝、镓或铟等杂质元素,那
么它就成为空穴型半导体,简称 p 型半导体。如果在硅晶体中掺入能够释放电子
的磷、砷或锑等杂质元素,那么它就成了电子型的半导体,简称 n 型半导体。若
把这两种半导体结合在一起,由于电子和空穴的扩散,在交界面处便会形成 p-n
结,并在结的两边形成内建电场,又称势垒电场。由于此处电阻特别高,所以也
称为阻挡层。太阳光或其他光照射半导体 p-n 结时,由于两种类型的半导体材料
载流子浓度存在着浓度差,因此载流子要做扩散运动。此时就会在 p-n 结的两边
出现电压,叫光生电压。该电压使 p-n 结短路从而产生电流,简称为短路电流。
下面来具体解释一下该过程。电子从 n 区扩散到 p 区,空穴从 p 区扩散运动到 n
区。在 n 区,电子的离开留下了带正电的电离施主,没有了电子与其保持电中性,
因此,在 p-n 结的 n 区一侧出现了一个正电荷区。同理,在 p 区一侧出现了一个
由电离受主构成的负电荷区。在 p-n 结附近由电离施主和电离受主构成的区域成
为空间电荷区,也叫势垒区,如图 2-7 所示。
图 2-7 p-n 结示意图
这样在空间电荷区内产生了由正电荷指向负电荷即由 n区指向 p 区的内建电
场,如图 2-8 所示。在内建电场的作用下电子由 p 区向 n 区运动,空穴由 n 区向
p 区运动,形成了载流子的漂移运动。漂移运动和载流子的扩散运动刚好相反,
因此内建电场起到阻碍载流子扩散运动的作用。由于载流子的扩散运动内建电场
28. 河海大学本科毕业论文
18
逐渐增强,漂移运动也随之增强。在无外加电压的情况下,载流子的扩散运动和
漂移运动相平衡时,即有多少的空穴由 p 区扩散到 n 区就有多少空穴由 n 区漂移
到 p 区。对于电子,情况一样。这样总的扩散电流和漂移电流大小相等方向相反,
总的电流为零。也就是说通过 p-n 结的净电流为零,这时就称为热平衡状态下的
p-n 结。
图2-8 太阳能电池能级图
当有能量为 hv 的太阳光照射到禁带宽度为 Eg(hυ≥Eg)的半导体材料时,就
有足够能量的光子能打断 n 型材料和 p 型材料中的共价键,从而产生了光生电子
-空穴对
[31]
。在内建电场的作用下光生电子由 p 区向 n 区运动,光生空穴由 n 区
向 p 区运动。通过 p-n 结界面层的分离光生电子和空穴分别在 n 区和 p 区形成了
电荷积累,这样在 p-n 结两边就产生了光生电动势,也叫光生电压。如果在两端
加上电极,再用导线连接起来通路中就有了电流,就叫光生电流。入射光的能量
越大界面层的面积越大,光生电流也就越大。若把几十个、数百个太阳能电池单
体串联、并连起来,组成太阳能电池组体,在太阳光的照射下,便可获得相当可
观的输出功率的电能。
2.4.3 太阳能电池的等效电路
为了清楚地描述太阳能电池的工作状态,通常用等效电路来模拟电池及负载。
假设在太阳能电池两端接一个电阻为 RL 的负载,则在工作状态下太阳能电池的
等效电路可以表示为图 2-9(a)所示。其等效电路相当于一个恒定的电流源和一
个正向的二极管并联。流过二极管的正向电流相当于在太阳能电池中所流过的暗
电流。等效电路图 1-6(a)是理想的太阳能电池。由太阳光照引起的光电流和太
29. 河海大学本科毕业论文
19
阳能电池的暗电流方向相反。但是在实际的太阳能电池中,由于存在并联(泄露)
电阻 RSh(等效于电池的漏电和电池电极制作时形成的小裂纹和划痕等形成了金
属桥漏电)和串联电阻 RS(表示附加电阻),它的等效电路如图 2-9(b)所示。
图 2-9 太阳能电池等效电路
(a)理想 p-n 结太阳电池的等效电路 (b)实际 p-n 结太阳电池的等效电路
在图 2-9 等效电路中,输出电流 I 和输出电压 V 之间的关系可以表示为
)]([ jbk
Sh
L
ShS
Sh
VI
R
V
I
RR
R
I
在上式中 Ibk 为暗电流,它是 p-n 结两边电压 Vj 的函数。而 Vj 和输出电压 V 之
间的关系为 Vj=V+IRs。光电流 IL 和太阳能电池接受到的太阳光的面积和强度有
关。当等效电路中的 RL 从 0 变化到∞时,太阳能电池的输出电压 V 由 0 变化到
VOC(即电路的开路电压),同时输出的电流也跟随着变化,其大小由 ISC(即短路
电流)变化到 0。由此得出了太阳能电池电流随着电压而变化的输出特性曲线,
如图 2-10 所示,其横纵坐标分别表示电压和电流。输出特性曲线上的每一点都
代表一个工作点。每一点的横坐标和纵坐标的乘积,即输出电压和电流的乘积,
就是太阳能电池的输出功率。由图 2-10 可以看出太阳能电池的最大输出功率
P=IV 对应最大的矩形面积为 B。
图 2-10 中矩形面积 B 与 A即最大输出功率与(VOC×ISC)之比称为填充因数,
用 FF 来表示。通常我们用填充因数来表示太阳能电池输出特性的好坏,填充因
数越大表示太阳能电池的性能越优越。当光强一定时,填充因数愈大,曲线愈接
近正方形,则输出功率也就愈大。这个参数可以表示为:
SCOC
mm
SCOC
m
IV
IV
IV
P
FF
32. 河海大学本科毕业论文
22
ASA软件包以及德国弗劳恩霍夫太阳能系统研究所(Fraunhofer Institute for Solar
Energy Systems)开发的Afors-Het2.2等。这些软件都为太阳能电池的理论研究和
实际制作提供了很大的帮助。
建立理论模型的基础是通过描述器件物理参数的理论公式、太阳能电池所采
用的材料以及结构参数等。为了方便计算或者是计算的可行性,通常需要加入一
些假设条件进行某些简化处理。当然,理论模拟计算的正确与否还需要实验来进
一步验证。因此,模拟计算能够指导实验的进行,而实验又可以检验模拟结果的
正确与否。正是在理论模拟和不断实验的基础上,太阳能电池的转换效率不断得
到提高,而其制造成本在不断的下降。相信在将来随着实验条件和理论模拟水平
的进步,将会制造出转换效率更高、更加经济实用的太阳能电池,光伏发电将在
未来能源利用中占有举足轻重的地位。
3.2 AMPS 模拟软件
3.2.1 wxAMPS 软件简介
AMPS(Analysis of Microelectronic and Photonic Structures)模拟软件是由宾夕
法尼亚大学 Fonash 教授及其学生们在 1988 年开发的程序,它是一个用于分析微
电子和光电子器件的模拟软件,即模拟半导体器件中载流子的输运情况,图 3-1
即为 AMPS 模拟软件所用的一维器件结构示意图。所有的双端光电子器件,无
论是最简单的肖特基结构还是较为复杂的多层结构,只要把半导体各层的能带结
构和电子亲和势及态密度分布等参数正确地输入,就能把载流子的分布用方程表
示出来。该软件主要利用第一原理、连续性方程和泊松方程等方法分析半导体光
电子器件的载流子输运情况,至今仍在不断的完善升级之中,wxAMPS 就是由
美国 UIUC 与中国南开大学联合开发的 AMPS 的修订版。新修正的软件主要模
型理论同 AMPS 相同,均基于电流连续性方程和泊松方程的联立求解,区别是
在原有 AMPS 的物理基础上多加入了两种隧穿模型和一个新的结合了 Newton 算
法和 Gummel 算法的运算法则,增加了隧穿电流的部分(使其更适合异质结及其
界面),提高了精度和稳定性,同时使得软件的使用界面更加华丽、使用更加简
单、结果更加清晰。
33. 河海大学本科毕业论文
23
隧穿模型公式如下:
kT
E
ET
kT
EE
JJ i
i
icETTunnel
i
)()
)0(
exp( )13(
ix
icni dxExEm
h
ET
0
*
)))((2
4
exp()(
)0(min
ci EEE )23(
图 3-2 异质结的导带图
已知半导体内的一维泊松方程:
dx
xdEx
dx
xd
s
)()()(
2
2
)33(
其中, )(x 为电场电势, )(xE 为电场大小, )(x 为电荷密度, s 为介电常数。
在稳态条件下载流子的分布遵循费米-狄拉克 (Fermi-Dirac)统计分布,可
以用一维的泊松方程式来表示空间电荷的一维空间分布
)]()()()()()([)
)(
)(( xnxpxNxNxnxpq
dx
xd
x
dx
d
ttAD
)43(
34. 河海大学本科毕业论文
24
)(xn 、 )(xp 分别表示自由载流子浓度;
DN 、
AN 分别代表电离施主和电离
受主浓度而 )(xnt 、 )(xpt 则表示受陷电子及受陷空穴浓度;式中 代表半导体层
中某一点的单位正电荷静电势的负值,而 dxd / 就可以表示相应位置电场强度
的大小。计算中所用 的值是半导体器件中每一点的真空能级(与电子亲和势或
功函数相联系)和器件后电极欧姆接触端的真空能级的差值,单位是 eV。
wxAMPS 程序对半导体器件进行直流模拟,在模拟过程中假设施主和受主
是完全电离的,也就是 DD NN
, AA NN
,此时 3-4 式中的各项可以表示为:
)()( 2/1
kT
EE
FNxn CF
c
dEEfEgxn A
E
E
At
C
V
)()()(
)()( 2/1
kT
EE
FNxp FV
v
dEEfEgxp D
E
E
Dt
C
V
)()()( )53(
(3-5)式中的 Nc 为导带底有效态密度,Nv 为价带顶有效态密度;F1/2 表示费米积
分; )(EgA 、 )(EgD 分别是 CE 、 VE 之间的类受主定域态和类施主定域态的总分
布函数。 )(EfD 和 )(EfA 分别表示电子和空穴占居能量值为 E 的类施主定域态和
类受主定域态的分布概率。为了得到太阳能电池的 J-V 特性需要计算在有光照
条件下的电流输出。由载流子的输运理论计算,可以得出电子和空穴的电流密度,
其表示式分别为
))(()(
dx
dE
xnqxJ nF
nn ))(()(
dx
dE
xpqxJ pF
pp )63(
式中 FnE 代表电子的准费米能级, FpE 代表空穴的准费米能级。另外还有半导体
的连续性方程,其中 )(xGOP 代表光生载流子的产生速率。
)()()(
1
xRxG
dx
dJ
q
OP
n
)73(
)()()(
1
xRxG
dx
dJ
q
OP
p
)83(
不过,仅有泊松方程式(3-4)和载流子的连续性方程式(3-7)、(3-8)在一般条件
下是无法求解的。要求出半导体器件中各参数的值,还必须加上一定的边界条件。
62. 河海大学本科毕业论文
52
参 考 文 献
[1] 张以漠编著.应用光学(修订本).北京机械工业出版社,1988 年.
[2] Jani O K. Development of Wide-Band Gap InGaN Solar Cells for High-
efficiecy Photovoltaics [D]. Atalanta: Georgia Institute of Technology,
2007:2~3
[3] Jones R E. Electrical and Optical Characterization of Group III-Nitride Alloys
for Solar Energy Conversion [D]. Berkeley: University of California, Berkeley,
2008:1~3
[4] Pachauri R K, Reisinger A. 2007: Climate Change 2007: Synthesis Report of
the Intergovernmental Panel on Climate Change [R].2008:104~105
[5] Wu J, Walukiewicz W, Yu K M, et al. Unusual properties of the fundamental
band gap of InN. Appl Phys Lett, 2002, 80(21):3967
[6] Tansley T L, Foley C P. Optical band gap of indium nitride. J Appl Phys, 1986,
59(9):3241
[7] Matsuoka T, Okamoto H, Nakao M, et al. Optical bandgap energy of wurtzite
InN. Appl Phys Lett, 2002, 81(7):1246
[8] Green M A, Emery K, Hisikawa Y. Solar Cell Efficiency Tables[J]. Progress in
Photovoltaics: Reasearch and Applications. 2007, 15(5):425~430
[9] 秦易. 太阳能电池技术进展与趋势 科技创新导报 2011 NO.16
[10] Martinot E. Renewables Global Status Report 2006 Update[R]. World Institute.
Washington, DC. 2006:1~30
[11] Deng Q W, Wang X L, Yang C B, et al. Theoretical Study on InxGa1-xN/GaN
Quantum Dots Solar Cell[J]. Physics B.2010,406(1):73~76
[12] Jeng M J, Lee Y L, Chang L B, et al. Temperature Dependences of NGaIn xx 1
Multiple Quantum Well Solar Cells[J].J.Appl.D:Appl.Phys.2009,42(10):
105101-1~105101-7
[13] Kailuweit P, Kellenbenz R, Philipps S P, et al. Numerical Simulation and
Modeling of GaAs Quantum-Well Solar Cells[J]. Journal of Applied Physics.
2010, 107(6):064317-1~064317-6