基于晶格大失配In0.58Ga0.42As材料的高效四结太阳电池

Ⅲ-Ⅴ族晶格失配多结太阳电池是实现高效太阳电池的主要途径之一,但面临晶格失配材料的高质量生长及其所导致的子电池光电转换效率下降的难题。重点针对晶格失配子电池结构中的(AlGa)InAs缓冲层开展台阶层厚度优化研究,设计了150、200和250 nm三组不同台阶层厚度的缓冲层结构,并完成三组样品的外延生长实验。通过材料测试和子电池电性能测试,系统分析了台阶层厚度对In_0.58Ga_0.42As材料外延生长质量和子电池电性能的影响。获得了晶格弛豫度为96.71%的In_0.58Ga_0.42As子电池材料,制备的子电池开路电压达到205.10 mV。在此基础上,结合GaInP/GaAs/In_0.3Ga_0.7As三结电池研制了晶格失配四结薄膜太阳电池,其光电转换效率达到32.41%(AM0,25℃)。     

基于InP衬底的晶格失配In0.68Ga0.32As的MOCVD生长及其特性研究

采用MOCVD生长技术在InP衬底上成功实现了晶格失配的3μm In0.68 Ga0.32As薄膜生长.通过As组分的改变,利用张应变和压应变交替补偿的InAsxP1-x应变缓冲层结构来释放由于晶格失配所产生的应力,在InP衬底上得到了与In0.68Ga0.32 As晶格匹配的InAsxP1-x“虚拟”衬底,通过对缓冲层厚度的优化,使应力能够在“虚拟”衬底上完全豫弛.通过原子力显微镜(AFM)、高分辨XRD、透射电镜(TEM)和光致发光(PL)等测试分析表明,这种释放应力的方法能够有效提高In0.68 Ga0.32 As外延层的晶体质量.     

晶格失配度达2.6%的波长扩展InGaAs/InP光电探测器结构

利用气态源分子束外延,采用相对较高的1.1%μm-1失配度变化速率,在InAlAs递变缓冲层上生长了晶格失配度高达2.6%的InP基InGaAs变形晶格探测器结构,并与采用相同结构而晶格失配度为1.7%和2.1%的探测器样品进行了比较。通过原子力显微镜、X射线衍射、光致发光和器件特性测试对样品进行了表征。结果显示该晶格失配度达2.6%的探测器结构具有较好的表面形貌、较大的晶格弛豫度和理想的光学特性。器件室温截止波长约为2.9μm,直径为300μm的器件室温下在反向偏压10mV时的暗电流为2.56μA。     

缓冲层材料对纤锌矿结构GaN(0001)光电发射性能的影响研究

利用金属有机物化学气相沉积技术在蓝宝石衬底上异质外延生长了GaN光电发射层,为降低GaN发射层和蓝宝石衬底间的晶格失配与热失配,在蓝宝石衬底和GaN发射层间分别采用了AlN和AlxGa1-xN两种不同的缓冲层材料。对具有不同缓冲层材料的两种样品进行了表面清洗与激活,在激活结束后利用多信息量测试系统分别测试了样品的光谱响应,其最大量子效率分别为13%和20%,依据激活后光电阴极的光谱响应作为评估标准,可以得出,采用组份渐变AlxGa1-xN作为缓冲层激活出的阴极具有更高的光电发射性能,从而实现了GaN光电阴极结构的优化设计。     

不同缓冲层对GaAs基In_(0.3)Ga_(0.7)As材料特性的影响

采用组分跳变和低温大失配缓冲层技术在GaAs衬底上外延了In0.3Ga0.7As材料。测试结果表明,采用组分跳变缓冲层生长的In0.3Ga0.7As主要依靠逐层间产生失配位错来释放应力,并导致表面形成纵横交错的Cross-hatch形貌;而采用低温大失配缓冲层技术则主要通过在低温缓冲层中形成大量缺陷来充分释放应力,并在后续外延的In0.3Ga0.7As表面没有与失配位错相关的Cross-hatch形貌出现。此外,仅需50nm厚的低温大失配缓冲层即可促使In0.3Ga0.7As中的应力完全释放,这种超薄缓冲层技术在工业批产中显得更为经济。     

50周期的In_(0.3)Ga_(0.7)As/GaAs应变超晶格的生长

在本文，我们用一个低组分的InxGa(1-x)As缓冲层（x～0．01），有效地限制了50周期的In0.3Ga0．7As／GaAs应变超晶格本身弛豫所产生的位错，X射线双晶衍射测量结果表明使用这样缓冲层的超晶格质量明显改善，可以观察到12级卫星峰，而在没有这个缓冲层的样品上只能观察到3个衍射卫星峰．透射电子显微镜上观察到产生的位错被限制在这个缓冲层中或弯曲进入了衬底而没有进入所需要的外延层。     

用X射线衍射研究缓冲层对GaInAs材料的影响

用分子束外延方法制备了具有GaInAs组分渐变缓冲层和不具有GaInAs组分渐变缓冲层的Ga0.9In0.1As/GaAs结构的外延材料。利用高分辨率X射线衍射法(HRXRD)对制备的两种样品分别进行了测试分析。实验结果表明,GaInAs组分渐变缓冲层对外延生长在GaAs衬底上的Ga0.9In0.1As外延材料的晶体质量具有显著的改善作用,极大降低了由于外延层与衬底晶格不匹配所带来的影响。从X射线倒易空间衍射(RSM)二维图谱结果来看,具有GaInAs组分渐变缓冲层结构的样品,其Ga0.9In0.1As外延层与GaInAs组分渐变缓冲层接近完全弛豫,Ga0.9In0.1As外延层的应变降低,表面残留应力小于0.06%,同时,GaAs衬底与Ga0.9In0.1As外延层之间的偏移夹角明显变小。     

Bathocuproine作为缓冲层改善Rubrene/C70太阳能电池的性能

制备了结构为ITO/Rubrene/C70/BCP/Al的双层有机太阳能电池(OSCs),通过优化缓冲层BCP的厚度研究了BCP对OSCs性能的影响及其作用机理。实验发现,BCP厚为6nm时,器件的效率最高达到1.78%,同时获得了较大的开路电压0.901V。相对于没有缓冲层,器件的效率、短路电流、开路电压和填充因子分别提高了432.9%、74.8%、95.4%和55.5%。     

分子束外延生长的GaSb热光伏电池器件特性研究

利用分子束外延的方法在GaSb衬底上生长GaSb热光伏电池单元,制作了两种不同的1 cm×1 cm面积尺寸的热光伏电池单元,它们有着不同的电极形状。通过不断优化分子束外延的生长条件,以期得到高质量的GaSb外延层。AFM图中显示的表面形貌表明器件有着高质量的外延层,其表面形貌的RMS只有1.5 ? （1 ?=0.1 nm）。测量和比较了两种热光伏电池的器件特性,包括开路电压、短路电流密度、光电转换效率、填充因子以及暗电流密度。在一个模拟太阳光照射下,热光伏电池单元有着0.303 V的开路电压和27.1 mA/cm2的短路电流密度。和只有简单电极形状的热光伏电池单元进行对比,有栅形电极形状的热光伏电池单元在短路电流密度和填充因子上具有更优异的表现。在红外光的照射下,有栅形电极形状的热光伏电池达到了一个最优的填充因子56.8%。     

GaInP/GaInAs 叠层太阳电池的结构设计及优化

我们计算了单级联GaInP/GaInAs叠层太阳能电池理论转换效率,在实验上它通常生长在GaAs衬底上。相比于传统的GaInP2/GaAs叠层电池,通过对禁带宽度组合的优化,我们得到了更高转换效率的体系结构。这里,对于所考虑禁带组合1.83eV/1.335eV,计算结果表明,当对其结构进行优化后（即顶电池GaInP厚度为1550nm,底电池GaInAs厚度为5500nm),其理论转换效率可以达到40.45% (300suns,AM1.5d),另外鉴于它相对于GaAs衬底较低的晶格失配（0.43%),在未来它将更具有应用前途。     

High-performance In/sub 0.53/Ga/sub 0.47/As thermophotovoltaic devices grown by solid source molecular beam epitaxy

In/sub 0.53/Ga/sub 0.47/As-based monolithic interconnected modules (MIMs) of thermophotovoltaic (TPV) devices lattice-matched to InP were grown by solid source molecular beam epitaxy. The MIM device consisted of ten individual In/sub 0.53/Ga/sub 0.47/As TPV cells connected in series on an InP substrate. An open-circuit voltage (V/sub oc/) of 4.82 V, short-circuit current density (J/sub sc/) of 1.03 A/cm/sup 2/ and fill factor of /spl sim/73% were achieved for a ten-junction MIM with a bandgap of 0.74 eV under high intensity white light illumination. Device performance uniformity was better than 1.5% across a full 2-in InP wafer. The V/sub oc/ and J/sub sc/ values are the highest yet reported for 0.74-eV band gap n-p-n MIM devices.     

0.6-eV bandgap In/sub 0.69/Ga/sub 0.31/As thermophotovoltaic devices grown on InAs/sub y/P/sub 1-y/ step-graded buffers by molecular beam epitaxy

Single-junction, lattice-mismatched (LMM) In/sub 0.69/Ga/sub 0.31/As thermophotovoltaic (TPV) devices with bandgaps of 0.60 eV were grown on InP substrates by solid-source molecular beam epitaxy (MBE). Step-graded InAs/sub y/P/sub 1-y/ buffer layers with a total thickness of 1.6 /spl mu/m were used to mitigate the effects of 1.1% lattice mismatch between the device layer and the InP substrate. High-performance single-junction devices were achieved, with an open-circuit voltage of 0.357 V and a fill factor of 68.1% measured at a short-circuit current density of 1.18 A/cm/sup 2/ under high-intensity, low emissivity white light illumination. Device performance uniformity was outstanding, measuring to better than 1.0% across a 2-in diameter InP wafer indicating the promise of MBE growth for large area TPV device arrays.     

NH_2D斯塔克效应调制CO_2激光器

在CO_2激光器外部一个20厘米长的气体盒上,加上400赫、20代有效值正弦波调制信号和440伏直流偏压,当气压为5托时,得到了41%的调制度.计算了气体盒的最大调制度,其值为42%,与实验所得到的最大调制度很好地符合.当正弦波调制信号为2兆赫、20伏有效值时,达到12%的调制度.NH_2D由ND_3和NH_3混合而制备,ND_3由作者自制.     

High-performance, metamorphic In/sub x/Ga/sub 1-x/As tunnel diodes grown by molecular beam epitaxy

Thin In/sub x/Ga/sub 1-x/As tunnel junction diodes having compositions from x=0.53 to 0.75 that span a range of bandgap energies from 0.74 to 0.55 eV, were grown on InP and metamorphic, step-graded In/sub x/Al/sub 1-x/As/InP substrates using molecular beam epitaxy and evaluated in the context of thermophotovoltaic (TPV) applications. Both carbon and beryllium were investigated as acceptor dopants. Metamorphic tunnel diodes with a bandgap of 0.60 eV (x=0.69) using carbon acceptor doping displayed highest peak current densities, in excess of 5900 A/cm/sup 2/ at a peak voltage of 0.31 V, within a 200 /spl Aring/ total thickness tunnel junction. Identically doped lattice-matched tunnel diodes with a bandgap of 0.74 eV exhibited lower peak current densities of approximately 2200 A/cm/sup 2/ at a higher peak voltage of 0.36 V, consistent with the theoretical bandgap dependence expected for ideal tunnel diodes. Specific resistivities of the 0.60 eV bandgap devices were in the mid-10/sup -5/ /spl Omega/-cm/sup 2/ range. Together with their 200 /spl Aring/ total thickness, the electrical results make these tunnel junctions promising for TPV applications where low-resistance, thin metamorphic tunnel junctions are desired.     

GaInSb单结热光伏电池的设计与优化

使用Silvaco/Atlas软件设计、模拟并优化了GaInSb/GaSb单结热光伏电池,研究了器件材料厚度和掺杂浓度对电池性能的影响。主要从最大输出功率(Pm)、开路电压(Voc)和短路电流(Isc)这三个参数表征并分析电池器件的优劣。器件厚度主要通过对入射光的吸收率和光生载流子的收集效率影响热光伏电池的性能。而掺杂浓度对于热光伏电池特性的影响主要是从复合机制以及少子迁移率等方面体现。最后得到了优化后的器件结构。     

Comparison of Photonic-Crystal-Enhanced Thermophotovoltaic Devices With and Without a Resonant Cavity

The ability to efficiently convert heat into usable energy using thermophotovoltaics (TPV) has been a topic of research for many years. Due to recent microfabrication advances, TPV and photonic crystals (PhC) have been the subject of renewed interest, especially as spectral emitters in TPV applications. However, PhC surface enhancements have also been shown to increase the efficiency of photon-to-current conversion for infrared photodetectors. Here, we investigate the potential efficiency enhancements gained by using PhC for a front-side TPV diode stage surface feature. A back reflecting plane was also added to increase the efficiency of TPV cells by introducing a resonant cavity. The simulations suggest an increased interaction time between photons and excitons leading to an increase in carrier generation. A simulated two-dimensional (2D) PhC consisting of Si₃N₄ rods in an ohmic contact material has demonstrated a possible 81% increase in absorption for a GaSb TPV cell.     

A proposed thermophotovoltaic solar energy conversion system

A solar-electric system is proposed and discussed. This system uses concentrated mirrors focusing on a thermophotovoltaic (TPV) converter. Within the TPV converter the concentrated sunlight heats a refractory radiator. A silicon photovoltaic cell faces the radiator, receives incandescent radiation from it, and converts this radiation into electricity.     

Performance of a mesoscale liquid fuel‐film combustion‐driven TPV power system

Combustion‐driven thermophotovoltaic (TPV) systems have obtained increasing attention in recent decades, but most studies have focused on developing narrowband photovoltaic cells and selective emitters. In terms of the heat source, conventional combustion configurations and light gaseous fuels are extensively utilized in macro‐ or meso‐scale TPV power systems to simplify thermal management and mechanical fabrication. As far as miniaturization is concerned, however, fuelling these systems with liquid hydrocarbons would provide inherent advantages of high energy density and low volatility. Liquid fuels also promise easy and safe fuel recharging for small‐scale power systems. In this paper, a central porous‐medium combustor was employed in a small scale TPV power system. The combustor incorporated an emitting chamber wall and a heat recuperator. The radiant efficiency and overall efficiency were compared using different liquid hydrocarbon fuels in the system. The electric output characteristics of the combustion driven TPV system have been investigated to demonstrate the feasibility of a GaSb cell‐based TPV power system and to provide design guidance for mesoscale liquid‐burning TPV systems. Copyright © 2008 John Wiley & Sons, Ltd.     

A Low Phase-Noise X-Band MMIC VCO Using High-Linearity and Low-Noise Composite-Channel Al0.3Ga0.7N/Al0.05Ga0.95N/GaN HEMTs

A low phase-noise X-band monolithic-microwave integrated-circuit voltage-controlled oscillator (VCO) based on a novel high-linearity and low-noise composite-channel Al_0.3Ga_0.7N/Al_0.05Ga_0.95 N/GaN high electron mobility transistor (HEMT) is presented. The HEMT has a 1 mumtimes100 mum gate. A planar inter-digitated metal-semiconductor-metal varactor is used to tune the VCO's frequency. The polyimide dielectric layer is inserted between a metal and GaN buffer to improve the Q factor of spiral inductors. The VCO exhibits a frequency tuning range from 9.11 to 9.55 GHz with the varactor's voltage from 4 to 6 V, an average output power of 3.3 dBm, and an average efficiency of 7% at a gate bias of -3 V and a drain bias of 5 V. The measured phase noise is -82 dBc/Hz and -110 dBc/Hz at offsets of 100 kHz and 1 MHz at a varactor's voltage (V_tune)=5 V. The phase noise is the lowest reported thus far in VCOs made of GaN-based HEMTs. In addition, the VCO also exhibits the minimum second harmonic suppression of 47 dBc. The chip size is 1.2times1.05 mm²