集中光伏發(fā)電( CPV )原位測量

集中光伏發(fā)電，基于III - V族化合物半導(dǎo)體材料的多結(jié)太陽能電池可以實(shí)現(xiàn)高達(dá)44 %的高效率。從大面積收集的太陽光集中在小面積太陽能電池上。LayTec原位測量系統(tǒng)使您可以跟蹤MOCVD或MBE生長多層太陽能電池結(jié)構(gòu)的所有工藝步驟。這些系統(tǒng)監(jiān)控：

● 層厚度和生長速率     ● 表面形貌

● 表面化學(xué)計(jì)量比        ● 薄膜應(yīng)變和晶片弓出

● 薄膜成分                  ● 真晶片溫度

● 摻雜濃度

以及其他關(guān)鍵參數(shù)。

對于工業(yè)CPV應(yīng)用，需要結(jié)合實(shí)時(shí)統(tǒng)計(jì)過程控制對增長進(jìn)行魯棒分析。 針對行業(yè)需求，采用LayTec公司的Epi TT和Epi Curve ? TT產(chǎn)品族，結(jié)合Epi Guard ?軟件包。這些原位系統(tǒng)提供了對生長參數(shù)的全面和穩(wěn)健的監(jiān)測。發(fā)射率校正測溫( ECP )已成為這些計(jì)量系統(tǒng)的支柱，因?yàn)榫馁|(zhì)量、成分和摻雜水平高度依賴于晶片表面溫度，因?yàn)樗怯蒐ay Tec公司的集成ECP模塊在III - V、Si或Ge襯底上測量的。

高性能CPV外延的第二個(gè)關(guān)鍵是生長過程中所有層的精確厚度監(jiān)測。在405nm、633nm和950nm處同時(shí)進(jìn)行反射率測量，提供了關(guān)于層厚度、表面形貌和界面質(zhì)量的信息。特別是較短的波長( 405 nm )已經(jīng)被廣泛用于表征AlInP工藝過程中的工藝窗口。

另一個(gè)關(guān)鍵參數(shù)是生長過程中和生長后的晶片弓形。Ⅲ-Ⅴ族化合物在Ge上的異質(zhì)外延導(dǎo)致了晶片的顯著彎曲。研究發(fā)現(xiàn)，在這些應(yīng)用中，經(jīng)過有意的緩沖器弛豫后，變體生長的曲率是強(qiáng)非球面的。LayTec公司的 高級分辨率( AR )曲率技術(shù) 使用戶能夠區(qū)分球面曲率和非球面性。由此產(chǎn)生的信號有助于在外延過程的早期和決定性階段優(yōu)化緩沖層的生長及其弛豫。

對于集中型多結(jié)太陽電池的研究和開發(fā)，直接實(shí)時(shí)獲取界面化學(xué)計(jì)量比和摻雜水平對于深入理解外延生長過程中發(fā)生的效應(yīng)是必不可少的。利用Lay Tec公司的EpiRAS ? TT中的光學(xué)方法- -反射各向異性光譜( RAS )，可以實(shí)現(xiàn)這種控制。其中一個(gè)技術(shù)挑戰(zhàn)是在IV族Ge襯底上生長低缺陷的III - V族半導(dǎo)體結(jié)構(gòu)。在這里，EpiRAS ? TT有助于在整個(gè)MOCVD過程中控制異質(zhì)結(jié)構(gòu)的關(guān)鍵生長參數(shù)。該計(jì)量系統(tǒng)可以避免在Ge界面III - V處形成初始反相邊界，并提供寬范圍的光譜反射測量以確定三元組分和生長速率，RAS信號測量摻雜水平，最后，發(fā)射率校正的高溫計(jì)用于精確的溫度監(jiān)測。 . . . 等等

通過原位監(jiān)測提升三結(jié)成品率

《化合物半導(dǎo)體》 雜志發(fā)表了一篇文章，報(bào)道了Lay Tec公司的原位計(jì)量工具在集中光伏電池開發(fā)和生產(chǎn)中的應(yīng)用。

英文：

In concentrated photovoltaics, high efficiency of up to 44% can be achieved nowadays with multi-junction solar cells based on III-V compound semiconductor materials. Sunlight collected from a large area is focused on small area solar cells. LayTec in-situ metrology systems enable you to follow all the process steps during MOCVD or MBE growth of multi-layer solar cell structures. These systems  monitor:
? Layer thickness and growth rate   ? Surface morphology
? Surface stoichiometry                     ? Film strain and wafer bowing
? Film composition                             ? True wafer temperature
? Doping concentration
and other key parameters.

For industrial CPV applications, robust analysis of the growth combined with a real-time statistical process control is needed. For industrial requirements, LayTec’s EpiTT and EpiCurve? TT product families in combination with the EpiGuard? software packageare applied. These in-situ systems provide a comprehensive and robust monitoring of growth parameters. Emissivity corrected pyrometry (ECP) has become the backbone of these metrology systems because crystalline quality, composition, and doping level highly depend on wafer surface temperature as it is measured on III-V, Si or Ge substrates by LayTec’s integrated ECP modules.

The second key to high performance CPV epitaxy is the precise thickness monitoring of all layers during growth. Simultaneous reflectance measurement at 405 nm, 633 nm and 950 nm provide information on layer thickness, surface morphology and interface quality. In particular the shorter wavelength (405 nm) is widely used for characterization of AlInP process window already during the process.

A further critical parameter is the wafer bow during and after growth. The heteroepitaxy of the III-V compounds on Ge leads to a significant bow of the wafer. It was found that the curvature in these applications is strongly aspheric after intentioned buffer relaxation for metamorphic growth. LayTec’s advanced resolution (AR) curvature technology enables the user to distinguish between spherical curvature and asphericity. The resulting signal helps to optimize the buffer growth and its relaxation at early and decisive stages of the epitaxial process.

For research and development of concentrated multi-junction solar cells, a direct real-time access to interface stoichiometry and doping levels is indispensable for deep understanding of the effects that occur during the epitaxial growth.  This kind of control is possible with Reflectance Anisotropy Spectroscopy (RAS) – an optical method applied in LayTec’s EpiRAS? TT. One of the technological challenges is the growth of low defect III-V semiconductor structures on co-valent group IV Ge substrates. Here, EpiRAS? TT helps control key growth parameters of the heterostructures throughout MOCVD process. The metrology system enables avoiding initial antiphase boundary formation at the III-V of Ge interface and provides wide-range spectral reflection measurements to determine ternary composition and growth rate, RAS signal to measure the doping level and, last but not least, the emissivity corrected pyrometry for an accurate temperature monitoring. ...more

Boosting triple-junction yield with in-situ monitoring

Compound Semiconductor Magazine published an article that reports about the application of LayTec’s in-situ metrology tools for development and production of concentrator photovoltaic cells.