奇异量子结构的自发辐射特性

现在,光辐射二极管(LED)和激光二极管(LD)已经广泛地用于人们的日常生活和科学研究领域,例如光纤通信、光互联、医学应用、工业测量和国防等等,但在世界范围内,研究人员仍然一直在从理论和实验上寻求更好的发光材料结构,并对它们的特性加以研究,以进一步提高半导体光辐射器件的性能。

在对LED 和LD的研究中,半导体材料和器件有一个共同本性,即非放大的自发辐射(SE)。对于发光材料和器件,这是一个基本但却非常重要的物理参量。依据爱因斯坦的光辐射理论,它刻画了光与物质相互作用的基本物理过程和影响器件的光学性质。

为了获得器件的自发辐射信息,研究人员提出了理论计算和实验测量的方法。然而一方面,当前的理论方法仅仅适用于理想或标准的量子限制模型,例如量子阱或量子点结构,对准确地表征任何奇异或非标准的量子限制结构的自发辐射特性存在困难,例如下文中提到的富铟团簇所致的量子结构就是一个典型的奇异量子结构。由于受富铟团簇(IRC)效应的影响,该结构由很多非规则和铟含量各异的InGaAs区构成。

另一方面,当前大多数获取器件自发辐射信息的实验方法需要制备一个复杂的测量样品,受限于技术,样品制备通常难以精确地处理,导致产生一些额外的测量误差。因此,这就迫切地需要开发用于表征和准确地获取任何类型量子结构,特别是非标量子结构的新实验方法。由于建立一个普适的能够计算各种材料结构自发辐射特性的理论模型非常困难,因此实验的方法更有希望破解此难题。

在Chinese Optics Letters 2020年第5期的文章中,北京航空航天大学的吴坚教授团队提出了一种获取半导体发光结构自发辐射特性的新实验方法(Ming Zheng, Qingnan Yu, Hanxu Tai, et al. Experimental investigation of spontaneous emission characteristics of InGaAs-based indium-rich cluster-induced special quantum structure[J]. Chinese Optics Letters, 2020, 18(5): 051403)。该方法提供了一个获取任何一种量子限制结构(包括非标结构)自发辐射特性的普适方法,不需要任何复杂的测量样品处理和准备,简单有效。该方法可以研究基于InGaAs材料的特殊富铟团簇量子限制结构的自发辐射特性。

富铟团簇量子限制结构是一种InGaAs材料中产生的特殊和非标准的量子结构,它源于InGaAs/GaAs材料中的富铟团簇效应。由于铟原子和镓原子的晶格系数和原子尺寸不同, InGaAs化合物中存在一个很大的应力。为释放这种应力,铟原子发生迁移,在InGaAs层的表面形成了很多岛形的铟原子集聚。这改变了初始的InGaAs量子阱结构和它的光学性质。这种现象称为InGaAs材料中的富铟团簇效应。富铟团簇效应所致的特殊量子结构和它的性质在近期才开始得到关注。

为了研究这种结构的光学性质,必须首先了解其自发辐射谱及特性。研究人员设计了新的实验方法,以便测量该结构的自发辐射谱,分析其特性。这项研究首次揭示了基于InGaAs材料的富铟团簇量子限制结构的自发辐射特性。因此,这是一项新的、非常有意义的研究工作。

在实验中,研究人员使用了一个简单的边发射单芯片,不需要任何复杂的处理,仅仅在芯片的一端镀全增透膜即可。这避免了因样品处理不精确导致的不必要的测量误差。文中展示并分析了因此所获得的富铟团簇量子结构的自发辐射信息。

结果显示,与标准InGaAs/GaAs量子阱相比,富铟团簇量子结构的自发辐射具有两个特点:首先,对横向电场(TE)和横向磁场(TE)偏振模式,自发辐射带宽得到了极大地拓展,达到870 -1000 nm;其次,在任一自发辐射谱上出现双峰结构。这些特点反映了富铟团簇量子结构的特殊辐射性质,并在此首次得到揭示。本文简单地分析了这些新的发现,更详细的解释需要未来从理论上做出进一步的研究。

吴坚教授认为,这项工作的重要意义在于:它不仅发明了一个全新且有效的获取LED 和LD器件中任何量子限制结构自发辐射信息的实验方法,而且首次揭示了产生于富铟团簇量子结构的自发辐射特性及其特殊的机制。

在这项研究的基础上,未来的工作将集中在发掘这种特殊的富铟团簇量子限制结构更多的光学性质及产生的机制上,以开发新型的高性能LED和 LD。

通过测量一个边发射芯片的两端面光致发光光谱(PL 谱)以获得InGaAs富铟团簇量子结构自发辐射特性的实验表征

Experimental investigation of spontaneous emission characteristics of InGaAs-based indium-rich cluster-induced special quantum structure

Although light-emitting diodes (LEDs) and laser diodes (LDs) have been widely used for people's daily life and scientific fields, e.g. fiber communication and optical interconnection, medical application, industrial measurement and military. nowadays, scientists in the world still have been undertaking the research on seeking for better lightening material structure and disclosing their characteristics by theory and experiment to further enhance these semiconductors light-emitting device performance.

In the research of LEDs and LDs, a common nature of the semiconductor materials and devices is the unamplified spontaneous emission (SE). It is a basic but very important physical parameter for the lightening materials and devices because it describes the fundamental physical process of the light-matter interaction, in terms of the Einstein's light-emitting theory, and affects optical characteristics of the devices. In order to obtain the SE information from devices, both theoretical calculation and experimental measurement are developed. However, on the one hand, the current theoretical methods are only suitable for the ideal or standard quantum-confined models, e.g. quantum well or quantum dot structure and it is difficult to exactly characterize the SE characteristics of any abnormal quantum-confined structure. For example, the indium-rich cluster-induced (IRC) quantum structure described in the following paper mentioned is typically an abnormal one, which consists of many irregular InGaAs regions with different indium contents due to the influence from the IRC effect.

On the other hand, most of the existing experimental methods for obtaining SE information of the devices need fabricating a complex sample for measurement, which is usually hard to process in accuracy so that some additional measurement errors would be generated in acquiring the SE characteristics by experiment. Therefore, new experimental approaches for characterizing or acquiring exactly the SE characteristics of any quantum-confined structure, especially of non-standard quantum-confined structures are needed urgently. Since it is difficult to build a global theoretical model to calculate the SE characteristics of various material structures, the experimental approach will be more expected. A research group led by Prof. Jian Wu from Beihang University proposed a new experimental approach to acquiring the SE characteristics of semiconductor lightening structure. The method is simple and effective, as it does not need any complex sample processing and preparation. This method offers a global tool for obtaining the SE characteristics of any quantum-confined structures involving non-standard ones. Certainly, it is also aiming at serving for the investigation on SE characteristics of the special IRC quantum-confined structure based on InGaAs materials. The research results are published in Chinese Optics Letters, Vol. 18, Issue 5, 2020 (Ming Zheng, Qingnan Yu, Hanxu Tai, et al. Experimental investigation of spontaneous emission characteristics of InGaAs-based indium-rich cluster-induced special quantum structure[J]. Chinese Optics Letters, 2020, 18(5): 051403).

The IRC quantum-confined structure is a special and non-standard one from the InGaAs materials. It is formed due to the IRC effect in the InGaAs/GaAs materials. In the growth process of InGaAs/GaAs materials, indium atoms would partially leave from the InGaAs compound and move up to the surface of the InGaAs layer along the growth direction. This is because there exists a large stress in the InGaAs compound due to different lattices and sizes between indium atoms and gallium atoms. As a result, the indium atom's migration forms many island-like accumulations of the indium atoms on the surface of the InGaAs layer. It changes the original InGaAs quantum-confined structure and the optical characteristics. This phenomenon is called the IRC effect in the InGaAs materials. The IRC-induced special quantum-confined structure and its characteristics were paid attention recently. In order to investigate its optical characteristics, the SE spectrum and its features have to be known at first. Therefore, the group invented this new experimental method to measure the SE spectrum and analyze its features of the structure at first. This investigation is also the first time to reveal the SE characteristics of the InGaAs-based IRC quantum-confined structure. Thus, it is the new and very meaningful research work.

The experimental design of the method used simply a single edge-emitting chip without any complicated sample treatments except for coating by complete transmittance at one end of the chip. This avoided unnecessary measurement errors from inaccurate sample processing. The SE information of the IRC quantum structure were obtained and analyzed in the paper. The results showed two unusual SE features different from that of a standard InGaAs/GaAs quantum well. One was that the SE bandwidth was enormously broadened by 870-1000 nm for both of transverse electric (TE) and transverse magnetic(TM) polarization modes. The other was that there were double peaks emerging in any SE spectrum. These reflected the special emission features of the IRC quantum structure and were revealed for the first time. The brief analysis on these new findings were made in the paper. It needs further investigation in theory for more details in the future.

In the authors' opinions, the important meanings of this work are that not only it invented a new and effective experimental method for acquiring the SE information of any quantum-confined structures in LED or LD devices, but also revealed the SE characteristics and the special mechanism to generate in the IRC quantum structure for the first time. The future work based on this investigation will focus on more optical characteristics findings and mechanism analysis relating to the special IRC quantum confined structure to develop new types and high performance of LEDs and LDs.

Experimental characterization of spontaneous emission (SE) characteristics for the InGaAs-based indium-rich cluster-induced quantum structure by measuring the Photoluminescence Spectroscopy (PL) spectra from both facets of a single edge-emitting chip