Yesim Anter, MBA Project Coordinator, Microphysics Laboratory University of Illinois at Chicago March 29, 2012 Edited by Christoph H. Grein, Ph.

Transcription

1 MPL Reporter Yesim Anter, MBA Project Coordinator, Microphysics Laboratory University of Illinois at Chicago March 29, 2012 Edited by Christoph H. Grein, Ph.D On February 6, 2012, students, faculty and staff of the Microphysics Laboratory (MPL) at the Department of Physics of the University of Illinois at Chicago (UIC) welcomed Dr. Lu Chen, a researcher from the Shanghai Institute of Technical Physics (SITP), which is part of the Chinese Academy of Sciences (CAS). Dr. Chen has been a molecular beam epitaxy (MBE) 1 researcher at the Research Center for Advanced Materials and Devices of SITP since 1998 and has been in charge of the II-VI semiconductor MBE group since She received Master s and PhD degrees in engineering from SITP in 2003 and 2005, respectively. The article below highlights her research interests and goals, and touches on her life outside work including her observations of progress made by women in science and engineering. Dr. Lu Chen in her office 2368 SES Early Challenges and Motivation Already as a graduate student, Dr. Chen was involved in the MBE growth of II-VI semiconductor materials, particularly HgCdTe (MCT) 2 on silicon (Si) substrates. In the early days of her PhD research, she faced one of her first complications when she was preparing a chemical treatment to clean Si substrates. The first trial was a failure, even though she used a chemical procedure described in published papers. However, she found a way to successfully clean the substrates after a little modification. This was her first exciting experiment, which made her understand that struggling with failed results and overcoming challenges in an experiment go hand in hand with understanding the fascinating world of science and technology. Of course the Si cleaning treatment for MCT/Si wasn t the only challenge she faced in her PhD study. Other issues followed, including polarization when going from diamond to zinc blend crystals, twin suppression and dislocation reductions at large mismatched interface, and the thermal reliability of multi-layers. But at the end she came to the same conclusion: Somehow, bigger challenges, bigger achievement[s]. I enjoy them says Dr. Chen. Research Interests and Current Challenges After obtaining her PhD, Dr. Chen focused on understanding the relationship between materials and devices. Her research focuses on materials in order to meet the demands for high performance detector 1 Molecular beam epitaxy (MBE) is a crystal growth technique used for processing the base layers of semiconductor devices and was pioneered by two scientists from Bell Laboratories in the late 1960s. Source: and Arthur Jr., J. R., J. Appl. Phys (1968) 39, In its 2003 Science and Technology Report 1 for Army Homeland Security, the U.S. National Research Council of the National Academies recognized MCT as a material of choice to fabricate high-performance detector arrays and placed a high priority for Army investment. 2003, ISBN-10: , page 44.

2 fabrication. Currently she is in charge of the MBE group and is involved in improving of uniformity on large area materials, structure design and new materials for other applications. She plans to expand her work to MCT avalanche photodiodes (APDs) 3 for 3D imaging sensor applications. Dr. Chen mentioned that manufacturing and production needs take resources away from research in her laboratory. She points out that most of the wafers she characterizes go to the production, leaving fewer solely for research. She also wishes that more experienced and trained personnel work in research rather than in manufacturing. She says People always said MCT on Si by MBE is a great technology, which may move the roadblock in front of us, when expanding pixel formats to millions. A thermal mismatch inherently exists and the only improvement [we achieved] is [the] atomic bonds between Si and MCT are stronger than [those of] indium boding the arrays and ROIC. Furthermore, compared with ZnCdTe substrates, the misfit dislocations between MCT and Si are the main challenge of this technology. This is a critical constraint [when it comes] to obtain[ing] state-of-the-art devices when expanding wavelengths [from midwave or longwave] to very-long wave Infrared and enlarging pixel formats. Coming to Microphysics Laboratory When asked about her decision to come to MPL, Dr. Chen says MPL is first-class in the II-VI material field. The theory and technology are well combined, which drives [the research] forward to applications and industry. In MPL, her goal is to study dislocations in MCT/Si. I want to learn something new, not only MBE technology but also other characterization details says Dr. Chen and she intends to characterize samples and eliminate multi-epilayer interfacial defects by using transmission electron microscopy (TEM) 4 and other techniques. Young Generations and Women in Science and Engineering There are a few barriers for scientists entering into basic research according to Dr. Chen. She indicates society s perceptions and expectations about science can be one the reasons preventing more young people from entering science and research. In her opinion, the young generations interested in science and research may not receive the same level of support from society as those entering other fields such as business. Compared with business, fewer people are engaged in basic research science, as motivated by [people s] interests she says and adds Family responsibilities are an additional challenge for women scientists. When asked for her opinion on progress made by women in science, she mentions that male scholars play major roles in scientific research. However she cautions that this is not because men are more intelligent than women. In her view, this gap can be reduced by educating society, correcting misperceptions about science and its benefits, and encouraging women to enter the field. She also points out that women need to motivate themselves and try harder. When the issue comes to sources of motivation for women, she states that boys and girls are offered equal opportunities in high schools and education in different fields. When it s time for girls to make a decision about their future, their environment and interests play a major role. So I do think girls need more encouragement [to enter] in science and engineering she says. However Dr. Chen doesn t forget to point out that she received support and found motivation along her career. In fact, she has received mentoring from other women in her area. Actually, we mentor each other. In my case, the opportunities are sufficient and equal. What you should do is seize the opportunity says Dr. Chen as she acknowledges the mentoring she received. 3 Systems that require a sensitive means of detecting very short laser pulses often choose the avalanche photodiode (APD) as the detector. The APD is a solid state version of the photomultiplier tube in that create many electrons from one incident photon. Source: 4 The transmission electron microscope (TEM) operates on the same basic principles as the light microscope but uses electrons instead of light. TEMs use electrons as "light source" and their much lower wavelength makes it possible to get a resolution a thousand times better than with a light microscope. Source: Page 2 of 5

3 Growing up When asked about the environment she grew up, she says she was brought up in military barracks. When I was a child, I was taught that independence and strong beliefs are important to [a] woman. Dr. Chen recognizes two significant figures in her life. My father and my advisor, Professor Li He, were influential individuals in my life. They have something in common that concentrated on work duties with complete passion and perfectionism. Time Outside Work On any given day, Dr. Chen works hard. As an MBE researcher, she doesn t have a lot of free time for herself. MBE needs patience and time she admits. There is not so much free time for me. So I spend most of my leisure time with my family, doing something for them says Dr. Chen, who has a 5-year old son named Chongwen. She says she tries to spend time outdoors or engage in sports when she is not at work. As a final note, her advice for aspiring scientists is to Keep going if you love it. [Do] Not give up even if you can only enjoy it for one second. For further discussions Dr. Chen can be reached at in room 2368 SES until May 1. MPL Interactions Dr. Lu Chen giving a presentation on recent developments in HgCdTe MBE on Si. MPL, found the information about growth techniques most interesting. In particular, implementing graded interfaces between CdTe and MCT, strain reduction through substrate tilting, and utilizing ZnTe nucleation layers said Alex when asked what captured his interest most. Stephen Fahey, who very recently successfully defended his dissertation, was most interested in the data Dr. Chen presented on tilt for different lattice mismatches. Experimentalists weren t the only ones who benefited from Dr. Chen s presentation. Chris Buurma, a PhD student in MPL, who is interested in the modeling and simulation of optical mediums, photovoltaic On March 8, 2012, Dr. Chen gave a presentation on recent progress made in HgCdTe MBE on Si. Her presentation included a brief introduction of the research topics pursued at the Key Laboratory of Infrared Imaging Materials and Devices at SITP, historical progress made at her department, various aspects of HgCdTe infrared focal plane arrays (IRFPAs) and future direction of MCT research. Dr. Chen s presentation received a lot of attention from MPL students, who study various growth and characterization techniques for materials like CdTe, CdZnTe, HgCdTe and ZnO for photovoltaic and IR applications. Alexander (Alex) Brown, one of the PhD students at Page 3 of 5 Alex Brown (at the back), Chris Buurma and Stephen Fahey. devices, and materials for solar cell and sensing applications, said that he found the discussion on the effects of various anneals on different materials and material preparations interesting. I found it encouraging that when confronted with data that seemed to be contrary to theory, she investigated the theory further and found agreement and confirmation of new phenomena rather than simply rejecting this data and excluding it said Chris as he commented on the sections of her presentation that caught

4 his attention. He further added I was impressed with her attention to detail and willingness to embrace more modern technology in approaching research. Another outcome of Dr. Chen s presentation was that it provided MPL students an opportunity to learn about the MCT research at SITP, one of the leading institutions in the world focusing on IR technology. Stephen points out that her lab s research is important because they have used several key substrates of interest, and are able to achieve high-quality films on those substrates. Alex, who wishes to learn more about their dual-band diode fabrication techniques and results, says studies concerning vacancy annealing, as well as defect reduction via thermal cyclic annealing, presented are very relevant in my studies and in the IR community as a whole and adds the research at SITP is expansive and to my knowledge all topics under consideration are very relevant to the IR detector community. Dr. Chen s presentation stimulated the exchange of ideas. Stephen s interactions with Dr. Chen focused on the growth on alternative substrates. Alex plans to discuss with Dr. Chen the techniques she mentioned in her presentation and hopes to apply those techniques himself. Chris is interested in participating in discussions on SITP s two-color architecture, color fusion, and the utilized annealing model. After listening to Dr. Chen s presentation, Chris concludes they seem to have a broad set of research interests that were tackled by her team, and for such a small team to have accomplished so much, is impressive. From Left to Right: Chris Grein, Chris Buurma, Brian Kaster, Lu Chen, Eric Colegrove, Stephen Fahey, Tejumade Durowade, Alex Brown and Brian Stafford on March 8, About Microphysics Laboratory, at the Department of Physics, University of Illinois at Chicago, IL, USA. The Microphysics Laboratory (MPL) at the University of Illinois at Chicago is currently the only university laboratory in the US performing fundamental research on HgCdTe (a.k.a. MCT) by Molecular Beam Epitaxy (MBE) since its inception in early 1980s. It is a center for applied physics research with an emphasis on II-VI materials and devices for infrared sensing and imaging and photovoltaic cells. Since 1982, MPL has been awarded over $30 million in external research support to develop better night vision and photovoltaic applications. Professor Sivalingam Sivananthan is the director of MPL since 1994 and has worked in semiconductors and infrared and night vision detector technology, helping to pioneer the synthesis of the now-dominant high-end infrared detecting/night vision semiconductor material, MCT. MPL s research is focused on the optimization of the MBE growth of MCT, the study of in-situ/exsitu doping and transport, and the growth of high quality alternative composite CdTe/Si substrates to be used for the growth of large area HgCdTe. MPL s fundamental research activities have resulted in the training of experienced MCT scientists who have transferred the lab s knowledge base and traditions of excellence to many industrial and governmental research institutes including DRS Technologies, Page 4 of 5

5 Northrop Grumman, Teledyne Scientific & Imaging, the Army Night Vision Laboratory, and the Army Research Laboratory. There are six faculty and a project coordinator, who work on MPL projects, programs and initiatives. It is also a home to six graduate and three undergraduate students, who are able to find summer internship opportunities at Army agencies or industry due to our strong network of collaborations. About Shanghai Institute of Technical Physics, Shanghai, China The Shanghai Institute of Technical Physics of the Chinese Academy of Sciences was founded in October It is an engineering-type and base-type institute which takes the basic application of infrared physics and optoelectronics as its main research direction and integrates the research on engineering technology with the high-tech industrialization. It was selected as one of the first institutes for the knowledge innovation program initiated by the Chinese Academy of Sciences in Professor Li He is the Director of SITP since The institute is now mainly engaged in the research on infrared optoelectronics and takes the basic research on new infrared photoelectric materials, new devices and new methods etc. as its main research direction toward the 21st century. It has placed its emphasis on the development of advanced airborne and space-borne payloads, infrared staring imaging and signal processing, infrared focal plane array and infrared photoelectric devices, optical coating, miniature coolers, processing of medical images and remote sensing information. It has 9 corresponding research departments, a national key laboratory for infrared physics, a national key laboratory for sensors (the branch of photo-sensor) and an innovation laboratory for infrared imaging materials and devices. As a holding limited company of the institute, Shanghai Tech-Phys Optoelecronics Company has made its investment in 14 companies such as Shanghai Nicera Sensor Co. Ltd. It is mainly engaged in the research and development, production and marketing of various kinds of sensor and inactive optical communication device products. In 2005, it achieved its sales income of RMB 500 million Yuan and a total profit of RMB 70 million Yuan. Page 5 of 5