{"id":28,"date":"2015-02-01T05:08:18","date_gmt":"2015-02-01T11:08:18","guid":{"rendered":"http:\/\/www.burcuozden.com\/?page_id=28"},"modified":"2016-11-03T15:51:12","modified_gmt":"2016-11-03T20:51:12","slug":"research","status":"publish","type":"page","link":"https:\/\/www.burcuozden.com\/?page_id=28","title":{"rendered":"Research"},"content":{"rendered":"<div class=\"wpb-content-wrapper\"><p>[vc_row][vc_column width=&#8221;1\/1&#8243;]<h1 class=\"fac-big-title fac-title text-left\" style=\"color:#4b4b4b\">Research<\/h1>\n[vc_row_inner][vc_column_inner width=&#8221;1\/2&#8243;][vc_column_text]<\/p>\n<p>Burcu Ozden\u2019s research focuses on revealing and understanding the basic physics involved exciton-photon transfer and electric transport properties of polariton condensates. Her research is highly experimental. She fabricates her own multiple quantum well microcavities at Nanotechnology Laboratories of at University of Pittsburgh and Carnegie Mellon University. She then create excitons or polaritons in semiconductor samples at liquid helium temperatures via an intense, ultrafast (picosecond or femtosecond) laser pulse and then investigates the transport properties of these quasiparticles. Moreover, she uses software tools to understand the underlying physics. She also collaborate with theorists to answer fundamental questions about exciton and polariton condensates. Her research is funded by Army Research Office.<\/p>\n<p>[\/vc_column_text][\/vc_column_inner][vc_column_inner width=&#8221;1\/2&#8243;]<ul class=\"ul-boxed list-unstyled\"><li class=\"\">Microcavity Polaritons<\/li><li class=\"\">Wide Band Gap Semiconductors<\/li><li class=\"\">Optoelectronic Characterization of III-V Materials<\/li><li class=\"\">Radiation Effect<\/li><\/ul>[\/vc_column_inner][\/vc_row_inner][\/vc_column][\/vc_row][vc_row][vc_column width=&#8221;1\/1&#8243;]<h1 class=\"fac-title text-center\" style=\"color:#4b4b4b\">Research Projects<\/h1>\n<ul class=\"ul-withdetails \"><li class=\"\">\n\t\t\t\t<div class=\"wrap\"><div class=\"image\" style=\"background-image:url(https:\/\/www.burcuozden.com\/wp-content\/themes\/faculty\/img\/project-default.png);\"><div class=\"imageoverlay\"><i class=\"fa fa-search\"><\/i><\/div><\/div><div class=\"meta\"><h3>Exciton-Photon Transfer and the Electrical Transport Properties of Polariton Condensates<\/h3><p>This project explores a new direction in the study of polariton condensates, the interplay between polariton coherence and electrical transport.<\/p><\/div><\/div>\n\t\t<div class=\"details\">\n\t\t\t<p>We create excitons or polaritons in semiconductor samples at liquid helium temperatures via an intense, ultrafast (picosecond or femtosecond) laser pulse while applying external electric field, and then examine the evolution of their momentum distribution and spatial distribution by detecting the light they emit. In this research we aim to achieve separate electrical contacts at di\u000berent positions on a quantum well boundary, and to separate quantum wells, when the wells are placed inside a microcavity in which an exciton-polariton condensate is produced by optical pumping. We predict that the electrical current couples to the condensate through quasiparticle-exciton and exciton photon transfer mechanisms that are similar to the quasiparticle-condensate mechanisms associated with Andreev scattering in superconductors and spin-transfer torques in magnetic systems. These novel phenomena may lead to new types of electro-optical like optical communications and memory devices.This would revolutionize technology in the way the electronic transistor did 50 years ago<\/p>\n\n\t\t<\/div> <\/li><li class=\"\">\n\t\t\t\t<div class=\"wrap\"><div class=\"image\" style=\"background-image:url(https:\/\/i0.wp.com\/www.burcuozden.com\/wp-content\/uploads\/2015\/02\/Photo-IV-Spectroscopy-Setup.jpg?fit=900%2C584&ssl=1);\"><div class=\"imageoverlay\"><i class=\"fa fa-search\"><\/i><\/div><\/div><div class=\"meta\"><h3>Spectroscopic photo I\u2013V diagnostics of HEMT wafer<\/h3><p>A novel method to diagnosis the homegenity of defect distribution<\/p><\/div><\/div>\n\t\t<div class=\"details\">\n\t\t\t<p>A simple and novel spectroscopic photo I\u2013V method of diagnosing the<br \/>\nhomogeneity of electrically-active defect distribution in the large area<br \/>\nAlGaN\/GaN HEMT (high electron mobility transistor) epi-structure<br \/>\ngrown on 6-inch silicon wafers is reported. It is of utmost importance<br \/>\nto produce the HEMT epi-structure electrically homogeneous across<br \/>\nthe wafer if devices with uniform electrical characteristics are to be<br \/>\nconstructed. AlGaN\/GaN HEMT epi structures were grown on a<br \/>\nsilicon substrate via metal\u2013organic chemical vapour deposition. An<br \/>\narray of circular semi-transparent Ni Schottky contacts was prepared<br \/>\non top of the diced AlGaN\/GaN HEMT structure substrates, which<br \/>\nwere selected from different locations of the 6-inch wafer. The information<br \/>\nof the electrical homogeneity across the wafer was elucidated<br \/>\nfrom the spectral dependences of the I\u2013V characteristics collected<br \/>\nfrom different locations of the AlGaN\/GaN HEMT wafer. It is successfully<br \/>\ndemonstrated that the proposed spectroscopic photo I\u2013V measurement<br \/>\ntechnique can be employed to diagnose electrical homogeneity of<br \/>\nthe electrically-active defect distribution in the AlGaN\/GaN HEMT epi<br \/>\nstructure constructed on Si with minimum sample preparation steps.<\/p>\n\n\t\t<\/div> <\/li><li class=\"\">\n\t\t\t\t<div class=\"wrap\"><div class=\"image\" style=\"background-image:url(https:\/\/i0.wp.com\/www.burcuozden.com\/wp-content\/uploads\/2015\/02\/drucspiv.jpg?fit=408%2C354&ssl=1);\"><div class=\"imageoverlay\"><i class=\"fa fa-search\"><\/i><\/div><\/div><div class=\"meta\"><h3>Depth-resolved ultra-violet spectroscopic photo current-voltage (DR-UV-SPIV) measurements<\/h3><p>An inexpensieve technique to measure depth dependent distribution of defects<\/p><\/div><\/div>\n\t\t<div class=\"details\">\n\t\t\t<p>We have demonstrated that the depth-dependent defect distribution of the deep level traps in the<br \/>\nAlGaN\/GaN high electron mobility transistor (HEMT) epi-structures can be analyzed by using the<br \/>\ndepth-resolved ultra-violet (UV) spectroscopic photo current-voltage (IV) (DR-UV-SPIV). It is of<br \/>\ngreat importance to analyze deep level defects in the AlGaN\/GaN HEMT structure, since it is<br \/>\nrecognized that deep level defects are the main source for causing current collapse phenomena<br \/>\nleading to reduced device reliability. The AlGaN\/GaN HEMT epi-layers were grown on a 6 in.<br \/>\nSi wafer by metal-organic chemical vapor deposition. The DR-UV-SPIV measurement was<br \/>\nperformed using a monochromatized UV light illumination from a Xe lamp. The key strength of<br \/>\nthe DR-UV-SPIV is its ability to provide information on the depth-dependent electrically active<br \/>\ndefect distribution along the epi-layer growth direction. The DR-UV-SPIV data showed variations<br \/>\nin the depth-dependent defect distribution across the wafer. As a result, rapid feedback on the<br \/>\ndepth-dependent electrical homogeneity of the electrically active defect distribution in the AlGaN\/<br \/>\nGaN HEMT epi-structure grown on a Si wafer with minimal sample preparation can be elucidated<br \/>\nfrom the DR-UV-SPIV in combination with our previously demonstrated spectroscopic photo-IV<br \/>\nmeasurement with the sub-bandgap excitation.<\/p>\n\n\t\t<\/div> <\/li><li class=\"\">\n\t\t\t\t<div class=\"wrap\"><div class=\"image\" style=\"background-image:url(https:\/\/i0.wp.com\/www.burcuozden.com\/wp-content\/uploads\/2015\/02\/trs.jpg?fit=768%2C554&ssl=1);\"><div class=\"imageoverlay\"><i class=\"fa fa-search\"><\/i><\/div><\/div><div class=\"meta\"><h3>Time-resolved photocurrent (TRPC) spectroscopy <\/h3><p>A simple method to measure decay current characteristics of AlGaN\/GaN HEMTs heterostructures<\/p><\/div><\/div>\n\t\t<div class=\"details\">\n\t\t\t<p>Time-resolved photocurrent (TRPC) spectroscopy with a variable-wavelength sub-bandgap light excitation was used to study the dynamics of the decaying photocurrent generated in the heterostructures of the AlGaN\/GaN high electron mobility transistors (HEMTs) layers. In AlGaN\/GaN HEMTs, reliability of the device is degraded due to the prevalence of current collapse. It is recognized that electrically active deep level defects at the surface\/interfaces and the bulk in the HEMTs layers can contribute to the unwanted current collapse effect. Therefore, it is of great importance to analyze the deep level defects if the reliability of the HEMTs device is to be improved. In this research, TRPC spectroscopy was used to elucidate the origin and nature of the deep level defects by analyzing the time evolution of the photocurrent decay excited at different wavelengths of light. The two devices that show similar characteristics for wavelength-dependency on photocurrent generation were chosen, and TRPC spectroscopy was conducted on these devices. Although the two samples show similar characteristics for the wavelength-dependency on photocurrent generation, they exhibited dissimilar time-dependent photocurrent decay dynamics. This implies that TRPC spectroscopy can be used to distinguish the traps which have different origins but have the same de-trapping energy.<\/p>\n\n\t\t<\/div> <\/li><\/ul>[vc_video title=&#8221;What is Polariton?&#8221; link=&#8221;https:\/\/youtu.be\/sWmvZ0IGrsU&#8221;][\/vc_column][\/vc_row]<\/p>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>[vc_row][vc_column width=&#8221;1\/1&#8243;][vc_row_inner][vc_column_inner width=&#8221;1\/2&#8243;][vc_column_text] Burcu Ozden\u2019s research focuses on revealing and understanding the basic physics involved exciton-photon transfer and electric transport [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"page-pagebuilder.php","meta":{"footnotes":""},"class_list":["post-28","page","type-page","status-publish","hentry"],"jetpack-related-posts":[],"jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.burcuozden.com\/index.php?rest_route=\/wp\/v2\/pages\/28","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.burcuozden.com\/index.php?rest_route=\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.burcuozden.com\/index.php?rest_route=\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.burcuozden.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.burcuozden.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=28"}],"version-history":[{"count":20,"href":"https:\/\/www.burcuozden.com\/index.php?rest_route=\/wp\/v2\/pages\/28\/revisions"}],"predecessor-version":[{"id":229,"href":"https:\/\/www.burcuozden.com\/index.php?rest_route=\/wp\/v2\/pages\/28\/revisions\/229"}],"wp:attachment":[{"href":"https:\/\/www.burcuozden.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=28"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}