Ms. Subhashree Seth, OSE PHD Student Showcases her Research at the UNM Shared Knowledge Conference

Departmental News


Posted: November 9, 2021

Photonic crystal surface emitting laser (PCSEL) 

Subhashree Seth1, Kevin J. Reilly1, Akhil Kalapala2, Alex Song3, Thomas Rotter1, Zhonghe Liu2, Emma Renteria1, Shanhui Fan3, Weidong Zhou2, Ganesh Balakrishnan1 

  1. Center for High Technology Materials, University of New Mexico, Albuquerque, NM, 87106 
  2. Department of Electrical Engineering, The University of Texas at Arlington, Arlington, TX, 76010 
  3. Department of Electrical Engineering, Stanford University, Stanford, California, 94305 


Molecular beam epitaxy (MBE) is investigated as a method of fabrication for photonic crystal surface emitting lasers (PCSELs). The influence of regrowth to photonic crystal morphology is documented. PCSEL devices are demonstrated by optical pumping and electrical injection.  PCSELs represent a new class of semiconductor laser that fulfills an industry need for high-power high-quality beams from a monolithic form factor. Traditional semiconductor lasers, edge emitting lasers and vertical cavity surface emitting lasers (VCSELs), make compromises between high-power and high-quality emission. For instance, edge emitting lasers are commonly chosen for high power applications, however, their oblong emission surface yields wide divergent ovular beams. VCSELs produce narrower circular beams but large device areas necessary for increased power enable high-order transverse modes that break coherent emission and sacrifice this advantage. PCSELs employ a 2D photonic crystal resonant cavity that isolates a single lasing mode and creates vertical emission. In this way, PCSEL devices can power scale with area whilst maintaining single-mode emission for high-quality beams. Early PCSELs were fabricated by way of wafer fusion where two wafers, one containing the active region and the other containing a photonic crystal layer, are joined together. Because it is impossible to match the two wafers in terms of atomic order, wafer bonding leaves a high density of light absorbing defects at the bonded interface. In the present research we investigate epitaxial regrowth as a method of PCSEL fabrication. By epitaxial regrowth, an initial epitaxy constructs the body of the PCSEL and terminates with the active region and photonic crystal layer. The photonic crystal is patterned by electron beam lithography and ICP etch. The surface is cleaned, and the device is reintroduced to the reactor for growth of top clad and contact layers. Epitaxial regrowth maintains the crystalline structure of the substrate throughout the entire device, thereby mitigating defects at the interface when compared to wafer bonding. Regrown 980 nm InGaAs quantum well PCSELs are demonstrated by optical pumping and electrical injection using the regrowth method.  

Dr. Ganesh Balakrishnan’s Research Group: 

Ms. Subhashree Seth is a doctoral student in the OSE program.  She is a member of OSE General Chair, Dr. Ganesh Balakrishnan’s research lab. Dr. Balakrishnan’s present research interests include III-V based optoelectronics, including epitaxy, characterization, microscopy, and device fabrication with a focus on lasers. 

Link to Dr. Ganesh Balakrishnan’s Research Group: 

About the Poster Showcase:  

In the poster session, graduate students from programs across campus display their research in poster format and engage directly with conference attendees and fellow scholars. Research posters come in a wide variety of topics, crossing fields throughout the humanities and sciences. Poster evaluators are also on hand to provide feedback to presenters. Students are nominated by their academic program to display a research poster at the conference.  

This year's Poster Showcase took place on Monday, November 8th from 11:00 AM - 1:00 PM in the Student Union Building, Ballroom C, with the top three finalists from the LoboBITES competition giving their presentations at noon.