Prithviraj Deshmukh – Seminar/PhD Preliminary Defense – Monday, December 18, 2017 at 11:00 A.M.
JSNN – Prithviraj Deshmukh – Ph.D. Preliminary Defense/Monday Seminar
Candidate: Prithviraj Deshmukh
Advisor and Committee Chair: Shanthi Iyer, Ph.D.
Time: 11:00 A.M. – 1:00 P.M.
Location: JSNN 209 Open Room2907 E. Gate City Blvd., Greensboro, NC 27401
Title: “GaAsSb(N) Nanowires for Short Wavelength Infrared Photodetectors.”
Optoelectronic devices operating in short wave infrared (SWIR) wavelength range have applications in spectroscopic analysis, maritime surveillance and infrared photodetection, etc. The integration of group III-V ternary and quaternary semiconductor nanowire (NW) based SWIR photonic devices with silicon technology remains a challenge. The band gap energy reduction in GaAsSb based devices for SWIR photodetection necessitates very high Sb content in the GaAsSb material system. The inherent incompatibility between Sb-rich III-V NWs and Si due to large lattice mismatch results in unsuccessful heteroepitaxial growth or undesirable growths with unavoidable secondary effects of these NWs. This study will focus on development of photodetectors in the SWIR spectrum using heteroepitaxial growth of GaAs based Sb-rich axial NWs and core-shell Sb-rich dilute nitride NWs.
A modified dual-temperature approach is taken towards the successful growth of self-catalyzed vertical GaAs1-xSbx (x>0.8) nanowires (NWs) on Si (111) substrates using molecular beam epitaxy. A simplistic approach that employs an uncracked As background pressure illustrates that low Ga flux is essential to obtain highly dense arrays of high Sb content NWs with minimal parasitic growth. Critical differences between low and high Ga beam equivalent pressure (BEP) growths of highly mismatched Sb-based NWs have been experimentally investigated. µ-photoluminescence emission up to 1680 nm with a narrow line width indicates good structural and optical quality of GaAs0.2Sb0.8 NWs. Raman spectroscopy and a detailed TEM analysis confirms homogeneity in composition and crystal structure of the axial GaAs1-xSbx (x>0.8) NWs.
An alternative approach of reaching 1.5 um -1.7 µm by incorporation of small amount of nitrogen in III-V ternary system NWs will also be the subject of investigation. However, Sb-rich dilute nitrides have not been explored in NW configuration since it is challenging to attain good structural and optical properties in this material system due to mismatch in size and electronegativity of Sb and N causing undesirable defects. Development of core-shell NWs with Sb-rich dilute nitride shells will provide access to integration of Sb-rich dilute nitrides on silicon platform for SWIR photodetection. A two-step approach coupled with lower shell growth rate can be the key to incorporation of higher amounts of Sb and N simultaneously in the GaAsSbN shell based heterostructured NWs. A systematic study of annealing the NWs of different shell composition and thickness will provide insights into point defects and carrier recombination mechanisms using photoluminescence spectroscopy (PL), I-V and low frequency noise (LFN) measurements. Schottky barrier NW ensemble photodetectors will be fabricated and performance evaluated. Successful completion of this work will lead to feasibility of heteroepitaxial growth of Sb-rich axial NWs and GaAs/ GaAsSbN core-shell nanowires on Si substrates, for the realization of Si-compatible SWIR photodetectors.