optimization of passivation for mid and long wavelength inas/gasb superlattice photodetectors
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Kelsey Poineau Research Advisor: Sid Ghosh. Optimization of Passivation for Mid and Long Wavelength InAs/GaSb Superlattice Photodetectors. Infrared Detection. Any object at non-zero temperature emits heat (electromagnetic radiation) - PowerPoint PPT PresentationTRANSCRIPT
Optimization of Passivation for Mid and Long Wavelength InAs/GaSb Superlattice
Photodetectors
Kelsey PoineauResearch Advisor: Sid Ghosh
Infrared Detection Any object at non-zero
temperature emits heat (electromagnetic radiation)
Use infrared wavelengths because they have good transmittance through the atmosphere
Motivation Detection of mid- and long-wavelength infrared
radiation is important in many industries
InAs/GaSb type-II superlattice materials have potential to outperform existing detectors Limited by poor surface quality
Military Biomedical Space
How to Detect Infrared Radiation
Object
IR Radiation
IR Detector
Detector OutputElectrical
Optical
Magnetic
Solid State Material
Semiconductor
Photogeneratedelectrons can be usedas the detector output
If Eph>EG, photons can be absorbed and create free electrons in conduction band
p-i-n detectors
IR photons absorbed in the depletion region generate an electron-hole pair; the electric field sweeps the electron to the n-side and hole to the p-side
Ideally, no current so when an incoming photon creates an electron-hole pair it is detected
Problem Surface leakage
considerably limits LWIR device performance
Native Oxides Charged ions Interfacial traps
Surface passivation provides a viable solution
Passivating layer over semiconductor surfaces prevents current flow in oxide and terminates unsatisfied bonds
III-V Semiconductor Wafers
Project Goal Comparative study of passivants (SiO2, SiN, ZnS)
ZnS degrades over time
Stacked passivation Investigated to enhance long term stability of interface
between passivation layer and InAs/GaSb substrate ZnS/Silicon nitride ZnS/Silicon oxide
Compared on basis of electrical properties and device performance
Work to date Stacked passivation
Unable to achieve good electrical insulation
Considering alternatives: SiN thin films Advantages
High quality dielectric Hard and strong High resistivity Low porosity
Disadvantages Effects of surface leakage in SiN>ZnS Possess high mechanical strain
Laying the groundwork
Strain may increase surface leakage and degrade passivation qualities
Passivate with multiple Si/N ratios to study electrical characteristics Plasma-enhanced Chemical Vapor Deposition (PECVD)
Vary gas flow rates of silane and ammonia
Low-stress SiN films
Change mechanical properties of SiN films
French, J. P., and P. M. Sarro. "Optimization of a low-stress silicon nitride process for surface-micromachining applications." Sensors and Actuators A 58 (1997): 149-57
Preliminary Results PECVD Parameters
Flow Rates SiH4 (silane) - 500 sccm NH3 (ammonia) - 70 sccm
Chamber Pressure - 650 mtorr Temperature - 300°C RF power - 20 W Time - 15 mins
Ellipsometer Data Thickness - 265 nm Refractive Index - 1.95
Summary Analysis of surface states is key to finding and
understanding improved processing leading to increased performance in devices
Could not examine effectiveness of stacked passivation in preventing ZnS degradation over time
Expect low stress (silicon-rich) silicon nitride films will improve device performance compared to stiochometric Si3N4 passivation layers
French, J. P., and P. M. Sarro. "Optimization of a low-stress silicon nitride process for surface-micromachining applications." Sensors and Actuators A 58 (1997): 149-57.
Pierret, Robert F. Semiconductor Device Fundamentals. N.p.: Addison-Wesley Company, Inc, 1996. Print.
Prineas, J. P., Mikhail Maiorov, and C. Cao. "Processes Limiting the Performance of InAs/GaSb Superlattice Mid-Infrared PIN Mesa Photodiodes." Proceedings of SPIE, the international Society for Optical Engineering 6119 (2006).
Saraswat. "Integrated Circuit Isolation Technologies." Http://www.leb.eei.uni-erlangen.de/winterakademie/2008/courses/course3_material/backEnd /Isolation_notes.pdf.
Streetman, Ben G., and Sanjay Kumar Banerjee. Solid State Electronic Devices. 6th ed. Upper Saddle River, New Jersey: Pearson Prentice Hall, 2006. Print.
References
Acknowledgements
Special thanks to my advisor Professor Sid Ghosh and Koushik Banerjee.
This project was funded by the National Science Foundation and the Department of Defense from the EEC-NSF Grant # 0755115. Additional financial support was awarded by the National Science Foundation from
the CMMI-NSF Grant # 0925425.
Questions?