Kelsey Poineau
Research Advisor: Sid Ghosh


Any object at non-zero temperature emits heat
(electromagnetic radiation)
 Use infrared wavelengths because they have good transmittance through the atmosphere


Detection of mid- and long-wavelength infrared radiation is important in many industries
Military Biomedical Space
 InAs/GaSb type-II superlattice materials have potential to outperform existing detectors
 Limited by poor surface quality

IR Radiation
IR Detector
Detector Output
Electrical
Optical
Magnetic
Object
Solid State Material
Semiconductor
If E ph
>E
G
, photons can be absorbed and create free electrons in conduction band
Photogenerated electrons can be used as the detector output

 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



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

 Comparative study of passivants (SiO
2
, 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

 Stacked passivation
 Unable to achieve good electrical insulation
 Considering alternatives:
 Advantages
 High quality dielectric
 Hard and strong

High resistivity
 Low porosity
 Disadvantages
 Effects of surface leakage in SiN>ZnS
 Possess high mechanical strain

 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


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

 PECVD Parameters
 Flow Rates




SiH
4
NH
3
(silane) - 500 sccm
(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

 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 Si
3
N
4 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.unierlangen.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.

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.