The document summarizes the research activities of Sandipta Roy at IIT Bombay. It describes their expertise in simulation tools like Lumerical FDTD and their current work simulating infrared detectors and thin film solar cells. It also outlines their PhD work, which included fabricating and characterizing nickel-silicide Schottky diodes for methane detection in the near infrared. Key results were a barrier height of 0.62 eV measured from electrical characterization and an optical responsivity of 2.6 mA/W for infrared detection at zero bias and 1.5 micrometers.

1. My Research Activities
Sandipta Roy
IIT Bombay

2. 2 of 18Sandipta Roy, CRNTS, IIT Bombay
Overview
1. Expertise in tools and software.
2. Present work, Simulation by Lumerical (FDTD)
of Infrared Detector and Thin film Solar cell.
3. Work during the PhD.
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Materials and Device
Characterization
Principle Application

3. 3 of 18Sandipta Roy, CRNTS, IIT Bombay
Tools handled
Lithography:
• Double side Aligner (DSA).
• Electron beam Lithography (EBL).
• Laser writer (for mask design).
Deposition tools:
• Metal-oxide chemical vapour deposition (MOCVD)
• Inductively coupled plasma chemical vapour deposition
(ICPCVD).
• Metal and dielectric sputter deposition.
• Electron-beam deposition
Characterization:
• Scanning Eelectron microscopy (SEM)
• UV-VIS-NIR 750
• Temperature dependent electrical characterization.
• Deep level transient spectroscopy (DLTS).
Setup design:
• Gas sensing setup, for optical process of gas
detection.
• Optical sensing setup

4. 4 of 18Sandipta Roy, CRNTS, IIT Bombay
Software skill
Simulation:
• Lumerical (FDTD)
• MATLAB.
• CST Microwave studio 2015.
• Synopsis (TCAD).
Analysis:
• Origin (Plotting and analysis).
• X’pert High score plus (XRD
analysis)
• XPS Peak fit 4.1 (XPS analysis).

5. 5 of 18Sandipta Roy, CRNTS, IIT Bombay
Present work on plasmonic-based optical device
1) Simulation of Narrow band optical
detector (FDTD) by using Ge as a substrate
Au
Si
Au/Si hot-electron based IR detector
Absorption
in Au
Ge

6. 6 of 18Sandipta Roy, CRNTS, IIT Bombay
Plasmonic solar cell
SiN
Si
(100 nm)
Al
etch
Found 2 time increase in Jsc
for 100 nm Si Solar cell

7. Fabrication and characterization of nickel-silicide
Schottky diode near infrared sensor for methane
detection
BY
SANDIPTA ROY
CRNTS
IIT BOMBAY
Ph.D. work

8. 8 of 18Sandipta Roy, CRNTS, IIT Bombay
IR detection principle
Absorb IR at silicide
Generate hot (energized) electron
Cross the barrier from at the metal and
semiconductor junction
The cutoff wavelength is
𝜆 𝑐(µ𝑚) = 1.24/𝜙 𝐵(𝑒𝑉)
For this case 𝜙 𝐵 must be lower than
(1.24/1.65=0.75 eV)

9. 9 of 18Sandipta Roy, CRNTS, IIT Bombay
Phase Analysis
The percentage of presence phases in
the film was determined by peak fitting
and it was found to be ~15% of NiSi2
and ~85% of the film is NiSi.
This validates the observation of
Raman analysis.

10. 10 of 18Sandipta Roy, CRNTS, IIT Bombay
Electrical characterization
From the slope of Richardson plot and it is found to be 0.62 eV
The barrier height is comparable to as reported by Jeng et al, 1983.

11. Optical Characterization
𝑅 = 𝐶1(1 −
𝜙 𝐵
𝑜𝑝𝑡
ℎ𝜈
)2
The responsivity of the diode is promising (2.6 mA/W
for zero bias condition at 1.5 µm). [Roy, 2014, J. Appl. Phys.].
the value has been found to be 0.54 eV.
n 𝝓 𝑩
𝑰−𝑽
(eV) 𝝓 𝑩
𝑪−𝑽
(eV) 𝝓 𝑩𝒄𝒂𝒍
𝑰−𝑽
(eV)
=
𝜙 𝐵
𝐶−𝑉
+ 𝑉𝑛(𝑛 − 1)
𝑛
𝝓 𝑩
𝒐𝒑𝒕
(eV)
1.28 0.62 0.76 0.64 0.54
The barrier height value observed in this case is much less than that derived by I–V–T and 1/C2–V method. Such behaviour
attributed to presence of acceptor like trap state at the interface [Li, 2007, Appl. Phys. Lett.]

12. 12 of 18Sandipta Roy, CRNTS, IIT Bombay
Arrhenius plot
The trap at 0.33 eV (E1), 0.52 eV (E2) and 0.55 eV (E3).
The E2 position corresponds to the bulk trap states.
The trap E1 causes by Ni interstitial position at in the Si Tian et al.
2002.
The E3 position is not reported till date (reported for GdSi2).
Considering the previous articles,
Therefore it can concluded that interface states are present in the
device and they are acceptor type.
Cont’d…
𝜏 𝑒 𝑇2 =
exp((𝐸 𝐶−𝐸 𝑇)/𝑘𝑇
𝜎 𝑛 𝛾 𝑛
, 𝜏 𝑒 =
𝑡2−𝑡1
ln(𝑡2/𝑡1)

13. As reported by Lu & Turut, 2002
𝐶𝑠𝑠 = 𝑞𝐴𝑁𝑠𝑠
tan−1 𝜔𝜏
𝜔𝜏
And 𝑁𝑠𝑠 =
𝐶 𝑠𝑠
𝑞𝐴
when 𝜔𝜏<<1 & 𝐸 𝐶 − 𝐸 𝑇 = 𝜙 𝐵
𝐶−𝑉
− 𝑞𝑉
Cont’d…
𝐶𝑠𝑠 = 𝑞𝐴𝑁𝑠𝑠
tan−1 𝜔𝜏
𝜔𝜏
(1) 𝑁𝑠𝑠 =
𝐶 𝑠𝑠
𝑞𝐴
(2)

14. 14 of 18Sandipta Roy, CRNTS, IIT Bombay
Methane detection
Because the optical absorption of the gas is confined to the overlapped
spectral region (𝜆1 𝑡𝑜 𝜆2) the effective absorption cross section becomes
𝑘 𝑒𝑓𝑓 = 𝑁0 න
𝜆1
𝜆2
𝑘(𝜆) 𝑑𝜆
𝑃𝐺𝑎𝑠 = 𝑃𝐴𝑖𝑟exp(−𝑘 𝑒𝑓𝑓 𝑐𝑙)
𝐼 𝑝ℎ = 𝑅𝑃
𝐼 𝐺𝑎𝑠/𝐼𝐴𝑖𝑟 = exp(−𝑘 𝑒𝑓𝑓 𝑐𝑙)

15. 15 of 18Sandipta Roy, CRNTS, IIT Bombay
NiSi/n-Si detector characterization for
1.65 µm laser diode
The total diode current is 𝐼𝑡𝑜𝑡 = 𝐼 𝑝ℎ + 𝐼 𝑏𝑔

16. 16 of 18Sandipta Roy, CRNTS, IIT Bombay
Gas sensing
Τ𝐼 𝐺𝑎𝑠 𝐼𝐴𝑖𝑟 ≈ exp(−𝑘 𝑒𝑓𝑓 𝑐𝑙)

17. 17 of 18Sandipta Roy, CRNTS, IIT Bombay
Conclusion
•The barrier height of the device was measured and found to be 0.62, 0.64 and 0.54 eV by I-V-T, C-V and optical technique.
(Roy, 2014, J. Appl. Phys)
•The optical responsivity of the device was found promising for this cost effective application.
•The difference in barrier height is attributed to the presence of acceptor like interface trap states. The trap density was
measured by DLTS and C-f technique and it was found to be ~1011 cm-2eV-1. (ICMAT 2015, Singapore)
•The operating condition of the diode for methane sensing was established and found that zero bias is more suitable for the
application.
•A moderate illumination power was used to avoid the shift in wavelength due to heating of the LD.
•The methane sensing was demonstrated and found that the low level of detection is 3%. (Communicated)
•The response and recovery time was found to be very swift, indicating the possibility in instantaneous detection.

18. Thank you for your time