Record-photodiode-quantum-efficiency-IEDM-preview

(November 16, 2010)

IEDM Previews:
Intel fabs highest mobility pFET with Ge channel
University of Tokyo first to demo III-V self-aligned source/drain
IBM, Macronix identify phase-change memory failure mode
Record photodiode quantum efficiency from Taiwan lab
How strain can protect devices from ESD
SEMATECH tipping III-V MOSFET, FinFET, and resistive RAM
TSMC anneal for gate-last HKMG process
Imec IEDM presentations to cover More than Moore, ITRS
When do TSV stresses affect device operation?
Multi-threshold-voltage flexibility in FDSOI
CMOS imager works from light to night
Carbon nanotube vias approach production densities
IBM Alliance simplifies pFET HKMG
IM Flash details 25nm NAND

— Laura Peters, contributing editor, covers a team led by the National Nano Device Laboratories (Hsinchu, Taiwan), which has achieved a record external quantum efficiency (QE) of >80% for photodiodes in the visible regime. This QE was achieved by harnessing a local surface plasmon resonance (LSPR) effect, which greatly enhances transmission efficiency in an otherwise conventional silicon photodiode. Quantum efficiencies in the 80% or higher range are needed for applications such as artificial eyes. The team, which includes researchers from National Taiwan University (Taipei) and National Cheng Kung University (Tainan), will present their results at the upcoming IEDM in San Francisco, CA, December 6-8.

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Figure 1. The optical array patterns that enable the local surface plasmon resonance effect.

LSPR involves the collective oscillations of conduction electrons in metallic nanostructures excited by electromagnetic energy. The team compared the improvement in quantum efficiency and polarized light energy enabled by the LSPR effects from four metallic optical array patterns (Figure 1) — C-shaped, square, striped, and chiral-shaped pattern — deposited over the metal finger electrodes in the photodiode device (Figure 2). The test device (control) does not contain the optical arrays. Each pattern has a period of 2.4µm and unit area of 1.44µm2. In this process, the p/n junctions are formed, contacts are deposited and etched, the top metal finger electrodes and metallic optical patterns are formed, followed by backside metal electrode deposition and sintering.

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Figure 2. Illustrations of the proposed device, with optical structures and the control photodiode.

The team determined that the devices with the chiral-shaped optical arrays demonstrated the greatest increase in current density with increasing illumination. The external quantum efficiency was also greatest with the chiral-shaped arrays, while demonstrating greater QE than previously reported organic devices or Schottky solar cells (Figure 3).

Click to Enlarge
Figure 3. External quantum efficiency of full device structures reaches 80% with the chiral-shaped optical structures.

The researchers observed that by having more corners of pattern above the metal electrodes, photocurrent density is enhanced due to self-accumulated local electric field in these corners. In addition to the reliance on LSPR pattern, transmission spectra are greatly influenced by the direction of the induced electric field, so the array layout must consider these polarity effects.

More IEDM 2010 previews:

How strain can protect devices from ESD

 SEMATECH tipping III-V MOSFET, FinFET, and resistive RAM 

TSMC anneal for gate-last HKMG process 

Imec IEDM presentations to cover More than Moore, ITRS

 When do TSV stresses affect device operation? 

Multi-threshold-voltage flexibility in FDSOI

 CMOS imager works from light to night

 Carbon nanotube vias approach production densities 

IBM Alliance simplifies pFET HKMG 

IM Flash details 25nm NAND

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