Si-Based Light Sources

Strategy & Focus

• Si-based light-emitting devices research
  
  We have demonstrated light emission from a multilayer α-Si/SiN stack grown by PECVD. The emission wavelength is a function of the α-Si layer thickness and can be tuned from 706 nm to 674 nm by varying the thickness of the α-Si layers from 7 nm to 3 nm. PL intensity has been demonstrated to be improved with a low thermal budget anneal. The weak dependence of PL emission on dielectric film thickness in terms of emission wavelength suggests the ability of using even thinner films as barrier. This work was published in Applied Physics Letters in May 2007.
  
  We also report for the first time electronluminescence (EL) on an electrically pumped silicon light-emitting device with thin multi-layer stacked amorphous silicon (∂-Si, in thickness of 3-7nm)/silicon nitride (~10nm) structure. EL from devices built upon the proposed structure originates from electron-hole pair recombination and the carrier injection mechanism is through Frenkel-Poole tunnelling. Our proposed structure, being CMOS-compatible, benefits from low thermal budget process coupled with accurate layer thickness control. This work was presented in the International Conference on Group IV Photonics (2007).

• ZnO on Si-substrates
  
  ZnO has higher performance potential than existing GaN due to its higher exciton binding energy, especially the potential to be integrated on Si-substrate. However, the persistent issue of crystal quality and inability to yield effective p-conduction prohibits the advancement of ZnO technology. One effort to achieve p-type conduction, as performed by the IME team, is through annealing.
  
  P-type conduction has been observed in unintentional carbon-doped ZnO thin films grown by metal organic chemical vapour deposition through post-growth annealing treatment. The existence of carbon, which has been verified by secondary ion mass spectrometry and x-ray photoelectron spectroscopy, was predicted to immobilise the oxygen in the interstitial site in ZnO thin films after annealing. Using first principles calculations, the formation of carbon-oxygen cluster defect in ZnO was found to be favourable and acts as a shallow acceptor. The cryogenic photoluminescence of the p-type carbon-doped ZnO thin films shows an additional peak located at 3.3564 eV, which was attributed to the acceptor (carbon-oxygen cluster defect ) bound exciton emission. This work was published in Applied Physics Letters (2007).

Significant Results

Electrically Pumped Si-Light-Emitting Devices based on Multi-Layer Quantum-Structure

Progressing from Si-microphotonics circuit application, IME’s NanoEP group demonstrated a first electrically excited light emitting device from a Si-based material based on a unique nano-superlattice structure of Si/SiN stacking. Light emission is facilitated through quantum confinement of the injected carriers within the nanoscale silicon structures.

 The picture below shows a square device lighted when an electrical bias is applied to it (inset shows the same chip taken under lighted conditions before electrical bias). Tuning of the emission wavelength (colour) was demonstrated despite its limitation of a small tuning range within the orange colour spectrum. While the intensity of the emitted light is still too low for practical applications, this represented a major step in our pursuit of a silicon-based light source.

L spectra of devices active layers identical to SL5, SL6 and SL7. The coupling has not been optimised for each measurement. This accounts for the lower EL intensity of device with 5 nm a-Si layer thickness. Picture showing a square device lighted when biased. The inset shows the same die taken under lighted condition, showing the details of the die.

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