Kyung-Hyun Kim

High efficiency visible electroluminescence from silicon nanocrystals embedded in silicon nitride using a transparent doping layer

We have fabricated light-emitting diodes with a transparent doping layer on silicon nanocrystals (nc-Si) embeded in silicon nitride matrix formed by plasma-enhanced chemical vapor deposition. Under forward biased condition, orange electroluminescence (EL) with its peak wavelength at about 600 nm was observed at room temperature. The peak position of the EL is very similar to that of the photoluminescence (PL) and the emitted EL intensity is proportional to the current density passing through the device. We suggest that the observed EL is originated from electron-hole pair recombination in nc-Si. By using indium tin oxide and n-type SiC layer combination as a transparent doping layer, we obtained high external quantum efficiency greater than 1.6%.

Enhancement in Light Emission Efficiency of a Silicon Nanocrystal Light‐Emitting Diode by Multiple‐Luminescent Structures

A lot of research has been devoted towards the Si-based microphotonics due to the applications in silicon-based optoelectronic devices. [ 1–4 ] The Si-based light sources could reduce the fabrication cost because the compatibility with a conventional Si technology is better than any other materials such as conventional GaAsand GaN-based materials. Bulk silicon has poor luminescence effi ciency due to the indirect nature of its band gap and is thus highly ineffi cient for the light sources. However, if the size of Si nanocrystals (nc-Si) is smaller than the free exciton Bohr radius of bulk Si ( ∼ 4.6 nm), the light emission effi ciency could be much enhanced due to an increase in overlapping of electron-hole wave functions, that is, a quantum confi nement effect. [ 5 ] Because of this, nc-Si light emitting diodes (LEDs) have been investigated as promising light sources for the next generation of photonic applications. [ 6 , 7 ]

Quantum-dot light-emitting diodes utilizing CdSe∕ZnS nanocrystals embedded in TiO2 thin film

Quantum-dot (QD) light-emitting diodes (LEDs) are demonstrated on Si wafers by embedding core-shell CdSe∕ZnS nanocrystals in TiO2 thin films via plasma-enhanced metallorganic chemical vapor deposition. The n-TiO2∕QDs∕p-Si LED devices show typical p-n diode current-voltage and efficient electroluminescence characteristics, which are critically affected by the removal of QD surface ligands. The TiO2∕QDs∕Si system we presented can offer promising Si-based optoelectronic and electronic device applications utilizing numerous nanocrystals synthesized by colloidal solution chemistry.

Enhancement of light extraction from a silicon quantum dot light-emitting diode containing a rugged surface pattern

The enhancement in light extraction efficiency from a periodic micron-scale rugged surface pattern on Si quantum dot light-emitting-diode (Si-QD LED) structures was investigated, both numerically and experimentally. Micron-scale rugged surface patterns were fabricated on the top layer of the Si-QD LED to increase the extraction of light from the active layer. The optimum light extraction condition for a Si-QD LED corresponded to a pattern size/period ratio of ∼0.7. In experiments, the luminescent powers of a Si-QD LED with/without micron-scale surface patterns increase linearly with current density, and the efficiency of light extraction was enhanced by a factor of 2.8.

Simultaneous amplification by Er ions and SRS in an Er-doped germano-silica fiber

A flat signal gain over in the entire C- and L-bands by erbium (Er) ions radiative transition and stimulated Raman scattering in an Er-doped germano-silica fiber can be obtained if proper values of the concentration of Er and background loss in a fiber core are obtained during the fiber fabrication process. The optimized conditions for the flat C- and L-band gain are analyzed as functions of Er concentrations. Even for a low-gain value provided by a germano-silica core fiber with a low Er concentration and an optimum fiber length, a relatively low pump is required to obtain the flat gain band.

Prediction of the limit of detection of an optical resonant reflection biosensor

A prediction of the limit of detection of an optical resonant reflection biosensor is presented. An optical resonant reflection biosensor using a guided-mode resonance filter is one of the most promising label-free optical immunosensors due to a sharp reflectance peak and a high sensitivity to the changes of optical path length. We have simulated this type of biosensor using rigorous coupled wave theory to calculate the limit of detection of the thickness of the target protein layer. Theoretically, our biosensor has an estimated ability to detect thickness change approximately the size of typical antigen proteins. We have also investigated the effects of the absorption and divergence of the incident light on the detection ability of the biosensor.

Effects of Ag/indium tin oxide contact to a SiC doping layer on performance of Si nanocrystal light-emitting diodes

We report on the effects of a very thin Ag (2.5nm) interlayer between the indium tin oxide (ITO) current spreading layer and a SiC doping layer on silicon nanocrystals (nc-Si) embedded in silicon nitride film on the electrical and optical performance of the light-emitting diodes (LEDs). The forward voltage at a current of 20mA of the nc-Si LED with a Ag interlayer was decreased by 2.5V compared to that of the nc-Si LED without one due to the decrease in the contact resistance. In addition, the light output power of the nc-Si LED with a Ag interlayer was also enhanced by 40%. This result strongly indicates that the Ag/ITO contact scheme can serve as a highly promising contact scheme to a SiC film for the realization of the nc-Si LEDs with a high efficiency.

Enhancement of Performance of Si Nanocrystal Light-Emitting Diodes by Using Ag Nanodots

Effects of Ag nanodots on silicon nanocrystal (nc-Si) light-emitting diodes (LEDs) are investigated. The electrical property of the nc-Si LED with Ag nanodots was enhanced compared to that of the nc-Si LED without ones. This was attributed to the increase in the electric field due to the formation of Ag nanodots at the contact interface, indicating that the current could flow more efficiently from the indium tin oxide layer to n-SiC film. The formation of Ag nanodots with a size of 3~6 nm was confirmed by using a high-resolution transmission electron microscope analysis. Moreover, light output power of the nc-Si LED with Ag nanodots was enhanced

Erratum: “High efficiency visible electroluminescence from silicon nanocrystals embedded in silicon nitride using a transparent doping layer” [Appl. Phys. Lett. 86, 071909 (2005)]

In the original publication titled “High efficiency visible electroluminescence from silicon nanocrystals embedded in silicon nitride using a transparent doping layer,” by Cho et al. Appl. Phys. Lett. 86, 071909 2005 , we reported on obtaining an external quantum efficiency of 1.6% from lightemitting diodes LEDs based on nitride-passivated nanocrystal Si nc-Si . However, we have recently discovered that there had been a mistake in converting the luminescence spectra into absolute light output values due to usage of an incorrect conversion factor. Therefore, Fig. 3 b in the original paper should be replaced as below. The correct value, obtained directly using a sensitive optical power meter Newport 818-SL , is about 0.005%, which is about 300 times less than what had been reported. Thus, while many of the advantages of using nitride passivation such as lower operating voltage and wide tunability in the visible range still remain valid, we can no longer claim that it leads to higher

Design of transmission optical fiber with a high Raman gain, large effective area, low nonlinearity, and low double Rayleigh backscattering

Designed was the transmission fiber with a high Raman gain, large effective area, low nonlinearity, and low double Rayleigh backscattering (DRBS). Basically the optical signal-to-noise ratio (OSNR) of distributed type Raman amplifier is superior to that of the lumped type Raman amplifier using a high Raman gain fiber such as dispersion compensation fiber. However, much pump power and long length of transmission fiber line are required to acquire a proper gain in the distributed type fiber Raman amplifier. Thus, compositional adjustment on the fiber for optical transmission is of benefit to reduce further the required pump power. In this regard, based on this simulation, the fluorine and germanium co-doped fiber showed a high Raman gain, high OSNR, and low DRBS.