Kwan Sik Cho

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%.

Physics and Device Structures of Highly Efficient Silicon Quantum Dots Based Silicon Nitride Light-Emitting Diodes

An electrically driven light emitter from silicon is a long-standing problem in silicon photonics. Recently, significant progress has been made using silicon quantum dots (Si QDs) embedded in the silicon nitride thin films, transparent doping layers and electrodes, and surface-modified structures. This paper provides an overview of the progress in the device physics and fabrications of the Si QD light-emitting diodes (LEDs) including new device structures to improve the light extraction efficiency as well as highlights in the growth of the Si QDs and their quantum confinement effects (QCEs)

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.

Effect of Amorphous Si Quantum-Dot Size on 1.54 μm Luminescence of Er

The role of the size of amorphous silicon quantum dots in the Er luminescence at 1.54 μm was investigated. As the dot size was increased, more Er ions were located near one dot due to its large surface area and more Er ions interacted with other ones. This Er-Er interaction caused a weak photoluminescence intensity, despite the increase in the effective excitation cross section. The critical dot size needed to take advantage of the positive effect on Er luminescence is considered to be about 2.0 nm, below which a small dot is very effective in the efficient luminescence of Er.

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

High efficiency silicon visible light emitter using silicon nanocrystals in silicon nitride matrix and transparent doping layer

Semiconductor electronics is strongly dominated by silicon technology. However silicon technology does not allow easy integration with optical component since silicon is a poor light emitter. The unique properties of Si nanocrystals (nc-Si) can be exploited to fabricate Si-based light source. We will introduce a quantum confinement effect in the nc-Si embedded in a silicon nitride formed by PECVD. The band gap of the nc-Si could be controlled from 1.38 to 3.02 eV by decreasing the nanocrystal size. In addition, we will demonstrate a silicon light emitter with a transparent doping layer on nc-Si embedded in silicon nitride active layer by using ITO and n-type wide bandgap semiconducting layer. This light emitter has high external quantum efficiency of 1.6%, which is the highest value ever reported in Si-based visible light emitters.

Fabrication of organic light-emitting diodes using ITO anodes grown on polyethersulfone (PES) substrates by pulse-laser deposition

Organic light-emitting diode (OLED) has a good candidate for next generation flat panel display (FPD). However, it is very difficult to fabricate high performance OLEDs on plastic substrate because its mechanical and thermal properties are very poor. Before the ITO deposition, we used a new plasma treatment for good contact with ITO and PES. PES substrate is stayed in vacuum above 12 hours to reduce humidity and unknown chemical gas. We successfully fabricate OLED on PES substrate using PLD-ITO anodes. We can observe more uniform and bright emission image from the OLED and fix the optimum conditions for fabrication process for OLED. Maximum electro luminescence (EL) and current density at a 100 cd/m2 are 2500 cd/m2, 2mA/cm2, respectively and external quantum efficiency of OLED is about a 2.0%.

Hydrogenation Effect on the Er Luminescence in Amorphous Silicon Quantum Dot Films

The hydrogenation effect on the Er luminescence at 1.54 μm in an Er-doped amorphous Si quantum dot film was investigated. After hydrogenation, the luminescent properties were different between large-dot (2.5 nm) and small-dot (1.4 nm) samples. In particular, the number of optically active Er ions was increased in a large-dot sample, but decreased in a small-dot sample. We propose that the hydrogenation causes the Er migration toward an Si dot, and the luminescent property depending on the dot size is originated from the number of Er ions near an Si dot before hydrogenation.

Effects of an Undoped Si1 − x C x Buffer Layer on Performance of Si Nanocrystal Light-Emitting Diodes

We report the effects of introducing an undoped Si 1-x C x buffer layer between a silicon nanocrystal (nc-Si) active layer and an n-type SiC layer on the performance of the nc-Si light-emitting diodes (LEDs). The electrical property of an nc-Si LED with a buffer layer was greatly improved compared to that of an nc-Si LED without a buffer layer. Moreover, the light output power of the nc-Si LED with a buffer layer was enhanced by a factor of 2. By employing a buffer layer, the efficiency of electron injection into the nc-Si layer was enhanced, which resulted in an increase in the light output power. The data show that the introduction of an undoped Si 1-x C x buffer layer is a very effective way to improve the performance of nc-Si LEDs.