Deokha Woo

Enhancement of hole injection and electroluminescence by ordered Ag nanodot array on indium tin oxide anode in organic light emitting diode

We report the enhancement of hole injection and electroluminescence (EL) in an organic light emitting diode (OLED) with an ordered Ag nanodot array on indium-tin-oxide (ITO) anode. Until now, most researches have focused on the improved performance of OLEDs by plasmonic effects of metal nanoparticles due to the difficulty in fabricating metal nanodot arrays. A well-ordered Ag nanodot array is fabricated on the ITO anode of OLED using the nanoporous alumina as an evaporation mask. The OLED device with Ag nanodot arrays on the ITO anode shows higher current density and EL enhancement than the one without any nano-structure. These results suggest that the Ag nanodot array with the plasmonic effect has potential as one of attractive approaches to enhance the hole injection and EL in the application of the OLEDs.

Nanohole arrays with sub-30 nm diameter formed on GaAs using nanoporous alumina mask

Nanohole arrays with a sub-30 nm diameter were formed on GaAs substrates by inductively coupled plasma reactive-ion etching (ICP-RIE) using nanoporous alumina films as transfer masks. Whether the pore configurations of the alumina masks were transferred onto the GaAs substrates depended on the exposure time of ICP-RIE. In spite of the sub-30 nm pore diameter of the alumina masks, the ion bombardment induced in SiCl4/Ar gas by ICP-RIE properly responded on the GaAs substrate through the pores of the alumina masks. ICP-RIE using nanoporous alumina masks can be used as a prospective method to produce nanostructures.

Carrier lifetimes in dielectric cap disordered GaAs/AlGaAs multiple quantum well with SiN capping layers

Time resolved photoluminescence (PL) characteristics of a SiN cap disordered GaAs/AlGaAs multiple quantum well (MQW) structure exhibit a decrease in carrier lifetime in conjunction with an increase in quantum well disordering (QWD) as the SiN capping layer thickness is increased. The decrease in carrier lifetime is attributed to enhanced carrier trapping due to the defects introduced during dielectric cap quantum well disordering and the relaxation of the momentum conservation during radiative recombination by QWD. Potential applications of these effects on high speed optical devices such as laser diodes (LD’s) and optical modulators are discussed.

High photoresponsivity of a p-channel InGaP/GaAs/InGaAs double heterojunction pseudomorphic modulation-doped field effect transistor

In this letter, we report the electrical and optical characteristics of p-channel In0.13Ga0.87As double heterojunction pseudomorphic modulation-doped field effect transistor (MODFET) structure grown by gas source molecular beam epitaxy. The Hall mobility and the density of 2-DHGs (two-dimensional hole gases) in the pseudomorphic In0.13Ga0.87As channel were measured to be 250 cm2/V s and 1.9×1012 cm−2 at 300 K, and 5800 cm2/V s and 1.5×1012 cm−2 at 23 K, respectively. The fabricated p-channel MODFET shows a good mobility property which is due to high valence band discontinuity of InGaP/GaAs/InGaAs double barriers. The peak energy in the photoluminescence spectrum from the p-channel pseudomorphic MODFET structure was found to be 1.4 eV (λ=881 nm). The photoresponsivity with this modified pseudomorphic MODFET structure shows outstandingly better than that of a pin photodiode, particularly at low incident optical power.

A Magneto-Optic Waveguide Isolator Using Multimode Interference Effect

We have investigated an optical waveguide isolator with a multimode interference section by wafer direct bonding, operating at a wavelength 1.55 ㎛. In order to fabricate the device for monolithic integration, the wafer direct bonding between a magnetic garnet material as a cladding layer and a semiconductor guiding layer has been achieved. We found that wafer direct bonding between InP and GGG (Gd₃Ga_5O₁₂) is effective for the integration of a waveguide optical isolator. The isolation ratio was obtained to be 2.9 ㏈ in the device.

Reverse-biased characteristics of GaAs/AlGaAs depleted optical thyristor with low depletion voltage

For the faster switching speed and the lower power consumption, we optimized the structure of a fully depleted optical thyristor (DOT) by the depletion of charge at the lower negative voltage. The fabricated optical thyristor shows sufficient nonlinear s-shape I-V characteristics with the switching voltage of 2.85 V and the complete depletion voltage of -8.73 V. In this paper, using a finite difference method (FDM), we calculate the effects of parameters such as doping concentration and thickness of each layer to determine the optimized structure in the view of the fast and low-power-consuming operation.

Characteristics and fabrication of nanohole array on InP semiconductor substrate using nanoporous alumina

Uniform arrays of nano-sized pore produced in porous alumina were transferred into InP substrates by inductively coupled plasma reactive ion etching (ICP-RIE). We observed a significant enhancement in the light output from InP substrate with nanohole arrays on the surface. Photoluminescence intensity of triangular arrays of air cylinders on InP substrate showed an enhancement up to 3 times compared with that from a raw InP substrate without such structure. The ICP-RIE technique using nanoporous alumina mask can be used as a prospective method in the fabrication of nanostructure materials for increasing the light output from semiconductor light emitting devices.

Optical logic gates based on integrated vertical cavity laser with depleted optical thyristor structure

Optical switches and optical logic gates with AND and OR functionality are demonstrated by the monolithic integration of a vertical cavity lasers with depleted optical thyristor structure. The thyristors have a low threshold current of 0.65 mA and a high on/off contrast ratio of more than 50 dB. By simply changing a reference switching voltage, this single device operates as two logic functions, optical logic AND and OR.

A multimode-interferenced electrooptic TE/TM mode splitter

TE/TM mode splitting is an important integrated-optic function for fiber communication system and fiber sensors, where orthogonal polarization states of the signals are particularly emphasized. Guided-wave TE/TM mode splitting has been demonstrated in LiNbO/sub 3/, III-V compound semiconductors and polymers. They used an asymmetric Y-junction with different preferences of polarizations, a double mode waveguide with different coupling lengths for TE and TM modes, and the photo-bleaching induced birefringence, respectively. We present a novel TE/TM mode splitter utilizing the multimode interference and the linear electrooptic (LEG) effect, It employs a new operating principle, and shows several important characteristics: high extinction ratio, low excess loss, easy fabrication and large fabrication tolerance, and integratibility with other photonic devices.

Optical characteristics of PnpN optical thyristor operating at 1.55 μm

InGaAs/InP multiple quantum well (MQW) PnpN depleted op- tical thyristors (DOTs) operating at 1.55 mm are proposed and fabricated. To analyze their switching characteristics, we simulate nonlinear s-shape current-voltage curves using the finite difference method (FDM) associ- ated with the current-oriented method. Using the FDM, we calculate the effects of such parameters as doping concentration and the thicknesses of the outer and inner layers of the thyristor to determine an optimized structure in the view of fast and low-power-consuming operation. With these results, we fabricate waveguide- and vertical-type InGaAs/InP MQW PnpN DOTs. The waveguide-type DOT shows sufficient nonlinear s-shape I-V characteristics with a switching voltage of 4.03 V and a holding voltage of 1.77 V, and spontaneous emission along the wave- guide. The current-voltage characteristics of the vertical-type DOT are shown very well under 150 mW of input power, while the s-shape disap- pears at 200 mW.