Jung-Ho Cha

Novel High-Radiance Surface-Emitting Light Emitting Diode Structure with Circular 45° Corner Reflector and Microlens

A new type of light-emitting diode(LED) with a circular 45° corner reflector and microlens is proposed and fabricated. The improvement of light output power of the proposed LED structure is calculated and compared with that of the conventional surface-emitting LED type. A microlens is fabricated on LED using the UV curing method. The HBr–H3PO4–K2Cr2O7 chemical etchant is developed for fabricating the circular 45° corner reflector. The measured light-current curve of the proposed LED shows that, compared to conventional LEDs, the output power increases considerably at high current level and the linearity is significantly improved by the circular 45° corner reflector. From the spectra measurement, we can confirm that the proposed LED structure shows combined characteristics of both conventional surface- and edge-emitting LEDs.

Monolithic Integration of InP-Based HEMT and MSM Photodiode Using InGaAsP (λ=1.3 µm) Buffer

A new epitaxial layer structure for the integration of a high-electron-mobility transistor (HEMT) and a metal-semiconductor-metal photodiode (MSM PD) is proposed. With the aid of an InGaAsP (?=1.3 ?m) buffer, this epitaxial layer structure has an additional function of light absorption without performance degradation of the HEMT. With this light absorption ability, the epitaxial layer structure can support a MSM PD structure and makes the fabrication process of the MSM PD identical to that of a HEMT. The characteristics of a monolithically integrated HEMT and MSM PD are presented and discussed. Measured ft and fmax are 18.7 GHz and 47 GHz, respectively, for the 1.5?100 ?m2 gate HEMT, and a responsivity of 0.7 A/W at a wavelength of ?=1.3 ?m has been acquired for the MSM PD.

Silicon Nitride Two-Level-Temperature Passivation on InP/InGaAsP Light-Emitting Diodes

The use of silicon nitride with a two-level temperature technique is proposed for the passivation of InP-based devices. InGaAsP/InP light-emitting diodes (LEDs) were fabricated by this passivation technique. The reverse current was decreased by about two orders of magnitude, and light–current linearity at a low current was improved.

InP/InGaAsP/InP double hetero-junction solar cells with increased short-circuit current

We have investigated the InP/InGaAsP double heterojunction (DH) structure solar cell and compared it with the InP control cells. The InP lattice matched InGaAsP has various band gap from 0.75 eV to 1.35 eV. We have investigated the InP/InGaAsP DH solar cell having the 1.1 eV InGaAsP absorption layer. The InP/InGaAsP DH cell has a lower open-circuit voltage by 20.17 % than the InP cell. The short-circuit current improves by 100 %. Consequently, the conversion efficiency of the cell improves by 50.18 % via the InP/InGaAsP DH structure.

Open-circuit voltage improvement in InGaAs/InP heterojunction solar cells

We proposed single-heterojunction and double-heterojunction cell structures to increase the open-circuit voltage in InGaAs/InP-based solar cells. Compared with a homojunction cell, an open-circuit voltage improvement for the single-heterojunction cell is not observed, but an increase of 30.2% in open-circuit voltage for the double hetero-junction cell is observed. As a result, the efficiency of the double-heterojunction cell is increased by 23.9% that of the homojunction cell.

InP/InGaAs/InP Double-Hetero-junction Solar Cells with Increased Open-Circuit Voltage

where α, β is constant, J0 is the dark current, EG is the band gap and kT is the thermal energy. And also the Voc is related to the dark current as The performance of solar cells is characterized by opencircuit voltage (Voc), short-circuit current (Jsc) and fill-factor (FF). As the dark current is decreased, the open circuit voltage of solar cells is increased. Therefore, if the dark current is reduced, we can increase the open-circuit voltage. In this paper, we investigated double hetero-junction structure to increase the open-circuit voltage by the reduction of the dark current. (2) 1) J J ln( φ V 0 L T oc + =

Fibre-optic plate bonded Al/sub 0.3/Ga/sub 0.7/As/GaAs transmission photocathode

An AlAs/GaAs/Al/sub 0.3/Ga/sub 0.7/As heterostructure on a GaAs substrate has been directly bonded on a fiber-optic plate for the first attempt of the 3rd generation transmission photocathode. The substrate is removed mechanically and etched chemically, utilizing high etching selectivities of GaAs and AlAs in potassium citrate/citric acid. The bonding strength between fiber optic and GaAs wafer exceeds 5.7 MPa without annealing, the final GaAs/Al/sub 0.3/Ga/sub 0.7/As structure on the fiber optic allows large dimension (1 cm /spl times/ 1 cm), thin (2 /spl mu/m) and uniform film thickness, and good transmission performance.

An InGaAsP/InP twin-guide laser diode with rectangular ring cavity

A twin-guide laser diode, which consists of an active waveguide with rectangular ring cavity and a transparent output waveguide coupled to each other as a directional coupler, has been fabricated and its performance has been investigated. Four straight waveguides and total internal reflection (TIR) mirrors conceptually construct the ring cavity, which enhances the traveling wave characteristics such as mode purity. Lasing light is coupled to the transparent passive output waveguide by vertical evanescent coupling. The cavity mirrors were fabricated by Ar/Cl2/H2 reactive ion beam etching (RIBE) at the elevated process temperature to enhance the desorption rate of InClx for a smooth etching surface. The threshold current was measured to be 230 mA, corresponding to a threshold current density of 4 kA/cm2. The emission peak wavelength is approximately 1.56 µm. The fabricated device shows single mode operation at current levels up to 1.4 times the threshold current.