Kyoung-ho Ha

High-power GaN-based blue-violet laser diodes with AlGaN∕GaN multiquantum barriers

AlGaN∕GaN multiquantum barriers (MQBs) were introduced into violet AlInGaN laser diodes with an InGaN multiquantum-well structure, resulting in drastic improvements in lasing performance. Comparing with conventional AlGaN single electron blocking layer (EBL), lower threshold current of 32mA and higher slope efficiency of 1.12W∕A at room temperature has been achieved by using the AlGaN∕GaN multiquantum barrier. This improvement implies that p-type AlGaN∕GaN MQBs are more effective in suppressing the overflow of electrons than p-type AlGaN single EBL. Effective barrier heights of the MQBs should be higher than the single EBL due to the quantum effect of MQBs and the enhancement of p-type doping efficiency. Additionally, the effect of strain on InGaN multiquantum wells from the single EBL can be reduced by using the AlGaN∕GaN MQBs structure.

Measurement of junction temperature in GaN-based laser diodes using voltage-temperature characteristics

We present a method to determine junction temperature in GaN-based laser diodes (LDs) for simple, fast, and reliable characterization of thermal properties. The large change of forward operation voltage with temperature in GaN laser diodes is advantageously used to measure junction temperature. Using this method, we compare junction temperature of LD structures with different substrates and chip mounting methods. It is found that the junction temperature can be reduced considerably by employing GaN substrates or epi-down bonding. For epi-down bonded LDs, as much as two-fold reduction in junction temperature is achieved compared to epi-up bonded ones and junction temperature rise in this case is only about 13 degrees for more than 100 mW-output power.

Bulk silicon photonic wire for one-chip integrated optical interconnection

We report a nano-sized silicon waveguide by forming partial silicon-on-insulator structure with SPE on bulk silicon substrate. The propagation loss is as low as 6.1 dB/cm, which is close to that of silicon-on-insulator based waveguide.

Single-mode blue-violet laser diodes with low beam divergence and high COD level

We demonstrate GaN-based high-power single transverse-mode laser diodes (LDs) emitting at 405 nm. LD structures are designed to exhibit a high level of catastrophic optical damage and small beam divergence angle. By the control of refractive index profiles, we achieved a vertical beam divergence angle of as low as 17.5/spl deg/ and maximum output power of as high as 470 mW under continuous-wave operation condition. In addition, nearly fundamental transverse-mode operation is demonstrated up to 500-mW pulsed output power by far-field investigation.

High-power AlInGaN-based violet laser diodes with InGaN optical confinement layers

InGaN optical confinement layers (OCLs) were introduced into blue-violet AlInGaN-based laser diodes (LDs), resulting in the drastic improvements of lasing performance. Comparing with conventional LD structure, the lowest threshold current density of 2.3kA∕cm2 has been achieved by adding 100-nm-thick InGaN OCLs which represented maximum optical confinement factor. Additionally, we observed the high quantum efficiency and the uniform emission intensity distribution of InGaN quantum wells grown on lower InGaN OCL than on typical GaN layer. Upper InGaN OCL can reduce Mg diffusion from p-type layers to InGaN active region by separating the distance between InGaN quantum wells and p-type layers.

Mach-Zehnder silicon modulator on bulk silicon substrate; toward DRAM optical interface

We present a Mach-Zehnder silicon modulator fabricated on a bulk silicon substrate featuring active length of 200 µm, modulation speed up to 5 Gb/s, power consumption of 2 pJ/bit, and extinction ratio of 10 dB.

Effect of active-layer structures on temperature characteristics of InGaN blue laser diodes

We investigate temperature characteristics of 445-nm-emitting InGaN blue laser diodes (LDs) with several types of active-layer structures. The double quantum-well (QW) LD structures having an n-type doped barrier show negative or very high characteristic temperature depending on the barrier In composition. On the contrary, the double QW structures having an undoped barrier and the single QW structure show normal temperature dependence of LD characteristics. From the simulation of carrier density and optical gain, it is found that the anomalous temperature characteristics of blue LDs are closed related to the inhomogeneous hole distribution between QWs due to the low hole mobility of InGaN materials.

Behaviors of Emission Wavelength Shift in AlInGaN-Based Green Laser Diodes

InGaN quantum-well (QW) green laser diodes (LDs) with an emission wavelength of 483.7 nm were characterized by controlling the injection pulsewidth. The emission wavelength of LDs showed a large blueshift (> 20 nm) of spontaneous emission peak with increasing injection current below the threshold current. The huge blueshift was ascribed to the deep In localization states and the strong piezoelectric field in the green InGaN QW structure with higher In contents than conventional violet/blue InGaN QWs. However, the lasing wavelength of LDs was slightly redshifted by increasing the injection pulsewidth due to the thermal heating effects.

Si-based optical I/O for optical memory interface

Optical interconnects may provide solutions to the capacity-bandwidth trade-off of recent memory interface systems. For cost-effective optical memory interfaces, Samsung Electronics has been developing silicon photonics platforms on memory-compatible bulk-Si 300-mm wafers. The waveguide of 0.6 dB/mm propagation loss, vertical grating coupler of 2.7 dB coupling loss, modulator of 10 Gbps speed, and Ge/Si photodiode of 12.5 Gbps bandwidth have been achieved on the bulk-Si platform. 2x6.4 Gbps electrical driver circuits have been also fabricated using a CMOS process.

Comprehensive study of time-lapsed peak shift in InGaN quantum well structures: Discrimination of localization effect from internal field effect

Time-lapsed emission peak shift behaviors in blue-light-emitting InGaN multiple quantum well (MQW) laser diodes with different well widths are systematically investigated by means of excitation power-dependent, time-resolved optical analysis. By investigating the main emission peak shift as a function of both time evolution and excitation power density, the amount of time-lapsed emission peak shift can be differentiated by two contributions: the excitation power dependent and independent ones. The authors conclude that the power-dependent (power-independent) time-lapsed peak shift can be attributed to the internal electric-field (carrier localization) effect present in vertical growth (lateral in-plane) direction of InGaN MQW laser diode structures.