Byueng-Su Yoo

All-Monolithic 1.55 µm InAlGaAs/InP Vertical Cavity Surface Emitting Lasers Grown by Metal Organic Chemical Vapor Deposition

We successfully demonstrate all-monolithic InAlGaAs/InP vertical cavity surface emitting lasers (VCSELs) grown by metal organic chemical vapor deposition (MOCVD) in the wavelength range of 1.55 µm. The devices showed the high performances such as single mode output power of 1.6 mW, side mode suppression ratio (SMSR) of 60 dB, divergence angle of 8°, the slope efficiency of 0.27 W/A, and the continuous wave (CW) operation of temperature over 80°C. We achieved the modulation bandwidth exceeding 2.5 Gbps and power penalty free transmission over 30 km.

GaN tunnel junction as a current aperture in a blue surface-emitting light-emitting diode

We have demonstrated surface-emitting GaN-based diodes with a buried tunnel junction (TJ) current aperture. The current confinement aperture for lateral injection current was defined by mesa etch of a TJ structure and regrowth of current blocking layer surrounding the TJ mesa. Lateral electron current drives a tunnel contact junction providing hole injection into the active region. The very uniform light emission just through a buried TJ aperture represents that the buried TJ structure acts very effectively as a confinement aperture of lateral current injection, particularly in GaN-based vertical-cavity surface-emitting lasers.

Transverse mode characteristics of vertical-cavity surface-emitting lasers buried in amorphous GaAs antiguide layer

We report the transverse mode characteristics of InGaAs-GaAs vertical-cavity surface-emitting lasers (VCSELs) buried in a low-temperature-deposited amorphous GaAs (a-GaAs) layer. The maximum current maintaining a stable fundamental transverse mode is increased by the antiguide effect of the a-GaAs clad with a high refractive index. For 10- and 15-/spl mu/m-diameter devices, we attain a stable single-mode emission over a wide range of current. The antiguide effects and transverse mode profiles in vertical cavity lasers buried in the high refractive index clad are calculated using a two-dimensional beam propagation method.

Structural and electrical properties of InSb epitaxial films grown on GaAs by low-pressure MOCVD

Abstract InSb heteroepitaxial films have been grown on GaAs by low-pressure(LP) MOCVD and the structural and electrical properties, thereof have been investigated. For 1.5–2.0 microm thick InSb heteroepitaxial films, the FWHM of the DCRC ranges from 420 to 894 arcsec and the 77 K electron Hall mobilities are inversely proportional to the square of the rocking-curve width. This result suggests that the electron mobility is limited to the scattering by dislocations. The scattering by the charged dislocations explains the mobility-temperature characteristics of the film having larger rocking-curve width.

Polarization control of vertical-cavity surface-emitting lasers by electro-optic birefringence

Polarization of vertical-cavity surface-emitting lasers (VCSELs) grown on (001) GaAs substrate has been controlled by electro-optic birefringence. Birefringence was induced at the top distributed Bragg reflector by applying an electric field along the [001] direction. The cavity resonance of the polarized light along the [110] or [110] direction shifted to shorter and longer wavelength, depending on the direction of the applied electric field. By varying the direction and strength of the electric field, we actively controlled the polarization of VCSELs. The dominant polarization mode occurred along the [110] direction for the negative electric field, and along the [110] direction for the positive electric field.

Thermal and chemical stability of reflowed-photoresist microlenses

We have investigated the effect of heat treatment on the thermal and chemical stability of photoresist microlenses which were made by a reflow method. The microlenses were formed by patterning a novolac-based photoresist (PR) to pillar shapes and by reflowing it at 140 °C. After reflowing, the microlenses were heat treated at a relatively high temperature between 250 °C and 350 °C. After the heat treatment, the fundamental functions as a lens were maintained for infrared laser beams with wavelengths above 800 nm, except volume shrinkage and increment of the refractive index. The heat-treated microlenses also were not attacked by methanol and acetone. Our results suggest wide application of the PR as a simple, cost effective and stable lens medium.

Reliability assessment of 1.55-μm vertical cavity surface emitting lasers with tunnel junction using high-temperature aging tests

Abstract In this paper, the long-term reliability of all monolithic 1.55-μm etched-mesa vertical cavity surface emitting lasers (VCSELs) with tunnel junction is investigated via high-temperature storage tests and accelerated life tests. Characteristic variations depend on the operating conditions are examined via the threshold current, the optical output power, and the dark current. The median device lifetime is extrapolated and the activation energy of the VCSELs is calculated based on the reliability testing results. In addition, the degradation mechanism of the tested VCSELs is analyzed using the correlation between the current–voltage characteristics (I–V) and the device lifetime. From these results, the long-term reliability of the VCSEL test structures for high-speed optical communication systems can be determined and the device parameters, such as dark current, can be used as a monitoring factor for estimating reliability of the VCSELs.

Fabrication method for multiple wavelength vertical-cavity emitter arrays by SiN x layer thickness control

We report very narrow and equally spaced eight-channel multiple-wavelength vertical-cavity emitter arrays emitting from 855 to 862 nm with the average spacing of 0.91 nm. For the postgrowth wavelength adjustment, a binary-coded multistep ion beam etching technique is applied to control the thickness of a SiN/sub x/ tuning layer located on the first Al/sub 0.15/Ga/sub 0.85/As quarter-wave layer above the active region. Our result indicates the possibility of the precisely spaced vertical-cavity surface-emitting laser arrays using this kind of postgrowth wavelength adjustment technique.

Polarization characteristics of index-guided surface-emitting lasers with tilted pillar structure

We report precise control of polarization states for index-guided surface-emitting lasers by tilted-etching of the laser pillar. Circular laser pillars were etched by tilting the substrate toward ~110\ or ~11~0\ direction with an angle of 15/spl deg/-30/spl deg/ using reactive ion beam etching. For the laser device with a diameter of 7-10 /spl mu/m, we observed selectivity of the polarization state. We found a dominant polarization with an electric field perpendicular to the tilted direction of laser pillar. The maximum orthogonal polarization suppression ratio was about 25 dB. The selectivity of polarization in the tilted laser pillar devices is interpreted to be originated from the difference in optical losses for the two waves polarized to ~110\ and ~11~0\ directions.

Reactive ion etching‐induced damage in GaAs/AlGaAs quantum well structures and recovery by rapid thermal annealing and hydrogen passivation

Reactive ion etching (RIE)‐induced damage in a GaAs/AlGaAs quantum well structure, consisting of four GaAs quantum wells with different thicknesses, has been investigated by photoluminescence (PL). RIE was performed using a mixture of He and CCl2F2 gases under a variety of etching conditions. The PL intensities from the quantum wells damaged under an etching condition of physical sputtering decrease uniformly across the depth through the sample. The reduced PL intensities from the damaged quantum wells are restored by rapid thermal annealing and hydrogen plasma treatment. In particular, PL intensities from the quantum wells situated at the deep region from the surface are more drastically recovered than those from the near surface region. This result suggests that the decreases in the PL intensities created in the deep region have different recovery efficiencies from those at the near surface region. It is indicated also that the defects in the deep region are closely related to the vacancies of sublattic...