Wen-Jen Lin

Long wavelength (1.3 μm) vertical-cavity surface-emitting lasers with a wafer-bonded mirror and an oxygen-implanted confinement region

We proposed and demonstrated a novel design for long wavelength (1.3 μm) vertical-cavity surface-emitting lasers (VCSELs). In this design, oxygen-implanted current-confinement regions were formed in a GaAs/AlGaAs Bragg reflector which is the bottom mirror wafer bonded to an AlGaInAs/InP cavity consisting of nine strain-compensated quantum wells. Room- temperature continuous-wave (cw) operation of 1.3 μm-VCSELs with a record low cw threshold current density of 1.57 kA/cm2 and a record low cw threshold current of 1 mA have been realized.

1.3-μm Vertical-cavity surface-emitting lasers with double-bonded GaAs-AlAs Bragg mirrors

We demonstrate, for the first time, double-bonded AlGaInAs strain-compensated quantum-well 1.3-/spl mu/m vertical-cavity surface-emitting lasers (VCSELs). GaAs-AlAs Bragg mirrors were wafer-bonded on both sides of a cavity containing the AlGaInAs strain-compensated multiple-quantum-well active layers sandwiched by two InP layers. The lasers have operated under pulsed conditions at room temperature. A record low pulsed threshold current density of 4.2 kA/cm/sup 2/ and a highest maximum light output power greater than 4.6 mW have been achieved. The maximum threshold current characteristic temperature T/sub 0/ of 132 K is the best for any long wavelength VCSELs. The laser operated in a single-longitudinal mode, with a side-mode suppression ratio of more than 40 dB, which is the best results for 1.3-/spl mu/m VCSELs.

InGaN/GaN light emitting diodes with a p-down structure

Nitride-based p-down blue light emitting diodes (LEDs) were successfully fabricated. It was found that we could improve the crystal quality of these nitride-based p-down LEDs by inserting a codoped interlayer between the p-type cladding layer and MQW active layers. It was also found that the turn-on voltage could be reduced from 15 V to less than 5 V for the p-down LED with codoped layer and tunnel layer. The 20 mA output power was 1 mW for the p-down LED with an Mg+Si codoped interlayer and a rough p-tunnel layer.

Very-low-threshold, highly efficient, and low-chirp 1.55-μm complex-coupled DFB lasers with a current-blocking grating

Low-threshold current DFB lasers have been fabricated based on a complex-coupled structure with a current blocking grating. A threshold current as low as 5 mA was obtained, which enabled high temperature operation up to 105/spl deg/C. Asymmetric facet coatings were applied to obtain a high efficiency of 0.3 W/A. The strained InGaAsP MQW active region and the antiphase coupling has resulted in a low modulation chirping. By direct modulation of the device at 2.488 Gb/s and using optical amplifiers, we have demonstrated digital transmission over a 235 km-long standard single-mode fiber with a power penalty of 1.55 dB.

P-Down InGaN/GaN Multiple Quantum Wells Light-Emitting Diode Structure Grown by Metal-Organic Vapor-Phase Epitaxy.

An inverted or p-down InGaN/GaN multiple quantum wells (MQW) light-emitting diode (LED) structure is studied. The crystalline quality of the quantum wells is comparable to that of the n-down structure by using a Si or In co-doped GaN:Mg layer underneath the active layer. It was found that I–V characteristics can be improved by insertion of a tunnel layer, either a 3D growth GaN:Mg layer or an AlGaN/GaN superlattice layer. The feasibility of such a structure for practical application is also evaluated by luminescence measurement.

ZnSTeSe metal-semiconductor-metal photodetectors

High-quality quaternary ZnSTeSe epitaxial layers were successfully grown by molecular beam epitaxy (MBE). It was found that a ZnS/sub 0.18/Se/sub 0.82/ layer was automatically formed in between the ZnSe buffer layer, and the ZnS/sub 0.17/Te/sub 0.08/Se/sub 0.75/ epitaxial layer, when we increased the ZnS cell temperature. ZnSTeSe metal-semiconductor-metal (MSM) photodetectors were also fabricated for the first time. It was found that we could achieve a photocurrent to dark current contrast higher than five orders of magnitude by applying a 10-V reverse bias. We also found that the maximum photoresponsivity is about 0.4 A/W under a 10-V reverse bias. Such a value suggests that the ZnSTeSe MSM photodetector is potentially useful in the blue-UV spectral region.

On the Carrier Concentration and Hall Mobility in GaN Epilayers

The dependence of Hall mobility and carrier concentration in GaN epilayers on light illumination was examined. It was found that Hall mobility and electron concentration both increased after illumination with red laser (632.8 nm) and green laser (530 nm). However, no changes in Hall mobility and carrier concentration were found, if IR-laser (850 nm) was used. The results reveal that deep-level defects were excited and hence extra carriers were generated by light illumination. The influence is more pronounced for thinner films. These observations indicate that donor-like defect-related states were located 1.48 to 2.33 eV below the conduction band edge.

Low-threshold proton-implanted 1.3-μm vertical-cavity top-surface-emitting lasers with dielectric and wafer-bonded GaAs-AlAs Bragg mirrors

We demonstrate a new structure for long-wavelength (1.3-/spl mu/m) vertical-cavity top-surface-emitting lasers using proton implantation for current confinement. Wafer bonded GaAs-AlAs Bragg mirrors and dielectric mirrors are used for bottom and top mirrors, respectively. The gain medium of the lasers consists of nine strain-compensated AlGaInAs quantum wells. A record low room temperature pulsed threshold current density of 1.13 kA/cm/sup 2/ has been achieved for 15-/spl mu/m diameter devices with a threshold current of 2 mA. The side-mode-suppression-ratio is greater than 35 dB.

Improved Output Power of Nitride-Based Light-Emitting Diodes With Convex-Patterned Sapphire Substrates

Nitride-based light-emitting diodes (LEDs) grown on different convex-patterned sapphire substrates are proposed and fabricated. The electrical and optical properties of these LEDs are discussed in detail. It is found that the LED with a ball-shape patterned sapphire substrate has the best crystalline quality and I-V characteristic. On the other hand, on reducing total internal reflection, the LED with hexagonal-shape patterned sapphire substrate (HPSS) has the best performance on output power and external quantum efficiency. In comparison to the LED without patterned substrate, the LED with HPSS has 175% and 165% enhancement on output power and external quantum efficiency, respectively.

ZnCdSeTe-based orange light-emitting diode

We report the fabrication of orange light-emitting diodes (LEDs) by introducing Te into the well layers of ZnCdSe-ZnSSe multiple quantum-well active region. It was found that a 15% Te can result in a 91 nm photoluminescence (PL) red-shift at 16 K and a 81 nm PL red-shift at room temperature. Such a ZnSe-based orange LED can be integrated easily with conventional ZnSe-based blue-green LED on the same GaAs substrate. Thus, such a ZnSe-based orange LED is potentially useful in realizing a new one-chip type white LED without the use of phosphor.