Fabrication of high-power VCSEL with radial bridge electrodes

We report the fabrication of a novel high-power vertical-cavity surface-emitting laser （VCSEL） with radial bridge electrodes in this letter. The analysis shows that the radial bridge electrodes can reduce the p-type distributed Bragg reflector （p-DBR） electric and thermal resistance, and improve the device beam quality. The high-power radial brigde electrode VCSELs with 200-μm aperture have been made and tested. The testing results show that the differential resistance of the VCSEL is 0.43 Ω and the maximal continuouswave （CW） output power is 340 mW, 1.7 times higher than the conventional electrode device. Its thermal resistance is 0.095℃/mW, and its near-field pattern exhibits a homogeneous distribution. The high-power radial bridge electrode VCSEL has better temperature and opto-electric characteristics.

Impact of multipath effects on theoretical accuracy of TOA-based indoor VLC positioning system

This paper discusses the time-of-arrival(TOA) based indoor visible light communication(VLC) positioning system in a non-line-of-sight environment. The propagation delay is assumed to be gamma distributed. The generalized Cramer–Rao lower bound for multipath propagation is derived as the theoretical accuracy limitation. The performance of the positioning system is affected by the shape parameter and the scale parameter of gamma distribution.The influences on positioning accuracy of multipath effects are analyzed through discussing the physical meaning of the gamma distribution parameters. It is concluded that the lower bound of positioning accuracy is attained when variance of the non-line-of-sight propagation-induced path lengths is zero. The simulation result provesthat the theoretical positioning accuracy is in the order of centimeters with the given scenario.

Preparation for Bragg grating of 808 nm distributed feedback laser diode

The second-order Bragg grating structure of an 808 nm distributed feedback semiconductor laser diode was designed and optimized. The grating with a period of 240 nm was fabricated on GaAs substrate by holographic photolithography and wet etching. Images of optical microscopy, scanning electron microscopy and atomic force microscopy show that the grating has a period of 240 nm, duty cycle of 0.25, depth of 80 nm, with perfect surface morphology, good fringe continuity and uniformity.

Effect of Pt diffusion barrier layer in Ni/AuGe/Pt/Au on ohmic contact to n-GaAs

The multi-layer metals of Ni/AuGe/Pt/Au with a Pt diffusion barrier layer of ohmic contact to n-GaAs were studied. The surface morphology and ohmic contact resistivity of multi-layer metals were characterized, with and without the Pt diffusion barrier layer for comparison. The SEM and EDS measurements show the Pt diffusion barrier layer can block the interdiffusion of atoms in multi-layer metals, and improve the surface morphology. The TLM results show that the samples with a Pt diffusion barrier layer have uniform ohmic contact resistance, indicating that the Pt diffusion barrier layer can increase the repetition and uniformity of ohmic contact to n-GaAs, and improve the thermal stability and reliability of GaAs-based devices.

VCSEL with reticular electrode and larger emitting aperture and its optoelectronic characteristics

The enlargement of the emitting aperture is usually one of the important methods of increasing vertical- cavity surface-emitting laser （VCSEL） optical output power. However, in a VCSEL with a larger aperture, the inhomogeneity in the injected current often causes inhomogeneous or even no emission. To solve this problem and to increase VCSEL output power, as well as to improve its thermal characteristics, we develop a new type of injected VCSEL with a larger aperture and a reticular electrode, where the conventional circular injection electrode of the P side is turned into a reticular one, and the heat sink is on the N side. The tests of the new VCSEL show an improvement in homogeneity in not only the injected current but also the emission intensity. The optical output power is also considerably increased, and the device optoelectronic performance is improved.

High performance 1.3 μm InGaAsN superluminescent diodes

High performance 1.3 μm InGaAsN superluminescent diodes (SLDs) were fabricated with Schottky contact. The structure was grown by metal organic chemical vapor deposition (MOCVD). Output power of 3 mW was obtained in continuous wave (CW) mode at room temperature. The full width at half maximum (FWHM) of the emission spectrum was 30 nm. The devices operated up to 100°C.

Effect of phosphor sedimentation on photochromic properties of a warm white light-emitting diode

In the process of producing a white light emitting diode, the consistency of the optical coherence and stability of the photochromic properties is a crucial index for measuring the quality of the product. Phosphor sedimentation is a significant factor affecting optical coherence, thus, in this paper, seven sets of control experiments were set up with the phenomenon of the phosphor precipitation at time intervals 0, 2, 5, 10, 20, 30, and 40 min.The color coordination concentration and optical properties were also tested. The results indicate that phosphor sedimentation occurs between 0 and 20 min, during which the color coordinate placement is concentrated, the central coordinates are(x = 0.4432 ± 0.004, y = 0.4052±0.002); the quality was verified because the supply demand chain management(SDCM) was no greater than 7. Later, between 30 and 40 min, the central coordinates are(x = 0.4366 ± 0.003, y = 0.4012 ± 0.003), which had an SDCM value higher than 7, and had a more discrete color placement; it does not meet the requirements of the national standard GBT24823-2016 general lighting LED module performance.

Study on the mechanism of color coordinate shift of LED package

In the paper, the influences of the chip, silicone and phosphors on the color coordinate shift of LED were studied. In the process of LED baking, it was found that the effect of the chip and silicone on the color coordinate drift is less than 3% through the analysis of each influencing factor. But the influence of the phosphors is large and accounted for 11.11% of the overall impact factors. Therefore, it is important to select the better green phosphors in thermal stability for the LED package and it has a guiding significance to the color coordinate of LED distribution.