GaAs-based VCSELs Research Articles

Monolithically integrated 940 nm VCSELs on bulk Ge substrates.

This research successfully developed an independent Ge-based VCSEL epitaxy and fabrication technology route, which set the stage for integrating AlGaAs-based semiconductor devices on bulk Ge substrates. This is the second successful Ge-based VCSEL technology reported worldwide and the first Ge-based VCSEL technology with key details disclosed, including Ge substrate specification, transition layer structure and composition, and fabrication process. Compared with the GaAs counterparts, after epitaxy optimization, the Ge-based VCSEL wafer has a 40% lower surface root-mean-square roughness and 72% lower average bow-warp. After device fabrication, the Ge-based VCSEL has a 10% lower threshold current density and 19% higher maximum optical differential efficiency than the GaAs-based VCSEL.

Thermomechanical model of an oxide-confined GaAs-based VCSEL emitter

A thermomechanical model for an oxide-confined GaAs-based VCSEL emitter is presented. The impact of the lattice mismatch, the oxide shrinkage and the thermal stress on the mechanical reliability is evaluated. Under standard operating conditions, calculations show that the temperature increase has a negligible influence on the overall mechanical stress. The oxide shrinkage highly deforms the epitaxial structure at the edge of the optical aperture. At oxide corners, the calculated stress is beyond the experimental yield strength of GaAs micro-pillars, enabling the nucleation of the dislocations forming dark line defects. The high misfit stress in the quantum well layers can favor there the dislocation propagation.

Impact of Cavity Design on the Modulation Properties of a Gaas-Based Vcsel

Impact of Cavity Design on the Modulation Properties of a Gaas-Based Vcsel

Impact of Cavity Design on the Modulation Properties of a Gaas-Based Vcsel

Impact of Cavity Design on the Modulation Properties of a Gaas-Based Vcsel

Improving Performance of GaAs-Based Vertical-Cavity Surface-Emitting Lasers by Employing Thermally Conductive Metal Substrate

We investigated the effect of the conducting substrate on the performance of GaAs-based VCSELs, where the substrates were 230 μm-GaAs (reference), 10 μm-GaAs/metal, and 0.5 μm-GaAs/metal. The VCSELs with the 10 μm- and 0.5 μm thick GaAs/metal-substrates produced higher light output power than the reference. For example, the thin GaAs/metal substrate samples showed 16.3%–16.7% higher light output power at 3.0 A than the reference. It was shown that the thin GaAs samples produced 12.2%–14.0% higher power conversion efficiency at 3.0 A than the reference. At a high current region, the metal-substrate samples yielded lower junction temperature than the reference, namely, the thin GaAs samples gave 42 °C–47.4 °C lower junction temperature at 2.0 A than the reference. Further, the thin GaAs samples revealed better light output degradation characteristics than the reference. For instance, the light output of the reference was degraded by 30.2% at 85 °C, whereas the thin GaAs samples were degraded by 20.1%–20.5%. Near-field images and emission profiles demonstrated that the metal-substrate samples suffered from no damage incurred during the VCSEL fabrication process.

Studying the light current characteristics of VCSEL by changing oxide confinement aperture

GaAs-based VCSELs with oxide-confined (OC) are performed by using fine selective radial “oxidation of AlAs-rich (AlGaAs) layers” from outside to the device axis leaving the central part unaffected. Such oxide apertures produced inside the cavities enhance the radial confinements related to current spreading and to a field that is optical altogether. A Modern design with a single fundamental mode is proposed to reduce threshold current operation to the extent of higher output by using the two OC VCSELs. Both of the oxide apertures were added to the node position of the resonator standing wave. Then, the diameters of together apertures can be adjusted independently giving VCSEL design an extra degree of freedom that allows optimization. It found that when both apertures had a radius of 4.2 µm, the low threshold current operation at a higher extent output is achieved with a single fundamental mode.

ESD tests on 850 nm GaAs-based VCSELs

Forward and reverse HBM, MM, CDM ESD tests have been performed on 850-nm VCSELs, together with EOS and overpower test. The physical analysis of the tested devices showed a variety of damages not easily correlated to the measured electro-optical degradations. The solution requires the detailed interpretation of the observed physical mechanism, by means of electron microscopy and device modelling.

The Influence of Imperfections and Absorption on the Performance of a GaAs/AlO $_{\rm x}$ High-Contrast Grating for Monolithic Integration With 980 nm GaAs-Based VCSELs

This paper discusses the influence of fabrication imperfections and absorption on high contrast grating (HCG) reflectivity and reveals that HCGs show considerable tolerance to both factors. A fully vectorial optical numerical model was used to design an HCG for use as the top mirror of a 980 nm GaAs-based vertical-cavity surface-emitting laser. Parameters providing a high degree of reflectivity were determined with special attention to optimizing the low refractive index layer.

Full 3D FDTD analysis of Electromagnetic Field in Photonic Crystal VCSEL

The effect of etch damage to the mode characteristics of photonic crystal vertical cavity surface emitting lasers was simulated in this paper. The devices simulated in this paper are 850-nm GaAs-based VCSELs with photonic crystal. And the devices were simulated by using finite difference time domain (FDTD) method. Limited to the computer resource, the top DBR was simulated only, and the traverse size was smaller than the real size. In order to highlight the impact of the etch damage, several kinds of light sources and photonic crystal structures were simulated separately, and each situation is calculated in the condition of ideal photonic crystal and photonic crystal with etch damage respectively. All parameters of device and light feature are referred to the real condition.

Single transverse mode control of VCSEL by photonic crystal and trench patterning

Single transverse mode control is achieved for multimode GaAs-based VCSEL by utilizing photonic crystal design and etched trench structure. Theoretical analysis is initially performed for photonic crystal design with various lattice constants and air holes diameter. The fabricated photonic crystal VCSEL with etched trench structure exhibits single mode output power of 0.7 mW, threshold current of 3.5 mA, slope efficiency of 0.10 W/A, and continuous single mode output spectrum throughout a wide operating current range. Comparison of typical oxide VCSEL, trench oxide VCSEL, and photonic crystal oxide VCSEL employing trench structure is presented. By combining photonic crystal and trench structure, single transverse mode operation of photonic crystal VCSEL can be much more strictly controlled.

Comprehensive uniformity analysis of GaAs-based VCSEL epiwafer by utilizing the on-wafer test capability

A comprehensive study of the uniformity of 850 nm VCSEL epiwafer grown by the MOCVD technique is presented. By utilizing the VCSEL planar structure, uniformity test is performed on-wafer directly, besides using the conventional photoluminescence technique. The VCSEL quantum wells are found to exhibit a peak emission wavelength of 839.5 nm. Also, the grown epiwafer is observed to exhibit a Fabry–Perot cavity resonance at 846.5 nm. Various VCSEL devices fabricated from the center to the edge of the VCSEL epiwafer show a similar trend towards the light–current and output spectral characteristics. However, the device existing near the epiwafer edge is observed to exhibit significantly different characteristics, which is attributed to the physical conditions of the device near the edge, and also the limitations of the epitaxial growth.

Physical Analysis of a Possibility to Reach the 1.30-μm Emission from the GaAs-Based VCSELs with the InGaAs/GaAs Quantum-Well Active Regions and the Intentionally Detuned Optical Cavities

Physical aspects of an operation of the GaAs-based InGaAs/GaAs quantum-well (QW) VCSELs with the intentionally detuned optical cavities have been considered in the present paper using the comprehensive three-dimensional self-consistent optical–electrical–thermal-gain simulation. In GaAs-based structures, very good DBR resonator mirrors and a very efficient methods to confine radially both the current spreading and the electromagnetic field with the aid of oxide apertures may be applied. It has been found using the above simulation that even currently available immature technology enables manufacturing the above devices emitting radiation of wavelengths over 1.20 μm. In particular, while the room-temperature 1.30-μm lasing emission is still beyond possibilities of the InGaAs/GaAs QW VCSELs, these structures may offer analogous 1.25-μm emission, especially for the high-power and/or high-temperature operation.

Investigation of data transmission characteristics of polarisation-controlled 850 nm GaAs-based VCSELs grown on (311)B substrates

The data transmission characteristics of polarisation-controlled 850 nm GaAs-based VCSELs grown on (311)B substrates are investigated and compared with those of VCSELs on (100) substrates. Large differences in the dependence of the BER on bias current and the power penalty between polarisation resolved and unresolved systems are observed in VCSELs on (311)B and (100) substrates. The beneficial effect of the polarisation stability of VCSELs on (311)B substrates is clearly demonstrated.