The Study Of High Speed 850nm VCSEL

Vertical-Cavity Surface-Emitting Laser(VCSEL) has been studied widely due to its attractive properties such as high resonance frequency enabling being used in high speed communication, a near-circular output beam enabling easy coupling into optical fibers, lower optical-loss when transmitting light in fiber, high-temperature stability enabling reducing cost of adjusting the driver electronics operating parameters to the temperature changes, low-threshold and high-efficiency benefiting for energy conservation, straightforward fabrication of dense arrays in 2D, high reliability and easy packaging, and easy integrating with other optoelectronic device, etc. Driven by the ever increasing market-demand for green communication with high speed and low power, the high speed VCSEL is becoming one of the most important devices. So, in order to resolve the contradiction between speed and power, the mechanisms of VCSEL’s resonance and the factors limiting its speed should be researched intensively.The aim of this paper is to achieve the high speed VCSEL with its-3d B bandwidth higher than 10 GHz. The mechanisms of VCSEL’s resonance and the factors limiting its speed have been researched deeply in theory, including the resonance frequency, temperature, parasitic parameters RC, damping, and the characteristic of electrode structure, and so on. Lastly, the static and dynamic characteristics of the fabricated VCSEL with its-3d B bandwidth higher than 10 GHz, has been studied. The results of the fabricated VCSEL consisted with the theory and the simulation. The main work can be summarized as following:1. In theory, the mechanisms of VCSEL’s high speed modulation and the factors limiting its speed mainly included: relaxation resonance frequency, damping, and the parasitic circuit.The relaxation resonance frequency was the main limitations for its speed. From the derivation, it was found that the main limiting factors for relaxation resonance frequency are quantum-well differential gain and the photo lifetime. The parasitic RC was studied and the parasitic circuit was built. Through 2-port theory, the dynamic feature of the parasitic circuit and the microwave reflection feature of the electrode structure were studied.2. The important fabrication processes were studied including wet etching, wet nitrogen oxidation processes and BCB etching. The anisotropic rate of wet etching and wet nitrogen oxidation processes leaded to the aperture presenting ocular form, but it had almost no effect on the RC of the fabricated VCSEL. The mechanism of appearing glass-like residue when etching BCB was studied.3. Four different size VCSELs with one mesa and electrodes on double sides were fabricated. The static characteristics and modulation response of the devices were studied, while the later was our focus. The VCSEL’s-3d B bandwidth was higher than 10 GHz, almost equaling 12 GHz, and the measured bandwidth was limited by the measurement equipment, whose maximum bandwidth was just 10 GHz. It was found that when increasing the driving current, the-3d B bandwidth firstly increased to the peak value and then decreased, because the increasing carrier-leakage in the quantum well leading to smaller different gain when the temperature was higher. The experiment results consisted with the theory and the simulation.4. Through 2-port theory, the influence of the electrode structure with its electrodes on double sides on the dynamic measurement was studied. The relationship between the impedance and the device electrode structure was also studied. The amplitude reflection coefficient of the fabricated VCSEL electrode structure was 22%. Increasing the width of the signal line and reducing the thickness of the device could make impedance matching. When the thickness of the device was 100μm and the width of the signal line was 70μm, the impedance was ~50Ω. In order to enable easy fabrication, the impedance matching electrode structure whose electrodes on the same sides was further designed. The relationship between the impedance and electrode structure was also studied. The thickness of the BCB and the width of the signal line had the important influence on the impedance.5. The RC of the device was extracted and the parasitic circuit was built, whose-3d B bandwidth was higher than 10 GHz.