High speed, low driving voltage vertical cavity MQW modulators for optical interconnect and communication

The circuit-switched public network infrastructure is being stretched by the incredible growth of the internet and data transmission and limits of scaling set by Moore's law and the shortcomings of high speed electrical interconnects, which have high power consumption, poor signal integrity due to cross talk, large signal skew and jitter. Vertical cavity multiple quantum well (MQW) optical modulators, which offer high bandwidth, high contrast ratio, low power consumption and easy two-dimensional integration with silicon electronics, offer the promise to relieve the bottleneck in dense interconnect and data communication. The devices consist of MQWs in a Fabry-Perot cavity configured as p-i-n diodes. The absorptive characteristics of the MQW region can be modified through a field induced absorption change, known as the quantum-confined Stark effect (QCSE). This absorption change modulates the optical reflection of the device.; High-speed modulation and low driving voltage are the keys for the device's practical use. At lower optical intensity operation, the ultimate limitation in speed will be the RC time constant of the device itself and the parasitics of the microwave probe pads. At high optical intensity, the large number of photo generated carriers in the MQW region will limit the performance of the device through photo carrier related voltage drop and exciton saturation. The focus of this thesis is the optimization of MQW material and cavity design, minimization of the parasitic capacitance of the probe pads for high speed, low voltage and high contrast ratio operation. The design, fabrication and high-speed characterization of devices of different sizes, with different bias voltages and termination resistor are presented. We demonstrated a modulator, with a high contrast ratio of 11dB, a small driving voltage of 3.5V and an f_3dB bandwidth greater than 18GHz. If the device is used as a high-speed photodetector, it has high quantum efficiency of 95% and an f_3dB bandwidth greater than 10GHz. Carrier dynamics under ultra-fast laser excitation and high-speed photocurrent response are also investigated.