Design and fabrication of wavelength tunable optoelectronic devices

Wavelength Division Multiplexing (WDM) is the key enabling technology for increasing the transmission capacity of optical fiber communication systems. Wavelength-tunable Vertical Cavity Surface Emitting Lasers (VCSELs) are potentially useful for WDM due to their ability to precisely control lasing wavelength and lasing channel spacing. The other key limitation to a dense WDM system is the receiving end since the linewidth of a single mode laser is much less than 1A. A Resonant Cavity Photodetector (RCP) with high quantum efficiency and good wavelength isolation can be employed, however, similar to VCSELs, the narrow linewidth of a RCP can be a potential disadvantage in transmitter to receiver wavelength matching. This disadvantage can be avoided by incorporating wavelength tunability, resulting in a more flexible device: the wavelength-tunable RCP.; This work focuses on developing wavelength tunable devices for both the transmitting and receiving end of a dense WDM system. Broad wavelength tunability is obtained using a vertical optical structure which incorporates a micromachined, electrostatically-movable, top mirror suspended above the semiconductor cavity by an air gap. This thesis describes various trade-offs among different optical cavity and air gap designs. Wavelength tunable VCSELs were demonstrated with a tuning range as large as 31nm multi-mode and 23nm single mode with submilliamp threshold current and a tuning voltage {dollar}<{dollar}20V. A dual function wavelength tunable VCSEL/RCP was demonstrated which can be used at both the receiving and transmitting ends of a dense WDM system. The device has over 20nm wavelength tuning range with threshold current {dollar}<{dollar}2mA when operated as a wavelength tunable VCSEL and linewidth {dollar}<{dollar}2nm when operated as a wavelength tunable RCP.; Despite their versatility, wavelength-tunable RCP/VCSELs suffer from linewidth and quantum efficiency trade-offs that plague traditional RCPs, since incorporation of the absorbing region inside the cavity results in a wider resonance linewidth and a reduced WDM system density. This intricate trade-off among speed, quantum efficiency, and linewidth can be avoided if an electrical gain region is added to the cavity. The resulting new device, a wavelength-tunable Resonant Cavity Phototransistor (RCPT), is capable of high quantum efficiency, narrow linewidth (hence small channel spacing), and high speed operation, making it an ideal device for WDM receivers.