Optical control of gallium arsenide and indium phosphide-based HBT oscillators.

Abstract

This thesis is primarily concerned with the development of heterojunction bipolar transistor (HBT) based devices and circuits for the conversion of a microwave signal from optical to electronic form. Three schemes to allow light access in HBTs have been investigated: (1) HBTs with annular emitter metalizations which allow light to pass through a hole in center of a circular emitter contact, (2) self-aligned HBTs with transparent indium-tin-oxide (ITO) emitter contacts in which light passes directly through the emitter contact, and (3) HBTs with integrated optical waveguides in which light is delivered via a waveguide directly into the absorption region of the device. With the ring-emitter HBT, device cutoff frequencies were $f\sb{T}$ = 11.7 GHz and $f\sb{max}$ = 5.8 GHz. Hybrid monolithic HBT oscillators operating at 2.65 GHz were constructed and optical control experiments were performed. An optical frequency tuning range of 5 MHz and an optical injection locking range of 6 MHz were observed. In these devices, the high frequency response was limited due to the high capacitances resulting from the large emitter area required for the ring emitter and also by the non-self aligned nature of the base metalization. The transparent emitter contact HBT used a standard multi-finger emitter design with a fully self-aligned base metalization. GaAs/Al$\rm\sb{.25}Ga\sb{.75}$As ITO-HBTs were fabricated and demonstrated cutoff frequencies of $f\sb{T}$ = 22 GHz and $f\sb{max}$ = 18 GHz. Optically controlled HBT oscillators operating at 5.68 GHz exhibited an optical tuning range of 25 MHz and an optical injection locking range of 2.5 MHz. The third HBT technology allows direct light input via an optical waveguide. This method allows the HBT to be fabricated using fully self-aligned low resistance metal contacts along with any desired performance enhancements features. Fabricated $\rm In\sb{.53}Ga\sb{.47}As/In\sb{.52}Al\sb{.48}As$ waveguide-HBTs demonstrated cutoff frequencies of $f\sb{T}$ = 32 GHz and $f\sb{max}$ = 48 GHz. Optically controlled MMIC oscillators operating at 13.9 GHz were fabricated. They exhibited an optical tuning range of 100 MHz and an optical injection locking range of 0.5 MHz. Optical waveguide modulators based on the blockaded reservoir and quantum well electron transfer (BRAQWET) structure were also investigated. Detailed studies of BRAQWET structures revealed that a single quantum-well intensity modulator could be made just as efficient as a multiple period device, but with a lower capacitance. Fabricated GaAs-based waveguide modulators suitable for use with 850 nm light were shown to have high contrast ratios with RC limited 3dB bandwidths of $f\sb{\rm 3dB}$ = 20 GHz.