OPTICAL TUNING BEHAVIOR OF AL0.25GA0.75AS GAAS HBT OSCILLATORS WITH TRANSPARENT ITO EMITTER CONTACTS/

Optical tuning experiments were performed on an Al0.25Ga0.75As / GaAs HBT oscillator operating at 6 GHz. The HBT was fabricated with a trans parent emitter ohmic contact made of indium-tin-oxide (ITO) to allow l ight input through the top of the device. Under direct illumination of the base and base-collector depletion regions, optical tuning was obs erved with an increase in oscillation frequency of rip to 25 MHz. The observed increase in frequency is attributed to a shift in resonance d ue to a decrease in the base-emitter-junction capacitance of the HBT u nder optical illumination. This effect is verified using detailed devi ce and circuit modeling techniques. (C) 1995 John Wiley & Sons, Inc.