Fabrication of Reduced Area InGaAs/InP and DHBT Devices

We have developed a fabrication procedure for reduced area InP/InGaAs based HBT and DHBT devices using a process involving both wet chemical and ICP plasma etching. Optical emission spectroscopy was used for end-point detection during plasma etching. We studied the effect of scaling down the base layer thickness as well as the device geometry on the dc and microwave characteristics. A 2x4 microns sup 2 device had a peak f sub t and f sub max of 160 and 155 GHz, respectively. When the emitter area was reduced to 1.2x3 microns sup 2, the f sub t remained about the same, around 160 to 170 GHz. However, the f sub max showed a substantial increase from 155 to 200 GHz for the DHBT and 280 GHz for the HBT. This improved microwave performance is due to reduced parasitics, such as C sub bc. The 1.2x3 microns sup 2 devices are attractive for high-speed circuit applications, since the microwave performance peaked at 5 mA, as opposed to 10 mA for the 2.4 microns sup 2 device. Furthermore, the f sub 6 and f sub max of the DHBT device were both above 150 GHz at 3 mA, which is a desirable operating current for a circuit.