MONOLITHIC INTEGRATION OF RESONANT-TUNNELING DIODES AND HETEROJUNCTION BIPOLAR-TRANSISTORS ON PATTERNED INP SUBSTRATES

We report the successful fabrication of coplanar, monolithic integrate d circuits based on heterojunction bipolar transistors (HBTs) and reso nant tunneling diodes (RTDs). Molecular beam epitaxy growth of the int egrated device structure is performed on an InP wafer, which is patter ned by photolithography and dry etching prior to growth. The substrate pattern consists of pedestals, which support RTDs after postgrowth de vice fabrication, and a lower level which ultimately supports HBTs. In situ sensors for layer thickness (photoemission oscillations) and sub strate temperature (absorption-edge spectroscopy) play a critical role in controlling key growth and structural parameters for the HBT and R TD devices. Utilization of the photoemission oscillation sensor during deposition of the AlAs barrier layers of the RTD structure has enable d control of peak currents to a design tolerance of +/-20% for devices with current densities in the mid-10(4) A/cm(2) range. Implementation of proportional - integral - derivative control based on a transmissi on-mo de absorption-edge spectroscopy sensor has enabled regulation of the substrate temperature to a precision of +/-1 degrees C throughout deposition of the RTD/HBT structure. (C) 1998 American Vacuum Society .