Monolithic integration of resonant tunneling diodes and heterojunction bipolar transistors on patterned InP substrates

Abstract

We report the successful fabrication of coplanar, monolithic integrated circuits based on heterojunction bipolar transistors (HBTs) and resonant tunneling diodes (RTDs). Molecular beam epitaxy growth of the integrated device structure is performed on an InP wafer, which is patterned by photolithography and dry etching prior to growth. The substrate pattern consists of pedestals, which support RTDs after postgrowth device fabrication, and a lower level which ultimately supports HBTs. In situ sensors for layer thickness (photoemission oscillations) and substrate temperature (absorption-edge spectroscopy) play a critical role in controlling key growth and structural parameters for the HBT and RTD devices. Utilization of the photoemission oscillation sensor during deposition of the AlAs barrier layers of the RTD structure has enabled control of peak currents to a design tolerance of ±20% for devices with current densities in the mid-104 A/cm2 range. Implementation of proportional–integral–derivative control based on a transmission-mode absorption-edge spectroscopy sensor has enabled regulation of the substrate temperature to a precision of ±1 °C throughout deposition of the RTD/HBT structure.