Metamorphic In/sub 0.53/Ga/sub 0.47/As/In/sub 0.52/Al/sub 0.48/As HEMTs on germanium substrates

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Abstract
We report for the first time the successful epitaxial growth and processing of high-performance metamorphic high electron mobility transistors (HEMTs) on Ge substrates, with a transconductance of 700 mS/mm and a saturation channel current of 650 mA/mm. To reduce parasitic capacitances due to the conductive substrate, a dry etch method based on CF/sub 4/ and O/sub 2/ reactive ion etching (RIE) is developed for selective substrate removal. Devices with 0.2 /spl mu/m gate length display an increase of the extrinsic cut-off frequency f/sub T/ from 45 GHz before, to 75 GHz after substrate removal, whereas the maximum oscillation frequency f/sub max/ increases from 68 GHz to 95 GHz. Based on this excellent rf performance level, in combination with the highly selective thinning process, we think that Ge as a sacrificial substrate is a promising candidate for the integration of thinned individual HEMTs with passive circuitry on low-cost substrates. This could result in low-cost advanced hybrid systems for mass-market millimeter wave applications.

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