Substrate crystallinity and the performance of InP-based pseudomorphic high electron mobility transistors

We demonstrate a novel technique by which to measure the degree of crystalline perfection across semi-insulating InP substrates and show that the substrate perfection influences the crystallographic perfection and the electrical properties of subsequently deposited epitaxial layers. The substrate characterization technique is based on triple axis diffraction omega scans which are performed across the entire wafer area. Substrates with localized defective spots as well as overall substrate perfection are quantitatively measured. Pseudomorphic high electron mobility-type structures with strained In/sub 0.60/Ga/sub 0.40/As channels and nominally lattice-matched In/sub 0.52/Ga/sub 0.48/As buffer and supply layers were grown by molecular beam epitaxy and characterized by double and triple axis diffraction, Hall effect, and X-ray topography. Structures grown on high quality regions of the substrate exhibit sharper diffraction features and higher mobilities than those grown on low quality regions and we observe that there is a strong correlation between the level of diffuse scattering determined by triple axis diffraction and the channel mobility.