Molecular beam epitaxy growth of indium-rich [formula omitted] structures towards high channel conductivity for a high electron mobility transistor using a linearly graded buffer layer

Abstract

In x Ga 1 − x As In y Al 1 − y As heterostructure with both high electron mobility and high carrier concentration has been fabricated on InP substrate by molecular beam epitaxy. The measured electron mobilities were 11 491 cm 2/V · s at 300 K and 53 316 cm 2/V · s at 77 K for two-dimensional electron gas concentrations of 4.7 × 10 12 and 3.5 × 10 12 cm −2, respectively. The high electron mobility and concentration resulted from the dislocation-free, relatively thick (200 Å), and high indium content (80%) channel layer. The high-quality In x Ga 1 − x As channel layer was successfully grown at a growth temperature of 520°C after introducing a linearly graded In y Al 1 − y As buffer structure grown at a reduced growth temperature of 420°C. The cross-sectional transmission electron microscopy observation revealed that the dislocations generated due to a large lattice mismatch between In y Al 1 − y As and InP substrate were locked up in the middle of the graded buffer layer. We believe that we have achieved to date for this materials system the highest room-temperature conductivity (mobility times carrier concentration) of 5.4 × 10 16/V · s.