Motivated by the stringent material requirements that low noise FET’s place upon underlying buffer layers, the electrical properties of unintentionally doped layers of GaAs grown by MBE have been investigated. A relatively shallow acceptor (0.027 eV) with a room temperature concentration of 2×1014 cm−3 is generally characteristic of undoped material presently grown by a number of laboratories involved in MBE. During experimental investigations, undesirable system configurations leading to higher background doping levels were identified. These configurations include BeO/Ta film substrate heaters (n?6×1016 cm−3), fused quartz/Ta film substrate heaters (n?2×1015 cm−3) and hot stainless steel fixtures illuminated by the Ga oven (p?1016 cm−3).
Molecular beam epitaxy has been used to grow good quality films of InGaAsP on InP substrates. The films have been characterized using infrared absorption, electroreflectance, x-ray diffraction, reflection electron diffraction, and Hall measurements. Lattice matching was achieved and room-temperature mobilities up to 4600 cm2 V−1 s−1 were measured.
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