Metamorphic 6.00 Å heterojunction bipolar transistors on InP by molecular-beam epitaxy

In this article we present results from heterojunction bipolar transistor (HBT) devices that were designed for low power consumption by taking advantage of the small bandgap of high-indium composition In0.86Ga0.14As in the base layer. These were grown by solid-source molecular-beam epitaxy. Both single- and double-HBT devices were grown and fabricated. The 6.00 A lattice parameter of these device structures was accommodated by first growing metamorphic, relaxed, linearly graded InxAl1−xAs buffers on semi-insulating InP substrates, grading from In0.52Al0.48As lattice-matched with InP at 5.87 A to In0.86Al0.14As at 6.00 A. The total thickness of each buffer was 1.2 μm or greater. These graded buffer layers developed the crosshatched morphology that is associated with the strain-relaxation process. The density of threading dislocations reaching the buffer surface was measured by EPD to be as low as 2×106 cm−2. Although this density is still more than an order of magnitude greater than that measured for latti...