Self-alignedIn0.52Al0.48As/In0.53Ga0.47As heterojunction bipolar transistors with graded interface onsemi-insulating InP grown by molecular beam epitaxy

A self aligned In_0.52Al_0.48As/In_0.53 Ga_0.47As double heterojunction bipolar transistor (HBT) with a graded heterointerface has been grown by molecular-beam epitaxy (MBE) and tested. The DC characteristics of HBT structures with a compositionally graded junction using a linear graded In_0.53Ga_0.47-xAl_xAs between two ternary layers were investigated. Typical quaternary graded devices with an emitter dimension of 50×50 μm² exhibited a current gain as high as 1260, as compared to 800 for abrupt devices, at a collector current density of 2.8×10³ A/cm²