Suppression of Beryllium Diffusion by Incorporating Indium in AlGaAs for HBT Applications using Molecular Beam Epitaxy

We developed a molecular beam epitaxy technique to suppress Be diffusion by incorporating In in the AlGaAs epilayer. Diffusion coefficients of Be-doped In y (Al0.1Ga0.9)1-y As (p: 7×1019 cm-3) grown at 600°C were reduced from 1×10-14 cm2/s to 2×10-15 cm2/s when the InAs mole fraction y was increased from 0 to 0.07, indicating that compressive stress in the epilayer caused by incorporating In plays an important role in suppressing Be diffusion. We fabricated a heterojunction bipolar transistor with a 100-nm-thick p+-In0.055(Al x Ga1-x )0.945As base layer (x: 0 to 0.1), and obtained a DC current gain of 27.