Suppression of Be diffusion in molecular‐beam epitaxy AlGaAs by the incorporation of In for heterojunction bipolar transistor applications

We report for the first time on the suppression of Be diffusion in molecular‐beam epitaxy Al0.1Ga0.9As by incorporating In into the epilayer. The minimum diffusion coefficient of Be‐doped Iny(Al0.1Ga0.9)1-yAs layers with a carrier concentration of 7×10¹⁹ cm^-3 and an InAs mole fraction of 0.07 grown at 600 °C was about 2×10^-15 cm²/s, which is five times smaller than that without In incorporation. The photoluminescence intensity of the layers drastically decreased above a value of y of 0.05, probably due to crystal degradation resulting from misfit dislocations. A heterojunction bipolar transistor with a 100 nm‐thick p⁺In0.055 (AlxGa1-x)0.945As base layer (Al graded composition x: 0 to 0.1, emitter area: 4×5 μm²) yielded a dc current gain of 27 at a collector current of 8 mA.