Control of Be diffusion in AlInAs/GaInAs heterostructure bipolar transistors through use of low‐temperature GaInAs

Low‐temperature (LT) GaInAs has been used to inhibit the diffusion of Be from the base to emitter in Npn AlInAs/GaInAs/GaInAs heterostructure bipolar transistors (HBTs) grown lattice matched to InP substrates by molecular‐beam epitaxy (MBE). A series of Be planar‐doped spikes (1.0–0.017 monolayers) were grown in LT GaInAs (over a temperature range of 225–445 °C as compared to normal growth at 500 °C) and it was determined by secondary‐ion mass spectroscopy (SIMS) that the Be full width at half‐maximum decreased by a factor of 3 for LT GaInAs grown below 350 °C. A series of LT GaInAs spacers of varying thicknesses (up to 150 Å) and Be dopings (2 × 10¹⁸–1 × 10²⁰ cm⁻³) were grown at 300 °C and placed at the emitter‐base junction of Npn HBTs. The optimum spacer configuration as determined by Be penetration into the AlInAs emitter, and rf performance, was with a LT GaInAs spacer of 150 Å and Be doped at 2 × 10¹⁸ cm⁻³ producing no observable (determined by SIMS) Be penetration into the emitter and an f_max of 73 GHz and f_t of 110 GHz.