Dopant incorporation in GaAs and AlGaAs grown by MOMBE for high speed devices

Continued improvement in GaAs/AlGaAs device technology requires higher doping levels, both to reduce parasitics such as source resistances, and to enhance speed in devices such as the heterostructure bipolar transistor (HBT). In this paper we will discuss doping issues which are critical to high speed performance. In particular, we will focus on doping of GaAs and AIGaAs using carbon as the acceptor and Sn as the donor. Due to the unique growth chemistry of metalorganic molecular beam epitaxy (MOMBE), both of these impurities can be used to achieve high doping levels when introduced from gaseous sources such as trimethylgallium (TMG) or tetraethyltin (TESn). Comparison of SIMS and Hall measurements show that both elements give excellent electrical activation to 1.5 × 10¹⁹ cm³ for Sn and 5 × 10²⁰ cm⁻³ for C. More importantly, we have found that both impurities canbe used to achieve high quality junctions, indicating that little or no diffusion or segregation is occurring during growth. Because of the excellent incorporation behavior of these dopants, we have been able to fabricate a wide range of devices including field effect transistors (FETs), high electron mobility transistors (HEMTs), and Pnp HBTs whose performance equals or exceeds that of similar devices grown by other techniques. In addition to these results, we will briefly discuss the key differences in growth kinetics which allow such abruptness and high doping levels to be achieved more readily in MOMBE than in other growth techniques.