Heavily Carbon Doped Base InP/InGaAs Heterojunction Bipolar Transistors Grown by Two-Step Metalorganic Chemical Vapor Deposition

A novel growth procedure for realizing high hole concentrations in the C-doped base layers of InP/InGaAs heterojunction bipolar transistors (HBTs) is presented. The H out-diffusion behavior from the epi-layer in relation to the cap layer thickness is investigated in detail. A relatively thin n-InP cap layer is found to be nearly transparent to out-diffusion of H at a relatively high annealing temperature of 550° C and to act as a barrier to re-hydrogenation during re-growth at 450° C. Using this non-reciprocal feature of thin n-InP cap layers with respect to hydrogen permeability, hydrogen was annealed out from the base layer outside the growth chamber, and then the rest of emitter and cap layers were re-grown without significant re-hydrogenation. The fabricated HBT has a base current ideality factor close to unity, indicating that the re-growth procedure has no serious influence on the device characteristics. A small device with a base layer hole concentration of 2.5×1019 /cm3 has a maximum oscillation frequency (f max) of 170 GHz at J C=1.7×105 A/cm2.