High-gain InGaP/GaAs HBTs with compositionally graded In/sub x/Ga/sub 1-x/As bases grown by molecular beam epitaxy

InGaP/GaAs single heterojunction bipolar transistors (SHBTs) with compositionally graded base have been successfully grown by solid source MBE using a GaP decomposition source. They were processed into 60/spl times/60 /spl mu/m/sup 2/ emitter contacts. The device characteristics of HBTs with In/sub x/Ga/sub 1-x/As graded bases (0/spl rarr/0.05, 0/spl rarr/0.1) are compared with non-graded base HBTs to investigate the optimum-grading profile. The average current gains of the non-graded base, the 5% graded base and the 10% graded base are 174, 321 and 342, respectively. To our knowledge, these current gains are the highest value ever reported in InGaP/GaAs HBTs with a compositionally graded base and with base sheet resistances of /spl sim/200 ohms/square. These high current gains at the high base doping used attest to the very high quality of the graded base HBT materials.