Graded-GaAs/sub 1-x/P/sub x/ base in heterojunction bipolar transistors with InGaP emitters

We have fabricated the graded-GaAsP base HBTs with InGaP emitters for the first time. It was confirmed that heavy carbon-doping into GaAsP, as well as GaAs, could be realized by using MOCVD. The measured current gain was as high as over 100 at a collector current density (J/sub c/) of 3/spl times/10/sup 4/ A/cm/sup 2/. Furthermore, compared with the uniform-GaAs base HBTs, current-gain enhancement due to the built-in field in the base of the graded-base HBTs was also confirmed in a range of J/sub c/=1/spl times/10/sup 2/ A/cm/sup 2/ to 3/spl times/10/sup 4/ A/cm/sup 2/.