Compositionally graded C-doped In1-xGaxAs base in InP/InGaAs D-HBTs grown by MOCVD with low base sheet resistance and high current gain

MOCVD-grown carbon (C)-doped InGaAs layers using CBr₄ as a C source were investigated with the van der Pauw method and PL measurement. A hole concentration of as high as 7×10¹⁹ cm^-3 was obtained at a growth temperature of 385°C. However, PL intensity of the C-InGaAs depends on the growth temperature, and was weaker than that of Mg- or Zn-doped InGaAs at a range of over 1×10¹⁹ cm^-3. Furthermore, DC measurement of D-HBTs revealed that there existed a strict tradeoff between the current gain and base sheet resistance of C-InGaAs uniform-base D-HBTs. To break through the tradeoff, we have fabricated D-HBTs with 150-nm-thick strain-compensated graded-In_1-xGa_xAs-base (X=0.42⇒0.53). As a result, a current gain of 55 with a base sheet resistance of 480 Ω/□ was achieved