Elimination of Current Blocking in Ternary InAlAs-InGaAs-InAlAs Double Heterojunction Bipolar Transistors

Molecular beam epitaxy-grown wafers are used to fabricate all ternary In
_0.52
Al
_0.48
As-In
_0.53
Ga
_0.47
As-In
_0.52
Al
_0.48
As double heterojunction bipolar transistors (DHBTs) with knee voltages of less than 1 V, showing no current blocking characteristic even at current densities of 200 kA/cm
²
. A set of wafers with a judicious combination of doping interface dipoles and composite collector designs were grown, and devices with a wide range of emitter areas from 20 × 20 down to 1 × 5 μm
²
were fabricated to investigate the effects of the different epitaxial and geometrical design tradeoffs that culminated in an optimum design that is able to achieve high breakdown and high current gain without introducing current blocking. Despite the use of a heavy dipole doping of 4 × 10
¹⁸
cm
^-3
, a breakdown voltage BV
_CEO
of 5.8 V at 0.2 kA/cm
²
is achieved at room temperature. We believe this to be the first demonstration of an all-ternary large band gap InAlAs-InGaAs-InAlAs DHBTs with no current blocking up to a high current density of 200 kA/cm
²
. These new DHBTs that use only ternary alloys may lead to simplified device growth and fabrication options and give deeper understanding of the design tradeoffs in these structures.