Novel Delta-Doped InAlGaP/GaAs Heterojunction Bipolar Transistor

The first successful demonstration of a delta-doped InAlGaP/GaAs heterojunction bipolar transistor (HBT) is reported. A comparison to a baseline InAlGaP/GaAs HBT without a delta-doping layer is made. Both of these devices exhibit near-ideal current gain (beta) versus the collector current (
I

_C
) characteristics (i.e., beta independent of
I

_C
) at high currents. The delta-InAlGaP/GaAs HBT exhibits a 40% reduction in offset voltage (
V

<sub>CE,

offset</sub>
) and a 250-mV reduction in knee voltage (
V

_k
) without sacrificing beta compared with the baseline InAlGaP/GaAs HBT. At a higher
I

_C
, the decrease in beta of the InAlGaP/GaAs HBTs with increasing temperature is significantly smaller than the corresponding effect measured in the formerly reported GaAs-based HBTs. The rather temperature-insensitive characteristics of these two InAlGaP/GaAs HBTs originate from their large valence-band discontinuity (Delta
E

_V
) at the emitter-base (E-B) junction. Furthermore, at intermediate base current
I

_B
levels (0.4-1.6 mA),
V

<sub>CE,

offset</sub>
falls as
I

_B
increases, which is a trend contrary to that of most HBTs in the literature. Finally, the experimental dependence of
V

<sub>CE,

offset</sub>
on temperature,
I

_B
, and the effective barrier height at the E-B junction is explained with reference to an extended large-signal model.