High-gain, low offset voltage, and zero potential spike by InGaP/GaAs δ-doped single heterojunction bipolar transistor (δ-SHBT)

We report on fabrication, characterization, and comparison of InGaP/GaAs single heterojunction bipolar transistors (SHBT´s) and heterostructure-emitter bipolar transistors (HEBT´s). The SHBT with a δ-doped sheet located at the E-B heterointerface (δ-SHBT) exhibits a common-emitter current gain as high as 410 and an extremely low offset voltage of 55 mV. Even though at the small collector current density of 1×10^-3 A/cm², the current gain is still larger than 20. Theoretical derivations show that the zero potential spike exists near the E-B junction under +1.5 V forward bias. However, an HEBT with a 700-Å narrow energy-gap emitter shows a small current gain and a collector current density due to the charge storage and bulk recombination effect. On the other hand, the increase of the CB capacitance in our δ-SHBT is very small as compared with conventional HBT´s