Base–collector leakage currents in circular geometry InGaP/GaAs double heterojunction bipolar transistors

Abstract

Circular geometry InGaP/GaAs double heterojunction bipolar transistors with spacings of 94.5, 44.5, 19, 10.5 and 5.5 µm between the base metal and emitter mesa were fabricated and characterized. The measured Gummel plots showed a current gain of 50 for the 94.5 µm device. As the spacing decreases to 5.5 µm, the base current increases due to the extrinsic base surface recombination current at V BE = 0.9 V thus reducing the current gain to a value of 10. It was found that the use of Ti/Au over Au/Zn/Au base metallization schemes eliminates this recombination current component of the base thereby improving the current gain significantly to 100. With a novel scheme employed here termed the δ + -layer composite collector structure, the collector leakage current was investigated.

n‐Doped InGaP Nanowire Shells in GaAs/InGaP Core–Shell p–n Junctions

“…The change in current density under forward and reverse bias affects the rectifying behavior of the junction resulting in a rectification ratio >100 for the nid‐sample at absolute bias of | V | = 1 V. But, even for this sample the current blocking under reverse bias is poor: a reverse current density of J ≈ 0.02 A cm −2 at bias V = −1 V was measured and the reverse saturation current density was estimated from the forward J – V characteristics as J 0 = 1.5 · 10 −5 A cm −2 . In planar GaAs/InGaP base emitter junctions with an emitter doping concentration N D ≈ 3 · 10 17 cm −3 , J 0 is much smaller and is in the range of 10 −18 A cm −2 . As the doping concentrations in the base and emitter of the analyzed NW are smaller, compared with the planar device, and the saturation current densities exceed those in the planar system by many orders of magnitude, additional transport mechanisms are considered.…”