Study of direct current characteristics of carbon-doped GaInP/GaAs heterojunction bipolar transistor grown by solid source molecular beam epitaxy

摘要

This article reports the dc characteristics of a GalnP/GaAs heterojunction bipolar transistor (HBT) with carbon-doped GaAs base layer grown by solid source molecular beam epitaxy using carbon tetrabromide (CBr_4) as p-type dopant precursor. Hydrofluoric acid (HF) was used to passivate the GaInP/GaAs HBTs. At base bias voltages below 0.9 V in the Gummel plot, the base current of large area devices after HF passivation, was greatly reduced indicating that the extrinsic base surface recombination current was significantly reduced. After HF passivation, detailed dc characterization of the device performance within the temperature range of 300-380 K was carried out, and the carrier transport properties were investigated. The base current and collector current ideality factors at 300 K were 1.12 and 1.01, respectively. This indicates that a space charge region recombination current is insignificant in the base. From the temperature dependent Gummel plot, the activation energies of the collector current and base current were obtained. For the collector current, the activation energy is 1.4 eV, which is close to the band gap of the GaAs base. This indicates that the collector current is determined by the drift-diffusion process. For the base current, the activation energy is also 1.4 eV, indicating that band-to-band recombination plays a dominant role in the base current. No trap-related recombination was observed in the base and collector currents, which further indicates the good base material quality in the HBT structure. The current gain versus collector current characteristics at different temperatures were also investigated and analyzed.