Effects of wet-oxidation treatment on Al0.45Ga0.55As/GaAs graded-like superlattice-emitter bipolar transistor with low turn-on voltage
Journal
Applied Physics Letters
Journal Volume
80
Journal Issue
18
Pages
3436-3438
Date Issued
2002-05
Author(s)
Abstract
We report an AlxGa1-xAs/GaAs heterojunction bipolar transistor (HBT) with a high Al mole fraction of x=0.45. A digital graded superlattice emitter, forming a step-wise graded composition, is used to smooth out the potential spike resulting from a large conduction-band offset. HBT's with such a digital graded emitter as a passivation layer exhibit a small offset voltage of 55 mV, a low turn-on voltage of 0.87 V and a current gain as high as 400. Effects of wet-oxidation treatment on fabricated HBT's are also investigated. Experimental results reveal that the studied HBT's exhibit reduced collector currents at a fixed base current in the early stage of the wet-oxidation treatment. However, better surface passivation and higher current gain are available after an appropriate wet-oxidation treatment is used to reduce base current. We qualitatively modeled these behaviors by introducing a concept of built-in field along the graded emitter. © 2002 American Institute of Physics.
SDGs
Type
journal article