Horizontal Current Bipolar Transistor DC Performance at Cryogenic Temperatures

The DC current gain ( $\beta {)}$ of Si bipolar junction transistors (BJTs) reported so far decreases at cryogenic temperatures (CT), or shows a very limited improvement at best. For temperatures above 90 K, the Horizontal Current Bipolar Transistor (HCBT) behaves comparably to other published Si BJTs. However, cryogenic measurements of HCBT devices show a steep $\beta $ increase at temperatures below 90 K. We report a current gain of 85 at 300 K, a minimum $\beta $ of 31 at 90 K and an increase of $\beta $ to 66 at 17 K. The collector-emitter breakdown voltage ( ${\textit {BV}}_{\textit {CEO}}{)}$ measured around the peak $\beta $ varies only within 0.2 V over the examined temperature range. Additionally, the Early voltage ( ${V}_{A}{)}$ increases for temperatures below 50 K, improving the $\beta {V}_{A}$ product at 20 K by 2.2x as compared to 300 K, which makes the HCBT a potentially attractive technology for deep cryogenic applications. TCAD simulations of an equivalent Si BJT structure show that such considerable increase of $\beta $ at CT can be attributed to the interplay between incomplete ionization (II) of acceptors in the base and bandgap narrowing (BGN) in the emitter in a specific range of HCBT doping profiles.