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.

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