Looking at the manufacturer's spice model for the Rohm 2SC4713 BJT, I was struck by the high reverse \$\beta\$:

  • BR=123.13

Is a value this high believable or an obvious misprint? Typically BJTs have a reverse \$\beta\$ value somewhere in the range 1 to 10.

Possibly the best way to find out is buy a device and test it!

  • 2
    \$\begingroup\$ Seems hard to believe, but there are transistors with reverse betas in the ~250 range. \$\endgroup\$ – Spehro Pefhany Mar 7 at 4:24
  • 4
    \$\begingroup\$ Zetex (now Diodes, Inc) alone has quite a few with high reverse betas. The FMMT497, FZT1047A/48A/49A/51A. FZT1147A, FZT788B/89A/90A, FZT948/68, and more. It may not be a misprint. The FZT1047A shows BF=550 and BR=400 and the FZT788B shows BF=770 and BR=350!! \$\endgroup\$ – jonk Mar 7 at 5:05
  • \$\begingroup\$ @jonk I still think of Zetex as the new name for Ferranti Semiconductors! \$\endgroup\$ – user_1818839 Mar 7 at 12:00

Heterojunction bipolar transistors (HBTs) feature high reverse current gains. The HBT are devices that have in their base region the semiconductor with a different bandgap than in the other regions. For example, Infineon's BFP840FESD (citing the product datasheet:

The BFP840FESD is a discrete RF heterojunction bipolar transistor (HBT) with an integrated ESD protection suitable for 5 GHz band applications

), well, Infineon's BFP840FESD can have a BR=108 with BF=946.1, as one can see in the BFP840FESD model:

GBJT 22 11 33 44 ID="Q1" TNOM=25 IS=2.009e-016 BF=946.1 &
    NF=1 VAF=300 IKF=0.1993 ISE=6.26e-015 NE=2 BR=108 &
    NR=1 VAR=1.288 IKR=0.0007328 ISC=8.126e-016 NC=2 &
    RB=17 IRB=0 RBM=1 RE=0.05 RC=4.145 XTB=-2.276 &
    EG=1.11 XTI=0 CJE=1.3e-013 VJE=0.6 MJE=0.5 TF=7.494e-013 &
    XTF=17.49 VTF=0.5295 ITF=1.025 PTF=4.667 CJC=1.1e-014 &
    VJC=0.67 MJC=0.88 XCJC=0.4894 TR=1.793e-009 CJS=3e-013 &
    MJS=0.5 VJS=0.7 FC=0.352 KF=6.4e-012 AF=1.44

Of all the HBT flavors with this feature (abrupt junction, graded junction, graded base, double HBT), this feature is most pronounced in the double heterojunction bipolar transistor: BR ~ BF. The double HBT is a symmetrical device like unipolar transistors, although the HBT is definitely bipolar using both majority and minority carriers for the device operation. See the slides of the Purdue University course ECE606, Solid State Devices, Heterojunction Bipolar Transistor, pages 20 and 24.

Disclaimer: I have not found any evidence in the documentation indicating that the 2SC4713K is an HBT device.

  • 1
    \$\begingroup\$ Looking at the datasheet and comparing with e.g., the Infineon device, it does look consistent with a HBT - apart from the high \$\beta\$R, the breakdown voltages are fairly low (esp. E-B), and the fT is decent. \$\endgroup\$ – user1998586 Mar 8 at 5:07

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