Fig. 3: Thickness and doping concentration of OBJTs.
a,b, Differential amplification of OBJTs with different base layer thicknesses (a) and tetrakis(hexa-hydropyrimidinopyrimidine)ditungsten(II) (W2(hpp)4) doping concentrations (b). c,d, Optical microscope images of different OBJT electrode designs (c) and corresponding device differential amplification curves (d). The solid lines denote experimental results and the hollow symbols denote TCAD simulation results. Scale bars, 100 μm. The device has a base thickness of 20 nm with 1 wt% W2(hpp)4 doping concentration. e, Normalized differential amplification as a function of effective base width and doping. The effective base width is the base thickness minus the space charge length (2LSCL is approximately 10 nm determined from TCAD simulation and electrical characterization). The differential amplification was taken at a base current of 10−5 mA, for which there is a good agreement between the TCAD and experiment results. The error bars denote the standard error of the mean by averaging over five devices prepared in a single run. The red curve is a coth fit with minority diffusion length of 50 nm. f, TCAD-simulated hole current density as a minority carrier (top) and electron current density (bottom) in the n-doped base layer.
