Analog Computer Measurements on Saturation Currents, Admittances and Transfer Efficiencies of Semiconductor Junction Diodes and Transistors

Under the usual simplifying conditions, the solution of the diffusion equations at low current densities in junction diodes and transistors is straightforward, if a one-dimensional structure is assumed. In reality, however, such structures are three dimensional, with rotational symmetry round an axis. No useful solutions of such diffusion equations are known for these cases. An analog computer was designed, allowing for diffusion, space, and surface recombination in cases of rotational symmetry. With this computer, saturation currents of junction diodes and ac admittances and transfer efficiencies of transistors were obtained and represented by curves. Actual junction diodes were manufactured in three batches according to specifications in concordance with the computer curves. Comparing measurements of saturation currents and admittances of the three batches of diodes with computer results, yielded fair coincidence. Some unexpected features of the computer curves are that the ratios of saturation currents obtained from the analog computer and from one-dimensional solutions exceed unity and may for instance be as high as 2. Similar figures hold for ac admittances. Some choices of transistor dimensions, leading to high transfer efficiencies, are suggested by the computer curves.