Energy Band Parameters of Germanium Indicated by Tunnel Diode Reverse Characteristics

Abstract

A precise method for analyzing the current—voltage characteristic of the reverse biased junction has permitted a direct observation of the voltage levels corresponding to the onset of tunneling into several energy subbands of germanium. The experimental technique involves fitting the experimental data to an equation of the form J = αV exp (−βV) derived from the calculations of Price, Radcliffe, and Kane. The onset of the tunneling interaction with each subband is noted as structure in the plots covering the reverse bias range. The values for EΓ₂ − R_L1 and EΔ₁ − E_L1, corresponding to the energy separations of the band minima, are found to be 0.152±0.005 and 0.208±0.008 eV, respectively, for slightly degenerate n‐type material at 4.2°K. The conduction energy bands are each found to move closer to the valence band level for increasing degeneracy by comparing the present data with the optical data of Pankove and Aigrain for the direct band gap. Energy spacing of the various conduction band minima is found to remain constant with increased electron concentration. Evidence for a ``tailing'' of the principal conduction band edge into low mass states is discussed for heavily doped n‐type material.