Tunnel Mechanisms and Junction Characterization in III-V Tunnel Diodes

Via a study of alloy tunnel diodes on GaAs: Zn substrates, we conclude that at high substrate doping levels, $p\gtrsim 5\times {10}^{19}$ ${\mathrm{cm}}^{-3\mathrm{}}$, average-barrier tunneling predominates, whereas at lower substrate dopings, $p\lesssim 1.3\times {10}^{19}$ ${\mathrm{cm}}^{-3\mathrm{}}$, impurity-assisted tunneling predominates. The photosensitive features of the tunneling characteristics in units made on the more lightly doped substrates permit us to identify both elastic and inelastic resonant ("two-step") tunneling processes associated with Au-Ge traps in the space-charge region. A summary of the predictions of a microscopic theory of resonant tunneling is presented and used to interpret both our own data and those already extant in the literature. The qualitative features of the predictions of this theory permit us to characterize defect structures and optical-phonon energies in III-V mixed-crystal alloy diodes on ${\mathrm{Ga}}_{1-x}{\mathrm{Al}}_x\mathrm{As}$, $\mathrm{Ga}{\mathrm{As}}_{1-x}{\mathrm{P}}_x$, and ${\mathrm{In}}_{1-x}{\mathrm{Ga}}_x\mathrm{P}$. This characterization indicates that in ternary crystals whose binary components exhibit appreciable lattice mismatch, alloy regrowth introduces numerous additional defects, and in some systems, like ${\mathrm{In}}_{1-x}{\mathrm{Ga}}_x\mathrm{P}$, even the introduction of high acceptor densities disorders the crystal lattice. Such defects cause pronounced minima near zero bias in the tunnel conductance.