Indium-Gallium-Arsenide and Germanium Tunnel Junctions

In0.53Ga0.47As tunnel junctions were fabricated towards use in tunneling field effect transistors which have shown promise as low-subthreshold-swing transistors. Tunnel junctions were fabricated with doping densities ranging from 1e19 /cm3 to 1e20 /cm3. Reverse tunneling current, the regime of operation in TFETs, was measured and modeled as function of doping density and electric field up to a current density of 1.5 mA/Ì_å_m2. High current density tunnel junctions are demonstrated as evidenced by forward bias peak current densities in the range 0.06 to 0.94 mA/Ì_å_m2, the latter comparable to the best reported results for In0.53Ga0.47As junctions. Tunnel junctions were also explored in Ge motivated by tunnel diode oscillator sensors. Germanium tunnel junctions were fabricated using two approaches: (1) rapid melt regrowth of Al-doped p+ Ge from an Al metal source into n+ Ge and (2) p+ Ga doping by diffusion from a Ga metal source, deposited by molecular beam epitaxy, into n+ Ge. The n-type dopant was P, introduced either via ion implantation or diffusion from spin-on diffusants. In the rapid melt regrown junctions, negative differential resistance characteristic was obtained with peak current density of up to 0.27 mA/Ì_å_m2 and peak to valley ratios of 1.1 1.23. In the diffusion based approach, p-type doping by Ga diffusion from a molecular beam epitaxy source was characterized as function of Ga flux and deposition time. Diodes fabricated using Ga as p-type, and P as n-type dopant, exhibited a backward diode behavior.