= Esaki tunnel-diode experiment
{c}
{title2=1957–1958}
<Leo Esaki>'s 1958 report describes alloy-fabricated <germanium> <p-n junctions>, with <acceptor impurity> concentration $1.6\times10^{19}\,\mathrm{cm}^{-3}$ and <donor impurity> concentration approximately $10^{19}\,\mathrm{cm}^{-3}$. Its readout was the <current-voltage characteristic>: a forward peak occurred at $0.035\pm0.005\,\mathrm V$. The report says specimens could be reproduced; above $0.3\,\mathrm V$ the forward branch approximately followed the ordinary <Shockley diode equation>.<New Phenomenon in Narrow Germanium p-n Junctions by Leo Esaki>[New Phenomenon in Narrow Germanium p-n Junctions, p. 603, opening paragraph and Fig. 1; opening reproduced on slide 2 of the Trinity College Dublin lecture PDF]{ref}
In his 1973 lecture, <Leo Esaki> recalls an earlier junction whose strong room-temperature reverse conduction preceded a negative-slope forward segment revealed by cooling. Its estimated zero-bias width was about $200$ <ångströms> ($20\,\mathrm{nm}$), supported by <capacitance> measurements. Increasing <semiconductor doping> further made the negative slope visible across the measured <temperatures>, including room temperature. Thus preparation and <temperature> variation were experimental controls, not merely changes to a theoretical diagram. The low onset voltage argued against avalanche production of <Electrons> and <electron holes>; the <energy band> explanation connected the forward decline to loss of available final states.<Long Journey into Tunneling by Leo Esaki>[Long Journey into Tunneling, section II, printed pp. 120–122, Figs. 3–5; inspected institutional mirror at kapitza.ras.ru]{ref}
The historical readouts were junction <electric current> versus applied <electric potential difference> and a separate <capacitance> check; preparation and <temperature> were varied. The cited descriptions do not identify a meter model or give a complete wiring diagram.
For a modern repetition, measure junction voltage directly while stepping the supply and recording <electric current>, repeat both sweep directions, and compare temperatures and differently doped specimens. These are proposed controls, not a reconstruction of the historical apparatus. Lead <electrical resistance>, <Joule heating>, contact quality and voltage resolution can obscure the result. The <tunnel-diode load-line stability> calculation also predicts that an external <resistor> can make a negative-slope <operating point> inaccessible in a slow sweep. A jump in terminal readings then need not mean the underlying <current-voltage characteristic> is discontinuous.
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