Measurement of the spot noise of germanium, gallium antimonide, gallium arsenide and silicon Esaki diodes

The spot (band-limited) noise of Ge, GaSb, GaAs and Si Esaki diodes was measured at 297°K for diodes having a peak current between 1 ma and 5 ma. The measurements were made at either 1 Mc or 30 Mc and at least one sample of each material was measured at a lower temperature (77°K or 188°K). The measured results are presented in terms of an equivalent noise current I
EQ
which, flowing in a thermionic diode, would produce the same noise as the Esaki diode at each measure point. At zero bias, I
EQ
was found in every case to equal the noise produced by a resistor having the same conductance as the diode and was, to a first approximation, related to the peak bias current and voltage, and the temperature. For small forward biases, I
EQ
was in reasonably good agreement with the value calculated from I
B
coth
(qV/2KT)
, where I
B
is the bias current. Many diodes showed a small inflection in I
EQ
near
\circ{I}_{B}
. In the negative resistance region, a peak of I
EQ
was observed for GaAs at 297°K and Si at 77°K. In the negative resistance, valley and second positive region, I
EQ
substantially exceeded I
B
. The bias current can be decomposed into a forward and reverse current by a linear combination of I
EQ
and I
B
. The forward current reached a peak near the peak of bias current and then declined to a value greater than the excess current in the valley. The reverse current declined rapidly from its value at zero bias and instead of tailing out often showed an inflection or anomalous peak. The noise figure and gain of a linear amplifier using Esaki diodes is strongly affected by the measure of noise
I_{EQ}/|- G_{D}|
. The diode materials were rank ordered according to this ratio with GaSb the quietest, followed by Ge, Si and GaAs. In all cases the measure of noise was reduced by cooling. For switching applications Esaki diodes are often biased in the first positive region, just before the peak current. There the relative magnitude of I
EQ
and I
B
determines the noise performance and GaAs was found the quietest at 297°K.