The above video shows the germanium transistor through three temperature ranges. At room temperature current gain is 183, leakage current is 851 milliamps. At 120° Fahrenheit current gain is 28, leakage current is 1,569 milliamps. With the germanium transistor cooled down the current gain is 159, and the leakage current is 38 milliamps, near zero.

Why is temperature important when using Germanium transistors?

Germanium transistors have a typical operating temperature range of -65C/-85F to 75C/167F. Their use in audio applications is limited at higher temperatures because leakage current increases significantly, which can lead to thermal runaway.

Germanium transistors have a much smaller bandgap 0.66 eV vs silicon 1.12 eV. This means less energy is needed to excite an electron from the valence band to the conduction band, making it more susceptible to thermal energy.

We have found during testing bringing down the temperature of the Geranium transistor, the leakage current drops to nearly zero, which puts it on the same playing field as the silicone transistor’s stability.

Bringing Down the temperature and stabilizing the transistors also helps with biasing during assembly.

The FreezeZone pedal achieves this by bringing down the Germanium transistor's temperature, with an internal refrigeration unit.