Thermal voltage of Ge diode

Question

What is the thermal voltage of a Ge diode?I know for a silicon diode is about 26mV at room temperature.

I have this circuit:

^{simulate this circuit – Schematic created using CircuitLab}

and a set of equation where X = Current through the diodes , Y = Voltage drop of Si diode and Z = Voltage drop of Ge diode:

x = (3-y-z)/1000

x = (10^-12)*(e^(y/0.026)-1)

x = (10^-9)*(e^(z/Vt(Ge))-1)

and I need it (at room temperature) so help really appreciated.

Answer 1

The thermal voltage does not depend on the semiconductor material; it's simply

$$V_T = \frac{kT}{q},$$

where \$k\$ is the Boltzmann constant, \$k = 1.380649 × 10^{-23}\ \mathrm{J}·\mathrm{K}^{-1},\ T\$ is the temperature, and \$q\$ is the electron charge, \$q=1.602176634 × 10^{-19}\ \mathrm{C}.\$

At 25 °C, this works out to approximately 26 mV, and does not depend on material.