this the bug?

src/14_doping_and_devices.md

@@ -63,9 +63,9 @@ $$
 However, the extra valance electron moves in the semiconductor's conduction band and not free space.
 Therefore, the electron's mass is the conduction band's effective mass. 
 Furthermore, the interactions between the electron and proton are screened by the lattice.
-As a result, we need to introduce the following substitutions: $m_e \to m_e^*$, $\epsilon_0 \to \epsilon\epsilon_0$.
+As a result, we need to introduce the following substitutions: $m_e \to m_e$, $\epsilon_0 \to \epsilon\epsilon_0$.
 We thus estimate the energy of the bound state created by the impurity:
-$$E = -\frac{m_e^*}{m_e \varepsilon^2} R_E = -0.01 \text{eV (in Ge)},$$
+$$E = -\frac{m_e}{m_e \varepsilon^2} R_E = -0.01 \text{eV (in Ge)},$$
 with Bohr radius $r_B = 4$ nm (vs $r_B = 0.5$ Å in Hydrogen).
 The electron is very weakly bound to the impurity!
 At room temperature (0.026 eV), the donor electron is easily thermally excited into the conduction band.