add diffusion length

.gitignore

@@ -2,3 +2,15 @@
 *.gz
 
 *.pdf
+
+*.aux
+
+*.fdb_latexmk
+
+*.out
+
+*.toc
+
+*.log
+
+*.fls

06_pn_junction_diode.tex

@@ -67,6 +67,13 @@ Or so simplify
     I_0 & = A q n_i^2 \left( \frac{D_n}{L_n N_A} + \frac{D_p}{L_p N_D} \right)
 \end{align}
 
+where we use the electron diffusion length $L_n$ and hole diffusion length $L_p$:
+\begin{alignat}{2}
+    L_n & = \sqrt{D_n\tau_n} & = W_p-x_p \\
+    L_p & = \sqrt{D_p\tau_p} & = W_n-x_n
+\end{alignat}
+
+
 Note that sometimes a non-ideality factor $n$ is used:
 \begin{equation}
     I  = I_0\left(\exp\frac{qV}{nkT}-1\right)