diff --git a/06_pn_junction_diode.tex b/06_pn_junction_diode.tex
index 6d879fa222a4a48c60efa0330234ebe1eaa68ca9..965334f656e5740d07dfb31a965a7410439b8525 100644
--- a/06_pn_junction_diode.tex
+++ b/06_pn_junction_diode.tex
@@ -67,6 +67,11 @@ 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}
+Note that sometimes a non-ideality factor $n$ is used:
+\begin{equation}
+ I = I_0\left(\exp\frac{qV}{nkT}-1\right)
+\end{equation}
+
\subsection{PN junction reverse bias}
When applying a reverse bias, the depletion region gets wider and the electric field increases.
diff --git a/07_diode_applications.tex b/07_diode_applications.tex
new file mode 100644
index 0000000000000000000000000000000000000000..ce3bf4ba757a7320dbd960359c108e8d8199c2fc
--- /dev/null
+++ b/07_diode_applications.tex
@@ -0,0 +1,129 @@
+\section{Diode applications}
+\subsection{Small signal}
+If $i\ll I$ and $v\ll V$, then we can use the small signal approximation.
+\begin{equation}
+ \begin{split}
+ I+i &= I_0\left(\exp\frac{q(V+v)}{kT}-1\right) \\
+ &=I_0\left(\exp\frac{q(V)}{kT}\exp\frac{q(v)}{kT}-1\right)\\
+ &\approx I_0\left(\exp\frac{q(V)}{kT}\left(1+\frac{qv}{kT}\right)-1\right)\\
+ &= I_0\left( \exp\frac{qV}{kT} - 1 \right) + I_0 \left( \exp\left(\frac{qV}{kT}\right)\frac{qv}{kT} \right)
+ \end{split}
+\end{equation}
+
+Which gives us the smallsignal current
+\begin{align}
+ i & = \frac{q\left(I+I_0\right)}{kT}v = g_d v \\
+ g_d & = \frac{q\left(I+I_0\right)}{kT}
+\end{align}
+
+
+\subsubsection{Capacitances of small-signal model}
+\begin{figure}[h]
+ \centering
+ \caption*{Small signal model for diode}
+ \begin{circuitikz}
+ \draw (-3,2) to [Do] (-3,0);
+ \draw[->] (-2,1) -- (-1,1);
+ \draw (0,0) to [R,l=$g_d$] (0,2);
+ \draw (2,0) to [C,l=$C_j$] (2,2);
+ \draw (4,0) to [C,l=$C_d$] (4,2);
+ \draw (0,0) to [short] (4,0);
+ \draw (0,2) to [short] (4,2);
+ \draw (2,2) to [short] (2,2.5);
+ \draw (2,-0.5) to [short] (2,0);
+ \end{circuitikz}
+\end{figure}
+\begin{align}
+ C_j & = \frac{C_{j0}}{\sqrt{1-\frac{V}{\phi_B}}} \\
+ C_d & = \frac{q}{kT}\tau_T I \\
+ \tau_T & \equiv \text{equivalent transit time of carriers}
+\end{align}
+Where $C_j$ dominates in reverse bias and small forward bias,
+and $C_d$ dominates in large forward bias ($V>\frac{\phi_B}{2}$).
+
+
+\subsection{Large signal}
+\subsubsection{Rectifier}
+This is pretty much trivial.
+\begin{center}
+ \begin{circuitikz}
+ \draw (0,-2) to [sV,l=$V_{in}$] ++(0,4)
+ to [short] ++(2,0)
+ to [Do,v=$V_D$] ++(0,-2)
+ to [R,l=$R_L$,v=$V_o$] ++(2,0)
+ to [Do] ++(0,-2)
+ to [short] (0,-2);
+ draw (4,0) to [Do] ++(0,2)
+ to [short] ++(-2,0);
+ \draw (2,-2) to [Do] ++(0,2);
+ \draw (4,0) to [Do] ++(0,2)
+ to [short] ++(-2,0);
+ \end{circuitikz}
+\end{center}
+\begin{equation}
+ V_o = V_{in}-2V_D
+\end{equation}
+
+\subsubsection{Voltage regulator}
+\begin{center}
+ \begin{circuitikz}
+ \draw (0,0) to [V,v<=$10\pm1\ V$] (0,8)
+ to [short] ++(2,0)
+ to [R,l=$R_1$] ++(0,-2)
+ to [short] ++(0,-2)
+ to [Do] ++(0,-1)
+ to [Do] ++(0,-1)
+ to [Do] ++(0,-1)
+ to [short] ++(0,-1)
+ to [short] (0,0);
+ \draw (2,5) to [nos] ++(2,0)
+ to [R,l=$R_2$] ++(0,-5)
+ to [short] (0,0);
+ \end{circuitikz}
+\end{center}
+
+How to go about it:
+\begin{align}
+ I & = \frac{V_{in}-\sum V_D}{R_1} \\
+ r_d & =\left[\frac{\mathrm{d}I_D}{\mathrm{d}V_d}\right]^{-1} =\frac{nV_t}{I_0} \\
+ r & = \sum r_d \\
+ \Delta V_o & = \Delta V_{in}\frac{r}{r+R_2} \\[1em]
+ n & \equiv\text{non-ideality factor} \\
+ V_t & = \frac{kT}{q}
+\end{align}
+
+Once the load is connected and draws current, we have a further small variation:
+\begin{align}
+ I_{load} & = \frac{\sum V_D}{R_2} \\
+ \Delta V_o & = I_{load}r
+\end{align}
+
+\subsection{Special diode types}
+\subsubsection{Zener}
+Is heavily doped making the depletion layer extremely thing, and thus allowing for QM tunneling in reverse biased diode.
+(In this case known as band-to-band tunneling.)
+
+\begin{figure}[h]
+ \centering
+ \caption[short]{Band-bending zener diode}
+ \includegraphics[width=.75\textwidth]{imgs/zener_diode_band_bending.png}
+\end{figure}
+The voltage at which the diode starts conducting is called the zener voltage $V_Z$.
+The diode then has a low resistance $R_Z$.
+
+\subsubsection{Esaki}
+Heavily doped with the tunneling effect in forward bias.
+\begin{figure}[h]
+ \centering
+ caption{Esaki tunnel diode}
+ \includegraphics[width=.75\textwidth]{imgs/esaki_tunnel_diode.png}
+\end{figure}
+
+\subsubsection{Schottky}
+A schottky diode has $I_0$ $10^3$ to $10^8$ times bigger than a PN diode.
+Preferred in low voltage high current applications.
+
+\subsubsection{Photodiodes}
+\begin{equation}
+ I = I_0\left( e^{\frac{qV}{kT}} - 1\right)-I_{photo}
+\end{equation}
\ No newline at end of file
diff --git a/imgs/esaki_tunnel_diode.png b/imgs/esaki_tunnel_diode.png
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diff --git a/imgs/zener_diode_band_bending.png b/imgs/zener_diode_band_bending.png
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diff --git a/semiconductor_summary.tex b/semiconductor_summary.tex
index 6c92d28f05d63ebd7915430b4b2f0ebbf084f24e..1e7e2e91208464905702aae3bfc2adf0ef349f9c 100644
--- a/semiconductor_summary.tex
+++ b/semiconductor_summary.tex
@@ -44,4 +44,5 @@
\include{04_pn_junction}
\include{05_pn_junction_bias}
\include{06_pn_junction_diode}
+\include{07_diode_applications.tex}
\end{document}