bigger image and diode equation reformulated

src/14_doping_and_devices.md

@@ -250,7 +250,7 @@ For that we consider a doped semiconductor in the extrinsic regime.
 
 Consider a pn-junction diode as follows 
 
-<img src="https://upload.wikimedia.org/wikipedia/commons/thumb/7/79/PN_diode_with_electrical_symbol.svg/640px-PN_diode_with_electrical_symbol.svg.png" width="50%" alt="pn diode"></img>
+<img src="https://upload.wikimedia.org/wikipedia/commons/thumb/7/79/PN_diode_with_electrical_symbol.svg/800px-PN_diode_with_electrical_symbol.svg.png" width="50%" alt="pn diode"></img>
 
 ??? info "source"
 
@@ -258,13 +258,13 @@ Consider a pn-junction diode as follows
 
 The current generated by the pn diode as a function of applied bias voltage is given by 
 
-$$ I(V) = I_0\left[exp(\frac{eV}{kT})-1\right]$$
+$$ I(V) = J_s(T)\left(e^{\frac{eV}{kT}}-1\right)$$
 
-where $I_0$ is the current flowing through a diode in reverse biased condition which is nearly independent of applied bias voltage but varies as a function of temperature.
+where $J_s(T)$ is the current flowing through a diode when it is reverse biased i.e. the positive terminal of battery is connected to n-type semiconductor and the negative terminal to p-type. $I_0$ is nearly independent of the applied bias voltage (V) but varies as a function of temperature (T).
 
-Display the I-V plot of a conventional pn diode
+<Add I-V plot of pn diode from simon's book>
 
-1. Write down two possible scenarios by which pn diode generates current in reverse biased condition.
+1. Write down two possible scenarios by which a pn diode generates current in reverse biased condition.
 2. How does the temperature affect the diode performance in the two scenarios written in 3.1.
 3. Sketch a plot of saturation current as a function of temperature
 4. Explain the dominant contribution to current in forward biased situation.