$4.($a$)$ State the diode current equation and specifically identify the terms that exhibit

temperature dependence. How does an increase in temperature impact on reverse saturation

current $($Iso$)$ and what are the overall consequences on the diode current?

$($b$)$ Analyze the practical implications of reverse bias characteristics of a p$-$n junction diode in

electronic circuits, emphasizing their role in applications such as varactor diodes for frequency

tuning. Identify how the reverse bias condition influences the leakage current and capacitance

in the diode.

$($c$)$ The reverse saturation current $($Iso$)$ of silicon diode is $3$ nA at $27$C$,$ find Iso at $37$C and

$87$C and justify the impact of temperature on reverse saturation current.