$1-($a$)$ Create a pn$-$junction made out of Si and make a pn diode out of it$.$ Explain the working principle of this diode under negative and positive potential difference.

$($b$)$ Place the right direction of bias in the following figure to turn$-$on the BJT transistor. i$.$e$.$ Just place the $"+"$ and $"-"$ ends of the voltage terminals in the right places to turnon the device. Name an application for it$.$

$2-$ Is it possible to create infinite potential barrier height in thin films theoretically and practically? What are the practical limitations to it$?$

$3-$ a$)$ Show and compare the electron wave$-$function of an electron for the first two quantized energy levels that is trappedin a finite and infinite potential well.

b$)$ how what happens when well width $"$L$"$ increased and decreased.