# Design an ideal abrupt silicon PN -junction at 300 K such that the donor impurity concentration in the n -side N d = 510 15 /cm 3 and the acceptor

Design an ideal abrupt silicon PN-junction at 300 K such that the donor impurity concentration in the  n-side Nd = 5×1015/cm3 and the acceptor impurity concentration in the p-side Na = 499 ×1015/cm3 Assume that the diode area A = 2×10−3 cm2 and ni = 1010/cm3.

Refer to text books, lecture notes, etc. for other parameters such Dn, tn, etc., and state clearly in your work. Note that the values obtained in the calculations may not be realistic as the Matric # varies greatly. The assignment is only to test your understanding, and must be handwritten.

Determine the following when a forward bias of 0.6 V is applied to the diode:

1.    The values (in mm) of the depletion width at the p-side xp and the depletion width at the n-side xn.

2.    The electric field at a distance of 0.2 xn away from the metallurgical junction in the n-side.

3.    Minority carrier hole diffusion current at the n-side depletion edge Ip (xn)

4.    Minority carrier electron diffusion current at the p-side depletion edge In (xp)

5.    The total diode current I.

6.    The junction capacitance Cj under forward bias

7.    Roughly, sketch the carrier distribution across the junction under forward bias. Label clearly.

8.    For the same forward bias of 0.6 V, an application requires higher diode current than that calculated in Part 5. If you have a choice to change the dopant concentration in one side of the junction (either p-side or n-side) to achieve this higher current, state whether you will increase or decrease the dopant concentration in the chosen side? Briefly describe to justify.

9.    If the pn-junction diode is made of GaAs semiconductor instead of Silicon, do you expect the total diode current I to remain the same, decrease or increase for the same forward bias of 0.6 V? Explain briefly without doing any calculation.