Question

In a p-i-n diode shown below, the doping concentration of p region is slightly larger than n' region and the wide i region is 1-11 undoped P+ N+ -X (a) Sketch the space-charge distribution (b) Sketch the electric field (c) Sketch the energy band diagram (d) Sketch IV characteristics in forward and reverse bias.

Answer 1

PIN Diode In PIN diode the i region is sandwiched between the p and n region as shown in Fig 11.5 $10_1_clip_image001.jpg$ Fig 11.5 The i-region is either a high resistivity layer. p(7) or n(v) PIN diodes are fabricated by -epitaxial process -Diffusion of p and n in high resistability substrate -ion drift method The concentration, charge density and electric field profiles are shown in Fig 11.6 N-ND Space charge density Electric field Fig 11.6 PIN diodes are used widely in microwave wave circuits such as microwave switch with constant depletion layer and high power. The switching speed 2v Where W is the total depletion region width and $10_1_clip_image005.gif$is the saturation velocity across i region. In addition the PIN diode can be used as -variable attenuator by varying device resistance that change approximately likely with forward current -Modulate signals up to GHz range. -Photo detection of internal modulated light in reverse bias. Under Riverse Bias the junction capacitance is $10_1_clip_image006.gif$ and the series resistance is $10_1_clip_image007.gif$ Where $10_1_clip_image008.gif$is the i-region resistance and $10_1_clip_image009.gif$is the contact resistance. The reverse bias current is $10_1_clip_image010.gif$ Where $10_1_clip_image011.gif$is the ambipolar life time. The I-V characteristics is shown in Fig 11.7 R, Vere Vre PIN Energy-Band Biagram Photogeneratedj electron Band gap EP Conduction band hv>Eg- IL 1 Photogenerated hole Valence band Depletion region hc 1.24 Cut off wavelength depends on the band gap energy E E(eV) IV-Characteristics of PIN Diode The forward series resistance characteristic and the reverse capacitance characteristic are shown graphically in Below Figure for a .typical pin diode. The pin diode is used as a dc-controlled microwave switch operated by rapid changes in bias or as a modulating device that takes advantage of the variable forward-res is tance characteris tic. Since no recti cation occurs at the pn junction, a highfrequency signal can be modulated (varied) by a lower-frequency bias variation. A pin diode can also be used in attenuator applications because its resistance can be controlled by the amount of current. Certain types of pin diodes are used as photodetectors in fiber-optic systems. 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 4.0 6.0 2.0 lo 12 16 8.0 l, forward current (mA