Properties of PN-Junctions

A good reference: Bart Van Zeghbroeck's, Principles of Semiconductor Devices: 4. p-n junctions

A hydraulic model of semiconducting behavior:

• A two-pipe model of an insulator or intrinsic semiconductor.

• A two-pipe model of carrier excitation mechanisms in a semiconductor.

Applets that demonstrate semiconductor energetics and statistics -- the Fermi level:

• For reference -- not applets: Energy Diagrams of p-type and n-type semiconductors

 
• For reference -- not applets: Energy diagrams of biased pn homojunctions

 
• Fermi Function and Localized Energy States and the Temperature effect.

 
• Carrier Concentration vs. Fermi Level and the doping of donor and acceptor impurities.

 
• Carrier Concentration vs. Fermi Level and the Density of States

 
• Moderate-doping vs. Heavy-doping [non-degenerate vs. degenerate]

Applets demonstrating pn junction behavior

PN Junction Diode at Equilibrium

• A graphical illustration of the formation of a PN junction diode and its band diagram.  It shows both the band diagram and a schematic cross-section of the device as the junction approaches its thermal equilibrium.

 
Points to note: (see Math. Analysis)
 
1. Barrier height        V₀ = (kT/q) ln(N_aN_d/n_i²)   { "built-in voltage" }

 
2. Depletion width  x_n N_d = x_p N_a    {  q A x_n N_d = q Ax_p N_a charge-equality condition}

 
• PN junction diode, space charge profile and electric field. It shows a cross-section of the sample, space charge and the electric field in depletion layer as the junction approaches the thermal equilibrium.

 
Note how the electric field varies with position in the depletion layer.

PN Junction Diode under Applied Bias Voltage

• Biased PN Junction: band diagram, diffusion and drift currents, etc.  It shows both the energy band under bias and the animated carriers flowing across the junction.

 
• Space charge and electric field in biased PN junction.
 
Note, in particular, how depletion layer stretches with increasing back bias.
• Current flow in forward-biased pn junction  An applet that shows an animated flow of carriers in a simplified band model.
 
Note, in particular, the importance of accounting for the recombination of carriers.

Semiconductor heterojunctions

Double Heterostructures

• See Winston Chan's wonderful applet Band Diagrams for Semiconductor Heterostructures (local copy)

 
• An example of an unbiased double heterostructure laser configuration

A veritable "gold mine" of relevant semiconductor properties can be found at the Ioffe Physico-Technical Institute Electronic archive: New Semiconductor Materials. Characteristics and Properties: