Dear Adnan Afzal,

For me, the term "Quasi-bound States" is frequently recognized when talking about quantum wells. Sometimes, it is referred to "Quasi States" as you mentioned.

A quasi state is generated when a quantum well or double heterostructure is formed. For example, a 10-nm-thick GaAs is sandwiched by double AlGaAs barriers. From this, GaAs/AlGaAs quantum well is obtained. Let us consider the conduction band, due to the finite thickness of GaAs layer and the surrounding barriers, electron states in GaAs become quantized in a form of energy band (not infinitely narrow!).

From application point of view, the concept of quasi states can be applied to "resonant-tunneling diodes" where the carrier transport and thus the conductivity can be controlled by external bias. You can see more details in Chapter 4 of Physical Models of Semiconductor Quantum Devices by Ying Fu.

Hope it helps!

Dear Maetee Kunrugsa

          Thanks. Your answer is very helpful for me. If you have that recommended book in soft form please send me on this e-mail. "[email protected]"                              

because the electron can leak out of a quantum well of finite height, there

is no true bound states, but are called quasi bound states, with finite lifetime,

and broadened.

Dear friends,

                     The above discussions are very good for understanding and i wish to add one more point. If you look at the Fermi energy in QWs we used to call that as Quasi-Fermi energy. This can tell you only about the number of carriers in that state; not more than that. So in order to differentiate from the conventional terms we used to add the scientific prefix "Quasi".