Multiphoton ionization of a quantum well

The paper deals with two problems of the ionization of a single quantum well formed in a heterostructure. In the first problem, the ionization is caused by an electromagnetic wave which has so low a frequency that the number of electromagnetic quanta necessary for the ionization is much more than unity. The electric field of the wave is oriented along the normal to the heterostructure boundaries, and is assumed to be uniform on the scale of the well width. Analytical expressions have been obtained to determine the multiphoton ionization probability of a rectangular well per unit of time. It has been shown that plots of ionization probability versus well width depend dramatically on whether the angular frequency of the field is larger or smaller than the inverse characteristic time of the electron motion in the classically forbidden region. In the former case, the ionization rate as a function of the well width at a fixed frequency (or as a function of the field frequency at a fixed width) is characterized by two types of peculiarity. We discuss the nature of these peculiarities. The second problem is devoted to the ionization of a quantum well by an alternating electric field superimposed on a strong de electric field. This problem is investigated analytically for a field frequency smaller than the inverse characteristic time of the electron motion through a potential barrier. The dependences of the ionization probability on the well width and the electric field amplitude are studied.