First observation of an extremely large-dipole infrared transition within the conduction band of a GaAs quantum well

Abstract

A new type of optical transition in GaAs quantum wells has been observed. The dipole occurs between two envelope states of the conduction-band electron wave function, and is called a quantum well envelope state transition (QWEST). The QWEST is observed by infrared absorption for two structures with 65-Å-thick- and 82-Å-thick wells. The transitions exhibit resonant energies of 152 and 121 meV respectively, full width at half-maximum linewidths as narrow as 10 meV at room temperature, and an oscillator strength of 12.2. The material is anticipated to have subpicosecond relaxation times and be ideal for low-power optical digital logic.

Twisted-Light–Ion Interaction: The Role of Longitudinal Fields

“…This has been suggested in several theoretical articles dealing with tightly-focused TL [14,15] and TL-related beams [16][17][18][19][20]. Longitudinal fields in structured beams promise new applications, such as the control of the spin state of electrons or impurities in quantum dots [14,21], and the excitation of intersubband [22] transitions in quantum wells [23].For propagating fields that are not tightly focused the complexity of the full vector model can be reduced, still retaining an excellent description of the physics under consideration. In the paraxial approximation [24] one assumes that the transverse profile changes slowly along the propagation direction, here z.…”

Growth of p-type GaAs∕AlGaAs(111) quantum well infrared photodetector using solid source molecular-beam epitaxy

“…Figure 9 shows that absorption and the photocurrent spectra of the p-type ͑111͒A QWIP exhibit polarization dependence opposite to that in n-type QWIPs which observe the intersubband transition selection rule. 25,26 The peak responsivity is 1.3 mA/ W for 90°polarization ͑s polarization, TE mode only͒, but only 0.4 mA/ W for 0°polarization ͑p polarization, TE+ TM modes͒. Therefore, the transition of in-plane ͑x-y͒ polarization is stronger than that of z polarization.…”

The Intersubband Approach to Si-based Lasers

“…(18), it is not difficult to see that the selection rules for intersubband transitions in the conduction band are such that only those EM fields that are polarized in the growth direction ( ) can induce optical transitions. The transition matrix element can then be given as where the momentum matrix element is evaluated as the envelope function overlap between the two subbands, which is related to the dipole matrix element [36] and to the oscillator strength [37] It is not difficult to see from Eq. (17) that the transition rate induced by an EM field between two eigen states is the same for upward and downward transitions.…”