Electric-field-dependent subband population in undoped GaAs/(Al,Ga)As quantum-cascade structures

Abstract

We have investigated the transport and population properties of undoped GaAs/(Al,Ga)As quantum-cascade structures (QCS) below and above the designed threshold field strength F crit using current-voltage characteristics and photoluminescence (PL) spectroscopy. The devices exhibit a negative differential conductance (NDC) at F crit . The NDC is correlated with an abrupt change of intensity and energy positions in the field-dependent PL spectra. Below F crit , the PL spectra show only emission from the lowest interband transition in the QCS exhibiting the usual Stark shift. Above F crit , a significant population of the laser levels is observed. The switching behaviour is tentatively attributed to an abrupt spatial redistribution of the carriers at F crit mediated by additional states within the (Al,Ga)As barriers.

Negative differential conductance and current bistability in undoped GaAs∕(Al,Ga)As quantum-cascade structures

“…6 for the GaAs/ Al 0.33 Ga 0.67 As QCS's and compare the results with measurements on GaAs/ Al 0.33 Ga 0.67 As QCS's. In particular, a comparison of the transport and population properties of QCS's containing Al 0.33 Ga 0.67 As and Al 0.45 Ga 0.55 As barriers is of great interest, since QCL's with Al 0.33 Ga 0.67 As barriers exhibit significantly higher threshold currents than lasers with Al 0.45 Ga 0.55 As bar-riers, which in part can be explained by the larger barrier height of the second system.…”

Intrinsic optical intersubband bistability in quantum‐well structures: External factor effect

“…For example, such an external factor could be an additional incident radiation beam. Modulation of the subband population can also be done by the external electric field (see, e.g., ) or magnetic field (see, e.g., ()) applied to the QW structure. In addition, the thermal factor can be employed to repopulate the subbands for QW systems with being of a few dozens of meV.…”