Dynamics of free carriers – neutral impurity related optical transitions in Be and Si δ-doped GaAs/AlAs multiple quantum wells: Fractional-dimensional space approach

Abstract

The dynamics of impurity-related optical transitions in 20 nm wide silicon and beryllium δ-doped GaAs/AlAs multiple quantum wells with various doping levels has been investigated at near liquid helium temperatures. The radiative lifetimes of the free electron-neutral acceptor and the free hole-neutral donor have been identified. The capture cross-sections of the free electrons by neutral Be acceptors were experimentally determined to σ e-Be = 4 × 10 -10 cm, whereas this corresponded to σ h-Si = 2.2 × 10 -8 cm for the free holes by neutral Si donors. The experimentally determined cross-section ratio of σ h-Si /σ e-Be = 55 is close to the estimated 2D value of σ h-D /σ e-A = 64 and remains lower compared to the calculated value for the 3D case of σ h-D /σ e-A = 121.

Excitonic light emission decay time measurements in moderatelyδ-doped GaAs/AlAs multiple quantum wells

“…In contrast, the long PL decay time is related to the lifetime of thermalized excitons. Considering the previous work reported on the excitonic recombination characteristic time [21], this may be attributed to the emission time of the non-thermalized excitons. Similar experimental results and a thorough discussion on the recombination of free excitons at low temperature are presented in Ref.…”

“…3) indicate the calculated values of these energy sublevels. More details about the experimental investigation and theoretical analysis of Si and Be doped MQWs CW PL spectra can be found in [30][31][32].…”

“…The cryostat was equipped with two thermometers; the first one was used to control the operation of the equipment and the second one was used to measure the temperature of the sample. More details of the experimental setup can be found in [21].…”

“…The magnitude and level of these effects will depend on the type and concentration of the impurities used. We note that in moderately doped QWs the shortest lifetime at low temperatures is the excitonic emission lifetime in comparison with lifetimes of free carriers -neutral impurity related optical transitions [19][20][21].…”

“…Impurities in quantum wells may introduce new recombination centers such as bound excitons, initiate new free electron-acceptor or free hole-donor light emission transitions as well as reduce the bandto-band and excitonic emission dynamics [19][20][21][22][23][24][25][26]. The magnitude and level of these effects will depend on the type and concentration of the impurities used.…”