Carrier transfer in coupled asymmetric GaAs/AlGaAs double quantum wells after ultrafast intersubband excitation

Abstract

Intersubband scattering processes are investigated in selectively doped asymmetric tunnel-coupled GaAs/AlGaAs quantum wells by infrared pump probe spectroscopy. Various subbands are excited by resonant absorption of a mid-infrared pump pulse and the carrier relaxation is observed via timeand frequency-resolved absorption changes monitored by a subsequent infrared probe pulse. The experimental data show that most of the carriers remain in the quantum well in which the excitation process mainly takes place. Only a minor fraction of the carriers is transferred between excited non-resonant subbands of the neighbouring quantum wells. The situation is different for electrons in the two lowest subbands which are separated only by 10 meV. Here a rapid and efficient transfer is observed. The scattering time is in the order of a picosecond at room temperature; it increases to values between 4 ps and 20 ps at 80 K. The data are interpreted with detailed model calculations taking into account phonon and impurity scattering. Both experimental and calculated data demonstrate the possibility of population inversion between excited states of quantum wells under optical or current electron injection.

Ion-Irradiated Laterally Graded Ni/C Multilayers: A Combined X-ray Standing Wave and X-ray Reflectivity Analysis

“…From [12] it can be deduced that times t 12 , t 13 and t 23 at the liquid nitrogen temperature remain close to their room temperature estimates of 0.1 ps. Times T 13 and T 23 also remain approximately the same, but T 21 grows by several times due to the non-resonant nature of longitudinal optical (LO) phonon emission at THz-range transition 2 ↔ 1 [40]. Time τ l at the liquid nitrogen temperature is 7 times larger than its value at room temperature [21] whereas time τ is 4 times smaller [51].…”

“…Due to intrasubband electronphonon and electron-electron scattering, they relax to the Fermi distributions ρ jj e determined by quasi-equilibrium chemical potentials μ j which, in turn, are determined by the instantaneous subband electron sheet densities N j ≡ +∞ 0 ρ jj 2πp dp/(2πh) 2 (the upper integration limit is put to infinity here due to the rapid exponential decrease of the integrand for large p) through the relation N j = +∞ 0 ρ jj e 2πp dp/(2πh) 2 . As the times of the intrasubband relaxation are typically much shorter than the times of intersubband relaxation [23,[32][33][34][35][36][37][38][39][40], it will be assumed for estimates below that ρ jj = ρ jj e .…”

“…According to [23,32,33,[35][36][37][38][39][40], at the parameters considered below T 21 T 13 T 23 1 ps. N j e are the equilibrium values of N j in the absence of external electromagnetic fields and are determined by the equilibrium chemical potential μ which, in turn, is determined by the whole electron sheet density N through the equation 2(N 1e + N 2e + N 3e ) = N. Here factor 2 in the lhs takes into account the two-fold subband degeneracy over the spin projections.…”

Proposal for an inversionless tunable THz laser driven by room-temperature mid-infrared quantum cascade lasers

“…Due to intrasubband electronphonon and electron-electron scattering, they relax to the Fermi distributions ρ jj e determined by quasi-equilibrium chemical potentials μ j which, in turn, are determined by the instantaneous subband electron sheet densities N j ≡ +∞ 0 ρ jj 2πp dp/(2π h) 2 (the upper integration limit is put to infinity here due to the rapid exponential decrease of the integrand for large p) through the relation N j = +∞ 0 ρ jj e 2πp dp/(2π h) 2 . As the times of the intrasubband relaxation are typically much shorter than the times of intersubband relaxation [23,[32][33][34][35][36][37][38][39][40], it will be assumed for estimates below that ρ jj = ρ jj e .…”

Spin-sensitive intersubband dynamics of optically generated carriers in semiconductor quantum wells

“…4,5 But also coherent aspects of the dynamics, many-body effects, and the identification of relevant relaxation mechanisms have been issues of interest. [6][7][8][9][10][11][12][13][14][15][16] For intersubband experiments, where the carriers in the conduction bands are provided by doping, the available spin orientations are initially equally occupied. With these initial conditions optical spin orientation can be achieved in intersubband transitions that are driven by circularly polarized in-plane fields.…”