Photocurrent resonances in short-period AlAs/GaAs superlattices in an electric field

The photocurrent was measured as a function of the external electric field in short-period AlAs/GaAs superlattices for various photon energies. Transport resonances, whose positions do not depend on the photon energy, were observed in these dependences together with optical resonances due to interband transitions in Wannier-Stark levels. It is shown that the transport resonances are due to tunneling of photoelectrons from the p-GaAs contact region into the first level in GaAs wells located 2–5 lattice periods from the contact layer. Fiz. Tverd. Tela (St. Petersburg) 41, 159–164 (January 1999)     

Two-step decoupling of excitonic states in a biperiodic GaAs/AlAs short period superlattice under electric fields

By low temperature photocurrent spectroscopy, we have investigated electric field dependence of excitonic states in a biperiodic GaAs/AlAs short-period superlattice which consists of a 20-period of GaAs-well(L_Z) / AlAs-barrier1(L_B¹) / GaAs-well(L_Z) / AlAs-barrier2(L_B²) (= 3.2nm / 0.45nm / 3.2nm / 0.9nm). Evidence is given for a two-step decoupling mechanism at low (< 10⁵V/cm) and high (> 10⁵V/cm) field regimes, which is derived from the successive decoupling of the superlattice potential coupling and of the symmetric two-well-coupling through the thinner barrier.     

Bloch oscillations in GaAs/AlGaAs superlattices after excitation well above the bandgap

Bloch oscillations of wave packets in semiconductor superlattices are observed by THz-emission spectroscopy after pulsed photo-excitation well above the fundamental band-gap. We show that Bloch oscillations are induced by excitation of states in both the first and the second electron miniband.     

Transmission intensity oscillations in GaAs/AlAs superlattices induced by photogenerated charged transport

Two superlattice p-i-n diodes connected in series to a constant dc bias, i.e., in the symmetric self-electro-optic effect device (S-SEED) configuration, exhibit pronounced oscillations of their transmission intensities immediately after optical pulse excitation of one of the diodes. The temporal variations directly reflect the transmission-voltage characteristics due to successive Stark ladder resonances, and they depend strongly on the amount of the illumination power and on the pulse width. The observed oscillatory behavior is explained by changes of the voltage balance between the two diodes induced by photogenerated charge transport.     

Phonon-plasmon interaction in tunneling GaAs/AlAs superlattices

The phonon-plasmon interaction in tunneling GaAs _n /AlAs _m superlattices (m=5and 6≥n≥0.6 monolayers) was studied by Raman scattering spectroscopy. The interaction of optical phonons localized in GaAs and AlAs layers with quasi-three-dimensional plasmons strengthens as the thickness of GaAs quantum wells decreases and the electronic states in the superlattices become delocalized due to tunneling. It is assumed that the plasmons also interact with the TO-like phonon modes localized in quantum islands or in thin ruffled layers.     

Donor-acceptor recombination in type-II GaAs/AlAs superlattices

A study is reported of steady-and nonsteady-state photoluminescence of intentionally undoped and uniformly silicon-doped type-II (GaAs)₇(AlAs)₉ superlattices grown by MBE simultaneously on (311)A-and (100)-oriented GaAs substrates. It has been established that at elevated temperatures (160>T>30 K) the superlattice spectra are dominated by the line due to the donor-acceptor recombination between donors in the AlAs layers and acceptors located in the GaAs layers. The total carrier binding energy to the donor and acceptor in a pair has been determined. Fiz. Tverd. Tela (St. Petersburg) 40, 1734–1739 (September 1998)     

Raman spectroscopy of resonance exciton tunneling in GaAs/AlAs superlattices in electric fields

Optical-resonance-Raman scattering by acoustic phonons is used to study the effect of an electric field on the state of excitons in GaAs/AlAs superlattices. When the energy of the exciting photon coincides with the energy of an exciton bound to Wannier-Stark states of a heavy hole and electron with Δn=0,±1, the acoustic Raman scattering is enhanced. Oscillations in the intensity of the Raman spectrum in the electric field are explained by resonance delocalization of the exciton ground state as it interacts with Wannier-Stark states of neighboring quantum wells or with Wannier-Stark states of a higher electron miniband. Fiz. Tverd. Tela (St. Petersburg) 40, 827–829 (May 1998)     

Cyclotron masses in InGaAs/GaAs superlattices and InGaAs/AlAs superlattices

Cyclotron resonance (CR) measurements have been carried out to evaluate the effective mass of electron in (InGaAs)_n/(GaAs)_nsuperlattices (SLs) and (InGaAs)_n/(AlAs)_nSLs. To clarify the dependence of cyclotron mass on the monolayer numbern , we measured CR signals using pulsed high-magnetic fields up to 150 T and a far-infrared laser. We found clear cyclotron resonances in the transmission of 10.6 μ m at 75 T at room temperature in (InGaAs)_n/(GaAs)_nSLs and little dependence on the monolayer number n in the SLs. However, for (InGaAs)_n/(AlAs)_nSLs, a large dependence of cyclotron mass on the monolayer number n was observed. We consider that these dependencies are related to the difference between the barrier height in the SLs and the influence of nonparabolicity on the conduction subbands in the SLs.     

Polarization of hot photoluminescence in GaAs/AlAs superlattices

The polarization characteristics of hot photoluminescence in GaAs/AlAs superlattices are investigated experimentally and theoretically. It is shown that the formation of an electronic miniband in the superlattice substantially changes the polarization characteristics of the photoluminescence. As a result of the quasi-three-dimensional character of the motion of hot electrons in the superlattice, the polarization depends on the ratio of the electron kinetic energies in the plane of the superlattice and along the axis of the superlattice. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 4, 285–289 (25 February 1996)