Observation of excitonic polariton and broadening of roomtemperature exciton in strained InGaAs/GaAs quantum wells

The luminescence of Si-doped GaAs with electron concentration up to 2.1 x 10'9 cm-3 is investigated. For the epitaxial layers with electron concentration less than 1 x 10'8 cm-3 the donor-acceptor pair luminescence was found to dominate, while at greater concentrations the indirect free electron transitions to the shallow acceptors prevail. The dependence of the luminescence spectra on the doping level was found to be different for two groups of layers. For the first group the spectra shifted to higher energies with increasing electron concentration in agreement with calculations of the Moss-Burstein effect, while for the second group there was almost no shift of the spectra up to n = 2.1 x 1019 cm-3. The measurements of luminescence excitation spectra have shown that the Fermi level is stabilised for the latter group of layers some 40-60 meV above the bottom of the conduction band. The presence of resonant levels in the conduction band of GaAs:Si was included to explain the Fermi-level stabilisation.

InxGa1−xAs/GaAs strained layer superlattices were studied by means of double-crystal x-ray diffractometry (DCXD), transmission electron microscopy (TEM), and selected area x-ray photoelectron spectroscopy (SAXPS) depth profiling techniques. The quality of superlattices, strain in the sublayers, and their thickness and chemical composition were evaluated. The effect of the real superlattice structure on the shape of x-ray rocking curves has been revealed. It was concluded that full identification of nonperiodic defects and the initial stage of stress relaxation can be determined by combining DCXD and TEM methods. The results of SAXPS depth profiling were found to be in good quantitative agreement with DCXD and TEM data. The linear dependence of depth resolution Δz on the sputtering depth, caused by sputtering induced development of heterointerface roughness was determined in SAXPS profiles.

Parabolic AlxGa1−xAs/GaAs quantum wells have been grown by molecular beam epitaxy with linear ramping of the Al effusion cell temperature, where the ramping rate was carefully analyzed to avoid a flux lag. The calculated potential profile from the temperature variation was very close to the parabolic one. Low-temperature photoluminescence showed clear interband transitions up to the n=3 sublevels. The equal energy spacing between adjacent transitions involving heavy-hole states confirmed the parabolic shape of the quantum well.

High-resistivity GaAs and InGaAs layers have been obtained by the MOCVD growth technique at low temperatures for the first time. The structural and physical properties of the LT-Mocvo-grown GaAs layers were similar to those 01 annealed LT-MBE GaAs layers-they were of a high crystalline quality with mobilities reaching 2600cm2 V -' s -' and had short carrier lifetimes of 50 ps. The resistivity of the LT-grown InGaAs layers was close to its intrinsic limits. Photoconductive switches with carrier lifetimes of 20 to 40 ps. long-wavelength cutoff of 1.7 pm, breakdown voltage of 10 V for a 5 @m gap and sensitivity reaching 0.05 A W -' were fabricated from those layers