Infrared magneto-photoluminescence spectra and electron–hole g-factor of an InAs-inserted channel InGaAs/InAlAs heterostructure

We performed infrared magneto-photoluminescence (PL) spectroscopy on an InAs-inserted-channel InGaAs/InAlAs heterostructure. Series of Landau levels were clearly observed in the infrared PL spectra. From the energy separation between σ+ and σ− components of PL, the electron–hole g-factor in each Landau level were determined. We discuss the obtained Landau fan-diagram from the points that nonparabolicity of conduction band structure and penetration of electron wavefunction into InGaAs layer.     

Photo-induced magnetic polarons in semiconductors

Exciton magnetic polarons observed in dilute magnetic semiconductors were investigated by steady-state and pico-second time-resolved photoluminescence measurements and have shown characteristic behavior of exciton localization processes in bulk-Cd_1-x Mn _x Te and also in the quantum structures composed of the dilute magnetic semiconductors. For the quantum structures spin-dependent coherent polarizations associated with excitons and biexcitons were studied by degenerate four-wave mixing experiment. Also investigated for different chalcogenide spinel ferromagnetic semiconductors was photo-induced enhancement of exchange interaction between magnetic ions by direct magnetic flux detection in the vicinity of the Curie temperatures.     

Magneto-photoluminescence study of InGaAs quantum dots fabricated by droplet epitaxy

We have successfully measured magneto-photoluminescence of InGaAs quantum dots (QDs) fabricated by droplet epitaxy with highly dense Ga droplets, termed separated-phase enhance epitaxy with droplets (SPEED). In the low magnetic field region, the PL peak energy shift increases linearly with square of the magnetic field. From the estimated Bohr radii for the QDs, it is found that the size of the QDs in the lateral direction is 2.7-times larger than that in the vertical direction. Moreover, using high magnetic region for estimating the detailed lateral size, the cyclotron radius around 25 T in the QDs becomes equal to the lateral size of the QDs. The cyclotron radius of 5.1 nm at 25 T suggests that the size of the InGaAs QDs in lateral direction might be as small as about 10 nm.     

Strain-induced quantum confinement of electron gases

Zero-dimensional electron gases have been fabricated by the strain-patterning of a GaAs/AlAs heterojunction using amorphous carbon stressors. We have used steady-state, time-resolved and temperature-dependent photoluminescence measurements to probe the occupied density of states of the electron gases. We observe a novel lateral confinement mechanism and efficient transfer of modulation-doped electrons from the regions between the stressors to the quantum dots. In finite magnetic fields we have mapped the evolution of the electron states from which we estimate the number of electrons per dot to be 15.     

Magneto-optics of zero-dimensional electron systems

Photoluminescence spectroscopy has been used to probe the occupied electron states below the Fermi energy of zero-dimensional electron systems (0DESs) in both zero and finite magnetic fields. The arrays of modulation-doped quantum dots investigated were fabricated by both reactive-ion etching and strain-confining GaAs heterojunctions with a -layer of Be present in the GaAs, in order to improve luminescence efficiency. For the etched quantum dots we show that the low magnetic field dispersion T) of the acceptor recombination line is directly related to the magnetic field dependence of the total ground-state energy of interacting electrons in the quantum dots. For the strain-confined 0DESs we have mapped the magneto-dispersion of the quantum confined electron states to reveal 15 electrons per dot.     

Electron–hole states in the fractional quantum Hall regime probed by photoluminescence

The electron–hole states in the fractional quantum Hall regime is investigated with a back-gated undoped quantum well by photoluminesccence in magnetic fields. The evolution of the photoluminescence spectra is discussed depending on the electron density. We find anomalies of the photoluminescence at the integer as well as the fractional filling factors.     

Photoluminescence and magneto-optical properties of multilayered type-II ZnTe/ZnSe quantum dots

Multilayered Zn–Se–Te structures grown by migration enhanced epitaxy are studied by temperature- and excitation-dependent photoluminescence (PL) as well as magneto-PL. The PL consists of two bands: a blue band, overlaid with band edge sharp lines, dominant at low temperatures and high excitation, and a green band, which appears at elevated temperature and low excitation. Upon varying excitation intensity by four orders of magnitude, the green band peak energy shifts by ∼60 meV, indicating recombination of excitons in type-II quantum dots (QDs); no significant shift is observed for the blue band. Therefore, the green emission is attributed to ZnTe/ZnSe type-II QDs, which co-exist with isoelectronic centers, responsible for the blue and band edge emissions. The existence of type-II ZnTe/ZnSe QDs is further confirmed by magneto-PL, for which the observed oscillations in the PL intensity as a function of magnetic field is explained in terms of the optical Aharonov–Bohm effect.