Optically detected magnetic resonance of Mn-related excitations in (Cd,Mn)Te quantum wells

Optically detected magnetic resonance (ODMR) was applied to reveal the exchange interaction effects between Mn²⁺ ions and confined holes in (Cd,Mn)Te quantum wells with 2D hole gas. Two anisotropic ODMR signals with different angular variations were found and ascribed to isolated manganese ions and to exchange-coupled complexes consisting of manganese and holes. It is shown that calculations on the basis of spin Hamiltonian for these systems are in agreement with the experimental data.     

Optically detected magnetic resonance of crystalline AgCl

The intrinsic ODMR spectrum of AgCl is due to holes trapped at tetragonally distorted Ag⁺ sites, recombining with electrons trapped at unidentified substitutional sites which are similarly distorted. Bromide ions induced characteristic changes in the spectrum.     

Optically detected nuclear magnetic resonance at the sub-micron scale

Nuclear magnetic resonance is arguably one of the most powerful techniques available today to characterize diverse systems. However, the low sensitivity of the standard detection method constrains the applicability of this technique to samples having effective dimensions not less than a few microns. Here, we propose a novel scheme and device for the indirect detection of the nuclear spin signal at a submicroscopic scale. This approach--for which the name Dipolar Field Microscopy is suggested--is based on the manipulation of the long-range nuclear dipolar interaction created between the sample and a semiconductor tip located close to its surface. After a preparation interval, the local magnetization of the sample is used to modulate the nuclear magnetization in the semiconductor tip, which, in turn is determined by an optical inspection. Based on results previously reported, it is shown that, in principle, images and/or localized high-resolution spectra of the sample can be retrieved with spatial resolution proportional to the size of the tip.     

Optically detected magnetic resonance of the zinc vacancy in ZnS

Optical detection of magnetic resonance (ODMR) is reported for the single negative charge state, V_Zn^?, of the isolated zinc vacancy in ZnS. Produced by 2.5 MeV electron irradiation, it is detected in a distant donor-acceptor (DA) pair luminescent band at 570 nm in which the vacancy acts as the acceptor. Excitation and emission spectral dependences of the V_Zn^? ODMR signals are analyzed in terms of a configurational coordinate model. We conclude that the double acceptor level (V_Zn⁼/V_Zn^?) is located ～1.1 eV from the valence band edge and that the trigonal Jahn-Teller relaxation energy for the V_Zn^? state is ～0.5 eV.     

Optically detected nuclear magnetic resonance in amorphous silicon related materials

Optically detected nuclear magnetic resonance (ODNMR) measurements have been carried out for a-Si:H samples with different hydrogen content and for a-Si_xN_1−x:H (x = 0.01 and 0.05). We have observed for the first time the ODNMR signal of hydrogen. The ODNMR spectrum is decomposed into two Lorentzians with different widths (FWHM) which arise from the dipole-dipole interactions of a trapped hole with its nearby and distant H¹ nuclei, respectively. The trapping site of the hole is discussed based on the experimental results.     

Optically detected magnetic resonance from a complex donor in CdS

A new optically-detected magnetic resonance at g = 1.885 for H|c, associated with a broad emission band at 2.17 eV, has been observed. The 2.17 eV band is attributed to donor-acceptor recombination involving a complex double donor, and the optically-detected magnetic resonance effect to spin-dependent electron transfer from a shallow donor to the complex donor.     

Optically detected magnetic resonance of α-deuterated 2-indanone

When 2-indanone is optically pumped into the phosphorescent triplet state, the excitation remains localized on the carbonyl moiety. Hence, the hydrogens at the α carbons play an important role in the electronic relaxation. Subtle perturbations can be introduced by exchanging these slightly acidic hydrogens with deuteriums. Various deuterated 2-indanone molecules were synthesized and the properties of their phosphorescent triplet state were experimentally determined by optically detected magnetic resonance (ODMR). Theoretical calculations showed that the shifts in the observed zero-field splitting parameters as a function of deuteration are a result of spin-orbit coupling. Finally, unexpected features in the ODMR spectra are explained in terms of the molecule's crystal structure.     

Optically detected cyclotron resonance in semiconductors

In high quality semiconductor crystals, occurrence of cyclotron resonance is beautifully reflected on luminescence spectra. This feature is demonstrated in typical elemental semiconductor Ge, both doped and undoped. One obtains new information of kinetics in free carriers, free excitons, bound excitons and electron-hole drops.     

Optically detected electron resonance in phosphorus-doped ZnTe

Samples of ZnTe showing near gap edge luminescence predominantly due to exciton recombination at shallow neutral acceptors and donor- acceptor pair recombination have been investigated using optically detected magnetic resonance (ODMR). Emission polarization changes at 2.318 eV were observed due to magnetic resonance of electrons at g_e = + 0.401 ± 0.004. The observations are consistent with the donor trapped electron resonance resulting from microwave induced changes in donor-acceptor pair photoluminescence.     

Saturation of the Mn2+ ionic subsystem in Cd0.5Mn0.5Te and Zn0.91Mn0.09Se bulk samples and in Cd0.6Mn0.4Te/Cd0.5Mg0.5Te superlattices

It is experimentally shown that the Mn²⁺ ionic subsystem in the three-and two-dimensional structures of diluted magnetic semiconductors of the II–VI groups is saturated upon pulsed excitation by high-power laser radiation with a wavelength of 532.1 nm at temperatures of 77 and 4 K. The direct excitation under these conditions leads to saturation of the inhomogeneously broadened ⁴ T ₁ level of a part of Mn²⁺ ions, which is confirmed by the estimation of the fraction of excited ions. Processing of the integral kinetic curves of the intracenter luminescence band in the region of 2 eV shows that an increase in the excitation intensity gives rise to a fast component with a decreasing lifetime. Based on the data obtained, it is assumed that, along with the previously studied cooperative effect, redistribution occurs of excitation from localized to delocalized states as a result of more effective saturation of the former.     

Optically detected magnetic resonance of the V- centre in ZnSe

Optically detected magnetic resonance of V^- centres and donors has been observed in ZnSe. The spectral dependence of these resonances show that they are both associated with an emission band at 632 nm.     

Optically detected electrophonon resonance effects in quantum wells

Optical detected electrophonon resonance (ODEPR) effects in quantum wells of n-GaAs materials are investigated for square potential and parabolic potential, respectively. We also obtain the ODEPR conditions as functions of confinement frequency in parabolic potential and well-width in square potential for the various photon frequencies, respectively. In particular, anomalous behaviors of the ODEPR lineshape such as the splitting of ODEPR peaks for incident photon frequency are discussed. Furthermore, we obtain the selection rules for transition in quantum wells of two different potentials, respectively.     

Localization of exciton excitation in planar structures Cd0.9Mn0.1Te/Cd0.7Mg0.3Te

The spectra of exciton emission in a series of periodic structures with ultrathin Cd_0.9Mn_0.1Te inclusions in the Cd_0.7Mg_0.3Te matrix have been studied. The complex structure of the luminescence spectra and their relation to the luminescence excitation spectra indicate large-scale fluctuations in thickness of narrow-band-gap layers. Two types of temperature dependences of the luminescence intensity of localized excitons are found: (1) the complete suppression of emission above 80 K and (2) the relative enhancement of temperature-insensitive low-energy band that corresponds to local bulges in planar Cd_0.9Mn_0.1Te layers.     

Optically detected resonance spectroscopy of interface fluctuation quantum dots

We have performed optically detected resonance (ODR) spectroscopy on modulation-doped GaAs/AlGaAs quantum wells of different widths in which lateral fluctuations of the well width were purposely introduced by growth interruption at the interfaces. These monolayer fluctuations form quantum dots for which confinement and Coulomb correlation energies are comparable. By monitoring resonant changes of the dot ensemble photoluminescence induced by far-infrared (FIR) radiation in a magnetic field, we have observed cyclotron resonance (CR) of free electrons in the widest wells, as well as internal transitions of mobile and localized charged excitons. The latter, which are forbidden by magnetic translational invariance, have previously not been observed. For the narrower wells the effects of non-parabolicity and carrier localization on the CR and CR-like transitions have to be included for a proper interpretation of the measurements.     

Heavy and light hole subbands exchange induced mixing in CdTe-(Cd,Mn)Te magnetic superlattices

We present the first calculation of the electronic structure of hole subbands in a semimagnetic superlattice in the presence of an applied magnetic field, taking into account the existence of a preferential axis of quantization for the hole spin and the fourfold degeneracy of the top of the valence band. We show that, for fields applied parallel to the layers, there is a strong exchange induced mixing of heavy and light holes subbands for any value of k, the Bloch wave vector parallel to the layers. This mixing dominates over the usual k·p induced mixing and should be observable in resonant tunneling and magnetotransport measurements on p-type samples.