Electrically-detected Electron Spin Resonance Research Articles

Direct electrical measurement of the electron g factor in ultra-thin InGaAs/InP single quantum wells

The Landé g factor has been measured for electrons in ultra-thin InGaAs/InP quantum wells by means of an electrically-detected electron spin resonance (EDESR) technique. These experiments, carried out in a range of applied magnetic fields, allowed direct, unambiguous determination of both the absolute value and sign of the normal component of the electron g factor, g ∥ ( g parallel to the structure growth axis and the magnetic field). We observed a linear magnetic field dependence to the g factor, in agreement with the expression g ∥ ( B , N ) = g ∥ 0 + c ( N + 1 / 2 ) B , where N is the Landau level index.

Temperature dependence and mechanism of electrically detected ESR at theν=1filling factor of a two-dimensional electron system

Electrically detected electron spin resonance (EDESR) signals were acquired as a function of temperature in the 0.3-4.2 K temperature range in a AlGaAs/GaAs multiple quantum well sample at the filling factor at 5.7 T. In the particular sample studied, the line width is approximately temperature independent, while the amplitude exhibits a maximum at about 2.2 K and vanishes with increased or decreased temperature. To explain the observed temperature dependence of the signal amplitude, the signal amplitude temperature dependence is calculated assuming a model based on heating. The model ascribes the resonant absorption of microwave power of the 2DES to the uniform mode of the electron spin magnetization where the elementary spin excitations at filling factor are taken to be spin waves, while the short wavelength spin wave modes serve as a heat sink for the absorbed energy. Due to the finite thermal conductance to the surroundings, the temperature of the 2DES spin wave system is increased, resulting in a thermal activation of the longitudinal magnetoconductance. The proposed heating model correctly predicts the location of the maximum in the experimentally observed temperature dependence of the EDESR amplitude. It also correctly predicts that the signal should vanish as the temperature is increased or decreased. The results of the present study demonstrate how experimental EDESR studies can, under appropriate conditions, provide data that can be used to discriminate between competing theories for the magnetic ordering and magnetic excitations of a 2DES in the regime of the quantum Hall effect.

Electrically detected electron spin resonance of Pt/C 60/In/Al Schottky-barrier cell

Electrically detected electron spin resonance (EDESR) study is done for Pt/C 60 /In/Al Schottky-barrier system at room temperature. An isotropic signal is observed at g = 2.0020 ± 0.0002 which has spin-flip satellites due to an interaction between an electron (or hole) spin and nuclear spins of protons. This indicates that the present EDESR observes electron-hole pairs which are localized at the defects formed by impurity protons.

Electrically detected electron spin resonance of doped-phthalocyanine/C 60 heterojunction

Electrically detected electron spin resonance (EDESR) study is done for H 2-phthalocyanine(H 2Pc)-(BF 4) x/ C 60 heterojunction with x in the order of 0.01. The action spectrum of the H 2Pc(BF 4) x/ C 60 shows a significant difference from that of H 2Pc/C 60, indicating that the BF 2 − affects the charge-separation process after the photoexcitation of H 2Pc and possibly C 60. The EDESR observes the spin-dependent recombination of localized electron-hole pairs produced by the photoexcitation. The EDESR results of the H 2Pc(BF 4) x/ C 60 do not show any significant difference from those of the H 2Pc/C 60. This indicates that the formation of the localized electron-hole pairs is independent of the BF 4 − effect on the charge separation process.

Spin-dependent recombination of photoinduced carriers in phthalocyanine/C60heterojunctions

Spin-dependent recombination of photoinduced carriers in ${\mathrm{H}}_{2}$-phthalocyanine $({\mathrm{H}}_{2}{\mathrm{P}\mathrm{c})/\mathrm{C}}_{60}$ heterojunctions is studied by electrically detected electron-spin resonance (EDESR) spectroscopy. The EDESR spectrum of the ${\mathrm{H}}_{2}{\mathrm{P}\mathrm{c}/\mathrm{C}}_{60}$ consists of two components A and B, the g values of which are 2.0018$\ifmmode\pm\else\textpm\fi{}$0.0002 and 2.0010$\ifmmode\pm\else\textpm\fi{}$0.0002, respectively. The two components are attributed to exchange-coupled localized electron-hole pairs trapped at different types of recombination centers. Component A has spin-flip satellites due to an interaction between the electron (or hole) spin, and its surrounding nuclear spins of protons which belong to the ${\mathrm{H}}_{2}\mathrm{Pc}$ rings. From the satellite intensity, the distance between the electron (or hole) and the protons is estimated to be 4.33$\ifmmode\pm\else\textpm\fi{}$0.25 \AA{}, indicating that the localized pairs for the component A locate close to the ${\mathrm{H}}_{2}\mathrm{Pc}$ rings. The spin dynamics of the localized pairs for the component A is studied by a microwave recovery experiment, in which the time dependence of the EDESR signal intensity is measured after turning the resonant microwave on and off. A theoretical model of the spin-dependent recombination of the exchange-coupled electron-hole pair is proposed with which the experimental results of the microwave recovery are explained. By a theoretical analysis, it is found that $R\ensuremath{\gtrsim}1\ifmmode\times\else\texttimes\fi{}{10}^{6}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$ and ${D+W}_{\mathrm{sl}}=6.2(\ifmmode\pm\else\textpm\fi{}0.8)\ifmmode\times\else\texttimes\fi{}{10}^{4}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$ for component A at room temperature, where R is the recombination rate of the localized pair in the ${S}_{z}=0$ triplet sublevel, and D and ${W}_{\mathrm{sl}}$ are the dissociation and the spin-lattice relaxation rates, respectively, of the pairs in the triplet sublevels. The photocurrent ${I}_{2}$ that is caused by the dissociation of the localized pairs for component A is about 5% of the total photocurrent.

Photovoltaic effect and electrically detected electron spin resonance of a H 2-phthalocyanine/C 60 heterojunction

The Au/H 2-phthalocyanine(H 2Pc)/C 60/Au heterojunction shows a photovoltaic effect with the conversion efficiency of 0.02%. An electrically detected electron spin resonance (EDESR) study is done for this system. The observed EDESR signal represents a decrease of the photocurrent due to the spin-dependent recombination of the localized electron-hole pair which is created by the photoinduced charge transfer between the H 2Pc and the C 60. The microwave-power-saturation behavior of the EDESR signal is not explained by the formula generally used.

Electrically detected electron spin resonance (EDESR) in thiophene thin films and a thiophene/C 60 double layer

We report on the investigation of EDESR signals under light illumination in thin films of an end-capped oligothiophen with four thiophene rings (EC4T) and a molecular photodiode made of a double layer of EC4T/C 60 between gold electrodes. The different EDESR signals are interpreted in terms of photogenerated positive (P +) and negative (P −) polarons which undergo spin-dependent recombination.