High-field Cyclotron Resonance Research Articles

High-field cyclotron resonance studies of InMnAs-based ferromagnetic semiconductor heterostructures

We report results of experimental and theoretical studies of hole cyclotron resonance (CR) in ferromagnetic InMnAs/GaSb heterostructures. We observe two clear resonances that exhibit strong temperature dependence in position, line width, and intensity, especially near and below the Curie temperature. We attribute the two resonances to the fundamental CR transitions expected for delocalized holes in the valence band in the magnetic quantum limit. Our theoretical calculations, based on an 8×8 k · p model with s(p)–d exchange interaction taken into account, reproduced temperature-dependent CR peak shifts with decreasing temperature, in qualitative agreement with experiment. We propose that the narrowing is due to the suppression of localized spin fluctuations at low temperature.

High field cyclotron resonance measurements of heavily doped Si : Mn

Cyclotron resonance (CR) measurements of heavily doped Si:Mn prepared by chemical vapour deposition have been performed at 4.2K by our high field CR measurement system equipped with a UV light illumination. The system is equipped with a pulsed magnetic field up to 16T and light sources from 30GHz to 700GHz. The field dependence of the effective masses and linewidths of CRs at 4.2K are discussed in connection with those observed by a conventional X-band ESR measurement system at 3.4K under UV light illumination.

High-field cyclotron resonance and electron–phonon interaction in modulation-doped multiple quantum well structures

A systematic study of electron cyclotron resonance (CR) in two sets of GaAs/Al0.3Ga0.7As modulation-doped quantum-well samples (well widths between 12 and 24 nm) has been carried out in magnetic fields up to 30 T. Polaron CR is the dominant transition in the region of GaAs optical phonons for the set of lightly doped samples, and the results are in good agreement with calculations that include the interaction with interface optical phonons. The results from the heavily doped set are markedly different. At low magnetic fields (below the GaAs reststrahlen region), all three samples exhibit almost identical CR which shows little effect of the polaron interaction due to screening and Pauli-principle effects. Above the GaAs LO-phonon region (B>∼23 T), the three samples behave very differently. For the most lightly doped sample (3×1011cm−2) only one transition minimum is observed, which can be explained as screened polaron CR. A sample of intermediate density (6×1011cm−2) shows two lines above 23 T; the higher frequency branch is indistinguishable from the positions of the single line of the low density sample. For the most heavily, doped sample (1.2×1012cm−2) there is no evidence of high frequency resonance, and the strong, single line observed is indistinguishable from the lower branch observed from sample with intermediate doping density. We suggest that the low frequency branch in our experiment is a magnetoplasmon resonance red-shifted by disorder, and the upper branch is single-particle-like screened polaron CR.

High-field cyclotron resonance in the conduction bands of GaSb and effective-mass parameters at theLpoints

High-field cyclotron resonance in the conduction bands of GaSb and effective-mass parameters at the<i>L</i>points

Magnetic field and dimensionality-induced population effects in HgSe : Fe quantum wells: the cyclotron resonance

Line shapes of the high-field cyclotron resonance are investigated both experimentally and theoretically for thin layers of the Fermi-level pinned system HgSe : Fe. Characteristic features are related to a subband population representing the two- and three-dimensional limits as well as intermediate steps.

Low-dimensional systems in ultra-high magnetic fields: magnetic-field-induced type I to type II transitions in short-period semiconductor superlattices

We present a review on the recent study of the type I to type II transition in short-period superlattices of GaAs/AlAs by means of cyclotron resonance and interband magneto-optical spectroscopy in pulsed high magnetic fields up to 500 T. In the magneto-photoluminescence spectra of excitons in , the magnetic-field-induced type I to type II transition was observed with and without the simultaneous application of high pressure. The behaviour of the transition varies depending on the thickness of the AlAs layers. In cyclotron resonance of , the resonance peak at the X minima was observed in the type II regime for n smaller than 14, whereas the resonance at the point was observed for n>15. It was found that the angular dependence of the peak position does not obey the simple cosine dependence due to the subband mixing in high magnetic fields. From the angular dependence, the effective masses at the X point were determined. In high-field cyclotron resonance measurements at 129 meV up to 400 T for n = 16 (type I), the resonance of the X minima expected at around 260 T was indiscernible, despite the fact that the transition should have occurred at lower fields.

Interface and layer thickness dependence of the effective mass in [formula omitted] superlattices studied by high field cyclotron resonance

The effective mass has been studied in a series of semiconducting and semimetallic InAs GaSb superlattices as a function of superlattice period and band gap. The mass is found to be determined almost entirely by the superlattice period, and is relatively insensitive to both the ratio of the InAs to GaSb thickness, and the structure of the interface layer, which was grown as both a monolayer of InSb and GaAs. Using pulsed magnetic fields of up to 180 T it was possible to observe spin-split cyclotron resonance at room temperature for all samples studied. On cooling the spin-splitting was found to be temperature dependent. This is attributed to the importance of electron-electron interactions which couple the two spin transitions as observed recently in high purity GaAs GaAlAs heterojunctions at low temperatures.

High-field cyclotron resonance and impurity transition in n-type and p-type 3C-SiC at magnetic fields up to 175 T.

Magnetotransmission experiments have been carried out on 3C-SiC thin films grown on Si(100) substrates, using the combination of pulsed high magnetic fields up to 175 T generated by the single-turn coil technique and pulsed far-infrared radiations from a ${\mathrm{H}}_{2}$O (${\mathrm{D}}_{2}$O) laser at photon energies up to 73.2 meV. In n-type 3C-SiC, two cyclotron-resonance (CR) peaks have been observed for B\ensuremath{\parallel}k\ensuremath{\parallel}〈100〉 over a wide range of photon energy 10.4--53.8 meV, corresponding to the light- and heavy-mass valleys at the X points, i.e., ${\mathit{m}}_{\mathit{t}}^{\mathrm{*}}$=(0.25\ifmmode\pm\else\textpm\fi{}0.01)${\mathit{m}}_{0}$ and (${\mathit{m}}_{\mathit{t}}^{\mathrm{*}}$${\mathit{m}}_{\mathit{l}}^{\mathrm{*}}$${)}^{1/2}$=(0.41\ifmmode\pm\else\textpm\fi{}0.01)${\mathit{m}}_{0}$. These values are in agreement with those of Kaplan et al. obtained from CR at low fields. This leads to the conclusion that the conduction band in 3C-SiC is very parabolic up to 53.8 meV, and that unlike GaP the effect of camel's-back structure is unobservable. A number of impurity transitions were observed at temperatures below 100 K with photon energies ranging from 34.4 to 73.2 meV. It was found that the observed lines originate from three different donor states which have different binding energies, ${\mathit{E}}_{\mathit{d}}$=19, 35, and 53 meV. The observation of hole CR was also made in p-type 3C-SiC. A broad but prominent peak was observed with an effective mass of 0.45${\mathit{m}}_{0}$, at temperatures around 210 K and at a wavelength of 119 \ensuremath{\mu}m.

High-field cyclotron resonance and valence-band structure in semiconducting diamond.

The cyclotron resonance of thermally excited free holes has been observed in synthetic semiconducting diamond at ultrahigh magnetic fields up to 150 T generated by the single-turn-coil technique with pulsed far-infrared laser radiations of 28, 36, and 119 μm. Three absorption peaks were observed at and above room temperature for the magnetic fields parallel to the , , and crystallographic directions. The typical value of ω c t was as small as 2 at 40 o C even in ultrahigh fields. One of the three peaks was observed in the cyclotron-resonance inactive circular polarization for holes, while the other two lines were observed in cyclotron-resonance active circular polarization for holes

High field cyclotron resonance and the electron effective masses in AlAs

We have measured far-infrared cyclotron resonance in n-type AlAs in pulsed high magnetic fields up to 150T. At a wavelength of 119μm, a prominent resonance peak was observed at 42T corresponding to the heavy effective mass of m ∗ tm ∗ l =0.47±0.01m 0 on the ellipsoidal equinergy surface at the X-point. Also observed a shoulder-like structure centered at 22T. Assigning it to the light effective mass m ∗ t , the effective masses were determined as m ∗ t=0.25±0.01m 0 and m ∗ l=0.88±0.06m 0 .

Two-dimensional defects in InSe

Two-dimensional precipitates associated with stacking faults in layer semiconductors have previously been put forward to explain transport properties of these crystals, especially their remarkable electrical anisotropy. High-field cyclotron resonance behavior, among others, can be accounted for by two-dimensional accumulation layers in the vicinity of these defects. Direct evidence for the existence of these defects has been obtained by electron microscopy and x-ray microprobe analysis in indium selenide. Planar faults act like sinks for impurity atoms. This accounts for the unique behavior of layer compounds which exhibit intrinsic behavior (low apparent carrier concentration—high mobilities) even with high (100 ppm) initial doping levels. Optical, transport, and magnetotransport properties at low temperature can be explained along this model. As regards the applications of indium selenide to the photovoltaic conversion of solar energy, the existence of these defects explains most features of this semiconductor in this respect: (i) Its comparatively low effective diffusion length parallel to the c axis. (ii) p- to n-type switching under thermal annealing which allows fabrication of p-n junctions. (iii) Low apparent carrier density which precludes abrupt profiles for p-n structures.