Yu. B. Vasilyev

Different components of far-infrared photoresponse of quantum Hall detectors

We have performed time-resolved measurements of the far-infrared photoresponse of two-dimensional electron systems in the quantum Hall regime. The photoresponse consists of two equally important components: the longitudinal component, caused by the photoinduced change of the longitudinal resistance Rxx, and the transversal component, caused by the photoinduced Hall currents and by the photoinduced change of Rxy. Both these components are connected with two mechanisms of the photoresponse: a nonresonant bolometric, and a cyclotron-resonant contribution.

The cyclotron resonance in Heterostructures with the InSb/AlInSb quantum wells

The absorption of two-dimensional electrons in InSb-based quantum wells in the quantized magnetic fields in the terahertz spectral region are studied. A p-Ge-based cyclotron laser was used as the radiation source. The effective mass of carriers at the Fermi level equal to 0.0219m0 (m0 is the mass of a free electron) is determined from the cyclotron resonance spectra. It is shown that the electron spectrum is described by the Kane model in a wide range of magnetic fields. An anomalously pronounced splitting of the cyclotron resonance line not associated with the nonparabolicity of the conduction band of InAs is observed in low magnetic fields, which can be attributed to the effect of the spin-orbit interaction.

Asymmetric AlAsSb/InAs/CdMgSe quantum wells grown by molecular-beam epitaxy

Asymmetric (6.7–300)-nm-thick InAs quantum wells (QWs) confined between AlAsSb and CdMgSe barriers have been fabricated by molecular-beam epitaxy. A special procedure of the CdMgSe-on-InAs growth initiation, exploiting an ex situ S passivation of InAs and in situ deposition of an ultrathin ZnTe buffer layer, results in the fabrication of high quality structures with a density of extended defects below 106 cm2. QW photoluminescence studies demonstrate a confinement effect and confirm the type I band alignment at the heterovalent InAs/CdMgSe interface mediated by the ZnTe interlayer. Observation of Shubnikov de Haas oscillations of magnetoresistance for an asymmetric 19-nm-thick InAs QW indicates an existence of the two-dimensional electron gas with the low-temperature sheet electron density of 1.3×1012 cm−2 and the mobility as high as ∼10 000 cm2/V s.

Cyclotron resonance study in InAs/AlSb quantum well heterostructures with two occupied electronic subbands

We report on the cyclotron resonance (CR) study in InAs/AlSb (001) quantum well (QW) heterostructures with two occupied electronic subbands. Experimental results are compared with the CR energy calculations in the self-consistent Hartree approximation. Our theoretical approach is based on the 8-band k · p Hamiltonian and takes into account the band nonparabolicity, lattice-mismatch deformation, and spin-orbit coupling. We find out a large splitting of CR line associated with a difference in cyclotron energies in the first and second electronic subbands. The results of CR study in InAs/AlSb QW heterostructures reveal pronounced effect of the “built-in” electric field on CR spectra in the samples with two occupied electronic subbands.

Highly sensitive submillimeter InSb photodetectors

Submillimeter photoconductivity of the electron gas in bulk InSb has been studied. A new design of the InSb photodetector in the form of planar coils with a length-to-width ratio of two orders of magnitude is suggested. This design enables fabrication of highly sensitive photodetectors with the responsivity peak tunable by magnetic field.

Fast terahertz detectors with spectral tunability based on quantum Hall Corbino devices

We present THz photoconductivity measurements on Corbino-shaped GaAs∕AlGaAs heterostructures. The THz source is a pulsed p-Ge laser, which provides photon frequencies of 1.7THzto2.5THz (corresponding to wavelengths of 180–120μm). We investigate the relaxation process from the dissipative state to the quantum Hall state time-resolved and find that the relaxation time depends on the applied voltage and on the mobility of the sample. Relaxation times of approximately 10ns to over 200ns are observed. A simple picture is suggested to explain the results. In addition, spectrally resolved measurements are discussed. The short response time and the useful spectral selectivity together with the high sensitivity make QH devices promising for high-performance THz detectors.We present THz photoconductivity measurements on Corbino-shaped GaAs∕AlGaAs heterostructures. The THz source is a pulsed p-Ge laser, which provides photon frequencies of 1.7THzto2.5THz (corresponding to wavelengths of 180–120μm). We investigate the relaxation process from the dissipative state to the quantum Hall state time-resolved and find that the relaxation time depends on the applied voltage and on the mobility of the sample. Relaxation times of approximately 10ns to over 200ns are observed. A simple picture is suggested to explain the results. In addition, spectrally resolved measurements are discussed. The short response time and the useful spectral selectivity together with the high sensitivity make QH devices promising for high-performance THz detectors.

Current injection induced terahertz emission from 4H-SiC p-n junctions

We report on current injection induced terahertz electroluminescence from 4H-SiC p-n junctions with operating temperature up to 270 K. The emission is assigned to intracenter optical transitions in donor centers, initiated by the injection of non-equilibrium carriers into the n-doped region of a SiC p-n junction. At a pumping current of 300 mA at 100 K, the integrated output power was 58 μW from the device surface with an area of 3 mm2. These results suggest that THz emitting devices can be fabricated with simple structures of SiC p-n junctions, with relatively high operating temperatures and reasonable output powers.

Control by an electric field of electron–hole separation in type-II heterostructures

Abstract We report the realization of multi-period devices in which each period consists of two-dimensional electron and hole layers whose effective distance is controlled by an external bias. The current–voltage characteristics of devices based on InAs/AlxGa1−xAsSb/Al0.1Ga0.9AsSb type-II quantum well structures show a behavior that is consistent with a predicted enhancement of the radiative recombination in this type of devices at T=77 K . We have found that increasing the number of periods and decreasing the operating temperature considerably improves the electrical performance of the devices.

PROPERTIES OF TWO-DIMENSIONAL ELECTRON GAS CONTAINING SELF-ORGANIZED QUANTUM ANTIDOTS

A nonuniform two-dimensional electron gas in a heterojunction with inserted self-organized electrically inactive dots (acting as antidots) has been fabricated by molecular-beam epitaxy of AlGaAs/AlInAs/GaAs layer sequences. Transport measurements give the ratio of the transport mobility to the quantum mobility less than four, which suggests that the dominant scattering at low magnetic fields is the short-range scattering from the lateral potential of the antidots. Far-infrared cyclotron resonance (CR) spectra show an absorption mode as narrow as 0.5 cm−1 at high magnetic fields associated with the high-mobility electron gas formed between the antidot islands and confined in the lateral directions. The confinement energy of 14 cm−1 is derived from the CR spectra.

Application of quantum Hall devices for FIR detection

Abstract We propose a novel concept for FIR light detection by means of Hall devices biased at strong currents. The base of the device operation is the effect of photoinduced breakdown of the integer quantum Hall effect (QHE). We demonstrate experimentally that the increase of the bias current from 100 to 300 μA leads to the photoresponse enhancement by over two orders of magnitude. Application of the presented results for designing a tunable high sensitive FIR photodetector is discussed.