The strong suppression of equilibrium magnetic tunneling in a graphene/hBN/graphene heterostructure caused by the Coulomb correlation gap in the tunneling density of states has been found. Comparison has shown that the suppression of the equilibrium tunneling conductivity G_0 in a high magnetic field with a decrease in the temperature and the dependence of the observed gap width Δ on the filling factor of Landau levels ν are qualitatively similar to the respective results of similar experiments in GaAs heterostructures and has confirmed our hypothesis concerning the nature of the effect. However, the determined gap width Δ is much larger than those measured in all previous works in semiconductor heterostructures probably because the cyclotron energy in graphene is much higher than that in GaAs in the region of low Landau levels.

As a result of studying the relaxation of photocurrent in p – i – n GaAs/AlAs heterostructures, abrupt features caused by resonant tunneling through the electronic levels of quantum dots in the barrier layers are found. It is shown that the time intervals for the manifestation of these resonances on the relaxation curves are determined by the charge-accumulation dynamics at hole levels of quantum dots and recombination with their participation. Strong random fluctuations of the photocurrent in the postresonant region caused by local fluctuations of the residual charge at hole levels of quantum dots are also found. The study of relaxation in the medium and long-wavelength optical ranges confirms our interpretation of the detected effects.

p - i - n semiconductor heterostructures are common optoelectronic devices with numerous applications hinging on the non-trivial kinetics of photoexcited charge carriers within them. One such effect manifests itself as an oscillation of the photocurrent versus the applied bias voltage and has been qualitatively studied recently. However, a model that would explain the experimentally observed magnitude of the oscillations is, to the best of our knowledge, still absent. In the present work we consider a model wherein electrons from the highly-doped p -region are resonantly captured into 2D states of the triangular quantum well formed by the undoped i -region via scattering on impurities. We find that the rate of capture into 2D states is determined by the form of the wave function of these states and increases sharply when the tail of the wave function penetrates deeply into the highly doped region, resulting in a sharp increase in the photocurrent. Our analysis of the dependence of the positions of the photocurrent maxima versus bias voltage shows good agreement with experiments and confirms the applicability of our model.

The behavior of the photocurrent in GaAs/AlAs p-i-n-heterostructures is studied in a magnetic field parallel to the heterolayers in the wavelength range from 395 to 650 nm. A strong dependence of the non-oscillating component of the photocurrent on the radiation wavelength associated with the suppression of the diffusion current by the magnetic field was found. It is shown that the behavior of the oscillating component of the photocurrent in a magnetic field does not depend on the wavelength of light and is determined by the transfer of electrons through the dimensional quantization level in a triangular near-barrier well. It is shown that the suppression of the oscillating component by the magnetic field is due to the smearing of the level in the triangular well due to the motion of electrons parallel to the walls of the well and perpendicular to the magnetic field. Keywords: heterostructures, photoconductivity, magnetotunneling.

The behavior of the photocurrent in GaAs / AlAs p-i-n heterostructures is studied in a magnetic field parallel to the heterolayers in the wavelength range from 395 to 650 nm. A strong dependence of the non-oscillating component of the photocurrent on the radiation wavelength associated with the suppression of the diffusion current by the magnetic field was found. It is shown that the behavior of the oscillating component of the photocurrent in a magnetic field does not depend on the wavelength of light and is determined by the transfer of electrons through the dimensional quantization level in a triangular near-barrier well. It is shown that the suppression of the oscillating component by the magnetic field is due to the smearing of the level in the triangular well due to the motion of electrons parallel to the walls of the well and perpendicular to the magnetic field.

Based on the study of photoconductivity in GaAs / AlAs p-i-n heterostructures in the visible light range, the dominant role of the diffusion channel of photoexcited electrons from heavily doped layers in the formation of photocurrent oscillations from the bias voltage and the determining contribution of this channel to the total current through the structure is shown. A qualitative model of the transport of excited carriers is considered, which assumes the diffusion channel as the main source of photooscillations. Keywords: heterostructures, photoconductivity.

Based on the study of photoconductivity in GaAs / AlAs p-i-n heterostructures in the visible light range, the dominant role of the diffusion channel of photoexcited electrons from heavily doped layers in the formation of photocurrent oscillations from the bias voltage and the determining contribution of this channel to the total current through the structure is shown. A qualitative model of the transport of excited carriers is considered, which assumes the diffusion channel as the main source of photooscillations.

The effect of the power of incident light radiation on the behavior of quantum oscillations of the photocurrent in single-barrier p–i–n GaAs/AlAs heterostructures with InAs quantum dots has been studied. The strong suppression of initial oscillations with increasing power caused by the destructive effect of random fluctuations of the potential generated by the accumulation of the charge at hole levels of quantum dots has been found. The critical effect of recombination in the region of the heavily doped p layer on the relative amplitude of oscillations at low powers has been revealed. The generation of the current observed in n–i–n resonant-tunneling structures has been detected at a high power. A new qualitative model of the formation of oscillations based on the diffusion transport of photoexcited electrons from the p layer has been proposed. This model has also been confirmed by measurements of oscillations at various wavelengths.

The strong effect of the wavelength of incident light λ on the fraction of the oscillatory component of the photocurrent in p–i–n GaAs/AlAs heterostructures has been revealed. The effect has been explained within the extended “resonant tunneling” model of the origin of oscillations taking also into account the dependence of the light absorption depth in the heterostructure on the wavelength λ. The behavior of photo-oscillations in the magnetic field appears to be similar to the behavior of tunneling resonances in n–i–n heterostructures with wide quantum wells and has confirmed both our interpretation of the effect of the wavelength on the relative contribution of the oscillatory component to the photocurrent and the applicability of our model of oscillations.

As a result of studying the relaxation of the photocurrent in p-i-n GaAs / AlAs heterostructures, we discovered/ registered sharp features caused by resonant tunneling through the electronic levels of quantum dots in the barrier layers. It was shown that the time intervals of the manifestation of these resonances on the relaxation curves are determined by the dynamics of charge accumulation at the hole levels of quantum dots and by recombination with their participation.Strong random fluctuations of the photocurrent in the postresonant region, caused by local fluctuations of the residual charge at the hole levels of quantum dots, were also found.The study of relaxation in the medium and long wavelength light ranges confirms our interpretation of the observed effects.

Resonant tunneling through defect levels in the h-BN barrier of van-der-Waals heterostructures is investigated. The effect of multiplication of the tunneling resonances through these levels due to the effect of a high degree of imperfection of the structure of the neighboring graphene layer formed intentionally by its processing in plasma is found. Various mechanisms of such an effect are discussed.

Investigated resonant tunneling through defect levels in h-BN barrier van der Waals heterostructures. The effect of multiplication of tunnel resonances through these levels was found, due to the influence of a high degree of defectiveness of the structure of the neighboring layer of graphene, created by intentionally processing in plasma. Various mechanisms of such influence are discussed.

AbstractTunneling and magnetic tunneling are investigated in graphene/ h -BN/graphene van der Waals heterosystems. Two new types of systems are found, in which negative differential conductivity regions are implemented due to resonant tunneling through defect levels in the h -BN barrier, and current caused by their presence is generated.

The evolution of the manifestation of levels of defects in h-BN in tunneling through graphene/h-BN/graphene heterostructures with various degrees of perfection, from completely defectless to those with several tens of levels in the band gap of h-BN, has been studied. It has been shown that the behavior of these levels is related to the motion of Dirac points and the chemical potentials of graphene layers at change in the bias and gate voltages, which is described by the electrostatic model of an ideal defectless heterostructure. The density of states of graphene in a magnetic field has been studied by its probing by the level of a single defect with a sensitivity allowing the detection of splitting of the zeroth Landau level caused by the lifting of the spin and valley degeneracy already at B ∼ 4 T.

The transfer of electronic charge across the interface of two van der Waals crystals can underpin the operation of a new class of functional devices. Among van der Waals semiconductors, an exciting and rapidly growing development involves the “post‐transition” metal chalcogenide InSe. Here, field effect phototransistors are reported where single layer graphene is capped with n‐type InSe. These device structures combine the photosensitivity of InSe with the unique electrical properties of graphene. It is shown that the light‐induced transfer of charge between InSe and graphene offers an effective method to increase or decrease the carrier density in graphene, causing a change in its resistance that is gate‐controllable and only weakly dependent on temperature. The charge transfer at the InSe/graphene interface is probed by Hall effect and photoconductivity measurmentes and it is demonstrated that light can induce a sign reversal of the quantum Hall voltage and photovoltaic effects in the graphene layer. These findings demonstrate the potential of light‐induced charge transfer in gate‐tunable InSe/graphene phototransistors for optoelectronics and quantum metrology.

Tunneling and magnetic tunneling are investigated in graphene/h-BN/graphene van der Waals heterosystems. Two new types of systems are found, in which negative differential conductivity regions are implemented due to resonant tunneling through defect levels in the h-BN barrier, and current caused by their presence is generated.

Works, mostly experimental, concerning the most interesting features of application of the resonant tunneling spectroscopy to a new type of heterosystems, van der Waals heterostructures, have been briefly reviewed. These heterostructures appeared after the recent discovery of two-dimensional crystals, which are a new class of materials beginning with graphene. The role of the angular matching of crystal lattices of conducting graphene electrodes of van der Waals systems in carrier tunneling between them has been analyzed together with the closely related problems of satisfaction of conservation laws in tunneling transitions. Manifestations of multiparticle correlation interactions between carriers in van der Waals systems such as Wigner crystallization of electrons in a two-dimensional electron gas in a magnetic field and Bose condensation of excitons in parallel two-dimensional electron gases have been briefly discussed.