V. Ryzhii

We study the dynamic ac conductivity of a nonequilibrium two-dimensional electron-hole system in optically pumped graphene. Considering the contribution of both interband and intraband transitions, we demonstrate that at sufficiently strong pumping the population inversion in graphene can lead to the negative net ac conductivity in the terahertz range of frequencies. This effect might be used in graphene-based coherent sources of terahertz radiation.

A novel device - the quantum-dot infrared phototransistor (QDIP) - is proposed and considered theoretically. The QDIP utilizes intersubband electron transitions from the bound states. The dark current and sensitivity are calculated using a proposed analytical model of the QDIP. It is shown that the QDIP can exhibit low dark current, high photoelectric gain and sensitivity surpassing the characteristics of other intersubband photodetectors.

Plasma waves in the two-dimensional electron-hole system in a graphene-based heterostructure controlled by a highly conducting gate are studied theoretically. The energy spectra of two-dimensional electrons and holes are assumed to be conical (neutrinolike), i.e., corresponding to their zero effective masses. Using the developed model, we calculate the spectrum of plasma waves (spatio-temporal variations of the electron and hole densities and the self-consistent electric potential). We find that

We study the effect of population inversion associated with the electron and hole injection in graphene p-i-n structures at the room and slightly lower temperatures. It is assumed that the recombination and energy relaxation of electrons and holes are associated primarily with the interband and intraband processes assisted by optical phonons. The dependences of the electron-hole and optical phonon effective temperatures on the applied voltage, the current-voltage characteristics, and the frequen

Terahertz (THz) lasers on optically pumped multiple-graphene-layer (MGL) structures as their active region are proposed and evaluated. The developed device model accounts for the interband and intraband transitions in the degenerate electron-hole plasma generated by optical radiation in the MGL structure and the losses in the slot or dielectric waveguide. The THz laser gain and the conditions of THz lasing are found. It is shown that the lasers under consideration can operate at frequencies ≳1 T

Plasma waves in graphene-based heterostructures with massless (neutrino-like) two-dimensional electron gas and with a highly conducting substrate (n+-Si) serving as a gate and an isolating gate layer (SiO2) are studied. Using the developed model, we show that the sufficiently long plasma waves exhibit a linear (sound-like) dispersion with the wave velocity determined by the gate layer thickness and the gate voltage. The plasma wave velocity in graphene heterostructures can significantly exceed t

A graphene bilayer phototransistor (GBL-PT) is proposed and analyzed. The GBL-PT under consideration has the structure of a field-effect transistor with a GBL as the channel sandwiched between the back and the top gates. The positive bias of the back gate creates the conducting source and drain sections in the channel, while the negatively biased top gate provides the potential barrier which is controlled by the charge of the photogenerated holes. The features of the GBL-PT operation are associa

We present a model for microwave photoconductivity of two-dimensional electron systems in a magnetic field which describes the effects of strong microwave and steady-state electric fields. Using this model, we derive an analytical formula for the photoconductivity associated with photon- and multi-photon-assisted impurity scattering as a function of the frequency and power of microwave radiation. According to the developed model, the microwave conductivity is an oscillatory function of the frequ

This paper deals with the comparison of quantum well, quantum wire and quantum dot infrared photodetectors (QWIPs, QRIPs and QDIPs, respectively) based on physical analysis of the factors determining their operation. The operation of the devices under consideration is associated with the intersubband (intraband) electron transitions from the bound states in QWs, QRs and QDs into the continuum states owing to the absorption of infrared radiation. The redistribution of the electric potential acros

Abstract We propose a detector of terahertz radiation based on a double graphene-layer heterostructure utilizing the tunnelling between graphene layers and the resonant excitation of plasma oscillations (standing plasma waves). Using the developed device model, we substantiate the detector operation and calculate the spectral characteristics. It is shown that the detector responsivity exhibits the resonant peaks when the frequency of incoming terahertz radiation approaches the resonant plasma fr

We propose to utilize multiple-graphene-layer structures with lateral p-i-n junctions for terahertz and infrared (IR) photodetection and substantiate the operation of photodetectors based on these structures. Using the developed device model, we calculate the detector dc responsivity and detectivity as functions of the number of graphene layers and geometrical parameters and show that the dc responsivity and detectivity can be fairly large, particularly, at the lower end of the terahertz range a

A model is presented for the performance of quantum well infrared photodetectors (QWIPs) utilizing intersubband electron transitions and tunneling injection electrons. The dark current and the responsivity are derived as functions of the QWIP parameters, including the number of the QWs, in an analytical form. Nonlinear effects in the QWIP operation at high infrared power are considered and the threshold value of power density is estimated.

We propose a device model for quantum dot infrared photodetectors (QDIPs) with relatively large lateral spacing between QDs as occurs in QDIPs fabricated and experimentally investigated recently. The developed model accounts for the self-consistent potential distribution and features of the electron capture and transport in realistic QDIPs in dark conditions. The model is used for the calculation of the dark current as a function of the structural parameters, applied voltage and temperature. It

We report on the analysis of thermally-limited operation of quantum-dot infrared photodetectors (QDIPs). A device model is developed and used to calculate the QDIP detectivity as a function of the structural parameters, temperature, and applied voltage, as well as to determine the conditions for the detectivity maximum. The QDIP detectivity is compared with that of quantum-well infrared photodetectors (QWIPs). This work clarifies why the existing QDIPs are still inferior to QWIPs and shows that

We demonstrated that modulated infrared radiation can cause the resonant excitation of plasma oscillations in quantum well diode and transistor structures with high electron mobility. This effect provides a new mechanism for the generation of tunable terahertz radiation using photomixing of infrared signals. We developed a device model for a quantum well photomixer and calculated its high-frequency performance. It was shown that the proposed device can significantly surpass photomixers utilizing