Argyrios C Varonides

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The neutrality equation in superlattices is discussed in detail. This is a relation that includes (1) all the available carriers contributed by donor impurities (2) the carriers trapped in quantum wells (3) free carriers in the conduction band (4) doping concentration and (5) layer thickness. The idea is to selectively dope the wide band gap material and(More)
– We derive excess carrier populations in quantum wells, embedded in the intrinsic region of p-i-n solar cells. In the process of the analysis, we (a) solve for photo-generated carriers in quantum wells and (b) determine explicit dependence on incident solar wavelength. We include in the computations the existence of optical gaps near 1eV or wavelengths in(More)
High efficiency in crystalline solar cells is currently of great importance and can be achieved by a combination of high and low band gaps in heterostructure designs. Such devices absorb in both short and long wavelengths, thus covering wider absorption areas from the solar spectrum. On the other hand, p-i-n cells provide space for excess absorption at(More)
The generalized Kubo-Greenwood formula for conductivity is used for an explicit calculation of the perpendicular conductivity of GaAs-AlGaAs (crystalline III-V) heterostructures. Two cases are discussed (a) evaluation of DC conductivity at low temperatures and (b) AC conductivity at any temperature T. The method involves the causal Green’s function and(More)
Thermionically escaping electrons comprise traveling quantum mechanical waves liable to trapping and backscattering due to nearest neighbor quantum wells in a multi-layer photovoltaic device. Such losses due to scattering and trapping are taken into consideration in this communication, where transmitted waves are calculated after scattering and trapping(More)
We propose a first principles method of calculating the photo-component of tunneling conductivity of a specific superlattice (SL) photovoltaic structure: an InP/InGaAs P-I(SL)-N solar cell. The method we follow is based on the generalized Greenwood-Kubo formulation and on the causal form of the Green’s function. The vertical conductivity (along the growth(More)
General p-i-n solar cell structures are suitable hosts for regions where quantum effects might occur; excess photo-carriers can be developed in quantum traps (quantum wells) grown along the direction of the cell (from p to n region). The cell absorbs at two different wavelengths (a) the host (Ehost=hc/λhost band-gap) and (b) the optical gap wavelength(More)
Progress in chemically vapor deposited graphene layers on semiconductors (Si) offers new avenues for graphene based Schottky contact solar cells. Direct CVD graphene on silicon forms intimate (ideal) Schottky contact solar cells. Under illumination, thermally excited carriers from the majority and the graphene side regions may overcome the contact barrier(More)
We propose an analytic calculation of the dark current density for GaAs/A1GaAs thick barrier quantum well infrared photo-detectors (QWIP's). We evaluate the dark current component, by integrating (a) drift velocity of the carriers via their kinetic energy (b) the non-tunneling probability factor 1-T (E) (c) the Fermi factor and (d) the 3-d density of states(More)
III-V semiconductor multiquantum-well (mqw) photovoltaic devices show improved collection and transport properties when they are selectively doped. Existence of multiple quantum wells is of advantage because of (a) easier carrier collection (b) photocarrier separation (electrons vs holes) that reduces recombination and (c) of Fermi level shifting. The(More)