We describe monocrystalline graphitic films, which are a few atoms thick but are nonetheless stable under ambient conditions, metallic, and of remarkably high quality. The films are found to be a two-dimensional semimetal with a tiny overlap between valence and conductance bands, and they exhibit a strong ambipolar electric field effect such that electrons and holes in concentrations up to 10 13 per square centimeter and with room-temperature mobilities of ∼10,000 square centimeters per volt-second can be induced by applying gate voltage.

http://science.sciencemag.org/content/sci/306/5696/666.full.pdf

Electric Field Effect in Atomically Thin Carbon Films

We propose an electron wave analog of the electro‐optic light modulator. The current modulation in the proposed structure arises from spin precession due to the spin‐orbit coupling in narrow‐gap semiconductors, while magnetized contacts are used to preferentially inject and detect specific spin orientations. This structure may exhibit significant current modulation despite multiple modes, elevated temperatures, or a large applied bias.

Electronic analog of the electro‐optic modulator

A new type of semiconductor laser is studied, in which injected carriers in the active region are quantum mechanically confined in two or three dimensions (2D or 3D). Effects of such confinements on the lasing characteristics are analyzed. Most important, the threshold current of such laser is predicted to be far less temperature sensitive than that of conventional lasers, reflecting the reduced dimensionality of electronic state. In the case of 3D‐QW laser, the temperature dependence is virtually eliminated. An experiment on 2D quantum well lasers is performed by placing a conventional laser in a strong magnetic field (30 T) and has demonstrated the predicted increase of T0 value from 144 to 313 °C.

Multidimensional quantum well laser and temperature dependence of its threshold current

Quantum dot (QD) solar cells have the potential to increase the maximum attainable thermodynamic conversion efficiency of solar photon conversion up to about 66% by utilizing hot photogenerated carriers to produce higher photovoltages or higher photocurrents. The former effect is based on miniband transport and collection of hot carriers in QD array photoelectrodes before they relax to the band edges through phonon emission. The latter effect is based on utilizing hot carriers in QD solar cells to generate and collect additional electron–hole pairs through enhanced impact ionization processes. Three QD solar cell configurations are described: (1) photoelectrodes comprising QD arrays, (2) QD-sensitized nanocrystalline TiO 2 , and (3) QDs dispersed in a blend of electron- and hole-conducting polymers. These high-efficiency configurations require slow hot carrier cooling times, and we discuss initial results on slowed hot electron cooling in InP QDs.

/pdf/quantum-dot-solar-cells-4f2pqetwm9.pdf

Quantum dot solar cells

This review provides numerical and graphical information about many (but by no means all) of the physical and electronic properties of GaAs that are useful to those engaged in experimental research and development on this material. The emphasis is on properties of GaAs itself, and the host of effects associated with the presence of specific impurities and defects is excluded from coverage. The geometry of the sphalerite lattice and of the first Brillouin zone of reciprocal space are used to pave the way for material concerning elastic moduli, speeds of sound, and phonon dispersion curves. A section on thermal properties includes material on the phase diagram and liquidus curve, thermal expansion coefficient as a function of temperature, specific heat and equivalent Debye temperature behavior, and thermal conduction. The discussion of optical properties focusses on dispersion of the dielectric constant from low frequencies [κ0(300)=12.85] through the reststrahlen range to the intrinsic edge, and on the ass...

Semiconducting and other major properties of gallium arsenide

Data are presented showing that Zn diffusion into an AlAs‐GaAs superlattice (41 Lz∼45‐A GaAs layers, 40 LB∼150‐A AlAs layers), or into AlxGa1−xAs‐GaAs quantum‐well heterostructures, increases the Al‐Ga interdiffusion at the heterointerfaces and creates, even at low temperature (<600 °C), uniform compositionally disordered AlxGa1−xAs. For the case of the superlattice, the diffusion‐induced disordering causes a change from direct‐gap AlAs‐GaAs (Eg∼1.61 eV) to indirect‐gap AlxGa1−xAs (x∼0.77, EgX∼2.08 eV).

Disorder of an AlAs‐GaAs superlattice by impurity diffusion

We report experimental results that replacing hydrogen with deuterium during the final wafer sintering process greatly reduces hot electron degradation effects in metal oxide semiconductor transistors due to a new giant isotope effect. Transistor lifetime improvements by factors of 10–50 are observed. A plausible physical theory suggests that the benefits of deuterium use may be general and also applicable to other areas of semiconductor device processing and fabrication.

Reduction of hot electron degradation in metal oxide semiconductor transistors by deuterium processing

We present a theoretical study of semiconductor T‐structures which may exhibit transistor action based on quantum interference. The electron transmission through a semiconductor quantum wire can be controlled by an external gate voltage that modifies the penetration of the electron wavefunction in a lateral stub, affecting in this way its interference pattern. The structures are modeled as ideal two‐dimensional electron waveguides and a tight‐binding Green’s function technique is used to compute the electron transmission and reflection coefficients. The calculations show that relatively small changes in the stub length can induce strong variations in the electron transmission across the structure. Operation in the fundamental transverse mode appears to be important for applications. We also show that a bound state of purely geometrical origin nucleates at the intersection between waveguide and stub. The performance of the device can be improved by inserting additional stubs of slightly different lengths. ...

Theory for a quantum modulated transistor

Preface. Acknowledgments. A Brief Review of the Basic Equations. The Symmetry of the Crystal Lattice. The Theory of Energy Bands in Crystals. Imperfections of Ideal Crystal Structure. Equilibrium Statistics for Electrons and Holes. Self--Consistent Potentials and Dielectric Properties. Scattering Theory. The Boltzmann Transport Equation. Generation--Recombination. The Heterojunction Barrier. The Device Equations of Shockley and Stratton. Numerical Device Simulations. Diodes. Laser Diodes. Transistors. Future Semiconductor Devices. Appendix A: Tunneling and the Golden Rule. Appendix B: The One Band Approximation. Appendix C: Temperature Dependence of the Band Structure. Appendix D: Hall Effect and Magnetoresistance. Appendix E: The Power Balance Equation. Appendix F: The Self--Consistent Potential at a Heterojunction. Appendix G: Schottky Barrier Transport. Index. About the Author.

Advanced Theory of Semiconductor Devices

1. Numerical Aspects and Implementation of the DAMOCLES Monte Carlo Device Simulation Program.- 2. Scattering Mechanisms for Semiconductor Transport Calculations.- 3. Evaluating Photoexcitation Experiments Using Monte Carlo Simulations.- 4. Extensions of the Monte Carlo Simulation in Semiconductors to Fast Processes.- 5. Theory and Calculation of the Deformation Potential Electron-Phonon Scattering Rates in Semiconductors.- 6. Ensemble Monte Carlo Investigation of Nonlinear Transport Effects in Semiconductor Heterostructure Devices.- 7. Monte Carlo Simulation of Quasi-One-Dimensional Systems.- 8. The Application of Monte Carlo Techniques in Advanced Hydrodynamic Transport Models.- 9. Vectorization of Monte Carlo Algorithms for Semiconductor Simulation.- 10. Full Band Monte Carlo Program for Electrons in Silicon.

Karl Hess

Papers

Disorder of an AlAs‐GaAs superlattice by impurity diffusion

Reduction of hot electron degradation in metal oxide semiconductor transistors by deuterium processing

Theory for a quantum modulated transistor

Advanced Theory of Semiconductor Devices

Monte Carlo Device Simulation: Full Band and Beyond