Photocatalytic properties and energy band offset of a tungsten disulfide/graphitic carbon nitride van der Waals heterojunction

WS2/GCN heterojunction is a type-II heterostructure and its electric field separates the electrons and the holes in space.

Simulation of Nonpolar p-GaN/i-N/n-GaN Solar Cells

It is well known that nitride-based devices suffer the polarization effects. A promising way to overcome the polarization effects is growth in a direction perpendicular to thec-axis (nonpolar direction). Nonpolar devices do not suffer polarization charge, and then they have a chance to achieve the high solar efficiency. The understanding of the solar performance of non-polar InGaN-based solar cells will be interesting. For a pin non-polar solar cell with GaN p- and n-cladding layers, the conduction band offset (or barrier height, ) between an intrinsic layer and n-GaN layer is an important issue correlating to the efficiency and fill factor. The efficiency and fill factor will be seriously degraded due to sufficiently high barrier height. To reduce a high barrier height, some graded layers with an energy bandgap between the energy bandgap of n-GaN and InxGa1−xN intrinsic layer can be inserted to the interface of n-GaN and InxGa1-xN layers. From simulation, it indicates that the insertion of graded layer is an effective method to lower energy barrier when there exists a high energy band offset in non-polar nitride devices.

Electronic Structure of CdSe/CdXZn1-XS Core/Shell Quantum Dots

The electronic structures of CdSe/CdxZn1-xS core/shell quantum dots are investigated systematically using the effective-mass approximation method. The calculated results have shown that both of the electron and hole are completely localized at the range of core, which can be ascribed to the large energy band offset in valence band and conduction band. The carriers appear in the region of core or shell, which mainly depend on the competition between the kinetic energy and the potential energy in the heterostrucuture QDs. The transition energies can be widely tuned by the changing the structure parameters.

Upper Limitation to the Performance of Single-Barrier Thermionic Emission Cooling

ABSTRACTWe have re-examined solid-state thermionic emission cooling from first principles and report two key results. First, electrical and heat currents over a semiconductor – semiconductor thermionic barrier are determined by the chemical potential measured from the conduction band edge, not the energy band offset between the two materials as is sometimes assumed. Second, we show the upper limit to the performance of thermionic emission cooling is equivalent to the performance of an optimized thermoelectric device made from the same material. An overview of this theory will be presented and instrumentation being developed to experimentally verify the theory will be discussed.