Range Of Doping Densities Research Articles

Characteristics of Planar and Conformal Contact GaAs Core–Shell Nanowire Array Solar Cells

As the transparent contact in radial p-n junction core-shell nanowire array solar cells can be either planar or conformal, the characteristics of these two types of device structure would be very different since conformal contact gives rise to severe band bending. Although radial p-n junction GaAs core-shell nanowire array solar cell with conformal transparent contact has been briefly inferred to have an inferior performance compared to the same nanowire array solar cell with planar transparent contact, the characteristics of these two types of radial p-n junction core-shell nanowire array solar cells are not known. Furthermore, it is unknown how the performance of these two types of solar cell compares with each other when the nanowire design parameters are optimized according to device physics of these two types of solar cell. In this paper, it is shown that radial p-n junction GaAs core-shell nanowire array solar cells with planar transparent contact are prone to carrier avalanche breakdown, and hence have a limited range of doping density. On the other hand, carrier diffusion in radial p-n junction GaAs core-shell nanowire array solar cells with conformal transparent contact is poor and hence requires a high doping to the core in order to increase the output voltage. All in all, this paper reveals that either type of transparent contact structure yields essentially the same energy conversion efficiency as long as the radial p-n junction GaAs core-shell nanowires are designed to suit the device physics of the type of transparent contact.

Self-Sustained Spin-Polarized Current Oscillations in Diluted Magnetic Semiconductor Superlattices

A direct current (dc) voltage biased II-VI semiconductor multiquantum well structure attached to normal contacts exhibits self-sustained spin-polarized current oscillations if one or more of its wells are doped with Mn. Self-sustained current oscillations are due to repeated triggering of charge dipole domains at the magnetic wells and motion towards the collector. Without magnetic impurities, the only configurations appearing in these structures are stationary. Analysis and numerical solution of a nonlinear spin transport model yield the minimal number of wells and the range of doping density needed to find oscillations, the current-voltage characteristic curve and the main features of stable stationary and time-periodic states. Our study could allow designing the oscillatory spin-polarized current injectors.

Influence of carrier diffusion on an anode trapped domain formation in a transferred electron device

This paper presents an influence of the electric field dependence of the diffusion coefficient of electrons (D(E) relation) on a formation of a stable domain at an anode contact in a transferred electron device. The stable domain (anode trapped domain) has been observed in a planar Gunn device experimentally, and it has been shown that a large trigger voltage is needed to launch a new domain if a preceding domain has been trapped. Computer simulations have been carried out in order to find a condition to form the trapped domain. Various D(E) relations of GaAs presented by many authors have been adopted to the simulation, and it is shown that one of these D(E) relations is suitable to describe the dynamic behaviors of electrons in GaAs. Simulated results have indicated that the trapped domain occurs in a certain range of doping density.