Current oscillations and stable electric field domains in doped GaAs/AlAs superlattices

The crossover between two regimes has been observed in the vertical electric transport of weakly coupled GaAs/AlAs superlattices (SLs). At fixed d.c. bias, the SLs can be triggered by illumination to switch from a regime of temporal current oscillation to the formation of a stable electric field domain. The conversion can be reversed by raising the sample temperature to about 200 K. An effective carrier injection model is proposed to explain the conversion processes, taking into account the contact resistance originating from DX centres in the n(+)-Al0.5Ga0.5As contact layers which is sensitive to light illumination and temperature. In addition, quasiperiodic oscillations have been observed at a particular d.c. bias voltage.

Suppression of ballistic electron transmission through a semiconductor II-structure by an external transverse electric field

We have conducted numerical studies of ballistic electron transport in a semiconductor II-structure when an external transverse electric field is applied. The device conductance as a function of electron energy and the strength of the transverse electric field is calculated on the basis of tight-binding Green's function formalism. The calculations show that a relatively weak electric field can induce very large decrease in the electron transmission across the structure. When the transverse electric field is sufficiently strong, electrons can hardly be transported through the device. Thus the performance of the device can be greatly improved for it is much easier to control electron transport through the device with an external transverse electric field.

Perpendicular-electric-field dependence of exciton binding energy studied by continuous-wave photoluminescence

The reduction of exciton binding energy induced by a perpendicular electric field in a stepped quantum well is studied. From continuous-wave photoluminescence spectra at 77 K we have observed an obvious blueshift of the exciton peak due to a spatially direct-to-indirect transition of excitons. A simple method is used to calculate the exciton binding energy while the inhomogeneous broadening is taken into account in a simple manner. The calculated result reproduces remarkably well the experimental observation.

An investigation of the formation mechanisms of electric field domains in GaAs/AlAs superlattices

We have studied the vertical transport and formation mechanisms of electric field domains in doped weakly-coupled GaAs/AlAs superlattices. Under hydrostatic pressure two kinds of sequential resonant tunneling are observed within the pressure range from 0 to 4.5 kbar. A transition from Gamma-Gamma to Gamma-X sequential resonant tunneling occurs at P-t approximate to 1.6 kbar. For P < P-t, the high electric field domain is formed by the Gamma-Gamma process, while for P > P-t it is preferentially formed by the Gamma-X process.

DIRECT OBSERVATION FOR THE REDUCTION OF EXCITON BINDING-ENERGY INDUCED BY PERPENDICULAR ELECTRIC-FIELD

We experimentally study the effect of perpendicular electric field on the exciton binding energy using a specially designed step quantum well. From photoluminescence spectra at the temperature of 77 K, we have directly observed remarkable blueshift of the exciton peak due to the transition from spatially direct to spatially indirect excitons induced by electric field. (C) 1995 American Institute of Physics.

Effect of a step quantum well structure and an electric-field on the Rashba spin splitting

Spin splitting of conduction subbands in Al_(0.3)Ga_(0.7)As/GaAs/Al_xGa_(1-x)As/Al_(0.3)Ga_(0.7)As step quantum wells induced by interface and electric field related Rashba effects is investigated theoretically by the method of finite difference. The dependence of the spin splitting on the electric field and the well structure, which is controlled by the well width and the step width, is investigated in detail. Without an external electric field, the spin splitting is induced by an in terface related Rashba term due to the built-in structure inversion asymmetry. Applying the external electric field to the step QW, the Rashba effect can be enhanced or weakened, depending on the well structure as well as the direction and the magnitude of the electric field. The spin splitting is mainly controlled by the interface related Rashba term under a negative and a stronger positive electric field, and the contribution of the electric field related Rashba term dominates in a small range of a weaker positive electric field.A method to determine the interface parameter is proposed.The results show that the step QWs might be used as spin switches.

Polarization switching current of vertical cavity surface-emitting Lasers in an applied electric field

The polarization of vertical-cavity surface-emitting laser (VCSEL) can be controlled by electro-optic birefringence. We calculated the birefringence resulted from external electric field which was imposed on the top DBR of VCSEL by assuming that the two polarization modes were in the same place of the gain spectra in the absence of electric field beginning. By modifying SFM, the affection of the electric field strength on the polarization switching currents between the two polarization modes had been shown.

Transport properties through quantum dot in a vertical electric field

The transport properties through a quantum dot are calculated using the recursion method. The results show that the electric fields can move the conductive peaks along the high- and low-energies. The electric field changes the intensity of conductance slightly. Our theoretical results should be useful for researching and making low-dimensional semiconductor optoelectronic devices. (C) 2002 Elsevier Science B.V. All rights reserved.

Static and dynamic electric field domain formation in a doped GaAs/AlAs superlattice

We have observed the transition from static to dynamic electric field domain formation induced by a transverse magnetic field and the sample temperature in a doped GaAs/AlAs superlattice. The observations can be very well explained by a general analysis of instabilities and oscillations of the sequential tunnelling current in superlattices based solely on the magnitude of the negative differential resistance region in the tunnelling characteristic of a single barrier. Both increasing magnetic field and sample temperature change the negative differential resistance and cause the transition between static and dynamic electric field domain formation. (C) 2000 Elsevier Science B.V. All rights reserved.

Formation mechanism of electric field domains

Hydrostatic pressure measurements are used to investigate the formation mechanism of electric field domains in doped weakly-coupled GaAs/AlAs superlattices. For the first plateau-like region in the I-V curve, two kinds of sequential resonant tunnelling are observed. For P<2 kbar the high-field domain is formed by the Gamma-Gamma process, while for P>2 kbar the high-field domain is formed by the T-X process. For the second plateau-libe region, the high-field domain is attributed to Gamma-X sequential resonant tunnelling. (C) 1998 Elsevier Science B.V. All rights reserved.

Effects of silicon incorporation on composition, structure and electric conductivity of cubic boron nitride thin films

We have achieved in-situ Si incorporation into cubic boron nitride (c-BN) thin films during ion beam assisted deposition. The effects of silicon incorporation on the composition, structure and electric conductivity of c-BN thin films were investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and electrical measurements. The results suggest that the content of the cubic phase remains stable on the whole with the incorporation of Si up to a concentration of 3.3 at.%, and the higher Si concentrations lead to a gradual change from c-BN to hexagonal boron nitride. It is found that the introduced Si atoms only replace B atoms and combine with N atoms to form Si-N bonds, and no evidence of the existence of Si-B bonds is observed. The resistance of the Si-doped c-BN films gradually decreases with increasing Si concentration, and the resistivity of the c-BN film with 3.3 at.% Si is lowered by two orders of magnitude as compared to undoped samples.