EFFECTS OF AN EXTERNAL MAGNETIC-FIELD ON SHALLOW DONOR LEVELS IN SEMICONDUCTORS

An extension of Faulkner's method for the energy levels of the shallow donor in silicon and germanium at zero field is made in order to investigate the effects of a magnetic field upon the excited states. The effective-mass Hamiltonian matrix elements of an electron bound to a donor center and subjected to a magnetic field B, which involves both the linear and quadratic terms of magnetic field, are expressed analytically and matrices are solved numerically. The photothermal ionization spectroscopy of phosphorus in ultrapure silicon for magnetic fields parallel to the [1,0,0] and [1,1,1] directions and up to 10 T is explained successfully.

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.

Effects of point defects on lattice parameters of semiconductors

A model for analyzing the correlation between lattice parameters and point defects in semiconductors has been established. The results of this model for analyzing the substitutes in semiconductors are in accordance with those from Vegard's law and experiments. Based on this model, the lattice strains caused by the antisites, the tetrahedral and octahedral single interstitials, and the interstitial couples are analyzed. The superdilation in lattice parameters of GaAs grown at low temperatures by molecular-beam epitaxy can be interpreted by this model, which is in accordance with the experimental results. This model provides a way of analyzing the stoichiometry in bulk and epitaxial compound semiconductors nondestructively.

Band structure parameters of zinc-blende GaN, AlN and their alloys Ga1-xAlxN

The electronic properties of wide energy gap zinc-blende structure GaN, AlN and their alloys Ga1-xAlxN are investigated using the empirical pseudopotential method. Electron and hole Effective mass parameters, hydrostatic and shear deformation potential constants of the valence band at Gamma and those of the conduction band at Gamma and X are obtained. The energies of Gamma, X, L conduction valleys of Ga1-xAlxN alloy versus Al fraction x are also calculated. The information will be useful for the design of lattice mismatched heterostructure optoelectronic devices in the blue light range.

Theoretical Study on the Butt-coupling of Semiconductor Laser and Fiber Bragg Grating

The butt-coupling between a semiconductor laser diode and a fiber Bragg grating external cavity acts a key roll on the laser characteristics. The scatter matrix method considering the butt-coupling efficiency is used to analyze the butt-coupling between them. It is found that the butt-coupling distance and coupling efficiency determine the laser characteristics. For strong feedback, the single lasing wavelength changes in the reflection bandwidth of the effective reflectivity ( approximately the Bragg region of the fiber Bragg grating) as the distances change. For weak feedback condition, some different results are obtained. The SMSRs in the two conditions are presented and analyzed. These results can provide important design guidance of device parameters for the practical fabrication.

Single steady frequency and narrow line width external cavity semiconductor laser

A single longitudinal mode and narrow line width external cavity semiconductor laser is proposed. It is constructed with a semiconductor laser, collimator, a flame grating, and current and temperature control systems. The one facet of semiconductor laser is covered by high transmission film, and another is covered by high reflection film. The flame grating is used as light feedback element to select the mode of the semiconductor laser. The temperature of the constructed external cavity semiconductor laser is stabilized in order of 10(-3)degreesC by temperature control system. The experiments have been carried out and the results obtained-the spectral fine width of this laser is compressed to be less than 1.4MHz from its original line-width of more than 1200GHz and the output stability (including power and mode) is remarkably enhanced.

Real-time far distance micro-vibration measurement using an external cavity semiconductor laser interferometer with a feedback control system

An external cavity semiconductor laser interferometer used to measure far distance micro-vibration in real time is proposed. In the interferometer, a single longitudinal mode and excellent coherent characteristic grating external cavity semiconductor laser is constructed and acted as a light source and a phase compensator. Its coherent length exceeds 200 meters. The angle between normal and incidence beam of the far object is allowed to change in definite range during the measurement with this interferometer, and this makes the far distance interference measurement easier and more convenient. Also, it is not required to keep the amplitudes of the first and second harmonic components equal, and then the dynamic range is increased. A feedback control system is used to compensate the phase disturbance between the two interference beams introduced by environmental vibration.

Experimental study on tunable external cavity photodetectors

In this paper, an experiment on tunable resonant cavity enhanced (RCE) photodetector with external cavity is reported. It is the first time to realize a tunable RCE photodetector in China. A tuning range about 10 nm has been obtained and further extension is expected. Corresponding theoretical analysis and discussions are presented. (C) 2000 Elsevier Science B.V. All rights reserved.

Broadly Tunable Grating-Coupled External Cavity Laser With Quantum-Dot Active Region

A broadly tunable and high-power grating-coupled external cavity laser with a tuning range of more than 200 nm and a similar to 200-mW maximum output power was realized, by utilizing a gain device with the chirped multiple quantum-dot (QD) active layers and bent waveguide structure. The chirped QD active medium, which consists of QD layers with InGaAs strain-reducing layers different in thickness, is beneficial to the broadening of the material gain spectrum. The bent waveguide structure and facet antireflection coating are both effective for the suppression of inner-cavity lasing under large injection current.

Generation of optimized wavelength-tunable optical pulse from an uncooled gain-switched Fabry-Perot semiconductor laser using optical amplifier as external light injection

We present a novel system design that can generate the optimized wavelength-tunable optical pulse streams from an uncooled gain-switched Fabry-Perot semiconductor laser using an optical amplifier as external light source. The timing jitter of gain-switched laser has been reduced from about 3 ps to 600 fs and the pulse width has been optimized by using our system. The stability of the system was also experimentally investigated. Our results show that an uncooled gain-switched FP laser system can feasibly produce the stable optical pulse trains with pulse width of 18 ps at the repetition frequency of 5 GHz during 7 h continuous working. We respectively proved the system feasibility under 1 GHz, 2.5 GHz and 5 GHz operation. (c) 2008 Elsevier B.V. All rights reserved.