Semiconductor Bars Research Articles

Non-Hermitian arrangement for stable semiconductor laser arrays.

We propose and explore a physical mechanism for the stabilization of the complex spatiotemporal dynamics in arrays (bars) of broad area laser diodes taking advantage of the symmetry breaking in non-Hermitian potentials. We show that such stabilization can be achieved by specific pump and index profiles leading to a PT-symmetric coupling between nearest neighboring lasers within the semiconductor bar. A numerical analysis is performed using a complete (2 + 1)-dimensional space-temporal model, including transverse and longitudinal spatial degrees of freedom and temporal evolution of the electric field and carriers. We show regimes of temporal stabilization and light emission spatial redistribution and enhancement. We also consider a simplified (1 + 1)-dimensional model for an array of lasers holding the proposed non-Hermitian coupling with a global axisymmetric geometry. We numerically demonstrate a two-fold benefit: the control over the temporal dynamics over the EELs bar and the field concentration on the central lasers leading to a brighter output beam, facilitating a direct coupling to an optical fiber.

High Power High Efficiency Diode Laser Stack for Processing

High-power diode lasers based on GaAs semiconductor bars are well established as reliable and highly efficient laser sources. As diode laser is simple in structure, small size, longer life expectancy with the advantages of low prices, it is widely used in the industry processing, such as heat treating, welding, hardening, cladding and so on. Respectively, diode laser could make it possible to establish the practical application because of rectangular beam patterns which are suitable to make fine bead with less power. At this power level, it can have many important applications, such as surgery, welding of polymers, soldering, coatings and surface treatment of metals. But there are some applications, which require much higher power and brightness, e.g. hardening, key hole welding, cutting and metal welding. In addition, High power diode lasers in the military field also have important applications. So all developed countries have attached great importance to high-power diode laser system and its applications. This is mainly due their low performance. In this paper we will introduce the structure and the principle of the high power diode stack.

Nonlocal response of tunable photonic metamaterials with semiconductor inclusions

Effective parameters of homogenized photonic crystals with a semiconductor bar in the unit cell are calculated and analyzed. The applied homogenization theory is based on the Fourier formalism within the form-factor division approach. The calculated effective parameters, namely, the components of the effective permittivity tensor, are nonlocal since they depend on not only frequency but also the wave vector. Using the nonlocal effective parameters, the complex dispersion relation for photonics modes propagating in a periodic semiconductor–dielectric array can be described even beyond the long-wavelength limit. We have analyzed the temperature dependence of the nonlocal effective parameters for photonic metamaterials composed of InSb square bars in a silica–glass host matrix. In the case of continuous (infinitely long) bars, the metamaterial shows plasma-like behavior with a temperature-dependent effective plasma frequency in the THz range. For the case of cut semiconductor bars, the metamaterial behaves as a dielectric in the lowest frequency band, whose width can also be tuned by varying the temperature. Using the nonlocal effective permittivity, the optical spectra (reflectivity and transmittance) for a slab of InSb square bars in a glass matrix were calculated and analyzed.

Influence of Semiconductor/Metal Interface Geometry in an EMR Sensor

The extraordinary magnetoresistance (EMR) is well known to be strongly dependent on geometric parameters. While the influence of the aspect ratios of the metal and semiconductor areas has been thoroughly investigated, the geometry of the semiconductor/metal interface has been neglected so far. However, from a fabrication point of view, this part plays a crucial role. In this paper, the performance of a bar-type hybrid EMR sensor is investigated by means of finite element method and experiments with respect to the hybrid interface geometry. A 3-D model has been developed, which simulates the EMR effect in case of fields in different directions. The semiconductor/metal interface has been investigated in terms of different layer thicknesses and overlaps. The results show that those parameters can cause a change in the output sensitivity of 2%-10%. In order to maintain a high sensitivity and keep the fabrication relatively simple and at low cost, a device with a thin metal shunt having a large overlap on the top of the semiconductor bar would provide the best solution.

Subwavelength B-shaped metallic hole array terahertz filter with InSb bar as thermally tunable structure

We propose a subwavelength B-shaped metallic hole array filter with an embedded thermally tunable InSb semiconductor bar in the terahertz regime. The resonance frequency of this filter can be actively tuned by controlling the temperature of InSb. The transmissions of the filter are calculated with the finite-difference time domain method at various temperatures. Narrowband THz wave with the full width at half maximum of 235 GHz can be selected in the frequency range from 0.74 to 2.02 THz at temperatures from 160 to 350 K.

GaAs-Based High Power Diode Laser

High-power diode lasers based on GaAs semiconductor bars are well established as reliable and highly efficient laser sources. The device structure and stack technology of edge-emitting diode laser were presented briefly as well as the development of electro-optical conversion efficiency ,lifetime , power .The technology of ten-thousand –watt level high power diode laser was introduced as a new generation of laser processing equipment. In order to output high power, we utilized polarization coupling technology to couple two 808nm and 880nm laser diode stack together, and designed the optical system to expand and focus the beam, through the experiment; we realize the overall efficiency more than 90%, power output 1000W.

Novel Experimental Setup to Study the Magneto-Resistance of Semiconductors and Its Industrial Application

Since its invention in the turn of 20 th century, semiconductors have always riddled the minds of contemporary science. The various properties of the semiconductors have been studied using spectroscopy, Hall Effect experiment or simple measurement methods under different conditions. The behavior observed has led to a different aspect and hence a different application. The aim of this paper is to study the properties of a semi-conductor bar specially the magneto-resistance, carrier concentration, Energy band gap and the effect of magnetic field on Hall coefficient using a new experimental setup and also discuss its application. Another objective of this paper has been validating the Drude's Model and proposing a solution to the Hall Effect drawback. The design can be used as a replacement to the Hall Effect experiment where as it incorporates the magnetic field's effect for the Hall co-efficient. This experiment employs only magnetic field to determine the magneto resistance unlike Hall Effect where along with magnetic field electric field is also used.

A unified theory of noise in nondegenerate semiconductors

Explicit forms of the Langevin noise sources due to both intraband and interband scattering are given for the Boltzmann transport equations with the relaxation-time approximation in nondegenerate semiconductors. A generalized formula for the short-circuited noise currents, which holds in both homogeneous and nonhomogeneous one-dimensional nondegenerate semiconductors, is derived in a unified manner by solving the Langevin-type Boltzmann transport equations. From this generalized noise formula the short-circuited noise currents for thermal noise, generation-recombination noise, and 1/f noise in a homogeneous nondegenerate semiconductor bar are calculated. It is shown that for homogeneous nondegenerate semiconductors, Nyquist’s theorem always holds both at thermal equilibrium and under an applied dc electric field with either intraband scattering or interband scattering dominant. Generation-recombination noise is shown to be caused by the electrons or holes whose scattering mechanism is dominated by intraband scattering, and the derived generation-recombination noise formula is the same as the one derived by the conventional methods. It is also shown that 1/f noise may be caused by a very small number of electrons (or holes) lying just around the bottom of the conduction band (or the top of the valence band) when interband scattering is dominant over intraband scattering for these electrons (or holes). The contribution of these small number of electrons (or holes) to the electrical conductivity is negligible because of the smallness of the number of these carriers. The derived 1/f noise formula has the same functional form as the Hooge’s empirical relation [Physica 83, 14 (1976)].

Current Oscillation in a Semiconductor Bar with Partially Narrow Cross-Section

Current Oscillation in a Semiconductor Bar with Partially Narrow Cross-Section

Surface potential probe operated at 77 K with nanosecond response

We describe the design, construction, and performance of an instrument for time-resolved surface potential distribution measurements on fragile specimens of small dimensions, e.g., semiconductor bars or wafers. The instrument can operate at 77 K and is easily adapted to computer control. Spatial resolution is about 10 μm in two dimensions. On low-resistivity material a time resolution of 1 ns can be achieved.

1/f noise of point contacts affected by uniform films

An experimental investigation has been carried out to confirm that contact noise of two crossed semiconductor bars with native oxide films in between can be understood as a volume 1/f noise. Noise and contact resistance have been measured as functions of the force F on the crossed bars. F varies between 6 N and 6×10−5 N. From a simple model, an equation is derived which relates the 1/f noise intensity C to the contact resistance R. The calculations are in agreement with the experimental C-R plots. Two extreme situations are possible: constriction dominated and film dominated. Which situation actually occurs can be seen in the C-R plot as well as in the R-F plot.

Effect of the Surface Recombination Velocity on the β-Conductive Signal

The β-conductive signal is analysed for a thin semiconductor bar, whose two parallel surfaces are taken into consideration. When the thickness of the specimen bar is 4 times longer than the diffusion length for minority carriers, the effect of the back surface is negligible. If the penetration depth of the electron beam is very short compared to the diffusion length, the β-conductive signal is most sensitive to the surface recombination velocity of the beam-irradiated surface, while the signal is practically non-sensitive to the recombination velocition when the penetration depth is 20 times longer than the diffusion length.

Voltage Signal due to Electron-Beam-Induced Conductivity in Semiconductors

A formula for a change in the terminal voltage due to the electron-beam irradiation is proposed for a d.c. biased semiconductor bar. The change is composed of three terms; an ohmic drop due to the irradiating beam current, an induced voltage due to the bulk electron voltaic effect and a signal due to the electron-beam-induced conductivity (β-conductivity). The last term, which is called β-conductive signal, is proportional to the square of electric field strength, or to the square of resistivity if the biasing current density is constant, and this was experimentally confirmed using a p-Ge bar whose volume and mean resistivity were 0.5×1×9.5 mm3 and 3.8 \\varOmegacm, respectively. The current, energy and diameter of the irradiating electron beam were 0.1 nA, 20 KeV and about 10 µm, respectively.

Potential distribution in a rectangular semiconductor bar for use with four-point probe measurements

The electric potential distribution is given for an arbitrary placement of current contacts on one side of a rectangular bar of semiconductor material having finite dimensions and two conducting ends. A factor is derived which can be used in conjunction with a four-point probe to correct the measured conductivity of such a bar for the effects of its dimensions and plated ends. This factor is of utility in the correlation of conductivity measurements made on a single specimen by means of two- and four-point probes.

Growing Helical Density Waves in Semiconductor Plasmas

An experimental and theoretical investigation is made of growing screw-shaped plasma density waves in a semiconductor bar subjected to parallel electric and magnetic fields. A particularly simple mode is used, requiring only a thermal-equilibrium electron-hole plasma, low-recombination surfaces, and moderate fields. It is shown that in extrinsic material the growth is spatial, corresponding to stable traveling-wave amplification, while for nearly equal densities of positive and negative carriers the wave is absolutely unstable and corresponds to the oscillistor phenomenon. Experimental observations of the waves were made in germanium at and above room temperature for frequencies from 20-400 kc and with electric and magnetic fields from 25-60 V/cm and 0-11 kG, respectively. The growth rates and phase characteristics were found to be in excellent agreement with theory and gain in excess of 35 dB/cm was obtained. At higher temperatures, corresponding to nearly intrinsic material, evidence of instability was found in accordance with the theoretical prediction.

Some problems in the development of a commercial thermoelectric refrigerator

Two basic problems in the development of a thermoelectric refrigerator are the construction of a cooling unit, consisting of the thermoelectric junctions, and the optimization of the complete refrigerator design to make best use of the thermoelectric material. It is essential for the unit to achieve good thermal contact with the cooling chamber and to have good electrical contact across the p and n semiconductor bars forming each junction. A simple but accurate method for measuring the junction resistance is shown, and the relative merits of various methods of forming the cooling unit are discussed. The heat balance equations for a refrigerator are given which include the cooling fin system, and the method of optimization of the design is noted.