Search

An investigation of mirror facets of broad area AlGaAs SQW 808 nm lasers with fast degradation of the output power is presented. The lasers with rapid degradation show dark lines running either parallel or in a V-shaped pattern on the mirror facet surface.

The study of the dark current behavior in n-type GaAs/AlAs/Al GaAs double barrier quantum wells (DBQW) reveals that tunneling occurs through the 2 nanometer wide AlAs tunnel barriers. The thermionic emission occurs in the 25 nanometer wide AlGaAs layers. The internal electric fields produced by the dopants in the GaAs/AlAs/AlGaAs DBQWs are found to modify the dark current.

Studies of the asymmetric photoresponse and dark current of GaAs/AlAs/Al(0.3)Ga(0.7)As(3. 5) mu m intersubband photodetectors lead to the development of a segregation model that takes into account the effects of an incident doping flux. The calculation of conduction band bending provides estimates of applied voltage necessary to compensate the doping asymmetry.

The degradation of 1.3 [micro]m GaIn NAs lasers is examined by using accelerated aging tests. The results have helped in identifying the generation of radiative deep level defects as the main causes of degradation of these uncaged devices.

A 'by-emitter' degradation analysis technique is used to examine the degradation process in high-power laser diodes, in particular, high-power laser bars at both the bar and emitter levels. The technique focuses on understanding the dynamic mechanisms by which packaging-induced strain and operating conditions lead to the formation of defects and subsequent emitter and bar degradations.

Photoluminescence is widely used to investigate the effect that annealing temperature and ambient, show on the annealed molecular beam epitaxy grown GaN. Results show the annealing GaN introduces a defect causing a donor acceptor pair (DAP) transition at approximately 3.42 eV.

The assessment of the refractive index data for the nitride alloys and formulas for evaluating the refractive indices for variations in both composition and photon energy is presented. A detailed understanding of the nitride refractive indices essential for the modeling and design of III-N structures is also investigated.

This paper investigates the evolution of kurtosis of the input Gaussian amplified spontaneous emission (ASE) noise in a nonlinear fiber with negligible dispersion. The nonlinear Schrodinger equation (NLSE) describing propagation in optical fibers is simplified such that the fiber represents a zero memory nonlinear (ZMNL) system, and this approximation allows the development of analytical formulas for the statistical moments of the output noise. It is possible to calculate moments of all integer orders and the explicit expressions for the first four moments are given. The investigations show that the ASE noise does not preserve its Gaussian character when Kerr nonlinearity is significant. This observation proves that the common assumption of the Gaussian output ASE is not necessarily valid. Numerical simulations are provided to support the derivation. Kurtosis deviating significantly from the value typical for Gaussian noise is also an indicator that BER calculation in the coherent systems based on the assumption that ASE is Gaussian is likely to be inaccurate. [ABSTRACT FROM PUBLISHER]

Using a quantitatively calibrated imaging system and specially fabricated tapered lasers with windowed n-contacts, the authors image the spontaneous emission distribution inside two different laser cavities as a function of injection current. In the first device, an array of narrow-angle index-guided tapered lasers, significant thermal and electrical coupling between the emitters was observed. In the second device, a wide-angle gain-guided tapered laser, significant spatial hole burning was observed above threshold. The spontaneous emission distributions of this wide-angle device have been compared with simulation results from a 2.5D laser simulator and show good quantitative agreement in the quantum well carrier density. [ABSTRACT FROM AUTHOR]

Studies the properties of a tapered semiconductor laser cavity, which can be used to generate a high-brightness optical beam. Influence of the input waveguide width and length; Application of beam spoilers.

The nonlinear phenomena accompanying the process of light generation in high-power tapered semiconductor lasers are studied using a combination of simulation and experiment. Optical pumping, electrical overpumping, filamentation, and spatial hole burning are shown to be the key nonlinear phenomena influencing the operation of tapered lasers at high output powers. In the particular tapered laser studied, the optical pumping effect is found to have the largest impact on the output beam quality. The simulation model used in this study employs the wide-angle finite-difference beam propagation method for the analysis of the optical propagation within the cavity. Quasi-three-dimensional (3-D) thermal and electrical models are used for the calculation of the 3-D distributions of the temperature, electrons, holes, and electrical potential. The simulation results reproduce key features and the experimental trends. [ABSTRACT FROM PUBLISHER]

A significant enhancement of the brightness is predicted in tapered lasers with the active layer asymmetrically located in the optical cavity. The balance between the reduced tendency to beam filamentation, the increase of threshold current, and the decrease of secondary mode discrimination is analyzed using numerical simulations. An optimized design for a 975-nm tapered laser is proposed. [ABSTRACT FROM PUBLISHER]

We present a computationally efficient approach to representing valence band (VB) anisotropies in semiconductor quantum-well optoelectronic devices. The VB dispersion is calculated along the high-symmetry lang100rang and lang110rang axes with the four-band kmiddotp method. The VB isoenergy contours are represented by a first-order Fourier series expansion, which is used to calculate the subband density of states (DOS), the optical DOS and gain. In this way, each photon is allowed to interact with electrons and holes over a finite range of energy states, even without including lifetime broadening effects [ABSTRACT FROM PUBLISHER]

A new detailed approach has been developed, whereby the individual performances of the emitters comprising a laser bar are assessed separately as part of a larger coupled system. The results reveal the existence of a strain threshold, wherefore degradation of the emitter performances is only observed when the local packaging-induced strain is above a certain critical value. This degradation which occurs after aging, is manifested in an increase in the "apparent" threshold current and a decrease in the "apparent" slope efficiency of the individual emitters. This degradation is also revealed by the presence of facet defects as previously reported. These results suggest that measurement and control of packaging-induced strain will allow significant improvement in the degradation behavior of high-power AlGaAs laser bars [ABSTRACT FROM PUBLISHER]

We have extracted the ratio between the carrier capture and escape times, η, for In0.25Ga0.75As-GaAs lasers containing one, two, or three quantum wells, from high-frequency subthreshold impedance measurements at different temperatures. Our results show that the carrier capture process dominates over the diffusion along the confinement region in the overall transport/capture process. The obtained value for η is comparable to unity, and this fact has to be taken into account to obtain real material parameters, such as the carrier lifetime and the radiative recombination coefficient [ABSTRACT FROM PUBLISHER]

Reports on time-resolved photocurrent measurements in indium gallium arsenide/gallium arsenide-quantum well p-i-n photodetector structures. Detection of photocurrent at different location in the sample; induction of the temporal broadening of the signal; Significance of the temporal behavior for the optimization of high-speed photodetectors.

Examines the strain relaxation in high speed photodetectors with In[sub 0.2]Ga[sub 0.8]As/gallium arsenide multiple quantum wells. Use of high-resolution x-ray diffraction and photocurrent spectroscopy; Influence of the relaxation on the optoelectronic and electronic properties.

Examines defect and strain redistribution in In[sub x]Ga[sub 1-x]As/gallium arsenide multiple quantum wells. Use of resonant Raman scattering by longitudinal optical phonons; Sensitivity of scattering intensity; Detection of the onset of the strain redistribution.

Examines the space charge effects in photovoltaic double barrier quantum well infrared detectors. Role of the spatial distribution of the dopants in the transport asymmetry of the photocurrent; Transport of photoexcited electron towards the substrate; Characteristics of photocurrent responsivity.