Yn Qiu

An improved band-anticrossing model - including the positional dependence of nitrogen - for InGaNAs/GaAs quantum well lasers

The positional dependence of the localized nitrogen (N) within the quantum well is included with the band-anti-crossing model that describes the interaction of the GaInAs conduction band with the localized N defect. It is found that N located at the center of the well interacts more strongly with the InGaAs conduction band than N localized near the edge of the quantum well. Different distributions of N are investigated by studying the conduction band edge shift, energy level splitting, dipole moments, and gain. These quantities are found to be highly dependent upon the position of the N.

Quantum-well intermixing influence on GaInNAs/GaAs quantum-well laser gain: theoretical study

The effect of quantum-well intermixing on the material gain of a GaInNAs/GaAs quantum-well laser is investigated theoretically. The diffusion of gallium and indium atoms in the intermixed sample is assumed and their compositional profiles are modelled using Ficks law. The band-anti-crossing model is used to calculate the band structure of the GaInNAs quantum well, which is appropriate for this non-randomly-alloyed material system. The calculated results show good agreement with the observed photoluminescence excitation for both non-intermixed and intermixed samples, which confirms this model. It is found that the strain gradient, the variation of material band gap and the degeneracy between heavy and light holes are the main factors determining the quantized energy levels of the intermixed quantum well. With the increase of diffusion length, the material gain and differential gain decrease due to the increase of the conduction band effective mass and the rapid decrease of the dipole moments. These characteristics of quantum-well intermixing effects will be useful in the design of integrated photonic devices based on this material.

Experimental study of temperature sensitivity of carrier lifetime and recombination coefficients in GaInNAs SQW lasers

This paper deals with the characterization of the differential carrier lifetime and the calculation of the monomolecular, radiative and non-radiative recombination coefficients and their temperature dependence as an evidence of the excellent temperature performance of this material system. The device characterized is a 1.25 /spl mu/m GaInNAs laser structure grown on a GaAs substrate. The active region consists of a single 6 nm thick single quantum well. Light current (L-I) characteristics performed over a temperature range of 20/spl deg/C to 80/spl deg/C, show a characteristic temperature of 50 K. Similar than in the case of commercial InGaAs. Good temperature performance of optical gain using Hakki-Paoli method, lasing wavelength and efficiency will also be presented and compared with modelling work.

Ion irradiation induced nitrogen mobility in a GaInNAs quantum well laser

Changes in the optical properties in GaInNAs/GaAs quantum wells after alpha particle bombardment followed by low temperature annealing are reported. Both blue and red shifts of the lasing wavelength are observed under different annealing conditions. This differs from the usually observed blue shift which is found after high-temperature post-grown annealing. Competing processes that result in the lasing wavelength shifts are energetic considerations which act to increase the number of Ga?N and In?As bonds (maximize the cohesive energy), minimizing the strain of the system which increases the number of In?N and Ga?As bonds (large-ion-small-ion links), maximizing the number of N located at lattice sites effective at shrinking the band-gap and moving the N position within the quantum well. For the case of high-temperature post-grown annealing the increase of Ga?As and In?N bonding wins, resulting in the blue shift observed. The wavelength shifts are discussed in terms of these competing mechanisms.

Carrier transport study in GaInNAs material using Monte-Carlo method

We have used the stochastic Monte-Carlo method to determine the carrier transport studies in the bulk GaInNAs material. We have incorporated phonon and impurity scattering processes and explicitly considered the role of the nitrogen impurities as scattering centers. We show that in the expression of the relaxation times it is the perturbed rather than the free electron density of states that should be incorporated. This is derived from the Greens functions and the many impurity Anderson model and yields an enhanced scattering rate. The nitrogen impurities can also act as centers with an infinite scattering cross-section when their broadening becomes infinitely small. We show that the increase of the electron effective mass in GaInNAs system is more important than the non-parabolicity parameter in the decrease of mobility. Monte-Carlo calculations take into account the total scattering rate, which is significantly enhanced due to nitrogen scattering. The average electric field and the average energy are found to decrease with increasing N concentration and increase of the effective mass.

SPIE - Semiconductor Lasers and Laser Dynamics III, Strasbourg, France

We have used the stochastic Monte-Carlo method to determine the carrier transport studies in the bulk GaInNAs material. We have incorporated phonon and impurity scattering processes and explicitly considered the role of the nitrogen impurities as scattering centers. We show that in the expression of the relaxation times it is the perturbed rather than the free electron density of states that should be incorporated. This is derived from the Greens functions and the many impurity Anderson model and yields an enhanced scattering rate. The nitrogen impurities can also act as centers with an infinite scattering cross-section when their broadening becomes infinitely small. We show that the increase of the electron effective mass in GaInNAs system is more important than the non-parabolicity parameter in the decrease of mobility. Monte-Carlo calculations take into account the total scattering rate, which is significantly enhanced due to nitrogen scattering. The average electric field and the average energy are found to decrease with increasing N concentration and increase of the effective mass.

QDot and GaInNAs/GaAs Broadband Semiconductor Optical Amplifiers for Simultaneous Multiwavelength Amplification

The need for simultaneous multi-channel transmission in optical communication systems has led to a requirement of semiconductor optical amplifiers (SOAs) with flat gain over a broad range of wavelengths and minimum channel interspacing for the independent and simultaneous amplification of several different laser sources. In addition for ultra-high speed communication with femto-second pulses, composed of a spectrum of wavelengths, simultaneous multi-wavelength amplification is required. The goal of this paper is the modelling, fabrication and characterization of SOAs made from GaInNAs/GaAs quantum-well edge emitting lasers and InAs/GaAs QDot edge-emitting lasers. Both QDots and GaInNAs/GaAs quantum wells (QWs) exhibit broad gain for a range of temperatures and current as measured experimentally.

GaInNAs/GaAs quantum wells: Advantages for SOAs

GaInNAs/GaAs quantum wells are a relatively new material system for telecom/data com application. Generally it has been thought that the material offers an improved temperature performance and lattice matching to GaAs both significant advances. However studies of the material show that it has more parameters to control: in particular controlling the N distribution within the QW and the nature of the N states- single, pair states or cluster states allows tunability of the band gap, conduction band effective mass and quantum-dot-like localised states. These features offer a number of new device applications which will be discussed in this talk

Quantum dot vs. GaInNAs/GaAs quantum wells for broad band amplification

Summary form only given. There has been a lot of interest in broad band amplifiers required for ultra-fast communications systems where a fast pulse with a wide spectral range is put through fibre. Quantum dot SOAs with inhomogeneous broadening provide broad gain. Different sizes of dots can amplify different wavelengths but their interaction is governed by their homogeneous linewidth. We examine the limitation that this puts on multi-wavelength amplification and examine the effect of barrier height. We consider the quantum well system GaInNAs/GaAs and consider whether local fluctuations within this system can act as localised centres for amplification as in the quantum dots. We examine the controlling parameters for this system and compare and contrast these two systems for use as broad band SOAs.

2005 Quantum Electronics and Laser Science Conference (QELS), Baltimore, USA

An improved band anti-crossing model is presented in which the position of the nitrogen within the quantum well is included. This is found to strongly influence the conduction band levels, the dipole moments and gain.