Year: 2012
Type: book-chapter
Abstract: IntroductionIn 1961, it is suggested that stimulated emission can occur in semiconductors by recombination of carriers that are injected across a p-n junction.This is the backbone in the concept of semiconductor lasers and amplifiers [1].This concept is connected with the "one dimensional electron in a box", a problem discussed by quantum mechanics text books, to generate a new field of confined semiconductor structures known thereafter as quantumwell (QW), quantum-wire (QWi) or quantum dot (QD) structures where the carriers are confined in semiconductor in one, two, or three directions, respectively [2].Semiconductor optical amplifiers (SOAs) and lasers performance may be substantially improved by using the QD-SOAs characterized by a low threshold current density, high saturation power, broad gain bandwidth and week temperature dependence as compared to bulk and multiquantum well devices [3].QD active region results from reducing the size of conventional (bulk) crystal to a nanometer size scale in all the crystal directions.This results in a complete quantization of energy states.The density of states becomes comparable to a delta-function.In order to cover losses of the waveguide of the SOA, QDs are then grown by a large number of dots grown on a WL which is already in the form of QW layer, see Fig. 1.In this chapter, we examine the effect of changing composition of the layers constructing the Antimony (Sb)-based quantum dot semiconductor optical amplifiers (QD-SOAs).We startoff in sections 2-3 a general description of QD-SOA and the importance of SOAs, especially Sb-based SOAs, in solving problems.Manufacture imperfection in the shape of QDs are taken into account in the gain calculations in section 4, where they are represented by an inhomogeneous function.Along with the gain description in this section, a global Fermifunction is used where the states in the barrier layer, wetting layer (WL) and ground and excited states of the dots are included in the calculations of Fermi-energy.This mathematical formulation coincides with our subject of study since we would like to see the effect of all the QD-SOA layers.QD-SOA is modeled in section 5 using rate equations (REs) model for the barrier layer which is assumed to be in the form of separate confinement heterostructure layer (SCH), wetting layer (WL), ground state (GS) and excited state (ES) in the QD region of Sb-based structures and then solved numerically.A 3 REs model is discussed first where the www.intechopen.comSelected Topics on Optical Amplifiers in Present Scenario 154 barrier SCH layer is neglected in this model, as done in many literatures, then a 4 REs model is described, where the SCH layer is included.Sb-based QD-SOA structures, the matter of study, are described in detail both in the shape and composition in section 6. Results of the calculations from these models are described in detail in section 7 where the material confinement is examined through the changing of Sb-composition in the QD, WL and SCH layers and it is shown to affects QD-SOA gain and dynamics.Changing WL composition affects the dynamics of ES and GS.InSb dots are shown to be more appropriate for inline static amplification.Results from 3 REs model overestimates the carrier dynamics in comparison with 4 REs calculations.Thus, the SCH barrier layer must be included in the RE models for convenient description of the processes in the QD-SOA.Our results supports the importance of inclusion global quasi-Fermi energy in explaining the results.Finally, section 8 concludes the main finding from this chapter.
Source: InTech eBooks
DOI: 10.5772/34191
Authors: B. Al-Nashy, Amin H.
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: hybrid
OpenAlex ID: W1552995489