No description available.

Room temperature vertical cavity lasing at the wavelength of 433nm has been successfully realized in InxGa₁₋xN/InyGa₁₋yN multiple quantum well without Bragg mirrors under photo-excitation. At high excitation intensity, one of the modes of the Fabry-Perot cavity formed by the GaN/sapphire and the GaN/air interfaces, shows a strong superlinear increase in intensity with excitation intensity rise. The vertical cavity surface emitting laser (VCSELs) structure is grown by metal-organic chemical vapor phase deposition and the threshold is as low as 200kW/cm². The lasing in the sample probably results from the ultrahigh material gain due to the spontaneous formation of dense array of nanoscale InGaN quantum dots (QDs) having an exceptional high area density. / Singapore-MIT Alliance (SMA)

No description available.

In this thesis, two methods to model quantum well lasers will be examined. The first model is based on well-known techniques to determine some of the spectral and dynamical properties of the laser. For the spectral properties, an expression for TE and TM modal amplitude gain is derived. For the dynamical properties, the rate equations are shown. The spectral and dynamical properties can be examined separately for specific operating characteristics or used in conjunction with each other for a complete description of the laser. Examples will be shown to demonstrate some of the analysis and results that can be obtained. The second model used is based on Wigner functions and the quantum Boltzmann equation. It is derived from general non-equilibrium Greens functions with the application of the Kadanoff-Baym ansatz. This model is less phenomenological than the previous model and does not require the separation of physical processes such as the former spectral and dynamical properties. It therefore has improved predictive power for the performance of novel laser designs. To the Author's knowledge, this is the first time such a model has been formulated. The quantum Boltzmann equations will be derived and some calculations will be performed for a simplified system in order to illustrate some calculation techniques as well as results that can be obtained.

In this thesis, two methods to model quantum well lasers will be examined. The first model is based on well-known techniques to determine some of the spectral and dynamical properties of the laser. For the spectral properties, an expression for TE and TM modal amplitude gain is derived. For the dynamical properties, the rate equations are shown. The spectral and dynamical properties can be examined separately for specific operating characteristics or used in conjunction with each other for a complete description of the laser. Examples will be shown to demonstrate some of the analysis and results that can be obtained. The second model used is based on Wigner functions and the quantum Boltzmann equation. It is derived from general non-equilibrium Greens functions with the application of the Kadanoff-Baym ansatz. This model is less phenomenological than the previous model and does not require the separation of physical processes such as the former spectral and dynamical properties. It therefore has improved predictive power for the performance of novel laser designs. To the Author's knowledge, this is the first time such a model has been formulated. The quantum Boltzmann equations will be derived and some calculations will be performed for a simplified system in order to illustrate some calculation techniques as well as results that can be obtained.

The incredible technological advancements over the last century have been possible due to tiny trinkets designed using semiconducting crystalline materials, especially Silicon and III-V compounds. Silicon, a group IV element has become the first choice in developing microchips serving an ever-growing set of applications including, computation, RF communications, solar cells, power electronics, quantum computing and its periphery, optoelectronics, IOT sensors, and lately artificial intelligence. Billions of Si-based complementary transistors (CMOS) are present at the center of most computing devices used today such as HPC servers, compute farms, laptops, and smartphones. The astonishing rise in transistor count, performance, and functionality as well as the exponential reduction in cost has been possible over the past decades due to a singular idea: shrinking the device. However, this rule, also called Moore's Law has been slowing over the past two decades and has eventually come to a standstill in its traditional definition. Moore's law has since been sustained by ingenious innovations such as high-k gate dielectrics, vertical scaling, lattice strain engineering, novel material developments and, lately chiplets as well as multi-die vertical packaging. As conventional Si CMOS approaches a roadblock, this work presents research on Germanium-based multi-gate devices providing promise for faster and low-power operation. This work discusses how Ge grown on a GaAs substrate can be tuned and utilized to form a virtually defect-free channel for ultra-scaled multi-gate transistors. Calibrated solvers informed using in-house materials and devices as well as literature are used to predict device performance for advanced structures. Further, a hybrid CMOS system with the high hole mobility p-channel device formed using tensile strained Ge, and the high electron mobility n-channel device formed using the underlying InGaAs layer is proposed and simulated. As scaling approaches Gate-all-around Nanosheet FETs in 2024 and complementary-FETs (CFETs) around 2034, Ge-on-AlAs based transistors can offer unique process simplifications, defect reduction, yield improvement, and high-performance advantages showing promise for future IRDS nodes. The process design, material stack, device, and circuit performance for this novel Ge-based NSFET is presented in this work. The lack of large strain or strain relaxation in the NS multilayer starting stack is seen to be a great process advantage for the Ge-AlAs NSFET system. To a certain extent, Si seems omnipotent for all things electronics. However, one exception is on-chip light generation. A coherent electrically controllable on-chip light source is a central component critical for optoelectronics, quantum technologies, fiber communications, and sensing. Due to the indirect bandgap, Si cannot produce light hence direct bandgap materials such as GaAs and GaN have been the primary choice for off-chip light sources integrable on the platform. Interestingly, Ge has a pseudo-direct bandgap, i.e., unlike Silicon, it can be manipulated to produce light using heavy doping, tensile strain, and Sn alloying. Similar to conventional III-V light sources, reduction in the dimensionality of the gain medium, i.e., Ge can enable a drastic reduction in the current required to produce light, among other performance considerations. This reduced dimensionality can be achieved by forming quantum wells and quantum dots. In this work, two new types of Ge-based quantum well lasers are introduced and analyzed along with qualitative and quantitive benchmarking. The first QW laser uses a small epitaxial biaxial tensile strain to improve the direct-ness of the Ge gain medium. The internal quantum efficiency, net gain, and threshold current can be improved drastically by choosing the right tensile strain while staying within a certain critical thickness value. For the first time, the impact of biaxial tensile strain on the optical properties of Ge is analyzed and reported through a systematic study of the dielectric spectra and optical constant using VASE. The changes in the band structure due to tensile strain are correlated with the critical points to uncover various optical transitions. An even better QW laser architecture is possible by utilizing a GeSn QW. This QW laser uses Sn-alloying to form a GeSn active region which is further lattice matched to the waveguide (InGaAs) and the optical confinement layers (InAlAs) around it. This completely lattice-matched laser structure can offer unique advantages such as virtually defect-free active region, tunability as well as improved efficiency and threshold current density. The absence of strain and consequently strain relaxation in the laser stack enables one to steer away from the critical thickness limitation while opening doors to designing multiple quantum well lasers among other complex architectures. The impact of Sn alloying on the atomic structure, lattice coherence, and relaxation is analyzed through XRD reciprocal space maps and rocking curves as a function of Sn concentration. Further, this lattice-matched system, GeSn-InGaAs-InAlAs has the potential to mirror the benefits of the mature GaAs-AlGaAs system which led to many great technological innovations over the past decades such as lasers and LEDs. / Doctor of Philosophy / This thesis introduces two transistor technologies to extend the scaling beyond conventional Si devices into the next decade, and two QW laser technologies for integrated photonics. Through calibrated numerical solvers, a high mobility Ge and InGaAs cointegrated CMOS system for 0.5 V is introduced, analyzed and benchmarked with literature. A lattice matched Ge-on-AlAs multilayer stack is shown to have great potential to form a novel CMOS system which uses Ge Nanosheets, providing process advantage and superior performance. The next part of the thesis introduces two types of Ge based quantum well lasers, one based on tensile strained Ge and the other based on lattice matched Ge. Both show large performance improvements over previous attempts in literature. Lasing from an indirect bandgap material such as Ge, the associated challenges and performance metrics are discussed. Lastly, the optical, dielectrics and CP properties of tensile strained are presented for the first time uncovering interesting trends. Ge samples with increasing tensile strain are grown using MBE and measured using VASE to elucidate the physical phenomenon.

This thesis describes the incorporation within a semiconductor laser of a multiple quantum well InGaAsP/InP Electron Bragg Reflector (EBR). The EBR is intended to improve laser performance by inhibiting the escape of hot electrons from the laser active region by quantum mechanical Bragg reflection. To the author's knowledge, this investigation represents the first attempt to realize an EBR in the InGaAsP/InP material system. Computer models based on a transfer matrix method for the solution of Schrodinger's equation were written to obtain the EBR design. The transfer matrix method is described. Extensions to the transfer matrix method for optics are presented and are demonstrated to provide more than an order of magnitude improvement in computational efficiency for the calculation of the complex TE-mode propagation constant for planar graded-index waveguides with absorption or gain. The EBR designed for this work incorporates several new features. Deleterious band bending in the vicinity of the EBR is minimized by exploiting material strain to reduce the density of hole states in the EBR quantum wells. To maximize reflection bandwidth and relax fabrication tolerances, the EBR design used well widths that decreased with increasing depth into the p-type InP cladding. By the placement of the EBR adjacent to the separate confinement region, a return path was provided for electrons that scattered inelastically within the EBR. Moreover, the EBR structure was designed to support no bound electron states, so that the recombination of electrons with holes in the EBR would be minimal. To the author's knowledge, the EBR-equipped laser fabricated for this work represents the first attempt to exploit electron state exclusion. To explore the effectiveness of EBRs in the InGaAsP/InP material system, two nearly identical ridge waveguide lasers (one with an EBR, and one without) were designed, fabricated, and tested. The EBR-equipped lasers exhibited an anomalous threshold current temperature dependence which featured a "negative-To" regime (in which the threshold current decreases with increasing temperature), attaining a minimum in threshold current between T=150 K and T=200 K. These lasers had a threshold current temperature stability superior to that of standard lasers within a ~70 K window around the minimum threshold temperature. Experimental evidence suggests that the improved stability is not due to quantum mechanical Bragg reflection provided by the EBR, but is attributable to the temperature-dependent rate of hole escape from the EBR quantum wells into the separate confinement region. The proposed mechanism is described in detail and is supported by theoretical and experimental evidence. The results have implications for device design, because the mechanism by which the superior temperature stability is achieved does not rely on the electron coherence effects; the mathematical model suggests that the mechanism can be exploited to provide superior temperature stability in semiconductor lasers at 300 K or above. / Thesis / Master of Engineering (ME)

La photonique du silicium a connu un développent massif pendant les dix derniers années. Presque toutes les briques technologiques de base ont été réalisées et ont démontrées des performances remarquables. Cependant, le manque d’une source laser intégrée en silicium a conduit les chercheurs à développer de composants basés sur l’intégration entre le silicium et les matériaux III-V.Dans cette thèse je décris la conception, la fabrication et la caractérisation des lasers hybrides III-V sur silicium basés sur cette intégration. Je propose un coupleur adiabatique qui permet de transférer intégralement le mode optique du guide silicium au guide III-V. Le guide actif III-V au centre du composant fourni le gain optique et les coupleurs, des deux cotés, assurent le transfert de la lumière dans les guides silicium.Les lasers mono longueur d’onde sont des éléments fondamentaux des communications optiques. Je décris les différentes solutions permettant d’obtenir un laser mono-longueur d’onde hybride III-V sur silicium. Des lasers mono longueur d’onde ont été fabriqués et caractérisés. Ils démontrent un seuil de 21 mA, une puissance de sortie qui dépasse 10 mW et une accordabilité de 45 nm. Ces composants représentent la première démonstration d’un laser accordable hybride III-V sur silicium. / Silicon photonics knew an impressive development in the last ten years. Almost all the fundamental building blocks have been demonstrated and reveal competitive performances. However, the lack of an efficient silicon integrated laser source has led the researchers to develop heterogeneous integration of III-V materials on silicon.In this thesis I describe the design, the fabrication and the performances of these hybrid III-V on silicon lasers. I propose the use of an adiabatic coupler that totally transfers the optical mode between the III-V and the silicon waveguides. The active waveguide on III-V materials at the center of the device provides the optical gain, while, on both side, adiabatic couplers allow a loss-less transfer of the optical mode to the silicon waveguide. Single wavelength emitting lasers are fundamental elements for high bandwidth optical links. I review all the effective solutions enabling single waveguide hybrid III-V on SOI lasers. DBR, microring based, DFB and AWG laser solutions were analysed. Single wavelength operating lasers have been fabricated and characterized. A laser threshold of only 21 mA, an output power of more than 10 mW and tunability over 45 nm with a SMSR of 45 dB have been measured. These devices represent the first demonstration of a monolithically integrated hybrid III-V/Si tunable laser made by wafer bonding technique.