Cavity Surface Emitting Laser Structures Research Articles

Artifact-free secondary ion mass spectrometry profiling of a full vertical cavity surface emitting laser structure

The optimization of the structure of vertical-cavity surface-emitting lasers (VCSELs) is required to produce more efficient devices. The secondary ion mass spectrometry (SIMS) technique can provide information about the structure and the distribution of dopants and contaminants. However, VCSELs are relatively thick, contain hundreds of layers with varying compositions, and consist of very thin layers. Classical SIMS is prone to artifacts which decreases the quality of the results. In this work, modifications of the SIMS measurement procedures are presented: high incident angle bombardment reduces the mixing effect; optimization of the extraction parameters increases the signal-to-noise ratio from 2.1 to 24.3 dB; Ion polishing and beam service preserves the quality of the measurement. Due to impact energy modulations quantum wells and barriers are registered as box-shaped features. The raw data is free of artifacts and reflects the realistic distribution of elements. Such accuracy may prove invaluable for further optimization of VCSELs.

Growth and fabrication of 850 nm AlGaAs/GaAs vertical cavity surface emitting laser structure

In this work, we demonstrate the NIP’s all in-house development of a vertical cavity surface emitting laser structure. The VCSEL structure grown via MBE consists of an AlAs/AlGaAs distributed Bragg reflector and an AlGaAs/GaAs quantum well designed to issue at the 850 nm region. Reflectance spectroscopy showed that the stop band is centered around the designed wavelength. The electroluminescence spectra displayed that the maximum light emission corresponded to its design. This is a crucial step in the NIP’s development of semiconductor lasers, leading towards future high-speed and highly-tunable VCSEL devices.

The Characteristics of Optical Pumped GaN-Based Vertical Cavity Surface Emitting Laser Structures

Time-resolved photoluminescence spectra of vertical cavity surface emitting laser (VCSEL) structures under different excitation intensity are investigated. The effect of the distributed Bragg reflectors (DBR) on the laser emission and the mechanism of multi-longitudinal-mode are analysed. A broad peak around 2.80eV is observed from the structure without DBR cavity when pumped under low excitation intensity. At higher excitation density up to 21.4kW/cm2, a lasing peak appears at 2.86eV, and exhibits a rapid growth and red shift with the increase of the excitation density. The decay time of the peak is about 66ps. When the spectrum is measured after the deposition of DBR on the top side of the grown nitride structure, the number of peaks increases to 7, and the free spectral range 0.21×1014 Hz is close to the value that calculated by the Fabry-Perot cavity length. After depositing the second DBR, multi PL peaks around 2.87eV are observed. The relationship of laser emission intensity and angle of the polarizer shows nearly a cosine square variation. However, the polarization characteristics of the four main peaks are different, which indicates that these peaks occurr by the oscillation of different optical cavities.

New Method of Distinguishing X-Ray Diffraction Curves about Laser Structure

Come up with a new method of rocking curves analysis, its using the software of the double-crystal X-ray diffraction rocking curves analysis to simulate vertical cavity surface emitting laser structure. Simulate the X-ray diffraction rocking curve of each part of laser structure, and then compare with the diffraction rocking curve of the overall structure in order to acquire the adscription of each diffraction peak, the method can also be applied to other semiconductor lasers. Compared with conventional PDF card library about diffraction position of all material peaks, the method has the advantages of fast and accurately to distinguish, high efficiency. In the end, the X-ray diffraction rocking curves analysis method is applied to the MOCVD growth of GaAs based vertical cavity surface emitting laser, and quoting strain relaxation mechanisms for explaining the reasons for the partial peak drifting.

Microphotoluminescence investigation of InAs quantum dot active region in 1.3 μm vertical cavity surface emitting laser structure

Microphotoluminescence (μ-PL) investigation has been performed at room temperature on InAs quantum dot (QD) vertical cavity surface emitting laser (VCSEL) structure in order to characterize the QD epitaxial structure which was designed for 1.3 μm wave band emission. Actual and precise QD emission spectra including distinct ground state (GS) and excited state (ES) transition peaks are obtained by an edge-excitation and edge-emission (EEEE) μ-PL configuration. Conventional photoluminescence methods for QD-VCSELs structure analysis are compared and discussed, which indicate the EEEE μ-PL is a useful tool to determine the optical features of the QD active region in an as-grown VCSEL structure. Some experimental results have been compared with simulation results obtained with the aid of the plane-wave admittance method. After adjustment of epitaxial growth according to EEEE μ-PL measurement results, QD-VCSEL structure wafer with QD GS transition wavelength of 1300 nm and lasing wavelength of 1301 nm was obtained.

Microscopic modeling of the optical properties of semiconductor nanostructures

A brief overview of a consistent microscopic approach to model the optical and electronic properties of semiconductor nanostructures is presented. Coupled semiconductor Bloch and Maxwell equations are used to investigate the performance of semiconductor microcavity structures, photonic band gap systems, and lasers. The predictive potential of the microscopic theory is demonstrated for several examples of practical importance. Optical gain and output characteristics are computed for modern vertical external cavity surface emitting laser structures. It is shown how design flexibilities can be used to optimize the device performance. Nanostructures are proposed where semiconductor quantum wells are embedded in one-dimensional photonic crystals. For field modes spectrally below the photonic band edge it is shown that the optical gain and absorption can be enhanced by more than one order of magnitude over the value of the homogeneous medium. The increased gain can be used for laser action by placing quantum wells and a suitably designed photonic crystal structure inside a microcavity.

Polarization control of vertical cavity surface emitting laser structure by using self-organized quantum wires grown on (775)B-oriented GaAs substrate by molecular beam epitaxy

Vertical cavity surface emitting laser (VCSEL) structures with self-organized InGaAs quantum wires (QWRs) in their active region were grown on (775)B-oriented GaAs substrate by molecular beam epitaxy. The (775)B self-organized InGaAs QWRs have a regularly corrugated AlAs-on-InGaAs upper interface with average lateral period of 40 nm and vertical amplitude of 1.5 nm and a flat InGaAs-on-AlAs lower interface. The (775)B VCSEL structure was optically pumped and showed room temperature lasing action for wavelength of around 830 nm. The light output was linearly polarized and the polarization direction was fixed to the QWR direction. This is the first demonstration of polarization control of VCSELs by self-organized QWRs in their active region.

Photoreflectance spectroscopy study of vertical cavity surface emitting laser structures

This paper summarises the application of the laser-based electro-absorptive technique of photoreflectance (PR) for the study of vertical cavity surface emitting lasers (VCSELs). PR results are shown to reveal the technologically important cavity mode and ground state quantum well exciton structures. AlGaAs/GaAs based quantum well VCSELs were examined with and without top mirror layers as a function of laser pump excitation conditions, with results compared with angle-dependent PR data. Cavity mode and quantum well alignments were also studied with reference to the un-modulated reflectance signal as well as correlated with photoluminescence data. The results demonstrate the importance of PR metrology for state-of-art VCSEL characterisation.

InP-based wavelength tunable vertical cavity surface emitting laser structures

We report on the design, fabrication and characteristics of both hybrid and monolithic micro-electro-mechanically wavelength tunable 1.55 μm InP-based Vertical-Cavity Surface-Emitting Laser (VCSEL) structures. Photo-pumped tunable VCSELs are successfully realized using both configurations, and a design for electrically pumped tunable VCSEL is presented. To cite this article: I. Sagnes et al., C. R. Physique 4 (2003).

A quasicontinuous wave, optically pumped violet vertical cavity surface emitting laser

We have fabricated and studied a violet (λ=403 nm) vertical cavity surface emitting laser structure, composed of an InGaN multiple quantum well active medium and a pair of high reflectivity dielectric mirrors. Lasing under high repetition rate (76 MHz) pulsed optical pumping has been achieved at temperatures up to T=258 K at average pump power of approximately 30 mW.

Control of wet-etching thickness in the vertical cavity surface emitting laser structure by in situ laser reflectometry

We have investigated the use of in situ laser reflectometry for etch depth control in vertical cavity surface emitting laser (VCSEL) structures. We can obtain the precise etch depth by simply counting the number of oscillations during the wet-etching process. After calibration on an AlGaAs/GaAs 20-period distributed Bragg reflector (DBR) structure, this technique was applied to the monolithic 1.55 μm VCSEL device process that is required to etch epilayers of several μm thickness. In the 1.55 μm VCSEL structure, the mesa was generated by monitoring the number of peaks in the bottom DBR that corresponded to an etch depth of about 11 μm. The overall spatial uniformity of the etched sample was within a layer (1000 Å) by the distinction between layers. This process offers the possibility of precise control of etch depth for any multilayer structure.

The use of in situ laser interferometry for MOCVD process control

This paper reports on the technique of single-wavelength laser interferometry for remote monitoring of the thin-film growth of semiconductors by metal-organic chemical vapour deposition (MOCVD). By on-line fitting of factors governing the complex refractive index of a growing layer, the quality of epitaxial growth can be monitored and early identification of a degradation in film growth identified. For example, sub-bandgap 633 nm (HeNe) radiation was used to monitor the pyrolytic and photo-assisted growth of several films of ZnTe on GaAs. Fitting of the effective extinction coefficient, , at each turning point (peaks and troughs) in the interferogram revealed that different growth mechanisms are dominant under photo-assisted conditions compared to strictly pyrolytic conditions. We propose a variation on the virtual-interface approach for the mathematical treatment of a dielectric stack for the real-time fitting of complex reflectance interferograms from multilayers. Using this model, interferograms for vertical cavity surface emitting laser structures have been theoretically generated and are in excellent agreement with the experimental interferograms recorded by Killeen and coworkers. Finally data are presented which demonstrate the use of laser interferometry for process control on an industrial reactor.

GaAs-based VCSEL-structures with strain-compensated (GaIn)As/Ga(PAs)-MQWH active regions grown by using TBAs and TBP

GaAs-based vertical cavity surface emitting laser structures (VCSEL) with strain-compensated (GaIn)As/Ga(PAs) multiple quantum well heterostructures (MQWH) active regions have been deposited using the less hazardous, liquid group-V-sources tertiarybutyl arsine (TBAs) and tertiary butyl phosphine (TBP) in metal organic vapour phase epitaxy (MOVPE). We report on growth optimization, characterization of the VCSEL structures, and ultrafast emission dynamics after femtosecond optical excitation. The improved decomposition characteristics of the alternative compounds yield a small variation in the cavity thickness of only ±0.35% across the 2″ wafer. The high quality of the VCSEL structures having a 2 λ cavity with 4 stacks of 3 (GaIn)As/Ga(PAs)-MQWH and AlAs/GaAs-Bragg mirrors is revealed by the large normal mode splitting of 10.6 meV. Excellent pulse response with a pulse width of 3.2 ps and a peak delay of 4.8 ps at 30 K is obtained after femtosecond optical excitation. The high crystalline perfection with respect to layer homogeneity, optical properties as well as ultrafast emission dynamics demonstrate the advantages of the strain-compensated material system for VCSEL structures grown by MOVPE using TBAs and TBP.

Kinetics of thermal oxidation of AlAs in water vapor

We have investigated the lateral thermal oxidation of AlAs in water vapor in vertical cavity surface emitting laser structures. At low temperatures and short oxidation times, oxide growth was found to be reaction rate limited. Conversely, diffusion across the oxide was the rate controlling mechanism at higher temperatures and longer oxidation times. Lasers are typically processed at intermediate values of temperatures and time. The observed growth can be modeled by rate equations by which the two component growth mechanisms can be separated. Activation energies of 1.6 and 0.8 eV were determined for the reaction rate and diffusion limited mechanisms, respectively.

Investigations of vertical cavity surface emitting laser by photoreflectance spectroscopy

We report photomodulated reflectance results on vertical cavity surface emitting laser structures. Photoreflectance spectra have been recorded under normal incidence at different temperatures between 9 and 300 K. The structure used is a λ cavity grown in the AlGaAs-based system emitting at a wavelength near 800 nm. We show that photoreflectance is a unique noninvasive tool to measure accurately the quantum well transition and the cavity mode alignment: both features can be distinguished very well. Furthermore, this technique offers the opportunity to determine the electric field within the undoped region from Franz–Keldysh oscillations, and gives the Al composition of the barrier material in the cavity.

Analysis of nonplanar wave propagation through multilayered Bragg reflectors for folded cavity and vertical cavity surface emitting laser structures

A theoretical approach to nonplanar wave propagation through Bragg reflector multilayer structures is presented. The theory is applied to the optical coupling and feedback in a folded cavity surface emitting laser using a 45/spl deg/ deflection mirror-epitaxial Bragg reflector arrangement. The effects of the nonplanar wave propagation on the Bragg mirror reflectivity in vertical cavity surface emitting lasers is also examined. Experimental verification of the theory is presented in a novel folded cavity surface emitting laser structure integrating a horizontal cavity InGaAs-GaAs laser grown on a structured substrate with a high reflectivity Bragg reflector.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

InGaAs/GaAs Strained-Layer QW Vertical Cavity Surface Emitting Laser Structures grown on GaAs (311)A Substrates by MBE

AbstractWe report the crystal growth conditions and lasing characteristics of InGaAs-GaAs strained-layer quantum well vertical cavity surface emitting lasers (VCSELs) grown on GaAs(311)A substrates by molecular beam epitaxy. A significantly smooth surface and high reflectivity of more than 99 % were achieved. Very flat and dislocation-free AlAs/GaAs hetero-interfaces were obtained. Furthermore, a very low threshold of 5.5 mA and current density of 270 A/cm2 have been achieved for the first time under CW operation at room temperature. In addition, we demonstrate stable polarization characteristics at high currents. These results are believed to be a consequence of both the predicted high gain and anisotropic gain distribution on the (311) surface.

Novel application of optically pumped vertical cavity surface emitting lasers : fast amplifying optical switch

An amplification of 30 dB of an external beam by a photopumped vertical cavity surface emitting laser structure is obtained. The temporal response of 20 ps points to the use of the structure as a fast amplifying switch, capabable of attaining several GHz frequency

Crystal defects in vertical cavity epitaxial structures on GaAs investigated by X-ray methods

The influence of doping on the generation of misfit dislocations in AlAs/GaAs Bragg reflectors and vertical cavity surface emitting laser structures grown by molecular beam epitaxy has been investigated by X-ray topography and diffractometry. While carbon doping reduces the lattice constants of AlAs and GaAs considerably, the influence of silicon doping is less clear. However, silicon is well known to reduce the mobility of dislocations. In the present work it is shown that both dopants prevent the relaxation of 3 μm thick Bragg reflectors and reduce considerably the density of misfit dislocations in complete laser structures. Laser structures with a beryllium-doped Bragg reflector, however, contain a high density of misfit dislocations for a wide range of growth temperatures. These dislocations are distributed over the whole layer stack; their topographic contrasts vary along the dislocation lines. Contrast simulations show that these changes may be attributed to the depth location of the defects in the stack.

Low threshold InGaAs/GaAs 45 degrees folded cavity surface-emitting laser grown on structured substrates

A novel folded cavity surface-emitting laser structure integrating a horizontal cavity InGaAs/GaAs laser grown on a structured substrate with a high reflectivity Bragg reflector has been fabricated. Devices with threshold currents of 8 mA and CW wall plug efficiencies at 5% at 6 mW output power have been demonstrated at a wavelength of 0.99 mu m. By combining a cleaved uncoated mirror with the 45 degrees deflecting mirror the authors have obtained threshold current as low as 5 mA for a device 450 mu m long. >