We present models for the optical functions of 11 metals used as mirrors and contacts in optoelectronic and optical devices: noble metals (Ag, Au, Cu), aluminum, beryllium, and transition metals (Cr, Ni, Pd, Pt, Ti, W). We used two simple phenomenological models, the Lorentz-Drude (LD) and the Brendel-Bormann (BB), to interpret both the free-electron and the interband parts of the dielectric response of metals in a wide spectral range from 0.1 to 6 eV. Our results show that the BB model was needed to describe appropriately the interband absorption in noble metals, while for Al, Be, and the transition metals both models exhibit good agreement with the experimental data. A comparison with measurements on surface normal structures confirmed that the reflectance and the phase change on reflection from semiconductor-metal interfaces (including the case of metallic multilayers) can be accurately described by use of the proposed models for the optical functions of metallic films and the matrix method for multilayer calculations.

Optical properties of metallic films for vertical-cavity optoelectronic devices.

The role of extended and point defects, and key impurities such as C, O, and H, on the electrical and optical properties of GaN is reviewed. Recent progress in the development of high reliability contacts, thermal processing, dry and wet etching techniques, implantation doping and isolation, and gate insulator technology is detailed. Finally, the performance of GaN-based electronic and photonic devices such as field effect transistors, UV detectors, laser diodes, and light-emitting diodes is covered, along with the influence of process-induced or grown-in defects and impurities on the device physics.

Gan : processing, defects, and devices

1. Introduction and overview 2. Film stress and substrate curvature 3. Stress in anisotropic and patterned films 4. Delamination and fracture 5. Film buckling, bulging and peeling 6. Dislocation formation in epitaxial systems 7. Dislocation interactions and strain relaxation 8. Equilibrium and stability of surfaces 9. The role of stress in mass transport.

Thin Film Materials: Stress, Defect Formation and Surface Evolution

The ability to control the modes oscillating within a laser resonator is of fundamental importance. In general, the presence of competing modes can be detrimental to beam quality and spectral purity, thus leading to spatial as well as temporal fluctuations in the emitted radiation. We show that by harnessing notions from parity-time (PT) symmetry, stable single–longitudinal mode operation can be readily achieved in a system of coupled microring lasers. The selective breaking of PT symmetry can be used to systematically enhance the maximum attainable output power in the desired mode. This versatile concept is inherently self-adapting and facilitates mode selectivity over a broad bandwidth without the need for other additional intricate components. Our experimental findings provide the possibility to develop synthetic optical devices and structures with enhanced functionality.

http://science.sciencemag.org/content/sci/346/6212/975.full.pdf

Parity-time–symmetric microring lasers

In this review article a comprehensive analysis of the developments in ultraviolet (UV) detector technology is described. At the beginning, the classification of UV detectors and general requirements imposed on these detectors are presented. Further considerations are restricted to modern semiconductor UV detectors, so the basic theory of photoconductive and photovoltaic detectors is presented in a uniform way convenient for various detector materials. Next, the current state of the art of different types of semiconductor UV detectors is presented. Hitherto, the semiconductor UV detectors have been mainly fabricated using Si. Industries such as the aerospace, automotive, petroleum, and others have continuously provided the impetus pushing the development of fringe technologies which are tolerant of increasingly high temperatures and hostile environments. As a result, the main efforts are currently directed to a new generation of UV detectors fabricated from wide band‐gap semiconductors the most promising ...

Semiconductor ultraviolet detectors

Using a self-imaged diffraction coupled model in a Talbot cavity for vertical cavity surface emitting laser arrays, the effect of self-imaged reflections on the lasing threshold of a finite 2-D array was investigated. Array size and the ratio defined by the element diameter/element spacing were found to affect the effective reflectivity as seen from the laser cavities and, ultimately, the device threshold. A general curve showing the dependence of the 2-D coupling coefficient on the array fill factor and array size has been found. Minimum levels of laser facet reflectivities have been obtained as a function of the array fill factor for practical devices with low threshold current densities.

Effective reflectivity from self-imaging in a Talbot cavity and its effect on the threshold of a finite 2-D surface emitting laser array

First, it has been made clear that the important parameters of the SE laser are its active layer thickness d and the mirror reflectivity R. The required values of three parameters such as threshold gain gth, threshold current density Jth, and differencial quantum efficiency ηd are obtained for d=2~3 µm and R=95%. At this condition gth is estimated as 300 cm-1 (Nth=3×1018 cm-3), Jth is 25~30 kA/cm2, and ηd is 40%. Next, in order to obtain a reflectivity as high as 95%, a TiO2/SiO2 multilayer Bragg reflector was introduced. It was found that a good quality TiO2 film could be evaporated by leaking oxygen through a variable leak valve to hold 1×10-4 Torr. Then, a 7-pair TiO2/SiO2 multilayer Bragg reflector was fabricated; its peak reflectivity was 95% at 8800 A. A room-temperature pulsed operation of a GaAlAs/GaAs SE layer was achieved and the minimum threshold current was reduced to as low as 150 mA when a round mesa was fabricated to 20 µm in diam.

https://iopscience.iop.org/article/10.1143/JJAP.26.410/pdf

GaAlAs/GaAs Surface Emitting Laser with High Reflective TiO2/SiO2 Multilayer Bragg Reflector

Detailed results on stripe Ga x In 1-x As y P 1-y /InP lasers ( \lambda = 1.3 \mu m) with chemically etched-mirrors are reviewed. These devices are fabricated from GaInAsP/InP wafers grown by liquid phase epitaxy. A simple stripe laser structure with one etched mirror and one cleaved mirror is proposed. Monolithic passivation has been achieved using a Si 3 N 4 film and metal coatings on the etched facets. These processes not only increase the reflectivity of the etched mirrors, resulting in threshold currents even lower than uncoated cleaved devices, but also ease the problem of bonding of the chips on heat sinks. CW operation at room temperature has been achieved. Threshold currents of devices with 10 μm stripe electrodes were about 180-200 mA. Short cavity lasers and integrated monitoring detectors have also been demonstrated.

Chemically etched-mirror GaInAsP/InP lasers - Review

We have fabricated a SiO2/TiO2 dielectric multilayer mirror applicable for ZnSe-based surface emitting lasers operating at green to blue spectral regions. The fabricated SiO2/TiO2 dielectric mirrors have exhibited a reasonably high reflectivity, greater than 96% at 493 nm. A photo-pumped ZnCdSe/ZnSe/ZnSSe single quantum well (SQW) with dielectric mirrors has shown the cavity mode emission in the surface normal direction at 10 K.

Fabrication of a ZnSe-Based Vertical Fabry-Perot Cavity Using SiO2/TiO2 Multilayer Reflectors and Resonant Emission Characteristics

A surface-emitting-type semiconductor laser device having a buried structure wherein a burying part having a current blocking function is formed around a buried part comprising an active region. A reflecting mirror consisting of a semiconductor multilayer film is installed on the buried part and the burying part, and the Bragg wavelength of this semiconductor multilayer film is set in matching with a longitudinal mode one mode higher than the longitudinal mode of oscillation in pulse operation. This semiconductor multilayer film has a configuration wherein two kinds of GaAlAs layers having different composition ratios of Al are laminated alternately, and the layer thickness of each GaAlAS layer constituting the semiconductor multilayer film is set so as to able to realize the Bragg wavelength calculated theoretically.

Kenichi Iga

Papers

Effective reflectivity from self-imaging in a Talbot cavity and its effect on the threshold of a finite 2-D surface emitting laser array

GaAlAs/GaAs Surface Emitting Laser with High Reflective TiO2/SiO2 Multilayer Bragg Reflector

Chemically etched-mirror GaInAsP/InP lasers - Review

Fabrication of a ZnSe-Based Vertical Fabry-Perot Cavity Using SiO2/TiO2 Multilayer Reflectors and Resonant Emission Characteristics

Surface emitting type semiconductor laser device