A II-VI compound semiconductor laser diode (10) is formed from overlaying layers of material including an n-type single crystal semiconductor substrate (12), adjacent n-type and p-type guiding lasers (14) and (16) of II-VI semiconductor forming a pn junction, a quantum well active layer (18) of II-VI semiconductor between the guiding layers (14) and (16), first electrode (32) opposite the substrate (12) from the n-type guiding layer (14), and a second electrode (30) opposite the p-type guiding layer (16) from the quantum well layer (18) Electrode layer (30) is characterized by a Fermi energy A p-type ohmic contact layer (26) is doped, with shallow acceptors having a shallow acceptor energy, to a net acceptor concentration of at least 1 x 1017 cm-3, and includes sufficient deep energy states between the shallow acceptor energy and the electrode layer Fermi energy to enable cascade tunneling by charge carriers

Blue-green laser diode

Plasma enhanced chemical vapor deposition(PECVD) is being increasingly used for the fabrication of transparent dielectric optical films and coatings. This involves single-layer, multilayer, graded index, and nanocomposite optical thin filmsystems for applications such as optical filters, antireflective coatings, optical waveguides, and others. Beside their basic optical properties (refractive index, extinction coefficient, optical loss), these systems very frequently offer other desirable “functional” characteristics. These include hardness, scratch, abrasion, and erosion resistance, improved adhesion to various technologically important substrate materials such as polymers, hydrophobicity or hydrophilicity, long-term chemical, thermal, and environmental stability, gas and vapor impermeability, and others. In the present article, we critically review the advances in the development of plasma processes and plasmasystems for the synthesis of thin film high and low index optical materials, and in the control of plasma–surface interactions leading to desired film microstructures. We particularly underline those specificities of PECVD, which distinguish it from other conventional techniques for producing optical films (mainly physical vapor deposition), such as fabrication of graded index (inhomogeneous) layers, control of interfaces, high deposition rate at low temperature, enhanced mechanical and other functional characteristics, and industrial scaleup. Advances in this field are illustrated by selected examples of PECVD of antireflective coatings, rugate filters, integrated optical devices, and others.

Plasma deposition of optical films and coatings: A review

The first measurements of two‐photon pumped upconverted lasing in a waveguide is reported. Nonlinear dependence of the upconversion signal on the square of the input pump intensity and associated spectral narrowing was experimentally observed in dye‐doped polymer waveguides. The pump wavelength was 736 nm and the center of the lasing spectrum was 570 nm. The spectra shows excitonlike features at 630 and 654 nm not seen in the absorption spectrum.

Two‐photon pumped upconverted lasing in dye doped polymer waveguides

Growth of ZnS, CdS and multilayer ZnS/CdS thin films by SILAR technique

Nitrogen-doped ZnSe layers have been grown on (100) GaAs substrates by metalorganic vapor phase epitaxy using NH3 as the doping material. The N-doped layers exhibit a strong free-to-acceptor transition emission at 77 K and a strong acceptor bound-exciton emission line at 15 K. The layers with a high doping level, which exhibit broader excitonic emission lines, indicate p-type conduction with low resistivities from 102 to 103 Ω·cm, carrier concentrations of the order of 1014 cm-3 and mobilities from 20 to 50 cm2/Vs. Current-voltage characteristics of the N-doped ZnSe/n-GaAs heterojunctions conform to the p-type conduction.

Nitrogen Doped p-Type ZnSe Layer Grown by Metalorganic Vapor Phase Epitaxy : Semiconductors and Semiconductor Devices

A ZnSe/ZnSSe blue semiconductor laser was demonstrated to show very low threshold by direct photopumping of the ZnSe active layer. The lowest threshold at the excitation wavelength of 445 nm was 10 kW/cm2 at 300 K which is equivalent to the current density of 3.6 kA/cm2. This is the lowest threshold ever reported in II‐VI photopumped lasers and is approaching the theoretically calculated threshold. The characteristic temperature of the threshold, which characterizes the temperature dependence of the threshold in the exponential form, was 124 K up to the measured 400 K and was comparable to III‐V double‐heterostructure lasers. The differential quantum efficiency remained the similar level up to 400 K and its decrease observed at 400 K was within 23% of the efficiency at 300 K.

Extremely-low-threshold and high-temperature operation in a photopumped ZnSe/ZnSSe blue laser

High output power of 24 W was observed from a photopumped ZnSe/ZnSSe blue laser operating at room temperature. A differential quantum efficiency greater than 25% was estimated in the lasing region of the photopumped wafer. The improved lasing property is attributed mainly to the improved waveguiding structure verified from the far-field measurement. The other is the introduction of a ZnSe/ZnSSe superlattice buffer which improved the crystalline property of the active layer grown above. The lowest threshold power was 50~70 kW/cm2 for a cavity length of 220 µm under pulsed operation.

High Output Power (>20 W) and High Quantum Efficiency in a Photopumped ZnSe/ZnSSe Blue Laser Operating at Room Temperature

Photopumped blue laser oscillation was achieved up to near room temperature (280 K) in a ZnS0.18Se0.82/ZnSe multilayer structure grown by MOVPE. This significant improvement in the lasing temperature is attributed to the higher heterobarrier which prevents thermoionic emission and to the multilayer structure which has an average lattice constant matched to the GaAs substrate at the growth temperature of 515°C. The threshold excitation optical power density below 200 K where the thermoionic emission is negligible is less than 50 kW/cm2, which corresponds to a current density of 14 kA/cm2.

Near-room-temperature photopumped blue lasers in ZnSxSe1-x/ZnSe multilayer structures

Optical waveguides consisting of a SiOxNy (0≤x,y≤1) core and SiO2 cladding layers have been fabricated using Si LSI technologies. Low‐pressure chemical vapor deposition (CVD) at 750 °C and remote‐plasma CVD at 300 °C have been employed for the deposition of core materials. The propagation loss of ridge type waveguides depends on the size (thickness and width), refractive index and surface roughness of the core. A minimum loss of 1.5 dB/cm has been obtained. Micromirrors made from substrate‐Si, poly‐Si or Al, which change the light propagation direction, have been fabricated using wet‐chemical or chemical dry etching. The light bending efficiency ranges from 60% to 80% depending on the material. Simulations and measurements of the propagation losses of branched and curved waveguides have been carried out. It is shown that the simulated results are in good qualitative agreement with the experimental data for both branched and curved waveguides. Single‐chip integration of light emitting diodes (LEDs), microm...

Optical waveguides on silicon chips

High efficiency compact mirrors and branched waveguides which can be integrated on LSI chips have been developed. The Al capped bent optical waveguides efficiently change the light direction. The Al capping also reduces the light propagation loss of the optical waveguide from 1.8 to 0.6 dB/cm. Various micromirror shapes have been investigated and a reflectivity of 81% has been obtained for a double-reflection micromirror with a corner radius of 34 µm. Using the micromirrors, compact four-branch waveguides have also been designed and fabricated.

http://iopscience.iop.org/article/10.1143/JJAP.35.941/pdf

Yasuhide Kuroda

Papers

Extremely-low-threshold and high-temperature operation in a photopumped ZnSe/ZnSSe blue laser

High Output Power (>20 W) and High Quantum Efficiency in a Photopumped ZnSe/ZnSSe Blue Laser Operating at Room Temperature

Near-room-temperature photopumped blue lasers in ZnSxSe1-x/ZnSe multilayer structures

Optical waveguides on silicon chips

High-Efficiency Micromirrors and Branched Optical Waveguides on Si Chips.