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

We have achieved a highly doped p‐type ZnSe layer using a Li3N diffusion technique. The hole concentration of the p‐type ZnSe layer, grown on a GaAs substrate by metalorganic vapor phase epitaxy, reached a level as high as 1017 cm−3. With the diffusion temperature of 470 °C, the resistivity of the layer is as low as 0.4 Ω cm, with hole concentration p≳9×1017 cm−3 and hole mobility μp=17 cm2/V s. We made an ohmic contact by using this p+‐type ZnSe as a contact layer for p‐ZnSe epilayers.

High p‐type doping of ZnSe using Li3N diffusion

We have fabricated InGaAs/GaAs vertical-cavity surface-emitting lasers with modulation-doped graded distributed Bragg reflectors (DBRs) grown by metal-organic chemical vapor deposition (MOCVD). The threshold current was 3.2 mA. By observing the spontaneous emission through DBRs, we found that transverse mode behavior depends on gain characteristics. Single fundamental transverse-mode lasing is achieved at a negative gain offset and multiple transverse-mode lasing is achieved at a positive gain offset.

Transverse-Mode Characteristics of InGaAs/GaAs Vertical-Cavity Surface-Emitting Lasers Considering Gain Offset

A GaNAs layer has been grown on a GaAs substrate using chemical beam epitaxy (CBE) with a radio frequency (RF) radical nitrogen source for the first time. The nitrogen (N) composition was well-controlled by the N2 flow rate and was increased up to 2.7%, maintaining a good crystal quality. The maximum N composition was estimated to be 20% by a secondary ion mass spectroscopy (SIMS) measurement. The N composition estimated from both X-ray diffraction measurements and SIMS measurements were in good agreement. This shows that the N composition can simply be determined by X-ray diffraction measurements. The optical absorption measurement of the grown GaNAs was also carried out. The bandgap bowing parameter of GaNAs was found to be not a constant and varied between 15–23 eV for N<2.7%. An empirical expression of bandgap vs. composition was obtained for a N composition below 3%.

Chemical Beam Epitaxy Growth and Characterization of GaNAs/GaAs

A semiconductor laser formed on an InP substrate to have a hetero structure comprising a plurality of In 1-x Ga x`As y P 1-y (0.42y≦x≦0.5y,0≦y≦1) layers which are lattice-matched with InP, in which a light emitting layer included in the layers and having a forbidden band width larger than 0.6 eV but smaller than 0.9 eV at room temperature is sandwiched between two InP layers on the InP substrate, and in which there is provided between the light emitting layer and the InP layer grown thereon at least one buffer layer having a forbidden band width larger than the forbidden band width of the light emitting layer but smaller than the forbidden band width of InP. The forbidden band width of the buffer layer at room temperature may be larger than 0.8 eV but smaller than 1.0 eV.

Semiconductor laser with buffer layer

In the letter the lasing characteristics of a multiquantum-well surface-emitting injection laser with 100 wells at 77 K under pulsed condition is reported. The output light of the device was linearly polarised.

Kenichi Iga

Papers

High p‐type doping of ZnSe using Li3N diffusion

Transverse-Mode Characteristics of InGaAs/GaAs Vertical-Cavity Surface-Emitting Lasers Considering Gain Offset

Chemical Beam Epitaxy Growth and Characterization of GaNAs/GaAs

Semiconductor laser with buffer layer

AlGaAs/GaAs multiquantum-well (MQW) surface-emitting laser