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

Room temperature continuous wave operation of ZnSe-based blue/green laser diodes grown homoepitaxially on conductive ZnSe substrates with threshold current densities as low as 176 A/cm2 has been demonstrated. This is the lowest reported threshold among all short wavelength lasers in the blue/green region. Lifetimes at room temperature of up to 2.1 h have been obtained for lasers with pre-existing defect densities lower than 3×104 cm−2.

Lasing characteristics of low threshold ZnSe-based blue/green laser diodes grown on conductive ZnSe substrates

One-pot facile synthesis of the ZnO/ZnSe heterostructures for efficient photocatalytic degradation of azo dye

A well‐defined exciton absorption peak from a localized state was observed for the first time. The localized state was formed by fluctuation of well‐barrier interfaces in a ZnSe/ZnSSe superlattice structure. Stimulated emission was observed from the localized state up to 100 K, and the physical origin is discussed from the temperature dependence of the stimulated emission peak. This opens the possibility to form a natural quantum box structure by controlling the well‐barrier fluctuation.

Blue‐light stimulated emission from a localized state formed by well‐barrier fluctuation in a II‐VI semiconductor superlattice

We present a model for lasing oscillation due to bi-excitons and localized bi-excitons in wide-gap II–VI semiconductor quantum wells. We introduce the condition for population inversion in bi-exciton–exciton optical transition, and show the importance of studying the thermodynamic equilibrium between bi-exciton and exciton states. The Saha equation shows that bi-excitons decompose into two free excitons at fairly low temperatures due to the small binding energy (10 to 30 meV) in II–VI quantum wells, making the population inversion possible only at low temperatures. We point out that bi-excitons localized at certain potential minima in the quantum-well plane will achieve the population inversion even at room temperature if the local potential is deep enough to prevent thermal activation (about 100 meV). By simple theoretical calculation, we show that the localized bi-exciton–exciton optical transition will produce sufficient optical gain for lasing oscillation and has potential application in low-threshold-current blue-light emitting lasers.

Model for lasing oscillation due to bi-excitons and localized bi-excitons in wide-gap semiconductor quantum wells

Photopumped ZnSe/ZnSSe blue semiconductor lasers and a theoretical calculation of the optical gain

Improvement of electrical and optical properties of ZnSSe p-n heterostructure diodes with optimization in metalorganic vapor phase epitaxy

It has been shown that silicon photonic crystal nanocavities excited by spectrally narrow light can be used to detect ionized air. Here, to increase the range of possible applications of nanocavity-based sensing, the use of broadband light is considered. We find that the use of a superluminescent diode (SLD) as an excitation source enables a more reproducible detection of ionized air. When our photonic-crystal nanocavity is exposed to ionized air, carriers are transferred to the cavity and the light emission from the cavity decreases due to free carrier absorption. Owing to the broadband light source, the resonance wavelength shifts caused by the carriers in this system (for example, due to temperature fluctuations) do not influence the emission intensity. SLD-excited cavities could be useful to determine the density of ions in air quantitatively.

Detection of ionized air using a photonic-crystal nanocavity excited by broadband light from a superluminescent diode.

http://ieeexplore.ieee.org/iel4/5395/14590/00665044.pdf

ZnSe/ZnSSe Superlattices Grown by MOVPE and Their Optical Characterization with Low and High Excitations

Ionized air is used in various industries to control electrostatic charge. On the other hand, ionized air molecules can also cause various problems since electrification of materials can induce electrostatic discharges. Therefore, compact sensors that enable a quantitative detection of ionized air will help to improve industrial processes and safety. Here we report on the detection of negatively ionized air using a photonic crystal (PC) waveguide with a length of 800 µm. In this type of detector, the PC is exposed to a flux of air ions that transfers a part of the excess charges to the PC. The light transmitted through the waveguide is then attenuated by free carrier absorption due to the excess charges from the ionized air molecules. We show that the electron density in the PC can be estimated from the magnitude of the attenuation, and that this magnitude depends on the wavelength of the light propagating in the PC waveguide. Due to the wavelength dispersion of the group velocity, light at longer wavelengths is subject to stronger attenuation than light at shorter wavelengths. This property is useful for the development of ionized-air sensors with a variable detection range. 

M. Fujimoto

Papers

Photopumped ZnSe/ZnSSe blue semiconductor lasers and a theoretical calculation of the optical gain

Improvement of electrical and optical properties of ZnSSe p-n heterostructure diodes with optimization in metalorganic vapor phase epitaxy

Detection of ionized air using a photonic-crystal nanocavity excited by broadband light from a superluminescent diode.

ZnSe/ZnSSe Superlattices Grown by MOVPE and Their Optical Characterization with Low and High Excitations

Control of the sensitivity of the detection of ionized air using photonic crystal waveguides