Optoelectronic Devices

Copper halides have been studied for several decades [1-3] but the importance of IB-VIIA semiconductors are still growing because of the potential applications occurring from the restricted excitons in micro-crystals made of these materials [4]. The copper halides crystallize in the zinc blend lattice (space group F-43m) and are tetrahedral coordinated semiconductors. Cu atom is located at position (0, 0, 0), while X (F, Cl, Br, I) atoms are located at (1/4, 1/4, 1/4) positions. The electronic configuration of zinc blend structure is derived from sp3-sp3 configuration while the valence bands of copper halides are due to sp3-sd3. As a result of the pd hybridization considerably changes physical properties of copper halides are considerably different compared with other members of ANB8-N series. B. Amrani et al [5] performed under pressure calculations on these materials and found that they transform from the zinc-blend (B3) to the rocksalt (B1) structure. Experimental studies [6-8] have revealed that CuCl, CuBr and CuI adopt the rocksalt structure at a pressure around in the region of 10 GPa, though the zinc blende-rocksalt transition occurs via several intermediate structures of lower symmetry. According to Amrani et al, the most interesting feature of the copper halides is the occurrence of a filled d10-shell.

This paper reviews recent progress toward intersubband (ISB) devices based on III-nitride quantum wells (QWs). First, we discuss the specific features of ISB active region design using GaN/AlGaN materials, and show that the ISB wavelength can be tailored in a wide spectral range from near-to long infrared wavelengths by engineering the internal electric field and layer thicknesses. We then describe recent results for electro-optical waveguide modulator devices exhibiting a modulation depth as large as 14 dB at telecommunication wavelengths. Finally, we address a new concept of III-nitride QW detectors based on the quantum cascade scheme, and show that these photodetectors offer the prospect of high-speed devices at telecommunication wavelengths. for control-by-design devices relying on quantum wells (QWs) or quantum dots (QDs). One famous example is the quantum cascade laser (QCL), which was invented in the mid-1990s at Bell Laboratories . Using materials such as GaAs/AlGaAs, InGaAs/AlInAs or antimonides, ISB devices such as the QCLs can be tuned from the mid-infrared to the THz spectral range. Operation at short wavelengths is limited by the available conduction band offset and by the material transparency. III-nitride semiconductors (GaN, AlN, InN and their alloys) are attracting much interest for ISB devices operating in the near-infrared spectral range and, in particular, in the 1.3-1.55 µm wavelength window used for fiber optic telecommunications. Not only are they transparent in a wide spectral region (360 nm to 13 µm for GaN), but the conduction band offset provided by their heterostructures is quite large, being of the order of 1.75 eV for GaN/AlN . In contrast to InAs/AlSb materials, which also exhibit a large conduction band discontinuity, the remote valleys of GaN lie very high in energy (>2 eV above the point [4]), offering the potential for ISB light-emitting devices at record short near-infrared wavelengths. Another specificity of nitride materials is substantial longitudinal-optical (LO) phonon energy (92 meV for GaN), as well as the presence of huge internal fields induced by spontaneous and piezoelectric polarizations along the c-axis, inherent in their wurtzite structure. Due to the rather heavy electron effective mass (0.22 × m 0 for GaN), ultrathin QW or QD layers, typically 1-1.5 nm thick, are required in order to tune the ISB wavelength in the 1.3-1.55 µm range.

In this work, the adopted method of the CdSe doped with Cu (CdSe: Cu) photodetector is presented. This detector is prepared by vacuum evaporation of CdSe films on a glass substrate followed by vacuum annealing under an argon atmosphere for doping with copper. The detector is found, for the first time, to cover a wide range of the infrared besides the visible region of the electromagnetic spectrum. This finding of the wavelength tuning is due to the localized energy states of copper atoms inside the band gap of the CdSe. These characteristics stem from the unique band structure of CdSe: Cu. This tuning is compared with recent work in the corresponding colloidal CdSe-ZnS core shell quantum dots and with the quantum well (QWIR) and quantum dots infrared detectors (QDIR). The major significance of this developed detector is in its synthesis simplicity and its fabrication processes costs in comparison with that of the (QWIR) and (QDIR) detectors. The structural analysis results demonstrated that the vacuum annealing in competition with the doping concentration improves significantly the film structure. A better crystalline structure is reported at 5 wt% of Cu concentration and at annealing temperature of 350ºC. Besides the measured specific detectivity at room temperature is D*=2.31×10 8 cm Hz 1/2 W-1. This value approaches the detectivity of the state of art mercury cadmium telluride (MCT). This result paves the way for further investigations and improvements.