The search for nano-scaled light sources and detectors, with an emission/absorption precisely controlled through the design of their morphology and structure, is fundamental for developing new synthesis and fabrication solutions in optoelectronics. In this context, a core-shell heterostructure with promising applications in telecommunications serves as an example to demonstrate the technical capabilities available at the hard x-ray nanoprobe beamline ID16B of the European Synchrotron Radiation Facility (ESRF) for characterizing optically active nanomaterials. The proposed case study focuses on an InGaAs/InP Multi-Quantum Well (MQW) structure grown with a perfectly hexagonal shape onto InP Nanowires (NWs). Nano-characterization, using a combination of X-Ray Fluorescence (XRF), X-ray Near Edge Spectroscopy (XANES), and X-ray Excited Optical Luminescence (XEOL) techniques, was conducted to locally probe the elemental homogeneity at the deep submicrometric scale and investigate the local optical properties and their correlations with the phase structure and defects.
Quantum dot infrared photodetectors (QDIPs) promise improved performance over existing technologies in the form of higher temperature operation and normal-incidence detection. Variation in the size of self-assembled quantum dots leads to a broadened spectral response, which is undesirable for multi-color detection. Photonic crystal slabs can filter the transmission of normally-incident light using Fano resonances, and thus may be integrated with QDIPs to create a narrowband detector. Finite-difference time-domain simulations were used to optimize such a filter for QDIPs grown by metal-organic chemical vapor deposition. The simulations predict that the integrated detector could show up to 76% decrease in the detector linewidth, with a tunable peak location. These devices were then fabricated by standard optical lithography, however the spectral width of the integrated device was similar to that of the unfiltered QDIP. This is attributed to imperfections in the filter, so alternative fabrication methods are discussed for future processing.
Post-growth techniques such as impurity-free vacancy disordering (IFVD) are simple and effective avenues to monolithic integration of optoelectonic components. Sputter deposition of encapsulant films can enhance quantum well intermixing through IFVD and an additional mechanism involving surface damage during the sputtering process. In this study, these two mechanisms were compared in a multi-quantum well structure. The compositions of different silicon oxy-nitride films were controlled by sputter deposition in different ambient gases. These different encapsulants were used to initiate IFVD in the same heterostructure and the observed intermixing is compared to the film properties.
In this paper, techniques of quantum dot interdiffusion such as impurity free vacancy disordering and ion implantation induced disordering as well as the selective area epitaxy by metal-organic chemical vapour deposition have been used to tune the emission wavelength of self-orgainsed quantum dot structures. Under optimized experimental conditions, large differential band gap energies have been achieved by all approaches which is essential for quantum dot-based photonic integrated circuits.
Titanium dioxide (TiO2) cap layers were deposited onto C-doped InGaAs/AlGaAS QW laser structures by electron-beam evaporation in order to investigate their effect on atomic interdiffusion. In comparison to the as-grown sample, a negligible shift of the photoluminescence peak was observed after annealing at 900°C, indicating that the atomic interdiffusion was greatly suppressed by TiO2 capping layers. For the uncapped sample, the high temperature annealing step significantly improves the threshold current density in laser diode devices but leaves the internal efficiency unchanged. We attribute these effects to the activation of the carbon p-type dopant, as demonstrated by electrochemcial C-V capacitance-voltage and X-ray measurements. SIMS analysis shows that the carbon atomic profile does not significantly change after annealing. In contrast, a similar Zn doped laser structure shows an almost flat Zn profile after annealing at 925°C, due to considerable indiffusion from the highly doped p++ GaAs top contact layer in to the rest of the structure.
There has been a great revival of interest in the area of ultrafast photodetectors after the discovery of low temperature (LT) MBE-grown GaAs [1-3]. These detectors have found numerous applications in picosecond electrical pulse generation and sampling, and as main components of spectroscopic arrangements for terahertz frequency range. The unique properties of LT GaAs such as short carrier lifetimes and high resistivity made it a promising material for ultrafast photoconductive switches and photodetectors. It has been reported that ion implanted material may provide an alternative material for these applications [4-6]. Defects introduced by implantation may act as traps or recombination centres that have large carrier capture cross sections which shorten the carrier lifetimes significantly. The work presented below is an overview of how ion implantation could be used to modify the properties of GaAs and InP for ultrafast photodetector applications. Also, in the area of quantum well infrared photodetectors (QWIPs), there has been much effort in developing the technology for multi-color QWIPs [7,8]. These devices are highly desirable in advanced high performance infrared (IR) systems as it provides not only the spatial information of the image but also the spectral information. Although the functionality of these devices could be designed right from the epitaxy stage, it requires complicated structures and processing steps. In this paper we will demonstrated an alternative method of realizing the multi-color QWIP by a technique known as intermixing. By implantation, the band structure of the quantum wells (QWs) could be modified and hence tune the detection wavelength of the device.
The intermixing techniques have been used to modify the behavior of the quantum well infrared photodetector (QWIP). It is demonstrated that the proton implantation assistant intermixing process is very effective to the modification of the quantum well potential. Both the inter-band transition and inter-sub-band transitions are used to study the intermixing effects. After the characterization on the modified detector, the dominant mechanisms in the QWIP are examined.
Due to the mature material growth and device fabrication technology, GaAs/AlxGa1-xAs quantum-well infrared photodetector (QWIP) has been extensively studied and used in remote sensing, particularly in long wavelength range, e.g. the atmospheric window region of 8 approximately 14 micrometers . This paper reports the using of intermixing techniques to modify GaAs/AlGaAs multiple quantum well photodetectors (QWIPs). A red shift in response wavelength of QWIP has been obtained both by rapid thermal annealing (RTA) and proton implantation. The peak response wavelengths has been shifted into the atmospheric window (8.3 micrometers ) from the originally 7.7 micrometers . The response spectra have been measured as the function of the different temperature of the RTA and the ion doses in the range from 4 X 1014 to 5 X 1015 cm-3, respectively. The device performance such as dark current and blackbody response are also measured at different conditions. The effect of RTA and ion implantation on the device performance has been interpreted theoretically by the interdiffusion of Al atoms across the GaAs/AlxGa1-xAs heterointerfaces.
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