Recent progress on the development of AlGaN based UVC detectors is discussed. This includes growth, fabrication, and characterization of AlGaN based devices grown on AlN substrates. Special focus is put on the impact of the growth condition and impurity concentration of the epitaxial layers on the dark current. Overall, it is shown AlGaN based detectors have a sensitivity in the range of 130–270 nm while rejecting solar emission. If operated as an Avalanche photodiode (APD), these detectors have an exceptional high linear gain of 300,000 and quantum efficiency <70%. Finally, the potential for 1D and 2D arrays is discussed.
Epitaxial lateral overgrowth (ELO) of GaN is a well-established technology to reduce the dislocation density of III-Nitride films grown on sapphire. One of the longstanding problems with ELO has been the so-called wing tilt. This wing tilt is a result of a tilt of the GaN crystal in the regions not grown on the SiO2 opening which results in high dislocation densities in the coalescence region of the film. In this study, we demonstrate that wing tilt in ELO is result of the SiO2 used to pattern GaN templates. We show that wing tilt occurs immediately at the start of the ELO growth process. Furthermore, we show that wing tilt can be avoided completely if an etched template is used in combination with facet controlled epitaxial lateral overgrowth (FACELO). Results are based on homoepitaxial GaN growth in combination with TEM, XRD, and PL studies.
AlN as an UWBG host for quantum emitters, especially color centers, is expected to address current challenges such as operation at room temperature and scalability of quantum-photonic devices for qubit applications. Significant challenges in the point defect management and existence of multiple defects charge states precludes the use of AlN as a simple practical host for qubits. In this work, a roadmap for the stabilization of Ti-related color centers in AlN for quantum computing applications is presented. The realization of (TiAlVN)0 defects as a candidate for single spin color center requires the control of the Fermi level of AlN via doping, a nitrogen vacancy supersaturation via implantation, and the use of CPC and dQFL control methods to suppress the formation of other defects. This work opens a pathway for the systematic management of color centers with particular charge states in nitrides for quantum computing applications.
There is an increasing demand in the realization of new color centers in ultrawide bandgap semiconductors with ability to operate at room temperature for the quantum computation. AlN with bandgap of 6.2 eV and availability of mature growth techniques and controllable doping seems to be a suitable host for many deep color centers as a candidate for qubit such as (Ti_Al-V_N)^0. However, stabilization of this defect configuration with certain charge state requires defect engineering in AlN. In this work, formation of Ti-V complex was enhanced by introducing nitrogen vacancy supersaturation through Ti implantation. Kinetics of Ti-Vacancy complex formation was studied by annealing the implanted samples at various temperatures. Furthermore, the structural and optical properties of these color centers were investigated via STEM and micro-PL measurement. This work opens up pathway for realization of any color centers in semiconductors as a candidate for qubit.
Defect incorporation in AlGaN is dependent on the defect formation energy and hence on associated chemical potentials and the Fermi level. For example, the formation energy of CN in Al/GaN varies as chemical potential difference (µN- µC) and -EF (Fermi level). Here, we demonstrate a systematic point defect control by employing the defect formation energy as tool by (a) chemical potential control and (b) Fermi level control. Chemical potential control (µN and µC) with a case study of C in MOCVD GaN is reported. We derive a relationship between growth parameters, metal supersaturation (i.e. input and equilibrium partial pressures) and chemical potentials of III/N and impurity atoms demonstrating successful quantitative predictions of C incorporation as a function of growth conditions in GaN. Hence growth environment necessary for minimal C incorporation within any specified constraints may be determined and C is shown to be controlled from >1E19cm-3 to ~1E15 cm-3. Fermi level control based point defect reduction is demonstrated by modifying the Fermi level describing the probability of the defect level being occupied/unoccupied i.e. defect quasi Fermi level (DQFL). The DQFL is modified by introducing excess minority carriers (by above bandgap illumination). A predictable (and significant) reduction in compensating point defects (CN, H, VN) in (Si, Mg) doped AlGaN measured by electrical measurements, photoluminescence and secondary ion mass spectroscopy (SIMS) provides experimental corroboration. Further, experiments with varying steady state minority carrier densities at constant illumination prove the role of minority carriers and DQFL in defect reduction over other influences of illumination that are kept constant.
Being a II-VI semiconductor material with a wide direct band gap corresponding to the U-V region, ZnO finds important
applications in U-V light sensors. In this work, we have developed and characterized Au-ZnO-ITO based UV
photosensitive devices whose I-V characteristics show p+-i-n type behaviour and show an increased current under UV
illumination. ZnO is employed as the active region. Both ZnO and gold were deposited via rf magnetron sputtering. The
I-V characteristics of the fabricated UV sensor indicated a knee voltage of 0.69V. The resistance was observed to
decrease by a factor of 3.5 under illumination. Further, we have optically characterized ZnO thin films deposited at
different power levels to determine the dependency of various optical constants on deposition process parameters. These
thin films were characterized using VASE (Variable Angle Spectroscopic Ellipsometer) and their optical properties
including refractive index dispersion, band gap along with film thicknesses were extracted and modeled using WVASE
modeling software.
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