Deep-level defects in n-type GaAsBi alloys grown by molecular beam epitaxy at low temperature and their influence on optical properties

Deep-level defects in n-type GaAs1-x Bi x having 0 ≤ x ≤ 0.023 grown on GaAs by molecular beam epitaxy at substrate temperature of 378 °C have been injvestigated by deep level transient spectroscopy. The optical properties of the layers have been studied by contactless electroreflectance and photoluminescence. We find that incorporating Bi suppresses the formation of GaAs-like electron traps, thus reducing the total trap concentration in dilute GaAsBi layers by over two orders of magnitude compared to GaAs grown under the same conditions. In order to distinguish between Bi- and host-related traps and to identify their possible origin, we used the GaAsBi band gap diagram to correlate their activation energies in samples with different Bi contents. This approach was recently successfully applied for the identification of electron traps in n-type GaAs1-x N x and assumes that the activation energy of electron traps decreases with the Bi (or N)-related downward shift of the conduction band. On the basis of this diagram and under the support of recent theoretical calculations, at least two Bi-related traps were revealed and associated with Bi pair defects, i.e. (VGa+BiGa)(-/2-) and (AsGa+BiGa)(0/1-). In the present work it is shown that these defects also influence the photoluminescence properties of GaAsBi alloys

Fabrication of two-dimensional InGaN-based micro-LED arrays

We have successfully fabricated two-dimensional InGaN-based 12 × 12 micro-light emitting diode (LED) arrays with individually addressable emitters having diameters of 8 and 12 m. A new planarisation scheme including gap-filling with plasma enhanced chemical vapour deposition (PECVD) SiO2 and a chemical-mechanical polishing process was successfully developed for the electrical isolation of individual diodes. The uniformity of elements within an array was demonstrated through their electroluminescence and I-V characteristics

(AlGaIn)N UV LEDs for integrated metal-oxide based ozone sensors

There is high demand for compact low-cost ozone (O3) sensors. It has been shown that indium oxide (In2O3) thin films grown by metal-organic vapor-phase epitaxy (MOVPE) act as an O3 sensitive material, which can be activated at room-temperature by ultraviolet (UV) light. In the present work we integrated the In2O3 sensing thin film and an (AlGaIn)N based near-UV LED back-to-back on a single sensor chip. The integrated in2O3 film-LED sensor was exposed to varying ozone concentrations ranging from 38 ppb to 726 ppb and found to be sensitive to even the lowest O3 concentration

(AlGaIn)N ultraviolet LED chips and their use in tri-phosphor luminescence conversion white LEDs

We report on the development of (AlGaIn)N quantum well LEDs covering the 380 to 430 nm wavelength range, which serve as the primary light source for tri-phosphor luminescence conversion white LEDs. Epitaxial layer growth was performed by low-pressure metal-organic chemical vapor deposition on sapphire substrates. Mesa LEDs were fabricated and either mounted in standard epoxy-based 5 mm radial LED packages or flip-chip bonded on ceramic submounts. Then, LED-chips with peak wavelengths matching the absorption spectrum of an appropriately chosen inorganic tri-phosphor blend, were used for the fabrication of single-chip tri-color luminescence conversion white LEDs. These devices allowed us to demonstrate the feasibility of the above concept for improved color rendering and tunability