Showing papers by "E. Muñoz published in 2004"

Response of ultra-low dislocation density GaN photodetectors in the near- and vacuum-ultraviolet

Abstract: The spectral response of metal-semiconductor-metal (MSM) and Schottky barrier photodiodes have been studied in the near- and vacuum ultraviolet (VUV). Devices were fabricated on micro-epitaxial lateral overgrowth GaN layers, which presented dislocation densities as low as 7×107 cm−2. Experimental results indicate that the surface properties become critical for the optical response at short wavelengths. Schottky barrier photodiodes showed a lower VUV sensitivity than MSMs as a result of the radiation absorption in the semitransparent Au top-layer. However, Schottky photodiodes yielded a better time stability operating in photovoltaic mode. For photon energies above 10.5 eV, the quantum efficiency of the MSM photodiodes was enhanced as a consequence of the different nature of light-semiconductor interactions, which provoke a decrease of the absorption coefficient and the generation of multiple electron-hole pairs for each impinging photon. The ionization energy for GaN has been also estimated.

Effect of nitrogen on the optical properties of InGaAsN p-i-n structures grown on misoriented (111)B GaAs substrates

Abstract: In this work, we demonstrate the growth, characterization, and processing of InGaAsN single quantum well p-i-n structures by solid-source molecular-beam epitaxy on misoriented GaAs (111)B substrates. Two different misorientations were studied simultaneously, 1° toward [−211] and 2° toward [2-1-1], the latter showing the highest optical quality. The roles of the arsenic flux, substrate misorientation, and amount of active nitrogen on the optical properties and crystal quality are discussed. We demonstrate photoluminescence emission at wavelength as long as 1.42 μm at 16 K on (111)B GaAs. Postgrowth rapid thermal annealing improves crystal quality and typical blueshifts of the peak emission are observed, like the case of (100).

Role of N ions in the optical and morphological properties of InGaAsN quantum wells for 1.3–1.5μm applications

Abstract: In this work, we show the effects of N ions coming from a nitrogen plasma source on the optical and structural properties of InGaAsN quantum wells. The presence of ions in the growth chamber was measured by a modified Langmuir probe method at the substrate position. A magnetic field was applied to deflect charged species from the growing surface, producing a lower concentration of ions in the growth surface that led to an improvement of the optical and structural properties of the InGaAsN layers. The samples grown with an applied magnetic field showed a more intense and narrower photoluminescence emission, as well as a lower surface roughness. Additionally, postgrowth annealing has a smaller impact on the photoluminescence emission when a magnetic field is used, and a much lower blueshift is observed.

Novel photodetectors based on InGaN/GaN multiple quantum wells

Abstract: Photodetectors based on InGaN/GaN multiple quantum wells (MQW), as an alternative to already established sensors based on bulk nitrides, have been fabricated and characterised. Three main configurations have been investigated: p-i-n junction diodes with quantum wells embedded into the intrinsic region, Schottky barriers with quantum wells in the space charge region, and photoconductors fabricated on top of the quantum well layers. Theoretical and experimental results are reported, showing very promising performance for these MQW-based nitride detectors. Photoconductive gain (>20) was found under a bias voltage, with an important impact on device responsivity and time response characteristics. A good contrast (>10 3 ) has also been determined in both p-i-n and Schottky barrier photodiodes.

Effect of nitrogen ions on the properties of InGaAsN quantum wells grown by plasma-assisted molecular beam epitaxy

Abstract: The advantages of the InGaAsN/GaAs system comprising the active layers of single- and multi-quantum well laser diodes (emission wavelengths in the second and third optical windows, AlGaAs reflectors etc.), in comparison with other materials, make this quaternary material an interesting field for study. The monoatomic nitrogen species required for the growth of InGaAsN layers by molecular beam epitaxy, using a radiofrequency power source, are mixed in the plasma with ionised species, among others. The authors present a detailed characterisation of the plasma in the vicinity of the growing surface by measuring its I–V characteristics. A magnetic field was used to deflect ions and their effect on the properties of InGaAsN quantum wells was observed. These ionised species were observed to damage the surface, introducing nonradiative centres. As observed by photoluminescence experiments, the optical quality is improved as the density of ions impinging on the surface is reduced. Rapid thermal annealing experiments were also carried out, showing that the observed PL intensity improvement is related to the ion concentration in the quantum wells.

Influence of substrate misorientation and growth temperature on N incorporation in InGaAsN/GaAs quantum wells grown on (1 1 1)B GaAs

Abstract: In this work, the effects of the substrate misorientation in the nitrogen incorporation in InGaAsN (1 1 1) B p–i–n diode structures grown by molecular beam epitaxy are discussed. The (1 1 1) B surfaces misoriented towards [2–1–1] are found to be more suitable to enhance the optical quality of the samples. We also found that the nitrogen incorporation is highly dependent on the growth temperature as well as on the V–III flux ratio. In addition to this, the optical properties and crystal quality of these structures depend strongly on the nitrogen content, as in the case of similar samples grown on (1 0 0) surfaces. High nitrogen contents (up to 3%) in InGaAsN layers grown on two different misoriented (1 1 1) B GaAs substrates are reported. Besides, low-temperature photoluminescence emission wavelengths longer than 1.4 μm are achieved using (1 1 1) B misoriented substrates.

Nitride Photodetectors in UV Biological Effects Studies

Abstract: The role of the solar UV radiation in our biosphere is highlighted. Action spectra of solar UV radiation in biological processes are summarized. The erythema-weighted response has become standard for UV biological action monitoring. Fluorescence techniques and the requirements of AlInGaN-based UV detectors in biophotonics are described. AlGaN detectors fitting the erythema action spectrum are presented. QW nitride-based photodetectors, suitable for multifunctional integrated biochips, are introduced. Problem areas are discussed.