Investigation of narrow gap dilute nitride materials for mid-infrared optoelectronic devices

This project investigates dilute nitrides such as InAsN and InGaAsN with a view to the fabrication of optoelectronic sources and detectors operating in the mid-infrared (2-5 um) spectral range which has many practical applications. Samples of both bulk epitaxial layers and state-of-the-art nanostructures have been grown by liquid phase epitaxy (LPE) and molecular beam epitaxy (MBE). The effect of N incorporation on the material quantum efficiency has been studied using temperature dependent photo- and electroluminescence spectroscopy, high resolution x-ray diffraction and other techniques. InAsN and InGaAsN bulk epilayers were grown by liquid phase epitaxy under standard and neutral solvent growth techniques to investigate the feasibility of high quality material production. Photoluminescence (PL) showed that the dominant peak in the majority of the material was from a defect related transition which quickly quenched leaving just band - band recombination. Raman spectroscopy was employed to identify the types of defect levels present within the material, the strange behaviour of the PL from InGaAsN material was determined to be from a doubly-ionised defect involving a combination of In vacancies and higher order nitrogen complexes. High quality InAsN layers were grown from neutral solvent growth with an XRD full-width-half-maximum (FWHM) of 17.5 arc-seconds obtained from 0.3% N incorporation; this however was only observed in thin layers of the dilute nitride believed to be due to the rapid depletion of N within the growth melt. High quality InAsN was grown onto GaAs substrates using molecular beam epitaxy; PL from this material persisted up to room temperature with a final emission wavelength of 4 urn and nitrogen incorporation of 1%. The temperature dependence of the material was found to be superior to that of similar material grown onto InAs substrates and shown to have an 'S' shaped behaviour at low temperatures originating from tail states caused by inhomogeneous nitrogen incorporation typical of all nitrogen inclusive materials. A comparison with LPE material was then carried out. PL measurements showed that the LPE material had comparable emission intensities with narrower FWHM for low N content samples but MBE proved more favourable for higher N content material with the maximum N inclusion from LPE being 0.5%. The addition of Sb to InAsN multi quantum wells was then studied with the view to device fabrication. The addition of Sb was found to improve both lattice quality and PL intensities while reducing the overall strain of the material. Interpretation of the 4 K PL was shown to be intense with the observation of recombination originating from both the first heavy hole and light hole consistent with a type I band alignment. A model to determine the band alignment of the InAsSbN multiple quantum wells (MQWs) was derived from a single-band Schrodinger solver and found to be in good agreement with the experimental results. Finally InAsSbN light emitting diodes (LEDs) were fabricated and shown to exhibit strong electroluminescence reaching room temperature with final wavelengths of 3.7 urn and the presence of hydrocarbon absorption in the spectrum reveals that this material has potential for gas detection. Output powers of over 3 μW under 100 mA drive current at 50% quasi- continuous operation were obtained leading to an internal efficiency of 0.63%, an improvement over InAsSb and InSb quantum dot LEDs. These prototype devices show promise for type I dilute nitride materials operating in the mid infrared region.