[en] Due to the wave-particle duality of high energy electron beam, RHEED describes a thin film surface through the interaction of reciprocal lattice rod (RLR) of the film. The RLR spacing of the crystal has been computed using RHEED streak spacing on a fluorescent screen. Present evolution study of RLR spacing has been performed for AlGaN/InGaN heterostructure on thick GaN buffer layer during plasma-assisted molecular beam epitaxy. Effect of composition, strain and temperature on the crystal has been identified as the function of lattice spacing during the growth. The calibrated reflectivity of LED signal has also been employed to map the thickness of different growing epilayers. RLR spacing decreases for interlayer GaN as compared to AlN. Initially, the RLR spacing of GaN buffer decreases more as compared to interlayer GaN owing to its increased growth temperature after the interlayer AlN. The RLR spacing of GaN again gradually increases with decrement of growth temperature up to the InGaN channel layer. The InGaN RLR spacing decreases again which attributes to the relaxation of InGaN on GaN. Additionally, AlGaN reveals strained state to InGaN in combination with effect of high growth temperature. The phenomena result in additional decrement of lattice distance in reciprocal space. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

[en] Physics based modeling of AlGaN/GaN heterostructure Schottky diode gas sensor has been investigated for high sensitivity and linearity of the device. Here the surface and heterointerface properties are greatly exploited. The dependence of two dimensional electron gas (2DEG) upon the surface charges is mainly utilized. The simulation of Schottky diode has been done in Technology Computer Aided Design (TCAD) tool and I-V curves are generated, from the I-V curves 76% response has been recorded in presence of 500 ppm gas at a biasing voltage of 0.95 Volt

[en] An AlGaN/GaN heterostructure based metal–semiconductor–metal symmetrically bi-directional Schottky diode sensor structure has been employed to investigate acetone sensing and to analyze thermodynamics of acetone adsorption at low temperatures. The AlGaN/GaN heterostructure has been grown by plasma-assisted molecular beam epitaxy on Si (111). Schottky diode parameters at different temperatures and acetone concentrations have been extracted from I–V characteristics. Sensitivity and change in Schottky barrier height have been studied. Optimum operating temperature has been established. Coverage of acetone adsorption sites at the AlGaN surface and the effective equilibrium rate constant of acetone adsorption have been explored to determine the endothermic nature of acetone adsorption enthalpy.

[en] Highly UV sensitive sub-5 nm Sn nanoparticles-Polyaniline (Sn (NPs)-PANI) composite material has been formulated by chemical polymerisation. A thin film of the composite is deposited on Micro-Interdigitated Electrode (µ-IDEs) array for photodetector application. Considerably, higher optical density (10–12), w.r.t carbon of Sn (NPs) in Sn (NPs)-PANI/Al-IDE/Glass structures exhibit the exceedingly enhanced sensitivity towards UV illumination. There is substantial large contrast ratio of ∼ 2290 at − 1 V, significantly large responsivity ∼ 3.05 A/W, detectivity of ~ 2.26E + 13 Jones and reasonable rise/fall time of ∼ 0.7/1.7 s observed for Sn (NPs)-PANI/Al-IDE/Glass devices. Surface morphology, phase analysis, and elemental composition of Sn–PANI systems have been investigated by X-ray diffraction and Energy Dispersive X-ray analysis (EDX), respectively. Transmission electron microscopy (TEM) analysis confirms the size of the Sn (NPs) and blend with Polyaniline. The significantly enhanced sensitivity of ~ 228514.3 for λ ~ 254 nm establishes the clear potential of the fabricated structure for UV-C detector application.

[en] Highlights: • AlGaN/InGaN heterostructure has been grown on GaN/Si(111) using plasma assisted molecular beam epitaxy. • Non-conventional two-step profile has been observed using capacitance-voltage and conductance-voltage techniques. • Impact of strain on phase separation of InGaN channel has been found in presence of V-defects and threading dislocations. • Grading of indium incorporation has occurred in InGaN channel along with InN alloy at the AlGaN/InGaN. • The heterojunction implicates to act as a pool of static charges for designing new devices. Immiscibility of InGaN hinders epitaxial growth of high-quality AlGaN/InGaN heterojunction, which could have superior performances than AlGaN/GaN in view of high-speed devices. AlGaN/InGaN/GaN double heterostructures have been grown on silicon (111) substrate using plasma assisted molecular beam epitaxy. All growth conditions for each sample have been kept identical except the InGaN channel thickness. Alloy inhomogeneity has been found to occur in the InGaN channel by high resolution (HR) X-ray diffractometer (XRD) and cross-sectional HR- transmission electron microscopy (TEM). This non-uniformity of alloy causes reduced indium incorporation with a decrease of channel thickness along with a thin InN binary alloy. Capacitance-voltage (C-V) profile has revealed non-uniformity of alloy and spatial position of InN in the channel due to variation of band-offset and carrier confinement. Unconventional two-step profile has been obtained for the heterostructure. Higher capacitance at near zero bias corroborates the formation of InN at AlGaN/InGaN due to larger band offset. Conductance-voltage (G-V) profiles further validate mapping of InGaN phase separation in terms of carrier trapping. Lower effect of trapping has been identified due to low bandgap InN formation at the interface. Effect of epilayer relaxation on the phase separation has also been discussed in terms of threading dislocation and V-defects.

[en] Highlights: • InGaAs graded MBs with different grading scheme has been grown by MBE on GaAs. • Continuously graded MB exhibits smoother surface morphology. • Grading scheme has been found to have little impact on lattice relaxation. • Grading schemeaffects the lattice tilt significantly. • Cross-hatch surface irregularities affect the crystallographic tilt. - Abstract: InGaAs graded metamorphic buffers (MBs) with different grading strategies have been grown by molecular beam epitaxy (MBE) on GaAs (0 0 1) substrate. A detailed comparative analysis of surface using atomic force microscopy (AFM), and bulk properties using high resolution X-ray diffraction (HRXRD) and room temperature photoluminescence (RTPL) of grown MBs have been presented to comprehend the effectiveness of different grading scheme on InGaAs MBs. Conventional, statistical and fractal analysis on measured AFM data has been performed for in-depth investigation of these surfaces. The grading scheme has been found to have little impact on residual strain while it affects the epitaxial tilt significantly. Moreover, the tilt has been found to depend on growth front irregularities. Tilt magnitude in a graded MB has been found to vary with composition while tilt azimuth has been found to be almost same in the graded layers. PL Intensity and a shift in the PL peaks have been used to study the quality of the MB and residual strain comparatively.