Conduction‐ and valence‐band offsets in GaAs/Ga0.51In0.49P single quantum wells grown by metalorganic chemical vapor deposition

We have independently estimated the conduction‐ and valence‐band offsets ΔEc and ΔEv in GaAs/Ga0.51In0.49P quantum wells by measuring the capacitance transient resulting from thermal emission of carriers from the respective wells. The heterostructure samples were grown by low‐pressure metalorganic chemical vapor deposition. The band offsets are extrapolated from the emission activation energies with appropriate corrections. The estimated values of ΔEc and ΔEv are 0.198 and 0.285 eV, respectively.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70070/2/APPLAB-56-9-833-1.pd

Fabrication and Characterization of Vanadium/Vanadium Pentoxide/Vanadium (V/V₂O₅/V) Tunnel Junction Diodes

A metal/insulator/metal (MIM) diode is a structure in which a thin oxide layer is sandwiched between two metal layers. Metal/insulator/metal (MIM) diodes coupled to antennas have been widely investigated as detectors for millimeter wave and infrared radiation for imaging and spectroscopic applications. In this work, we report on the fabrication and characterization of MIM tunnel junction diodes by using a new material combination, vanadium-vanadium pentoxide-vanadium (V/V₂O₅/V), with contact areas of 2× 2 μm². The V/V₂O₅/V MIM was fabricated using electron-beam lithography, sputter deposition and conventional liftoff methods. The fabricated V/V₂O₅/V MIM diodes showed a maximum absolute sensitivity of 2.35 $V^{-1}$. In addition, noise spectra for the fabricated MIM diodes were measured and analyzed

HIGH-SPEED INP/GAINAS METAL-SEMICONDUCTOR-METAL PHOTODETECTORS GROWN BY CHEMICAL BEAM EPITAXY

We report the fabrication and characterization of lateral metal-semiconductor-metal (MSM) photodiodes on an InP substrate. The photoabsorbing layer is made of InGaAs covered by a thin InP Schottky barrier enhancement layer. Schottky contacts for the detectors were formed by the evaporation of Au and patterned using a lift-off technique. The MSM photodiodes exhibit a dark current lower than 200 nA at 15-V bias, an efficient photoresponse up to 1.6 mum, and a fast deconvoluted full width at half maximum response of about 25 ps at 12-V bias

Design and Optimization of Microbolometer Multilayer Optical Cavity

Microbolometers are the most widely used detectors in long-wave infrared uncooled thermal imagers. An optical cavity is required within a microbolometer structure to increase its optical absorption. In this work we present a detailed study on the design and optimization of a microbolometer optical cavity using Essential-Macleod package. In the simulations, the cavity is considered as thin film multi-layers that form cascaded Fabry-Perot optical cavities. In the design phase, the structures of layers are selected, which includes selection of materials and initial thickness. The absorbing layers are chosen to be made of vanadium-pentoxide (V₂O₅) and titanium (Ti). In the optimization phase, the designed layer thicknesses are varied to maximize optical absorption within the absorbing layers. The simulations show that Ti layer absorption dominates over the V₂O₅ layer. Also, the optimization proves that the thickness of cavity's air-gap is not equal simply to quarter-wavelength, because of the presence of a complex cascaded Fabry-Perot structure. The optimized air-gap thickness is found to be ≈ 3.5 μm at wavelength of 10.6 μm

A critical examination of the molecular‐beam‐epitaxial growth of InxGa1−xAs/GaAs strained quantum well structures

We have investigated the molecular‐beam‐epitaxial growth and optical properties of InxGa1−xAs/GaAs (0.07≤x≤0.20) single and multiple quantum well structures. Photoluminescence and absorption measurements were made to characterize the various structures. Low‐temperature excitonic linewidths as small as 1.2–2.4 meV have been obtained in 80–120‐Å InxGa1−xAs/GaAs (0.07≤x≤0.20) single and multiple quantum wells up to total thicknesses of 2.0 μm. The Stokes shift in these samples is ∼1–2 meV. This result is independent of the absence or presence of an intermediate composition buffer layer and indicates that the latter does not influence the optical properties of strained multiquantum wells. The growth kinetics and growth modes are more important factors in this respect.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69411/2/JAPIAU-65-3-1361-1.pd

Enhancement in excitonic absorption due to overlap in heavy‐hole and light‐hole excitons in GaAs/InAlGaAs quantum well structures

In this letter we present experimental and theoretical results for excitonic transitions in coherently strained GaAs/InGaAlAs multiquantum well structures grown on a GaAs substrate. Absorption spectra of the structure with the substrate removed show an extremely sharp exciton peak with an absorption constant corresponding to nearly twice the value of that in the lattice‐matched GaAs/AlGaAs system. Theoretical calculations suggest that the biaxial tensile strain in the well region, occurring after the substrate is removed, causes the heavy‐hole and light‐hole exciton states to coincide for a specific composition of the quaternary alloy. A comparison between the experiments and theory is made and the potential for devices based on this phenomenon is discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71251/2/APPLAB-51-14-1091-1.pd