Structural, morphological, and defect properties of metamorphic In0.7Ga0.3As/GaAs0.35Sb0.65 p-type tunnel field effect transistor structure grown by molecular beam epitaxy Apparent critical thickness versus temperature for InAs quantum dot growth on GaAs (001) High-performance InAs/GaAs quantum-dot infrared photodetectors with a single-sided Al 0.3 Ga 0.7 As blocking layer Appl.Optical absorption spectra of intersubband transitions in In 0.3 Ga 0.7 As/ GaAs multiple quantum dots were investigated using the optical absorption as a function of the number of In 0.3 Ga 0.7 As monolayers deposited using the molecular-beam epitaxy Stranski-Krastanow technique. The peak position energy reached 13.7 m for a sample containing 50 monolayers of In 0.3 Ga 0.7 As. The lack of the observation of intersubband transitions in small quantum dots, where the number of the deposited monolayer is less than 15 monolayers, is an indication of the absence of quantum confinement. On the other hand, the presence of high dislocations density in larger quantum dots, where the deposited number of monolayers exceeds 50, could be the reason of why the intersubband transitions are degraded.

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Intersubband transitions (ISTs) in GaN/AlxGa1-xN multiple quantum wells (MQWs) were investigated using an optical absorption technique. Several samples were grown by either Molecular Beam Epitaxy (MBE) or Metal-Organic Chemical Vapor Deposition (MOCVD) and were investigated using both normal incident and waveguide configurations. The waveguides were fabricated by dicing each sample into 2 mm wide by 5 mm long pieces with two facets polished at 45 degrees with respect to the surface such that light propagates across the sample's width. Preliminary results indicate that ISTs are observable in Si-doped and undoped GaN/AlxGa1-xN MQWs. The source of these charge carriers in the undoped samples are explained as being due to the spontaneous polarization effect which exists at the GaN/AlxGa1-xN interfaces where the GaN surface has Ga-polarity. Scanning Electron Microscopy indicates that a sample containing what appeared to be a large number of cracks and or hexagonal voids lacked the presence of ISTs.

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The optical absorption spectra of intersubband transitions in In 0.3 Ga 0.7 As/GaAs multiple quantum dots (MQDs) grown by molecular beam epitaxy were investigated. By varying the number of In 0.3 Ga 0.7 As monolayers deposited, a series of samples with varying dot sizes ranging from 10 -50 monolayers were obtained. The quantum dots grown with size less than 15 monolayers or more than 50 monolayers did not yield any observable measurements of intersubband transition. This suggests that there exist a critical upper and lower limit of In 0.3 Ga 0.7 As quantum dots for infrared detectors. A wavelength range of 8.60 -13.70 µm is achieved for structures grown with the above monolayers range. The theoretical line-shape of the intersubband transition absorption was compared to the experimental measurements. From the lineshape, it was deduced that bound-to-continuum transtition is present in thick quantum dots and bound-to-bound transition is present in thinly grown quantum dots.