Browsing by Subject "QMSA"

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    DX-center energy calculation with quantitative mobility spectrum analysis in n-AlGaAs/GaAs structures with low Al content
    (ELSEVIER, 2009-03-17) Lisesivdin, S. B.; Altuntas, H.; Yildiz, A.; Kasap, M.; Özbay, Ekmel; Ozcelik, S.
    Experimental Hall data that were carried out as a function of temperature (60-350 K) and magnetic field (0-1.4 T) were presented for Si-doped low Al content (x=0.14) n-AlxGa1-xAs/GaAs heterostructures that were grown by molecular beam epitaxy (MBE). A 2-dimensional electron gas (2DEG) conduction channel and a bulk conduction channel were founded after implementing quantitative mobility spectrum analysis (QMSA) on the magnetic field dependent Hall data. An important decrease in 2DEG carrier density was observed with increasing temperature. The relationship between the bulk carriers and 2DEG carriers was investigated with 1D self consistent Schrödinger-Poisson simulations. The decrement in the 2DEG carrier density was related to the DX-center carrier trapping. With the simulation data that are not included in the effects of DX-centers, 17 meV of effective barrier height between AlGaAs/GaAs layers was found for high temperatures (T>300 K). With the QMSA extracted values that are influenced by DX-centers, 166 meV of the DX-center activation energy value were founded at the same temperatures.
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    The effect of strain relaxation on electron transport in undoped Al0.25Ga0.75N/GaN heterostructures
    (Elsevier BV * North-Holland, 2007-11-01) Lişesivdin, S. B.; Yıldız, A.; Acar, S.; Kasap, M.; Özçelik, S.; Özbay, Ekmel
    The two-dimensional electron gas (2DEG) transport properties of two-step growth undoped Al0.25Ga0.75N/GaN heterostructures with semi-insulating buffer, grown by MOCVD, were investigated in a temperature range of 20–350 K. Using the quantitative mobility spectrum analysis (QMSA) method, it was shown that significant parallel conduction does not occur in worked structures. In-plain growth axis strains are calculated using the total polarization-induced charge density taken as the sheet carrier density measured from the Hall effect. It was found that the calculated strain values are in good agreement with those reported. Influences of the two-step growth parameters such as growth ramp time, the annealing temperature of the GaN nucleation layer on the mobility, and density of the 2DEG are also discussed.
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    A simple parallel conduction extraction method (SPCEM) for MODFETs and undoped GaN-based HEMTs
    (ELSEVIER, 2008-07-14) Lisesivdin, S. B.; Balkan, N.; Özbay, Ekmel
    We report a simple method to extract the mobility and sheet carrier densities of conduction channels in conventional modulation doped field-effect transistor (MODFET) structures and unintentionally doped GaN-based high-electron mobility transistor (HEMT) structures for a special case. Extraction of the conduction channels from the magnetic field-dependent data can present number of problems; even the most recent methods encounter great difficulties. For the GaN-based HEMT structures which have lower mobilities and larger effective masses than that of GaAs-based counterparts, these difficulties become more prominent. In this study, we describe a simple method for magnetotransport analysis to extract conduction channels successfully for a special case that is commonly encountered: one bulk channel and one two-dimensional electron gas (2DEG) channel. Advantage of this method is mainly its simplicity. The analysis can be done with only two magnetic field-dependent measurements per temperature step. The method is applied to the magnetotransport results of an unintentionally doped AlGaN/AlN/GaN/AlN heterostructure over a temperature range of 29-350 K and in a magnetic field range of 0-1.5 T (μB<1). The results are then compared with those obtained using a commercial package for these calculations namely: quantitative mobility spectrum analysis (QMSA).
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    Strain calculations from hall measurements in undoped Al 0.25Ga0.75N/GaN HEMT structures
    (American Institute of Physics, 2007) Lişesivdin, S. B.; Yıldız, A.; Kasap, M.; Özbay, Ekmel
    The transport properties of undoped Al0.25Ga0.75N/GaN HEMT structures grown by MOCVD were investigated in a temperature range of 20 K-350 K. With Quantitative Mobility Spectrum Analysis (QMSA) method; it was found that, all conduction in undoped Al0.25Ga0.75N/GaN HEMT structures belong to the two dimensional electron gas (2DEG). With the acception of Hall sheet carrier density is the total polarization induced charge density, strains of 2DEG interfaces were calculated. Calculated strain values are in good agreement with the literature. Effects of the growth parameters of the nucleation layers of samples on the mobility and density of the 2DEG are listed.
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    Well parameters of two-dimensional electron gas in Al0.88In 0.12N/AlN/GaN/AlN heterostructures grown by MOCVD
    (Wiley, 2009-12-01) Tasli, P.; Lisesivdin, S. B.; Yildiz, A.; Kasap, M.; Arslan, E.; Özcelik, S.; Özbay, Ekmel
    Resistivity and Hall effect measurements were carried out as a function of magnetic field (0-1.5 T) and temperature (30-300 K) for Al0.88In 0.12N/AlN/GaN/AlN heterostructures grown by Metal Organic Chemical Vapor Deposition (MOCVD). Magnetic field dependent Hall data were analyzed by using the quantitative mobility spectrum analysis (QMSA). A two-dimensional electron gas (2DEG) channel located at the Al0.88In 0.12N/GaN interface with an AlN interlayer and a two-dimensional hole gas (2DHG) channel located at the GaN/AlN interface were determined for Al 0.88In0.12N/AlN/GaN/AlN heterostructures. The interface parameters, such as quantum well width, the deformation potential constant and correlation length as well as the dominant scattering mechanisms for the Al 0.88In0.12N/GaN interface with an AlN interlayer were determined from scattering analyses based on the exact 2DEG carrier density and mobility obtained with QMSA