M.R. Brenner

The Ohio State University, Columbus, OH, United States

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Publications (9)7.34 Total impact

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    ABSTRACT: Direct integration of GaP/Si must face a small, but non-negligible lattice constant mismatch, which due to thermal expansion differences between GaP and Si, reaches 0.5% at 900 K. This lattice mismatch results in the nucleation of misfit dislocations at the GaP/Si interface, requiring careful strain management and refinement of epitaxial processes. However, Si0.88Ge0.12 virtual substrates grown on Si provide a nearly ideal lattice-matched template for GaP epitaxy. This paper describes the successful heteroepitaxial integration of lattice-matched GaP/Si0.88Ge0.12/Si, based upon the previously-demonstrated methodology for successful GaP/Si integration, which provides a potential alternative pathway for low defect density III-V/Si multijunction photovoltaics, parallel to that of direct GaP/Si.
    Photovoltaic Specialists Conference (PVSC), 2012 38th IEEE; 01/2012
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    ABSTRACT: The work discussed here focuses on the integration of InGaAs Stranski-Krastanov type quantum dots within a GaAsP metamorphic photovoltaic material matrix via molecular beam epitaxy. Two basic parameters, growth rate and substrate temperature, were studied to determine the nucleation behavior on the GaAsP surface, followed by exploratory growths of encapsulated quantum dot multilayer structures on both tensile (GaAsyP1-y/GaAs) and compressive (GaAsyP1-y/Si) graded buffers. X-ray diffraction measurements show the presence of satellite peaks due to the superlattice-like periodic structures, indicating sharp, uniform interfaces. Photoluminescence spectra reveal quantum confinement of the InGaAs quantum dots, with 400 meV blue-shifted emission and 52 meV peak width at 20 K.
    Photovoltaic Specialists Conference (PVSC), 2012 38th IEEE; 01/2012
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    ABSTRACT: Deep levels in solid-source MBE-grown n- and p-type (Al<sub>0.09</sub>Ga<sub>0.91</sub>)<sub>0.51</sub>In<sub>0.49</sub>P are investigated using deep level transient spectroscopy (DLTS). These results are correlated with background oxygen impurities measured by secondary ion mass spectroscopy and electrical properties using Hall effect. Oxygen impurity concentration is found to depend weakly on substrate offcut conditions in MBE-grown AlGaInP films. This is used to investigate the role of oxygen on deep levels in the n- and p-type samples using (100) GaAs substrates with three different substrate offcut conditions (A, B, and C). The DLTS of n-type AlGaInP reveals deep levels at E<sub>C</sub>-0.22, E<sub>C</sub>-0.31, E<sub>C</sub>-0.69 eV and E<sub>C</sub>-1.0 eV. The E<sub>C</sub>-0.69 eV concentration tracked oxygen incorporation while the other levels decreased while the oxygen incorporation increased indicating possible secondary offcut effects. In general, we find a direct correlation between reduced carrier compensation, increased carrier mobility, lower trap concentration and lower oxygen content as a function of systematic changes in substrate offcut conditions.
    Photovoltaic Specialists Conference (PVSC), 2010 35th IEEE; 07/2010
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    ABSTRACT: GaAsyP1-y anion-sublattice compositionally graded buffers and device structures were grown directly on Si(100) substrates by way of a high-quality GaP integration layer, yielding GaAsP target layers having band gaps of photovoltaic interest (1.65-1.8 eV), free of antiphase domains/borders, stacking faults, and microtwins. GaAsyP1-y growths on both Si and GaP substrates were compared via high-resolution X-ray diffractometry of the metamorphic buffers and deep-level transient spectroscopy (DLTS) of p+-n diodes that are lattice matched to the final buffer layer. Structural analysis indicates highly efficient epitaxial relaxation throughout the entire growth structure for both types of samples and suggests no significant difference in physical behavior between the two types of samples. DLTS measurements performed on GaAsP diodes fabricated on both Si and GaP substrates reveal the existence of identical sets of traps residing in the n-type GaAsP layers in both types of samples: a single majority carrier (electron) trap, which is located at EC - 0.18 eV, and a single minority carrier (hole) trap, which is located at EV + 0.71 eV. Prototype 1.75-eV GaAsP solar cell test devices grown on GaAsyP1-y/Si buffers show good preliminary performance characteristics and offer great promise for future high-efficiency III-V photovoltaics integrated with Si substrates and devices.
    IEEE Transactions on Electron Devices 01/2010; 57(12):3361-3369. · 2.06 Impact Factor
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    ABSTRACT: Electrical changes in p+n GaAs photodiodes are monitored using illuminated current-voltage, quantum efficiency and electron beam induced current measurements after irradiation with 1 and 5 MeV electrons and 2 and 225 MeV protons. Electron beam induced micrographs have revealed the presence of localized defects or active recombination centers after irradiation with protons that are not observed after irradiation with electrons. Moreover, the 225 MeV protons clearly produce defects that are more electrically active compared with those produced by 2 MeV protons, but the implications deduced from the images can be deceiving when compared with the photovoltaic response of the photodiode.
    Photovoltaic Specialists Conference (PVSC), 2010 35th IEEE; 01/2010
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    ABSTRACT: Electrical changes in p+n GaAs photodiodes are monitored using illuminated current-voltage, quantum efficiency and electron beam induced current measurements after irradiation with 1 and 5 MeV electrons and 2 and 225 MeV protons. Electron beam induced micrographs have revealed the presence of localized defects or active recombination centers after irradiation with protons that are not observed after irradiation with electrons. Moreover, the 225 MeV protons clearly produce defects that are more electrically active compared with those produced by 2 MeV protons, but the implications deduced from the images can be deceiving when compared with the photovoltaic response of the photodiode.
    01/2010;
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    ABSTRACT: Using migration enhanced epitaxy nucleation followed by molecular beam epitaxy bulk growth on pristine, intentionally offcut Si(001) substrates, we have produced high-quality GaP/Si virtual substrates, successfully demonstrating full control and elimination of heterovalent nucleation-related defects (antiphase domains, stacking faults, and microtwins). These virtual substrates provide a pathway to direct integration of III-V photovoltaic materials and devices on Si substrates. Prototype GaAsP solar cell test devices grown on anion-sublattice step-graded GaAs<sub>y</sub>P<sub>1-y</sub> buffers on early-stage GaP/Si substrates show good preliminary performance characteristics and offer great promise for future devices integrated with the newly-developed defect-free GaP/Si virtual substrates.
    Photovoltaic Specialists Conference (PVSC), 2009 34th IEEE; 07/2009
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    ABSTRACT: GaP films were grown on offcut Si(001) substrates using migration enhanced epitaxy nucleation followed by molecular beam epitaxy, with the intent of controlling and eliminating the formation of heterovalent (III-V/IV) nucleation-related defects—antiphase domains, stacking faults, and microtwins. Analysis of these films via reflection high-energy electron diffraction, atomic force microscopy, and both cross-sectional and plan-view transmission electron microscopies indicate high-quality GaP layers on Si that portend a virtual GaP substrate technology, in which the aforementioned extended defects are simultaneously eliminated. The only prevalent remaining defects are the expected misfit dislocations due to the GaP–Si lattice mismatch.
    Applied Physics Letters 06/2009; 94(23):232106-232106-3. · 3.79 Impact Factor
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    ABSTRACT: The application of an In0.7Al0.3As window layer material on the properties of lattice-mismatched (LMM) single-junction (SJ) In0.69Ga0.31As thermophotovoltaic (TPV) cells grown by solid source molecular beam epitaxy (MBE) was studied as an alternative to conventional InAsP window layers. For these 0.60 eV bandgap SJ devices, high performance was achieved, displaying open-circuit voltage of 355 mV, power density of 0.532 W/cm2 and a fill factor of 66.5% measured at a current density value of 2.26 A/cm2. The measured internal quantum efficiencies were close to ∼100% at wavelengths between approximately 1.2–1.4 mm, suggestive that low carrier recombination rates in the vicinity of this alternative In0.70Al0.30As/In0.69Ga0.31As window/emitter interface has been achieved. The quantum efficiency data coupled with the device parameters show that InAlAs can be successfully substituted for conventional InAsP window layers in metamorphic TPV devices. By using an interface consisting solely of III-As alloys for the window/emitter material pairing as opposed to the conventional InAsP/InGaAs window/emitter design, this approach avoids the problematic III-P/III-As interface transition for MBE growth of TPV devices that has been shown to impact carrier collection efficiency [Hudait MK, Lin Y, Palmisiano MN, Ringel SA. 0.6-eV band gap In0.69Ga0.31As thermophotovoltaic devices grown on InAsyP1−y step-graded buffers by molecular beam epitaxy. IEEE Electron Dev Lett 2003;24(9):538–40].
    Solid-State Electronics 01/2009; · 1.48 Impact Factor