In this paper the internal electric fields of nearly lattice matched InAlN/GaN heterostructures were determined. Pin-diodes containing InAlN/GaN heterostructures grown on (0 0 0 1) sapphire substrates by metalorganic vapour phase epitaxy were fabricated by standard lithography and metallization techniques. To determine the polarization fields in the InAlN quantum wells capacitance-voltage-measurements were performed on the pin-diodes. To reduce the measurement error, the heterostructure thicknesses were accurately determined by transmission electron microscopy. Large polarization fields, which correspond mainly to the spontaneous polarizations, for In 0.15 Al 0.85 N (5.9 ± 0.8 MV cm −1 ), In 0.18 Al 0.82 N (5.4 ± 0.9 MV cm −1 ) and In 0.21 Al 0.79 N (5.1 ± 0.8 MV cm −1 ) quantum wells were observed. The results of the internal field strength and field direction are in excellent agreement with values predicted by theory and a CVM-based coupled Poisson/carrier transport simulation approach.
High quality polycrystalline bilayers of aluminium doped ZnO (Al:ZnO) were successively electrodeposited in the form of columnar structures preferentially oriented along the 1011 crystallographic direction from aqueous solution of zinc nitrate (Zn(NO 3 ) 2 ) at negative electrochemical potential of E C = (−0.8)-(−1.2) V and moderate temperature of 80 • C on gallium rich (30% Ga) chalcopyrite selenide Cu(In,Ga)Se 2 (CIGS) with chemically deposited ZnSe buffer (ZnSe/Cu(In,Ga)Se 2 /Mo/glass). The aluminium doped ZnO layer properties have initially been probed by deposition of Al:ZnO/i-ZnO bilayers directly on Mo/glass substrates. The band-gap energy of the Al:ZnO/i-ZnO reference layers was found to vary from 3.2 to 3.7 eV by varying the AlCl 3 solute dopant concentration from 1 to 20 mM. The electrical resistivity of indium-pellet contacted highly doped Al:ZnO sheet of In/Al:ZnO/i-ZnO/Mo/glass reference samples was of the order ρ~10 −5 Ω·cm; the respective carrier concentration of the order 10 22 cm −3 is commensurate with that of sputtered Al:ZnO layers. For crystal quality optimization of the bilayers by maintenance of the volatile selenium content of the chalcopyrite, they were subjected to 2-step annealing under successive temperature raise and N 2 flux regulation. The hydrostatic compressive strain due to Al 3+ incorporation in the ZnO lattice of bilayers processed successively with 5 and 12 mM AlCl 3 dopant was ε h = −0.046 and the respective stress σ h = −20 GPa. The surface reflectivity of maximum 5% over the scanned region of 180-900 nm and the (optical) band gap of E g = 3.67 eV were indicative of the high optical quality of the electrochemically deposited (ECD) Al:ZnO bilayers.
Due to changes in the spontaneous and piezoelectric polarization, AlGaN/GaN heterostructures exhibit strong polarization fields at heterointerfaces. For quantum wells, the polarization fields lead to a strong band bending and a redshift of the emission wavelength, known as quantum-confined Stark effect. In this paper the polarization fields of thin AlGaN layers in a GaN matrix were determined by evaluating the changes in the depletion region width in comparison to a reference sample without heterostructure using capacitance–voltage-measurements. The polarization fields for Al0.09Ga0.91N (0.6 ± 0.7 MV cm−1), Al0.26Ga0.74N (2.3 ± 0.6 MV cm−1), Al0.34Ga0.66N (3.1 ± 0.6 MV cm−1), Al0.41Ga0.59N (4.0 ± 0.7 MV cm−1) and Al0.47Ga0.53N (5.0 ± 0.8 MV cm−1) heterostructures were determined. The results of the field strength and field direction of all samples are in excellent agreement with values predicted by theory and a capacitance–voltage based Poisson-carrier transport simulation approach giving experimental evidence for a nonlinear increasing polarization field with Al-concentration.
The first step in modelling a real grid in the frequency range 2-500 kHz is discussed in this paper. The distributed parameters of the equivalent transmission line (TL) model are determined combining the benefits of three techniques: Four-terminal (4T) sensing is used to evaluate resistances, time-domain reflectometry (TDR) to determine lengths of cables, and impedance (Z) measurements to estimate inductances and capacitances. Finally, a measurement of the network impedance is performed in order to have a more complete view of the behaviour of the network.
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