Deep Surface Trap States at ZnO Nanorods Arrays

ABSTRACTDeep surface trap states present in hydrothermally grown ZnO nanorod (NR) arrays are monitored by photoelectrochemical and impedance spectroscopy. NR arrays were grown on a thin compact ZnO film deposited by pulsed laser deposition. Photocurrent responses upon square-wave illumination and lock-in detection of the as-grown NR arrays in the presence of Na2SO3 at pH 10 were characterized by a complex potential dependence indicating the presence of deep trap states. At a given frequency of light perturbation, the photocurrent amplitude increases as the potential bias is shifted towards values more positive than the flat band potential. Increasing the potential further than 0.8 V positive to the flat band potential leads to a decrease in the photocurrent amplitude. The potential of maximum photocurrent amplitude overlaps with a sharp decrease in the interfacial capacitance. The dependence of the photocurrent amplitude on bias potential strongly suggests the presence of deep electron trap states. The effect of the deep trap states are minimized by annealing of the NR arrays in air at 340° C.

Comparison of deep level spectra of MBE- and MOCVD-grown InGaAsN

Deep level transient spectroscopy (DLTS) studies of both p-type (uid) and n-type (Sidoped), lattice-matched, 1.05 eV bandgap InGaAsN grown by molecular-beam epitaxy (MBE) are reported, and the results are compared to previous measurements of similar materials grown by metal-organic chemical-vapor deposition (MOCVD). In MBE-grown p-type InGaAsN, two majority-carrier hole traps were observed: H3' (0.37 eV) and H4' (0.51 eV), and no evidence was found for the presence of minority-carrier electron traps. These two traps appear to be similar to two levels, H3 (0.48 eV) and H4 (0.5 eV), previously characterized in MOCVD-grown InGaAsN. In MBE-grown n-type InGaAsN, we observed a shallow distribution of electron levels, E1' (0 < EA < 0.35 eV), as well as a deep electron trap E4' (0.56 eV) and a deep hole trap H5' (0.71 eV). E1' appears to be coincident with a superposition of two levels observed in MOCVD-grown InGaAsN, a shallow distribution termed E1 (0 < EA < 0.20 eV) and a discrete (though broadened) level E3 (0.34 eV). Further, E4' appears to be similar in character to a level observed in MOCVD-grown material, E4 (0.82 eV), although a disparity in activation energy exists. This disparity may be due to a temperature-dependent capture cross-section for one or both levels, a possibility that is currently under investigation. In contrast, H5' appears to have no analogue in MOCVD-grown material and thus may be unique to the MBE growth technique.

“On the Growth - and Annealing - Temperature Dependence of the Electrical Properties of Ga0.51In0.49P/GaAs Heterostructures Grown by Mombe”

ABSTRACTWe study the effect of growth temperature (TG) and post-growth rapid thermal annealing (RTA) on the electrical properties of Schottky diodes fabricated on undoped, lattice-matched Ga0.51In0.49P/GaAs heterostructures. The samples were grown by metalorganic molecular beam epitaxy (MOMBE) in the temperature range 480 – 560°C. Ga0.51In0.49P grown in this temperature range undergoes spinodal decomposition, as shown by cross-section TEM analysis. The dislocation-free epilayers grown at TG≤520°C are characterized by a deep electron trap with an activation energy of 800meV while growth at higher temperatures renders trap-free films. Furthermore, the Schottky barrier ideality factor (n) depends strongly on TG and takes the best value of 1.4 for TG=540°C, while the barrier height remains nearly constant at about 0.75eV. Finally, upon capped rapid thermal annealing the value of n improves while the trap concentration decreases significantly. Based on the presented experimental evidence we can propose that MOMBE growth at 540°C renders films with improved electrical properties.

Properties of the EL2 Level in Organometallic Ga1−xAlxAs

ABSTRACTWe have studied by means of deep level transient spectroscopy and photocapacitance measurements deep electron traps in undoped Ga1−xAlxAs of n-type grown by metalorganic chemical vapor deposition with 0≤x≤ 0.3. A dominant deep electron trap is detected in the series of alloys. Its activation energy is found at EC-0.8 eV in GaAs and it increases with x. Its concentration is found nearly independent of x. For the first time we observed for this level in the Ga1−xAlxAs alloys, the photocapacitance quenching effect typical for the EL2 defect in GaAs thus confirming clearly that EL2 is also created in MOCVD Ga1−xAlxAs.