Al 2 O 3 was deposited on In 0.15 Ga 0.85 As/ GaAs using atomic-layer deposition ͑ALD͒. Without any surface preparation or postthermal treatment, excellent electrical properties of Al 2 O 3 / InGaAs/ GaAs heterostructures were obtained, in terms of low electrical leakage current density ͑10 −8 to 10 −9 A/cm 2 ͒ and low interfacial density of states ͑D it ͒ in the range of 10 12 cm −2 eV −1. The interfacial reaction and structural properties studied by high-resolution x-ray photoelectron spectroscopy ͑HRXPS͒ and high-resolution transmission electron microscopy ͑HRTEM͒. The depth profile of HRXPS, using synchrotron radiation beam and low-energy Ar + sputtering, exhibited no residual arsenic oxides at interface. The removal of the arsenic oxides from Al 2 O 3 / InGaAs heterostructures during the ALD process ensures the Fermi-level unpinning, which was observed in the capacitance-voltage measurements. The HRTEM shows sharp transition from amorphous oxide to single crystalline semiconductor.

Most studies of spin caloritronic effects to date, including spin-Seebeck effect, utilize thin films on substrates. We use patterned ferromagnetic thin film to demonstrate the profound effect of a substrate on the spin-dependent thermal transport. With different sample patterns and on varying the direction of temperature gradient, both longitudinal and transverse thermal voltages exhibit asymmetric instead of symmetric spin dependence. This unexpected behavior is due to an out-of-plane temperature gradient imposed by the thermal conduction through the substrate and the mixture of anomalous Nernst effects. Only with substrate-free samples have we determined the intrinsic spin-dependent thermal transport with characteristics and field sensitivity similar to those of the anisotropic magnetoresistance effect.

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