Abhijit Chinchore

Spontaneous formation of quantum height manganese gallium islands and atomic chains on N-polar gallium nitride(0001¯)

Deposition of manganese onto the gallium-rich, nitrogen-polar GaN(0001¯) surface results in the formation of quantum-height island structures. Two unique island heights differing by one atomic layer are observed, including 0.93 nm high islands which are unstable against the formation of 1.13 nm high islands. A row structure at the islands’ surface suggests a mixture of Mn and Ga, while growth of one-dimensional atomic chains at the surface of the stable 1.13 nm high islands indicates a strongly anisotropic diffusion. The observed behavior is consistent with a quantum size effect driven growth mechanism.

Formation of manganese δ-doped atomic layer in wurtzite GaN

We describe the formation of a δ-doped manganese layer embedded within c-plane wurtzite gallium nitride using a special molecular beam epitaxy growth process. Manganese is first deposited on the gallium-poor GaN (0001¯) surface, forming a 3×3−R30° reconstructed phase. This well-defined surface reconstruction is then nitrided using plasma nitridation, and gallium nitride is overgrown. The manganese content of the 3×3−R30° phase, namely one Mn per each 3×3−R30° unit cell, implies that the MnGaN alloy layer has a Mn concentration of up to 33%. The structure and chemical content of the surface are monitored beginning from the initial growth stage up through the overgrowth of 20 additional monolayers (MLs) of GaN. An exponential-like drop-off of the Mn signal with increasing GaN monolayers, as measured by Auger electron spectroscopy, indicates that the highly concentrated Mn layer remains at the δ-doped interface. A model of the resultant δ-doped structure is formulated based on the experimental data, and impl...

A modular designed ultra-high-vacuum spin-polarized scanning tunneling microscope with controllable magnetic fields for investigating epitaxial thin films.

A room-temperature ultra-high-vacuum scanning tunneling microscope for in situ scanning freshly grown epitaxial films has been developed. The core unit of the microscope, which consists of critical components including scanner and approach motors, is modular designed. This enables easy adaptation of the same microscope units to new growth systems with different sample-transfer geometries. Furthermore the core unit is designed to be fully compatible with cryogenic temperatures and high magnetic field operations. A double-stage spring suspension system with eddy current damping has been implemented to achieve ≤5 pm z stability in a noisy environment and in the presence of an interconnected growth chamber. Both tips and samples can be quickly exchanged in situ; also a tunable external magnetic field can be introduced using a transferable permanent magnet shuttle. This allows spin-polarized tunneling with magnetically coated tips. The performance of this microscope is demonstrated by atomic-resolution imaging of surface reconstructions on wide band-gap GaN surfaces and spin-resolved experiments on antiferromagnetic Mn(3)N(2)(010) surfaces.

Atomic layer structure of manganese atoms on wurtzite gallium nitride (0001)

Submonolayer quantities of Mn are deposited on wurtzite GaN (0001¯). The surface is monitored using reflection high energy electron diffraction, which shows a pattern consisting of 3× reconstruction along [101¯0], but only 1× along [112¯0]. Diffraction analysis shows that the 3× streak intensity is maximized at ≈0.86 monolayer of Mn deposition. The results indicate that Mn forms linear chains along the [101¯0] direction with a spacing of 3a/2 along chains and 3a/2 between chains. Correcting the peak coverage for sticking coefficient and accounting for the observed periodicities, a 3×3-R30° model, consisting of 2/3 monolayer of Mn atoms, is proposed.

Delta-phase manganese gallium on gallium nitride: a magnetically tunable spintronic system

Ferromagnetic delta-phase manganese gallium with Mn:Ga ratio between 1:1 to 1.5:1 is grown on wurtzite gallium nitride and scandium nitride substrates, using molecular beam epitaxy. The dependencies of growth properties, e.g. interface formation, surface reconstruction and crystalline quality, on substrate crystallographic structure and polarity are investigated. Results suggest that for growth on wurtzite GaN, Ga-polar surface promotes quicker interface formation, and also results in better crystalline quality of the MnGa film, as compared to N-polar. The crystal orientation and magnetic anisotropy are found to be different than those grown on cubic scandium nitride substrates.

A Two-Dimensional Manganese Gallium Nitride Surface Structure Showing Ferromagnetism at Room Temperature

Practical applications of semiconductor spintronic devices necessitate ferromagnetic behavior at or above room temperature. In this paper, we demonstrate a two-dimensional manganese gallium nitride surface structure (MnGaN-2D) which is atomically thin and shows ferromagnetic domain structure at room temperature as measured by spin-resolved scanning tunneling microscopy and spectroscopy. Application of small magnetic fields proves that the observed magnetic domains follow a hysteretic behavior. Two initially oppositely oriented MnGaN-2D domains are rotated into alignment with only 120 mT and remain mostly in alignment at remanence. The measurements are further supported by first-principles theoretical calculations which reveal highly spin-polarized and spin-split surface states with spin polarization of up to 95% for manganese local density of states.