Hexacoordinated Gallium(III) Triazenide Precursor for Epitaxial Gallium Nitride by Atomic Layer Deposition

Gallium nitride (GaN) is the main component of modern-day high electron mobility transistors due to its favorable electronic properties. As electronic devices become smaller with more complex surface architecture, the ability to deposit high-quality GaN films at low temperatures is required. Herein, we report a new highly volatile Ga(III) triazenide precursor and demonstrate its ability to deposit high-quality epitaxial GaN by atomic layer deposition (ALD). This new Ga(III) triazenide, the first hexacoordinated Ga-N bonded precursor used in a vapor deposition process, was easily synthesized and purified by either sublimation or recrystallisation. Thermogravimetric analysis showed single-step volatilization with an onset temperature of 155 degrees C and negligible residual mass. Three temperature intervals with self-limiting growth were observed when depositing GaN films. The GaN films grown in the second growth interval at 350 degrees C were epitaxial on 4H-SiC without an AlN seed layer and found to have a near stoichiometric Ga/N ratio with very low levels of impurities. In addition, electron microstructure analysis showed a smooth film surface and a sharp interface between the substrate and film. The band gap of these films was 3.41 eV with the Fermi level at 1.90 eV, showing that the GaN films were unintentionally n-type-doped. This new triazenide precursor enables ALD of GaN for semiconductor applications and provides a new Ga(III) precursor for future deposition processes

Characterization of InGaN/GaN quantum well growth using monochromated valence electron energy loss spectroscopy

The early stages of InGaN/GaN quantum wells growth for In reduced conditions have been investigated for varying thickness and composition of the wells. The structures were studied by monochromated STEM–VEELS spectrum imaging at high spatial resolution. It is found that beyond a critical well thickness and composition, quantum dots (&gt;20 nm) are formed inside the well. These are buried by compositionally graded InGaN, which is formed as GaN is grown while residual In is incorporated into the growing structure. It is proposed that these dots may act as carrier localization centers inside the quantum wells.On the day of the defence date the status of this article was Manuscript.</p

Ab initio calculations and experimental study of piezoelectric YxIn1-xN thin films deposited using reactive magnetron sputter epitaxy

By combining theoretical prediction and experimental verification we investigate the piezoelectric properties of yttrium indium nitride (YxIn1-xN). Ab initio calculations show that the YxIn1-xN wurtzite phase is lowest in energy among relevant alloy structures for 0 <= x <= 0.5. Reactive magnetron sputter epitaxy was used to prepare thin films with Y content up to x=0.51. The composition dependence of the lattice parameters observed in the grown films is in agreement with that predicted by the theoretical calculations confirming the possibility to synthesize a wurtzite solid solution. An AIN buffer layer greatly improves the crystalline quality and surface morphology of subsequently grown YxIn1-xN films. The piezoelectric response in films with x=0.09 and x=0.14 is observed using piezoresponse force microscopy. Theoretical calculations of the piezoelectric properties predict YxIn1-xN to have comparable piezoelectric properties to ScxAl1-xN

Sequential magnetic switching in Fe/MgO(001) superlattices

Polarized neutron reflectometry is used to determine the sequence of magnetic switching in interlayer exchangecoupled Fe/MgO(001) superlattices in an applied magnetic field. For 19.6 Å thick MgO layers we obtain a 90◦periodic magnetic alignment between adjacent Fe layers at remanence. In an increasing applied field the toplayer switches first followed by its second-nearest neighbor. For 16.4 Å MgO layers, a 180◦periodic alignment isobtained at remanence and with increasing applied field the layer switching starts from the two outermost layersand proceeds inwards. This sequential tuneable switching opens up the possibility of designing three-dimensionalmagnetic structures with a predefined discrete switching sequenc