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In this article, we report the temperature-dependent transistor characteristic of Epi-Gd2O3/AlGaN/GaN metal oxide semiconductor high electron mobility transistor (MOSHEMT) and compare its properties with that of AlGaN/GaN metal-Schottky high electron mobility transistor (HEMT) grown on 150 mm Si (111) substrate. Introducing an epitaxial single crystalline Gd2O3 between the metal gate and AlGaN barrier not only improves the gate leakage current significantly but also enhances its thermal stability. We observe that there is no significant change in the gate leakage current even at 473 K compared to that measured at room temperature (RT) (298 K), and this is also evident in the transistor’s subthreshold behavior at 473 K. We have determined the electric field within the Gd2O3 as well as AlGaN and investigated the leakage conduction mechanism through Gd2O3. The ${I}_{ \mathrm{ON}}/{I}_{ \mathrm{OFF}}$ of the transistor was measured as high as ~108 even at 473 K with the lowest ${V}_{\text {TH}}$ shift (91.4 mV) with temperature. Our measurements also confirm the presence of polar optical phonon scattering, which directly affects the 2-D electron gas (2DEG) mobility at high temperatures and thus the electrical characteristics of HEMT and MOSHEMT.

Gadolinium oxide (Gd2O3) was grown at low temperatures (250 °C) on Si(001) using molecular beam epitaxy. The crystal structure was investigated with X-ray diffraction experiments, where the crystal structure changes from cubic to monoclinic depending on the oxygen supply. We propose that Gibbs-Thomson effect is responsible for the change in crystal structure due to the initial nucleation of nanometer-sized islands and its variation in diameter depending on the growth conditions. The dielectric properties of the monoclinic structure were investigated using Capacitance-Voltage measurements, where platinum was used as contact material. Dielectric constants larger than 20 were obtained, which is higher than for the cubic structure. The monoclinic Gd2O3 layers suffer from flat-band voltage instabilities, which is most likely due to defects located at the interface or near-interface region of the Gd2O3 and silicon. Forming gas annealing results in an improvement of the dielectric behaviour.

The influence of growth conditions on the layer orientation, domain structure and crystal structure of gadolinium oxide (Gd2O3) on silicon (001) has been investigated. Gd2O3 was grown at low (250°C) and high (850°C) temperatures with different oxygen partial pressure as well as a temperature ramp up during growth. At low temperature, the cubic bixbyite type of crystal structure with space group Ia{\bar 3} was grown at low oxygen partial pressure. The layers consist of two domains oriented orthogonal to each other. The epitaxial relationships for the two domains were found to be Gd2O3(110)[001]||Si(001)[110] and Gd2O3(110)[001]||Si(001)[{\bar 1}10], respectively. Applying additional oxygen during growth results in a change in crystal and domain structures of the grown layer into the monoclinic Sm2O3-type of structure with space group C2/m with (20\bar 1) orientation and mainly two orthogonal domains with the epitaxial relationship Gd2O3(20\bar 1)[010]||Si(100)〈110〉 and a smooth surface morphology. Some smaller areas have two intermediate azimuthal orientations between these variants, which results in a six-domain structure. The change in crystal structure can be understood based on the Gibbs–Thomson effect caused by the initial nucleation of nanometre-sized islands and its variation in diameter with a change in growth conditions. The crystal structure remains stable even against a temperature ramp up during growth. The layers grown at high temperature exhibit a nanowire-like surface morphology, where the nanowires have a cubic crystal structure and are aligned orthogonal to each other along the 〈110〉 in-plane directions. An increase in oxygen supply results in a reduced length and increased number of nanowires due to lower adatom mobility. The results clearly indicate that both kinetic and thermodynamic factors have a strong impact on the crystal structure, epitaxial relationship and morphology of the grown layers.

The structural and morphological properties of gadolinium oxide (Gd

Germanium-on-insulator (GeOI) technology is a potential-alternative to the bulk-silicon based devices for radio-frequency (RF), and complementary metal oxide semiconductor applications at advanced technology nodes. A thin germanium channel is the key enabler of high mobility transistors and group-IV photonic devices. A prohibitive cost of GeOI wafers may discourage high volume manufacturing (HVM) despite promising performance. Here, we demonstrate epitaxial Gd 2 O 3 -Ge-Gd 2 O 3 thin film growth on Si(111) substrate in an HVM platform - RF magnetron sputter system, where, the first Gd 2 O 3 layer acts as buried-oxide (BOX) in the GeOI wafer. The second Gd 2 O 3 layer is used as a cap-layer to be removed later using wet etching. Both the Gd 2 O 3 layer is grown epitaxially at 750 ∘ C , while the germanium layer is grown at room temperature and crystallised later by solid phase epitaxy (SPE) technique. The entire growth is performed without vacuum-break, to enable high throughput and excellent interface control. To compare the quality of the heterostructure, this sputter based SPE is performed on: (1) in-situ sputter grown, versus (2) ex-situ molecular-beam-epitaxy (MBE) grown epitaxial Gd 2 O 3 BOX layer. The x-ray diffraction analysis confirms the formation of twin-free epitaxial Ge layer in the case of in-situ sputtered Gd 2 O 3 while twinned Ge layer is observed in the case of ex-situ MBE grown Gd 2 O 3 . The twinning of the Ge layer in the ex-situ process is further supported by transmission electron microscopy analysis. Finally, we have performed an experiment to study the impact of Gd 2 O 3 BOX layer thickness on the crystal quality of Ge layer and show that the Ge layer crystal quality remains intact irrespective of BOX layer thickness. Therefore, we have achieved twin free Ge epitaxy in RF magnetron sputter system, equivalent to in-situ All-MBE SPE process. Such a process enables low-cost GeOI wafer manufacturing for cost-effective RF transistors.

In this letter, we report the impact of epitaxial Gd2O3 on the electrical properties of an AlGaN/GaN high electron mobility transistor (HEMT) grown on a 150 mm diameter Si (111) substrate. Incorporation of epitaxial Gd2O3 grown by the molecular beam epitaxy technique under a metal gate (metal/Gd2O3/AlGaN/GaN) causes six orders of magnitude reduction in gate leakage current compared to metal/AlGaN/GaN HEMT. We observe that epi-Gd2O3 undergoes complete structural changes from hexagonal to monoclinic as the thickness of the layer is increased from 2.8 nm to 15 nm. Such structural transformation is found to have a strong impact on electrical properties whereby the gate leakage current reaches its minimum value when the oxide thickness is 2.8 nm. We find a similar trend in the density of interface traps (Dit) having a minimum value of 2.98 × 1012 cm-2 eV-1 for the epioxide layer of thickness 2.8 nm. Our measurements also confirm a significant increase in the two dimensional electron gas (2DEG) density (∼40%) at AlGaN/GaN interface with epioxide grown on AlGaN, thus confirming the contribution of epitaxial lattice strain on 2DEG modulation.

The influence of growth conditions on the layer orientation, domain structure and crystal structure of gadolinium oxide (Gd

The step-flow growth condition of Si on Si(111) near the (7×7)-“1×1” surface phase transition temperature T C are analyzed within the framework of Burton-Cabrera-Frank theory. In particular, coexistence of both surface phases well below T C and their specific influence on the step-flow growth behavior are considered. We presume that under dynamical condition of growth, the surface initially covered by only the (7×7) phase separates into domains surrounded by “1×1” areas. On such a surface, the overall supersaturation should be reduced drastically compared to a surface with only (7×7), resulting in much larger critical terrace width for nucleation.