Vol 48, No 1 (2019)

In this work, atomic-layer deposition (ALD) of yttrium oxide (Y₂O₃) was demonstrated using tris(butylcyclopentadienyl)yttrium (Y(CpBut)₃) and H₂O . Yttrium precursor showed thermal stability and a high reactivity in surface reactions with H₂O. In situ monitoring of the deposition process by quartz crystal microbalance (QCM) showed that the growth of oxide is accompanied by the absorption of water into the bulk of the film, which can lead to chemical vapor deposition (CVD) type processes. Reducing amount of dosed water as well as purge time extension during ALD cycling allow to mitigate the CVD effects. The Y₂O₃ film growth rate 230°C varied depending on the number of cycles and had maximum value of 1.7 Å/cycle. The films obtained at 230°C had a cubic polycrystalline structure with an average density of 96% of the Y₂O₃ bulk density. The X-ray photoelectron spectroscopy (XPS) measurements showed a carbon impurity level below the detections limit (~0.2 at %). The O/Y atomic concentration ratio estimated by Rutherford backscattering spectroscopy (RBS) was ~1.58. As deposited Y₂O₃ films had a refractive index of 1.85 (at 632.8 nm), whereas with protective ALD Al₂O₃ film, the refractive index was 1.73.

This study deals with the capacity–voltage (С–V) characteristics of the gate–drain regions of crystals of high-power microwave HEMT transistors with a large gate periphery of the S and Х bands and a source–drain breakdown voltage V_DS ranging from 30 to 150 V, as well as test Schottky diodes formed in a single technological cycle together with HEMTs. Capacitance deep-level transient spectroscopy (DLTS) was used to investigate the structural defects creating deep levels. During the investigations, it was shown that the С–V curves of HEMT crystals always had two areas of change in capacitance with differing slope angles, while there were no such knees in the curves for the test Schottky barriers (SBs). The DLTS technique revealed that НЕМТs and test SBs contained electron-like and hole-like traps, occurring, most probably, in the buffer layer, and also a hole-type peak behaving anomalously. The knee in the С–V curves of НЕМТs is due to the strong electric fields arising at the edge of the gate of the transistor structures.

Magnetooptical studies of nanostructures, including three-dimensional ones, formed by the deposition of a metal layer on the surface of structured silicon are discussed. A comparison of the results of the magnetooptical studies of various fabricated systems demonstrates their different behavior. A vortex domain structure and multivortex states are observed on the spherical surface of nanoobjects obtained by computer simulation with a common center for different vortex domains.