Articles you may be interested inUltraviolet GaN photodetectors on Si via oxide buffer heterostructures with integrated short period oxide-based distributed Bragg reflectors and leakage suppressing metal-oxide-semiconductor contacts J. Appl. Phys. 116, 083108 (2014); 10.1063/1.4894251 Virtual GaN substrates via Sc 2 O 3 / Y 2 O 3 buffers on Si(111): Transmission electron microscopy characterization of growth defectsThe preparation of GaN virtual substrates on Si wafers via buffer layers is intensively pursued for high power/high frequency electronics as well as optoelectronics applications. Here, GaN is integrated on the Si platform by a novel engineered bilayer oxide buffer, namely, Sc 2 O 3 / Y 2 O 3 , which gradually reduces the lattice misfit of ϳ−17% between GaN and Si. Single crystalline GaN͑0001͒ / Sc 2 O 3 ͑111͒ / Y 2 O 3 ͑111͒ / Si͑111͒ heterostructures were prepared by molecular beam epitaxy and characterized ex situ by various techniques. Laboratory-based x-ray diffraction shows that the epitaxial Sc 2 O 3 grows fully relaxed on the Y 2 O 3 / Si͑111͒ support, creating a high quality template for subsequent GaN overgrowth. The high structural quality of the Sc 2 O 3 film is demonstrated by the fact that the concentration of extended planar defects in the preferred ͕111͖ slip planes is below the detection limit of synchrotron based diffuse x-ray scattering studies. Transmission electron microscopy ͑TEM͒ analysis reveal that the full relaxation of the Ϫ7% lattice misfit between the isomorphic oxides is achieved by a network of misfit dislocations at the Sc 2 O 3 / Y 2 O 3 interface. X-ray reflectivity and TEM prove that closed epitaxial GaN layers as thin as 30 nm can be grown on these templates. Finally, the GaN thin film quality is studied using a detailed Williamson-Hall analysis.

Photoreflectance ͑PR͒ and contactless electroreflectance ͑CER͒ spectroscopies have been applied to study optical transitions in undoped and Si-doped AlGaN / GaN heterostructures at room temperature. Spectral features related to excitonic and band-to-band absorptions in GaN layer and band-to-band absorption in AlGaN layer have been resolved and analyzed. In addition, a broad spectral feature related to two-dimensional electron gas has been observed for the Si-doped heterostructure. It has been found that some of the mentioned optical transitions are not observed in CER spectra whereas they are very strong in PR spectra. This phenomenon is associated with different mechanisms of the modulation of built-in electric field in the investigated structure. A combination of PR and CER gives the possibility of a richer interpretation of both PR and CER spectra.

The gas-sensing properties of antimony sulfoiodide (SbSI) nanosensors have been tested for humidity and carbon dioxide in nitrogen. The presented low-power SbSI nanosensors have operated at relatively low temperature and have not required heating system for recovery. Functionality of sonochemically prepared SbSI nanosensors made of xerogel as well as single nanowires has been compared. In the latter case, small amount of SbSI nanowires has been aligned in electric field and bonded ultrasonically to Au microelectrodes. The current and photocurrent responses of SbSI nanosensors have been investigated as function of relative humidity. Mechanism of light-induced desorption of H2O from SbSI nanowires’ surface has been discussed. SbSI nanosensors have been tested for concentrations from 51 to 106 ppm of CO2 in N2, exhibiting a low detection limit of 40(31) ppm. The current response sensitivity has shown a tendency to decrease with increasing CO2 concentration. The experimental results have been explained taking into account proton-transfer process and Grotthuss’ chain reaction, as well as electronic theory of adsorption and catalysis on semiconductors.

The design of modern semiconductor devices often requires the fabrication of three-dimensional (3D) structures to integrate microelectronic components with photonic, micromechanical, or sensor systems within one semiconductor substrate. It is a technologically challenging task, as a strictly defined profile of the device structure is obligatory. This can be achieved either by chemical etching or selective deposition on a masked substrate. In this paper, the growth uniformity of AlGaN/GaN heterostructures during selective-area metalorganic vapour-phase epitaxy (SA-MOVPE) was studied. Such structures are typically used in order to fabricate high-electron-mobility transistors (HEMT). The semiconductor material was deposited through 200 μm long stripe-shaped open windows in a SiO2 mask on GaN/sapphire templates. The window width was varied from 5 μm to 160 μm, whereas mask width separating particular windows varied from 5 μm to 40 μm. The experiment was repeated for three samples differing in GaN layer thickness: 150 nm, 250 nm, and 500 nm. Based on theoretical models of the selective growth, a sufficiently uniform thickness of epitaxially grown AlGaN/GaN heterostructure has been achieved by selecting the window half-width that is smaller than the diffusion length of the precursor molecules. A Ga diffusion length of 15 μm was experimentally extracted by measuring the epitaxial material agglomeration in windows in the dielectric mask. Measurements were conducted while using optical profilometry.