Improvement of Crystal Quality of AlN Films with Different Polarities by Annealing at High Temperature

High-quality AlN film is a key factor affecting the performance of deep-ultraviolet optoelectronic devices. In this work, high-temperature annealing technology in a nitrogen atmosphere was used to improve the quality of AlN films with different polarities grown by magnetron sputtering. After annealing at 1400–1650 °C, the crystal quality of the AlN films was improved. However, there was a gap between the quality of non-polar and polar films. In addition, compared with the semi-polar film, the quality of the non-polar film was more easily improved by annealing. The anisotropy of both the semi-polar and non-polar films decreased with increasing annealing temperature. The results of Raman spectroscopy, scanning electron microscopy and X-ray photoelectron spectroscopy revealed that the annihilation of impurities and grain boundaries during the annealing process were responsible for the improvement of crystal quality and the differences between the films with different polarities.

Reducing Threading Dislocations of Single-Crystal Diamond via In Situ Tungsten Incorporation

A lower dislocation density substrate is essential for realizing high performance in single-crystal diamond electronic devices. The in-situ tungsten-incorporated homoepitaxial diamond by introducing tungsten hexacarbonyl has been proposed. A 3 × 3 × 0.5 mm3 high-pressure, high-temperature (001) diamond substrate was cut into four pieces with controlled experiments. The deposition of tungsten-incorporated diamond changed the atomic arrangement of the original diamond defects so that the propagation of internal dislocations could be inhibited. The SEM images showed that the etching pits density was significantly decreased from 2.8 × 105 cm−2 to 2.5 × 103 cm−2. The reduction of XRD and Raman spectroscopy FWHM proved that the double-layer tungsten-incorporated diamond has a significant effect on improving the crystal quality of diamond bulk. These results show the evident impact of in situ tungsten-incorporated growth on improving crystal quality and inhibiting the dislocations propagation of homoepitaxial diamond, which is of importance for high-quality diamond growth.

Improvement of crystal quality and surface morphology of Ge/Gd2O3/Si(111) epitaxial layers by cyclic annealing and regrowth

The role of post-growth cyclic annealing (PGCA) and subsequent regrowth, on the improvement of crystal quality and surface morphology of (111)-oriented Ge epitaxial layers, grown by low temperature (300 C) molecular beam epitaxy (MBE) on epi-Gd2O3/Si(111) substrates, is reported. We demonstrate that PGCA is efficient in suppressing rotational twins, reflection microtwins and stacking faults, the predominant planar defect types in Ge(111) epilayers. Continuing Ge growth after PGCA, both at low (300 C) and high (500 C) temperatures, does not degrade the crystal quality any further. By promoting adatom downclimb, PGCA is observed to also heal the surface morphology, which is further improved on Ge re-growth. These results are promising for development of high-quality Ge(111) epitaxial layers for photonic and electronic applications.

Analysis of GaN-based HEMTS with AlN buffer layers by using Raman spectroscopy

In this paper, AlGaN/GaN HEMTs with an AlN buffer layer were fabricated. Analyses on the crystal quality of the GaN epitaxial layer by Raman spectroscopy have been purposed. By introducing an AlN layer on sapphire substrate, the maximum drain current of the HEMT increased from 481 mA/mm to 522 mA/mm at [Formula: see text] V. Subthreshold slope was reduced from 638.3 mV/decade to 240.9 mV/decade and the electron mobility increased from 1109 cm2 V[Formula: see text]s[Formula: see text] to 1781 cm2 V[Formula: see text]s[Formula: see text]. These results showed that using an AlN buffer layer can improve the crystal quality of the GaN epitaxial layer, thus optimize the device performances of the GaN-based HEMTs.