Aizhen Li

High-Quality GaN Film Grown by HVPE with an Anodized Aluminum Oxide Mask

High-quality GaN films were deposited by hydride vapor phase epitaxy (HVPE) on metalorganic chemical vapor deposition GaN templates using an anodized aluminum oxide mask. High-resolution X-ray diffraction, scanning electron microscopy, and cathod-oluminescence were used to highlight the excellent crystalline quality of the films, and the optical properties at different positions of the as-grown layers. The optical properties of the GaN films improved with increased film thickness. The PL peak position indicates stress relaxation by the AAO mask.

Improved GaN film overgrown with a molybdenum nanoisland mask

We report the improved crystalline and optical quality of GaN film overgrown by hydride vapor phase epitaxy adopting a molybdenum (Mo) nanoisland mask (MNM). The MNM is fabricated following thermal annealing of the nanometer-thick Mo film deposited by electron-beam evaporation. The full width at half maximum values of high-resolution x-ray diffraction (HRXRD) rocking curves for the GaN film with MNM are 188arcsec (002 reflection) and 219arcsec (102 reflection), while those for the GaN film without MNM are 256 and 364arcsec, respectively. This result indicates a significant reduction of dislocation density in the overgrown GaN film with MNM. Photoluminescence spectra measurements reveal the compressive strain relaxation and improvement in the quality of the overgrown GaN film with MNM as compared to the regrown GaN film without MNM, which is consistent with the trend observed by HRXRD.

Thick GaN grown on a nanoporous GaN template by hydride vapor phase epitaxy

High-quality thick gallium nitride (GaN) films were overgrown by hydride vapor phase epitaxy (HVPE) on a nanoporous GaN template which was prepared by inductively coupled plasma etching employing an anodized aluminum oxide mask. An obvious reduction of the dislocation density in the thick GaN layer was demonstrated by high-resolution X-ray diffraction, which exhibited the improved crystalline quality in GaN films overgrown on a nanopattemed surface. Moreover, the peak redshift in photoluminescence and micro-Raman spectroscopy indicates a significant strain relaxation in the HVPE-GaN layer. Compared with conventional overgrowth, such a deposition pathway is a more promising technique for the growth of thick GaN layers.

Silicon behavior in GaN grown by radiofrequency plasma molecular beam epitaxy

Abstract The behavior of Si in GaN has been investigated in the wide doping range from 1×1017 to 9×1019 cm−3 by photoluminescence (PL). PL studies at 77 K for doped specimens show that the intensity of the near-band-edge emission increased monotonically as the Si concentration increases. The intensity of the yellow luminescence (YL), however, remains almost constant, which indicates that Si does not strongly influence the density of deep centers in GaN. The red-shift of the near-band-edge emission due to increase the Si concentration shows that bandgap renormalization (BGR) effect is much more important than the Burstein–Moss (B-M) effect in Si-doped GaN. With Si doping as high as 9×1019 cm−3, a new peak due to donor-to-acceptor recombination appears in the PL spectrum. This donor-to-acceptor emission peak can also be observed in the PL spectrum of Si-doped GaN after thermal annealing. We attributed the appearance of the new acceptor level to the formation of SiN. A model has been proposed to illustrate the Si behavior in GaN in a wide range of Si concentrations.

High-Quality Thick GaN Overgrown on an Array of SiO2 Nanomasks by HVPE

We report nanoepitaxy of thick GaN films by hydride vapor-phase epitaxy (HVPE) using a uniform array of SiO 2 nanomasks that were prepared by electron-beam evaporation and anodic aluminum oxide membranes. The controllable size and density of the SiO 2 nanoisland mask were about 65 nm and 10 10 cm -2 , respectively. Subsequent overgrowth takes place selectively on the exposed GaN surface without the SiO 2 masks to the formation of the continuous layer. High-resolution X-ray diffraction shows reduction of threading dislocations in the overgrown layers. Improved optical property and significant stress relaxation in the epilayer are demonstrated by photoluminescence and micro-Raman spectra. The deposition method is a more promising technique for obtaining freestanding GaN substrates with high-quality and uniform features.