Initial growth control of GaN on Si with physical-vapor-deposition-AlN seed layer for high-quality GaN templates

Abstract

An ex situ AlN seed layer was formed by physical vapor deposition (PVD) on a Si substrate, aiming at the production of high-quality GaN on Si by metal–organic vapor-phase epitaxy. A low density of initial GaN islands were obtained by reducing the trimethylgallium (TMGa) flow rate. The dislocation density of GaN was dramatically reduced with 3D growth compared with 2D growth, as indicated by measurements of XRD rocking curves (FWHM of 384 and 461 arcsec for 0002 and diffractions, respectively) and cathodoluminescence (CL) mapping (dark-spot density of 3.4 × 108 cm−2) for 1-µm-thick crack-free GaN on a Si substrate. The values were almost equivalent to those of the layers grown on sapphire substrates.

Comparative study of GaN-based ultraviolet LEDs grown on different-sized patterned sapphire substrates with sputtered AlN nucleation layer

“…In recent years, an ex situ sputtered AlN NL on PSS has been utilized for the realization of high-efficiency LEDs with reduced TD density in GaN epitaxial layers. [39][40][41][42][43][44][45] It is well known that the PSS size plays an important role in improving the efficiency of LEDs. The effects of pattern size and shape on the crystalline quality and performance of GaN-based LEDs grown on PSSs with low-temperature GaN NLs have been investigated.…”

Low radio frequency loss and buffer-free GaN directly on physical-vapor-deposition AlN/Si templates

“…Recently, to address these issues, the introduction of ex situ AlN has been demonstrated as a potential approach since this ex situ AlN layer can prevent the Si-Ga melt-back. [12][13][14][15] It is also expected that ex situ AlN may prevent Ga/Al diffusing into Si and hence reduce the RF loss even though there are no reports on this issue at present. The technology for employing ex situ AlN such as physical vapor deposited (PVD) AlN or sputtered AlN on sapphire substrates is very mature, and already makes a big success in applications of light-emitting diodes.…”

“…[16][17][18][19] However, it is a great challenge to achieve a high-quality and crack-free GaN layer on Si substrates with sputtered AlN. [12][13][14][15] Yamada et al firstly realized the growth of GaN layers on Si substrates using ex situ sputtered LT-AlN intermediate layers. 12) However, the dislocation density in the as-grown GaN was one order of magnitude lower than that of GaN grown by conventional in situ AlN growth.…”

“…Wang et al adopted ex situ sputtered AlN layers to grow 1 μm thick crack-free GaN-on-Si, but the surface morphology was rough due to the 3D growth mode. 15) Therefore, it is still highly desirable to further understand the growth mechanisms and develop a growth strategy to obtain high-quality and crack-free GaN-on-Si substrates with ex situ AlN.…”

“…It is worth mentioning that the thickness of GaN is among the highest so far reported in the literature for crack-free and buffer-free GaN-on-Si substrates in MOCVD. [12][13][14][15]26) To find out whether the PVD-AlN layer could prevent the diffusion of Ga and/or Al into the Si substrates, secondary ion mass spectrometry measurements were carried out for samples A and D. As shown in Fig. 4(a), by comparing the concentrations profiles for these two samples with MOCVD-AlN and PVD-AlN respectively, one can find that by replacing the MOCVD-AlN with PVD-AlN, the Ga concentration, especially that at the AlN/Si interface, is significantly reduced from 2.5 × 10 16 cm −3 to below 1 × 10 15 cm −3 .…”