SiNx Interlayer Research Articles

Effects of SiNx interlayer on characterisation of amorphous diamond-like carbon films

The magnetron sputtering amorphous diamond-like carbon film is successfully deposited by SiNx interlayer approach. The scanning electron microscopy study reveals the creation of high uniform surface micrograph diamond-like carbon films with SiNx interlayer. For comparison, diamond-like carbon films with different interlayers are also grown. The Raman spectra are analyzed in order to characterize the stressed induce peak shifts of the films. The interactions of C atom with Si(100) and SiNx surface are studied by density functional theory simulation. The effects of interlayers on the films deposition and the considering deposition mechanism are discussed. It is suggested that the diamond-like carbon and SiNx bilayer structure can help to render applications in protective coatings and high quality silicon on diamond related radiation tolerance devices.

Reducing GaN-on-diamond interfacial thermal resistance for high power transistor applications

Integration of chemical vapor deposited polycrystalline diamond offers promising thermal performance for GaN-based high power radio frequency amplifiers. One limiting factor is the thermal barrier at the GaN to diamond interface, often referred to as the effective thermal boundary resistance (TBReff). Using a combination of transient thermoreflectance measurement, finite element modeling and microstructural analysis, the TBReff of GaN-on-diamond wafers is shown to be dominated by the SiNx interlayer for diamond growth seeding, with additional impacts from the diamond nucleation surface. By decreasing the SiNx layer thickness and minimizing the diamond nucleation region, TBReff can be significantly reduced, and a TBReff as low as 12 m2K/GW is demonstrated. This enables a major improvement in GaN-on-diamond transistor thermal resistance with respect to GaN-on-SiC wafers. A further reduction in TBReff towards the diffuse mismatch limit is also predicted, demonstrating the full potential of using diamond as the heat spreading substrate.

Lattice distortion analysis of nonpolar a-plane $$(11\bar 20)$$ GaN films by using a grazing-incidence X-ray diffraction technique

This work examines the anisotropic microstructure and the lattice distortions of nonpolar a-plane \((11\bar 20)\) GaN (a-GaN) films by using the grazing-incidence X-ray diffraction technique. Faulted a-GaN films typically exhibit an in-plane anisotropy of the structural properties along the X-ray in-beam directions. For this reason, the anisotropic peak broadenings of the X-ray rocking curves (XRCs) were observed for various angle (phi) rotations for a-GaN films with and without SiNx interlayers. Analysis revealed the peak widths of the XRCs displayed an isotropic behavior for a nonpolar a-GaN bulk crystal. Thus, the in-plane anisotropy of the XRC peak widths for nonpolar a-GaN films apparently originates from the heteroepitaxial growth of the a-GaN layer on a foreign substrate. The lattice distortion analysis identified the presence of compressive strains in both the two in-plane directions (the c- and the m-axis), as well as a tensile strain along the normal growth direction. In addition, the observed frequency shifts in the Raman E2 (high) mode for the a-GaN films showed the existence of considerable in-plane compressive strain on both a-GaN films, as confirmed by the lattice distortion analysis performed using the grazing-incidence XRD method.

Effect of Basal-plane Stacking Faults on X-ray Diffraction of Non-polar (1120) a-plane GaN Films Grown on (1102) r-plane Sapphire Substrates

We report the effect of basal-plane stacking faults (BSFs) on X-ray diffraction (XRD) of non-polar (1120) a-plane GaN films with different SiNx interlayers. Complete SiNx coverage and increased three-dimensional (3D) to two-dimensional (2D) transition stages substantially reduce BSF density. It was revealed that the Si-doping profile in the Sidoped GaN layer was unaffected by the introduction of a SiNx interlayer. The smallest in-plane anisotropy of the (1120) XRD ω-scan widths was found in the sample with multiple SiNx layers, and this finding can be attributed to the relatively isotropic GaN mosaic resulting from the increase in the 3D-2D growth step. Williamson-Hall (WH) analysis of the (h0h0) series of diffractions was employed to determine the c-axis lateral coherence length (LCL) and to estimate the mosaic tilt. The c-axis LCLs obtained from WH analyses of the present study’s representative a-plane GaN samples were well correlated with the BSFrelated results from both the off-axis XRD ω-scan and transmission electron microscopy (TEM). Based on WH and TEM analyses, the trends in BSF densities were very similar, even though the BSF densities extracted from LCLs indicated that the values were reduced by a factor of about twenty.

Characterization of a-plane InGaN light-emitting diodes with a SiNx interlayer grown on a patterned sapphire substrate by metal–organic chemical vapor deposition

Nonpolar, a-plane InGaN light-emitting diodes (LEDs) were grown on a hemispherical r-plane patterned sapphire substrate (HPSS) by the in situ deposition of SiNx masks and on a planar sapphire substrate by metalorganic chemical deposition (MOCVD). The use of the SiNx interlayer together with HPSS resulted in a reduced density of defects, such as basal plane stacking faults (BSFs) and partial dislocations (PDs) in the GaN epilayers, as compared with the use of GaN on a conventional planar substrate. The optical power of the InGaN LEDs with the SiNx layer and HPSS was approximately 2.5- and 10-fold higher than those of LEDs on SiNx and on a planar substrate at a current of 100 mA, respectively.

Crack-free AlGaN/GaN distributed Bragg reflectors synthesized by insertion of a thin SiNx interlayer grown on 6H-SiC substrate by metal–organic chemical vapor deposition

Crack-free AlGaN/GaN distributed Bragg reflectors (DBRs) for the near-UV region were grown on 6H-SiC substrates by metal–organic chemical vapor deposition (MOCVD). To suppress the generation of cracks, a thin SiNx interlayer was introduced between the first pair of AlGaN/GaN DBR layers. Using this approach, crack-free 30-pair Al0.2Ga0.8N/GaN DBRs were obtained with peak reflectivity of 92.8% at 388nm and a stop-band bandwidth of 16nm. Our results reveal that a SiNx interlayer not only decreased the tensile strain but also improved the reflectivity via suppression of cracks.

Defect reduction of SiNx embedded m-plane GaN grown by hydride vapor phase epitaxy

Nonpolar (10−10) m-plane GaN has been grown on m-plane sapphire substrates by hydride vapor phase epitaxy (HVPE). We studied the defect reduction of m-GaN with embedded SiNx interlayers deposited by ex-situ metal organic chemical vapor deposition (MOCVD). The full-width at half-maximum values of the X-ray rocking curves for m-GaN with embedded SiNx along [11−20]GaN and [0001]GaN were reduced to 528 and 1427arcs, respectively, as compared with the respective values of 947 and 3170arcs, of m-GaN without SiNx. Cross-section transmission electron microscopy revealed that the basal stacking fault density was decreased by approximately one order to 5×104cm−1 due to the defect blocking of the embedded SiNx. As a result, the near band edge emission intensities of the room-temperature and low-temperature photoluminescence showed approximately two-fold and four-fold improvement, respectively.

Probing the role of an atomically thin SiNx interlayer on the structure of ultrathin carbon films.

Filtered cathodic vacuum arc (FCVA) processed carbon films are being considered as a promising protective media overcoat material for future hard disk drives (HDDs). However, at ultrathin film levels, FCVA-deposited carbon films show a dramatic change in their structure in terms of loss of sp3 bonding, density, wear resistance etc., compared to their bulk counterpart. We report for the first time how an atomically thin (0.4 nm) silicon nitride (SiNx) interlayer helps in maintaining/improving the sp3 carbon bonding, enhancing interfacial strength/bonding, improving oxidation/corrosion resistance, and strengthening the tribological properties of FCVA-deposited carbon films, even at ultrathin levels (1.2 nm). We propose the role of the SiNx interlayer in preventing the catalytic activity of Co and Pt in media, leading to enhanced sp3C bonding (relative enhancement ~40%). These findings are extremely important in view of the atomic level understanding of structural modification and the development of high density HDDs.

An investigation into defect reduction techniques for growth of non‐polar GaN on sapphire

AbstractIn this paper we describe the implementation and the characterisation of five different in‐situ defect reduction techniques for non‐polar (a ‐plane) GaN growth on r ‐plane sapphire. Sample 1 (3D/2D) employs a methodology frequently applied on the c ‐plane, involving a low temperature nucleation layer (LTNL) followed by 3D GaN island formation and lateral coalescence. For Sample 2 (d3D) GaN islands are grown directly onto the sapphire with no LTNL, followed by lateral growth. Sample 3 (d3D Si) follows a similar procedure, but with high silicon doping in order to adjust the 3D GaN island shape. Sample 4 (SiNx) utilises a silicon nitride interlayer between a LTNL and subsequent growth of a GaN layer. Sample 5 is grown by epitaxial lateral overgrowth (ELOG) coupled with a SiNx interlayer. X‐ray diffraction, scanning electron microscopy and cathodoluminescence are used to identify defects, and determined the threading defect density to vary from 1 x 1010–1 x 109 cm–2 and basal‐plane stacking fault (BSF) density to vary from 5 x 105 – 5 x 103 cm‐1. The improvement in crystal quality is reflected in the photoluminescence spectra by a comparison of the ratio of the GaN near band edge (NBE) emission to the BSF associated emission. It was determined that the ELOG method was most successful in blocking BSFs, with a density reduction of 2 orders of magnitude resulting in a fifteen‐fold increase in the NBE:BSF emission ratio increase. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Improvements of MOVPE grown (11$ \bar 2 $2) oriented GaN on pre‐structured sapphire substrates using a SiNx interlayer and HVPE overgrowth

AbstractIn this article two methods for improvements of (11$ \bar 2 $2) oriented semipolar GaN grown by MOVPE on prestructured sapphire substrates are investigated.The integration of a SiNx interlayer helps to obtain a better crystal quality.Also the overgrowth of the MOVPE samples by HVPE is a way to obtain a smoother GaN surface. A high incorporation of oxygen on (11‐22) oriented GaN compared to (0001) oriented GaN grown by HVPE was observed. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Non‐polar (11$ \bar 2 $0) InGaN quantum dots with short exciton lifetimes grown by metal‐organic vapour phase epitaxy

AbstractInGaN quantum dot (QD) structures have been grown by metal organic vapour phase epitaxy (MOVPE) on non‐polar (11‐20) GaN surfaces by employing an anneal step in nitrogen immediately after the growth of the InGaN. Here, we compare the growth of such structures on pseudo‐substrates grown using an epitaxial lateral overgrowth (ELOG) technique and on pseudo‐substrates grown using a simpler in situ SiNx interlayer. The less complex defect reduction approach results in a significantly higher defect density, but does not detrimentally effect the QD formation. For both types of pseudo‐substrate, sharp peaks with resolution limited widths are observed in both cathodoluminescence at 9 K and micro‐photoluminescence at 4.2 K. The QDs demonstrate significantly reduced exciton lifetimes compared to structures grown on c‐plane, which has advantages for possible applications in single photon sources. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Defect reduction in Si-doped Al0.45Ga0.55N films by SiNx interlayer method

The dislocation density in AlGaN epitaxial layers with Al content as high as 45% grown on sapphire substrates has been effectively reduced by introducing an in-situ deposited SiNx nanomask layer in this study. By closely monitoring the evolution of numerous material properties, such as surface morphology, dislocation density, photoluminescence, strain states, and electron mobility of the Si-Al0.45Ga0.55N layers as the functions of SiNx interlayer growth time, the surface coverage fraction of SiNx is found to be a crucial factor determining the strain states and dislocation density. The dependence of the strain states and the dislocation density on the surface coverage fraction of SiNx nanomask supports the very different growth models of Al-rich AlGaN on SiNx interlayer due to the reduced nucleation selectivity compared with the GaN counterpart. Compared with GaN, which can only nucleate at open pores of SiNx nanomask, Al-rich AlGaN can simultaneously nucleate at both open pores and SiNx covered areas. Dislocations will annihilate at the openings due to the 3D growth initiated on the opening area, while 2D growth mode is preserved on SiNx and the threading dislocations are also preserved. During the following growth process, lateral overgrowth will proceed from the Al0.45Ga0.55N islands on the openings towards the regions covered by SiNx, relaxing the compressive strain and bending the dislocations at the same time.

Channel Length Dependent Bias-Stability of Self-Aligned Coplanar a-IGZO TFTs

We report channel length L ( L ranging from 2 to 40 μm) dependence of the electrical stability of amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs). The a-IGZO TFTs employ a coplanar structure with a SiNx interlayer used to dope the source/drain regions. After application of positive gate bias stress (PBS), short-channel devices ( L = 2 μm) exhibit smaller threshold voltage shifts ( ΔVth) compared to longer-channel devices ( L ≥ 4 μm). It is proposed that carrier diffusion takes place from the high carrier concentration regions under the SiN∞ interlayer to the intrinsic channel region, thereby shifting the Fermi level closer to the conduction band. Higher Fermi levels mean less defect states available for carrier trapping - hence the small ΔVth in short devices under PBS.

Improved interface properties of an HfO2 gate dielectric GaAs MOS device by using SiNx as an interfacial passivation layer

A GaAs metal-oxide-semiconductor (MOS) capacitor with HfO2 as gate dielectric and silicon nitride (SiNx) as the interlayer (IL) is fabricated. Experimental results show that the sample with the SiNx IL has an improved capacitance—voltage characteristic, lower leakage current density (0.785 × 10−6 A/cm2 at Vfb + 1 V) and lower interface-state density (2.9 × 1012 eV−1 cm−2) compared with other samples with N2− or NH3—plasma pretreatment. The influences of post-deposition annealing temperature on electrical properties are also investigated for the samples with SiNx IL. The sample annealed at 600°C exhibits better electrical properties than that annealed at 500°C, which is attributed to the suppression of native oxides, as confirmed by XPS analyses.

Structural and electrical anisotropies of Si-doped a-plane (11–20) GaN films with different SiNx interlayers

The effects of different SiNx interlayers on the structural and electrical properties of nonpolar Si-doped a-plane (11–20) GaN films grown on r-plane (1–102) sapphire were investigated. The surface roughness depends strongly on the SiNx coverage, deposition temperature and number of SiNx layers. The in-plane anisotropy of on-axis x-ray rocking curves (XRCs) (full width at half-maximum) was significantly decreased by the introduction of multiple SiNx-treated GaN interlayers, indicating coherently scattering domains of uniform size. Off-axis XRC measurements were also employed to investigate the effects on the mosaic twist corresponding to edge dislocation and the I1-type basal-plane stacking fault (BSF) density. Hall effect measurement showed that the electrical conductivity was the highest when multiple SiNx/GaN interlayers were employed. The measured sheet resistances (Rsh) along the c-axis were higher than those along the m-axis. These anisotropic conductivities could be explained by BSFs acting as carrier scattering centers. The ratios of Rsh along the two in-plane orientations also correlated well with the BSF densities.

Improvement of quality and strain relaxation of GaN epilayer grown on SiC substrate by in situ SiNx interlayer

Improved structural quality and tensile stress releasing were realized in GaN thin films grown on 6H–SiC by metal organic chemical vapor deposition using an in situ porous SiNx interlayer. The SiNx was formed in situ in the growth chamber by simultaneous flow of diluted silane and ammonia, leading to the formation of a randomly distributed mask layer and induced lateral overgrowth similar to conventional epitaxial lateral overgrowth of GaN. The full width at half maximum (FWHM) of X-ray diffraction peaks decreases dramatically by the SiNx interlayer, indicating an improved crystalline quality. Also, it was found that the biaxial tensile stress in the GaN film was significantly reduced by in situ SiNx interlayer from Raman spectra. Low temperature photoluminescence spectra exhibited a narrower FWHM by the SiNx interlayer.

Improvement of the quality of GaN epilayer by combining a SiNx interlayer and changed GaN growth mode

GaN epilayers with porous SiNx interlayer and changed growth modes were grown by metal–organic chemical vapor deposition on c-plane sapphire substrates. Comparing with GaN epilayer grown by ordinary method, the crystalline qualities were significantly improved. The improvement was attributed to the reduction of the density of threading dislocations causing by over-growth process combining with delayed coalescence of individual GaN islands. The influence of the deposition and annealing of nucleation layer on the GaN regrowth was also discussed.

Improved performance of semi-polar (11-22) GaN-based light-emitting diodes grown on SiNx interlayer

We report on the effectiveness of the in-situ SiNx nanomask in reducing defects in semipolar (11-22) GaN films grown on m-plane sapphire. The properties of the semipolar InGaN/GaN double quantum well (DQW) LEDs were improved with a high-quality (11-22) GaN epilayer grown on the SiNx interlayer. High resolution X-ray diffraction analysis revealed that there was a great reduction in the full width at half maximum of both on-axis and off-axis planes on SiNx interlayer. The room temperature cathodoluminescence (CL) band-edge emission intensity of (11-22) GaN grown on the SiNx interlayer was approximately 4 times higher than that of GaN without the SiNx interlayer, which suggests reduction in the nonradiative recombination centers. The optical power of LEDs with the SiNx interlayer was 200% and 270% higher at injection currents of 20mA and 100mA, respectively, compared to the reference LEDs.

Improvement of the Quality of a GaN Epilayer by Employing a SiNx Interlayer

GaN epilayers with a porous SiNx interlayer were grown by metal-organic chemical vapor deposition on c-plane sapphire substrates. It is found that the crystalline qualities are significantly improved with SiNx growth. The improvement is attributed to the reduction of the density of threading dislocations (TDs) by an over-growth process of GaN grown on a SiNx interlayer. The influence mechanism of SiNx interlayers on GaN growth mode is also discussed.

High resolution synchrotron X-ray studies of phase separation phenomena and the scaling law for the threading dislocation densities reduction in high quality AlGaN heterostructure

High resolution X-ray coplanar (symmetric X-ray diffraction (SXRD) and asymmetric X-ray diffraction (ASXRD)) and non-coplanar diffraction (grazing incidence diffraction (GID)) have been used to investigate the quality of AlGaN epilayers with 20% Al content, grown on sapphire using SiNx interlayers. The measurement of reciprocal space maps (RSM) with higher orders of reflections of SXRD and ASXRD which is readily performed at the synchrotron with high resolution and intensity reveals the presence of several diffraction peaks originating from the occurrence of local differences in the lattice constants. Two distinguishable AlGaN phases having different crystalline parameters were clearly recognized from X-ray data and the corresponding densities of screw dislocations have been determined measured as function of the overgrowth thickness varying from 0.5μm to 3.5μm. The variation of the screw and edge type dislocation densities with the overgrowth thickness has been found to follow the scaling law h−n where h is the thickness of the buffer layer.