Aluminum Nitride Nucleation Layer Research Articles

More than 60% RF loss reduction and improved crystal quality of GaN-on-Si achieved by in-situ doping tert-butylphosphorus

In this work, the parasitic conductive channel in a silicon substrate is compensated using in-situ doping for the first time. The experimental results show that in-situ doping of tert-butylphosphorus (TBP) has little adverse effect on the mobility and the density of two-dimensional electron gas but the compensation of the parasitic channel in the substrate is effective, and the aluminum nitride (AlN) / Si template based on the optimized conditions reduces the radio frequency loss by more than 60%. In addition, it was found that a suitable preflow of TBP can enhance the migration of Al atoms on the substrate surface and improve the crystal quality of gallium nitride (GaN), which reduces the dislocation density of GaN by 25% compared to the sample without TBP preflow. The hypothesis is that TBP preflow can affect the strain of the substrate, which makes the dislocations more likely to annihilate during the subsequent growth of AlN nucleation layer, resulting in the eventual improvement of GaN crystal quality.

Improved wavelength stability and heat dissipation of InGaN-based light-emitting diodes using a graphene interlayer on patterned sapphire substrate

This study presents a straightforward strategy that embeds a graphene interlayer between InGaN-based light-emitting diodes (InGaN LEDs) and patterned sapphire substrate (PSS substrate) for substantial improving device performances of wavelength stability and heat dissipation. The InGaN LEDs on the graphene interlayer/PSS substrate (Gr-LED) have lower piezoelectric fields of 1.16 MV/cm than 1.60 MV/cm for InGaN LEDs on the PSS substrate (Ref-LED). The low piezoelectric field diminishes the screen of the polarization field resulting in a stable electroluminescence peak wavelength. At 100 mA driving current, the chip temperature of Gr-LED shows a decrease in around 24.4 °C relative to Ref-LED. The thermal resistances measured in a vacuum environment are 351 and 128 °C/W for Ref-LED and Gr-LED, respectively. The low thermal resistance of Gr-LED is believed to be due to a low misfit dislocation density of the aluminum nitride nucleation layer that increases the vertical direction of heat transport to PSS. This work demonstrates that the graphene/PSS substrate is a promising substrate for high-power InGaN LEDs.

Effect of H Plasma Treatment of the Nucleation Layer on AlN Epitaxy in Microwave Plasma Chemical Vapor Deposition

The crystallinity of nucleation layers has significant influence on the crystallinity of aluminum nitride (AlN) epilayers. In this work, the etching effect of hydrogen (H) plasma was used to improve the nucleation-layer crystallinity. AlN nucleation layers were first cooled in a H-plasma atmosphere; then, AlN films were deposited on the processed nucleation layers, and the whole epitaxial process was carried out in high-temperature microwave plasma chemical vapor deposition (MPCVD) without the participation of ammonia. X-ray rocking curves (XRCs) showed that the cooling process obviously improved the crystal quality of AlN films, which was attributed to the preferential etching effect of H plasma on low-crystallinity nucleation islands. When a H2 flow rate of 135 sccm was used to process the nucleation layer, the AlN film with the narrowest (002) XRC full width at half-maximum (FWHM) of 86 arcsec was obtained. Possible growth mechanisms were suggested for the observations.

Suppression of p-type parasitic channel formation at the interface between the aluminum nitride nucleation layer and the high-resistivity silicon substrate

In this study, GaN-based epitaxial structures were grown on high-resistivity silicon (HRSi) substrates by metalorganic chemical vapor deposition. The p-type parasitic channels generated at the interfaces of the aluminum nitride (AlN) nucleation layers and HRSi substrates were characterized by surface capacity measurement, backside secondary ion mass spectrometry, and spread resistance profiling. The 2-nm thick silicon nitride (SiNx) layer formed by nitridation on the HRSi substrates was used to suppress the Al diffusion from the 50-nm AlN nucleation layer and also prevented from generation of the p-type parasitic channels. The p-type parasitic channels induced insertion losses at high frequencies. Transmission line measurement was used to determine the insertion losses. The insertion loss of the GaN-based epitaxial structure with the optimized 25-nm AlN nucleation layer on the 2-nm SiNx layer was -2.72 dB/mm. It was only 0.04 dB/mm higher than that of the annealed HRSi substrate (-2.68 dB/mm) at 10 GHz. Obviously, the diffusion of Al from the optimized 25-nm thick AlN nucleation layer into the HRSi substrate can be alleviated by the SiNx layer, thereby reduced insertion loss.

Suppressing P-Type Parasitic Channel Generation at the Interface of an Aluminum Nitride Nucleation Layer and a High Resistivity Silicon Substrate

Suppressing P-Type Parasitic Channel Generation at the Interface of an Aluminum Nitride Nucleation Layer and a High Resistivity Silicon Substrate

The van der Waals Epitaxy of High‐Quality N‐Polar Gallium Nitride for High‐Response Ultraviolet Photodetectors with Polarization Electric Field Modulation

AbstractHigh‐quality and polarity‐controlled III‐nitride is crucial for realizing high‐performance and new types of device designs with rich functionalities, but there are still many difficulties for obtaining N‐polar III‐nitrides till now. In this work, the van der Waals epitaxy of high‐quality N‐polar gallium nitride (GaN) is reported by innovatively inserting a thin MoS2 layer. Due to the remission of thermal and lattice mismatch by the week van der Waals force in 2D MoS2 insert layer, the N‐polar GaN exhibits high crystalline quality and reduced residual stress. The proposed atom deposition kinetics for the van der Waals epitaxy of the polarity‐controlled aluminium nitride nucleation layer and GaN epilayer on the MoS2 lighten the great potentiality for the application of similar 2D materials. The ultraviolet photodetector based on N‐polar GaN possesses over seven times’ response higher than that of the Ga‐polar one, which is both beneficial from the high crystalline quality and efficient polarization electric field control of the N‐polar GaN. Present work provides a new strategy for the polarity control of high‐quality III‐nitrides by the van der Waals epitaxy with a novel 2D insert layer, which would be also extended in other optoelectronic and electronic devices.

Fabrication and characterization of InN-based metal-semiconductor-metal infrared photodetectors prepared using sol–gel spin coated technique

We report on the growth and characterization of undoped indium nitride (InN) thin films grown on a silicon substrate. The InN thin films were grown on aluminium nitride (AlN) template with gallium nitride (GaN) nucleation layer using a relatively simple and low-cost sol–gel spin coating method. The crystalline structure and optical properties of the deposited films were investigated. X-ray diffraction and Raman results revealed that InN thin films with wurtzite structure were successfully grown. For InN thin film grown on a substrate with the GaN nucleation layer, its strain and dislocation density are lower than that of the substrate with the AlN nucleation layer. From the ultra-violet-visible diffuse reflectance spectrum analysis, the energy bandgap of the InN thin films with the GaN layer was 1.70 eV. The potential application of the sol–gel spin-coated InN thin films was also explored. Metal–semiconductor–metal (MSM) infrared (IR) photodetectors were fabricated by depositing the platinum contacts using two interdigitated electrodes metal mask on the samples. The finding shows that the device demonstrates good sensitivity and repeatability towards IR excitation at a wavelength of 808 nm. The photodetector characteristics at dark and photocurrent conditions such as Schottky barrier height (SBH) and ideality factor are determined. Upon exposure to the IR source at 3V applied bias, InN/AlN/Si device configuration displays rapid rise time of 0.85 s and decay time of 0.78 s, while InN/GaN/AlNSi demonstrates slow rise time of 7.45 s and decay time of 13.75 s.

Diminishing the Induced Strain and Oxygen Incorporation on Aluminium Nitride Films Deposited Using Pulsed Atomic-Layer Epitaxy Techniques at Standard Pressure MOCVD

A pulsed atomic-layer epitaxy growth technique has been introduced to substantially diminish the induced strain and oxygen incorporation on aluminium nitride films grown at standard pressure by metal organic chemical vapour deposition. The qualities of the as-deposited aluminium nitride films were studied by varying the aluminium nitride nucleation layer growth temperature at 700°C, 800°C, 900°C, 1000°C and 1100°C, respectively. The compressive strain inside the as-deposited aluminium nitride films, induced by the hetero-epitaxial growth on sapphire, was investigated through Raman spectroscopy by focusing on the evolution of E2 (high) peak frequency, where almost stress-free aluminium nitride films were attained at nucleation layer growth temperature of 1100°C. Then, the correlation between luminescence defect and level of foreign impurities respective to the varied nucleation layer growth temperatures were also systematically analysed through photoluminescence spectroscopy and x-ray photoelectron spectroscopy, respectively.

Epitaxial ZnO Layer Growth on Si(111) Substrates with an Intermediate AlN Nucleation Layer by Methane-Based Chemical Vapor Deposition

The growth of high-quality single-crystalline zinc oxide (ZnO) layers on silicon (Si(111)) substrates with an intermediate aluminum nitride (AlN) nucleation layer was investigated. The ZnO layers w...

High-Quality ZnO Layers Grown by CVD on Sapphire Substrates with an AlN Nucleation Layer

The growth of single-crystalline high-quality zinc oxide (ZnO) layers by a methane (CH4)-based chemical vapor deposition (CVD) growth process on sapphire substrates with an aluminum nitride (AlN) n...

Vertical breakdown of GaN on Si due to V-pits

Gallium nitride on silicon (GaN/Si) is an important technological approach for power electronic devices exhibiting superior performance compared to devices based on a pure silicon technology. However, the material defect density in GaN/Si is high, and identification of critical defects limiting device reliability is still only partially accomplished because of experimental difficulties. In this work, atomic force microscopy, scanning electron microscopy, secondary ion mass spectrometry, and cathodoluminescence were employed to investigate commonly occurring epitaxial overgrown V-pits and inhomogeneous incorporation of oxygen and carbon across layer stacking in the vertical direction. These experiments identified V-pits as regions with higher n-type carrier concentrations and paths for vertical leakage through the buffer, as directly probed by conductive atomic force microscopy. The deleterious effect of V-pits on device performance is demonstrated by evaluating test devices fabricated on two wafers with significantly diverse density of buried V-pits induced by varying growth conditions of the aluminum nitride nucleation layer. A clear correlation between observed vertical breakdown and density of V-pits within the C-doped GaN layer below the device structures is obtained. Back-gating transient measurements also show that the dynamic device behavior is affected by the V-pit density in terms of the detrapping time constants.

Heteroepitaxial Growth of High-Quality and Crack-Free AlN Film on Sapphire Substrate with Nanometer-Scale-Thick AlN Nucleation Layer for AlGaN-Based Deep Ultraviolet Light-Emitting Diodes.

High-quality and crack-free aluminum nitride (AlN) film on sapphire substrate is the foundation for high-efficiency aluminum gallium nitride (AlGaN)-based deep ultraviolet light-emitting diodes (DUV LEDs). We reported the growth of high-quality and crack-free AlN film on sapphire substrate with a nanometer-scale-thick AlN nucleation layer (NL). Three kinds of nanometer-scale-thick AlN NLs, including in situ low-temperature AlN (LT-AlN) NL, oxygen-undoped ex situ sputtered AlN NL, and oxygen-doped ex situ sputtered AlN NL, were prepared for epitaxial growth of AlN films on sapphire substrates. The influence of nanoscale AlN NL thickness on the optical transmittance, strain state, surface morphology, and threading dislocation (TD) density of the grown AlN film on sapphire substrate were carefully investigated. The average optical transmittance of AlN film on sapphire substrate with oxygen-doped sputtered AlN NL was higher than that of AlN films on sapphire substrates with LT-AlN NL and oxygen-undoped sputtered AlN NL in the 200–270 nm wavelength region. However, the AlN film on sapphire substrate with oxygen-undoped sputtered AlN NL had the lowest TD density among AlN films on sapphire substrates. The AlN film on sapphire substrate with the optimum thickness of sputtered AlN NL showed weak tensile stress, a crack-free surface, and low TD density. Furthermore, a 270-nm AlGaN-based DUV LED was grown on the high-quality and crack-free AlN film. We believe that our results offer a promising and practical route for obtaining high-quality and crack-free AlN film for DUV LED.

Standard pressure deposition of crack-free AlN buffer layer grown on c-plane sapphire by PALE technique via MOCVD

A high-quality aluminium nitride buffer layers were grown on (0 0 0 1) sapphire substrate at standard pressure with a subsequent low growth temperature via metal organic chemical vapour deposition. The preparation of aluminium nitride buffer layers was accomplished by growing a thin aluminium nitride nucleation layer through a nominal growth condition followed by depositing a thick aluminium nitride film using pulsed atomic-layer epitaxy technique. In 13.3 kPa ambient, the influence of aluminium nitride nucleation layer on the crystal quality of the aluminium nitride film atop was studied by varying the nucleation layer growth temperature at 700, 800, 900, 1000 and 1100 °C, respectively. It was observed that the growth temperature of nucleation layer substantially affected the structural properties of the top aluminium nitride film where the lowest value for symmetric (0 0 0 2) and asymmetric (1 0–1 2) x-ray rocking curve analysis were achieved at 1100 °C, indicating the reduction of dislocation density in the aluminium nitride films. In line with that, this result was sustained by the root mean square surface roughness evaluated via atomic force microscopy. Moreover, an atomically-flat crack-free aluminium nitride buffer layer was demonstrated by field emission scanning electron microscopy measurement.

Improved performance of GaN based light emitting diodes with ex-situ sputtered AlN nucleation layers

The crystal quality, electrical and optical properties of GaN based light emitting diodes (LEDs) with ex-situ sputtered physical vapor deposition (PVD) aluminum nitride (AlN) nucleation layers were investigated. It was found that the crystal quality in terms of defect density and x-ray diffraction linewidth was greatly improved in comparison to LEDs with in-situ low temperature GaN nucleation layer. The light output power was 3.7% increased and the reverse bias voltage of leakage current was twice on LEDs with ex-situ PVD AlN nucleation layers. However, larger compressive strain was discovered in LEDs with ex-situ PVD AlN nucleation layers. The study shows the potential and constrain in applying ex-situ PVD AlN nucleation layers to fabricate high quality GaN crystals in various optoelectronics.

Effect of nitridation surface treatment on silicon (1 1 1) substrate for the growth of high quality single-crystalline GaN hetero-epitaxy layer by MOCVD

A single-crystalline with high quality of gallium nitride epilayers was grown on silicon (111) substrate by metal organic chemical vapor deposition. The process of nitridation surface treatment was accomplished on silicon (111) substrate by flowing the ammonia gaseous. Then, it was followed by a thin aluminum nitride nucleation layer, aluminum nitride/gallium nitride multi-layer and a thick gallium nitride epilayer. The influence of in situ nitridation surface treatment on the crystallinity quality of gallium nitride epilayers was studied by varying the nitridation times at 40, 220 and 400s, respectively. It was shown that the nitridation times greatly affect the structural properties of the grown top gallium nitride epilayer on silicon (111) substrate. In the (0002) and (1 0 1¯ 2) X-ray rocking curve analysis, a narrower value of full width at half-maximum has been obtained as the nitridation time increased. This is signifying the reduction of dislocation density in the gallium nitride epilayer. This result was supported by the value of bowing and root mean square roughness measured by surface profilometer and atomic force microscopy. Furthermore, a crack-free gallium nitride surface with an abrupt cross-sectional structure that observed using field effect scanning electron microscopy was also been obtained. The phi-scan curve of asymmetric gallium nitride proved the top gallium nitride epilayer exhibited a single-crystalline structure.

GaN-Based Ultraviolet Light Emitting Diodes With Ex Situ Sputtered AlN Nucleation Layer

We demonstrated the electro-optical characteristics of gallium nitride (GaN)-based ultraviolet (UV) light emitting diodes (LEDs) with sputtered aluminum nitride (AlN) nucleation layer. The introduction of the ex situ sputtered AlN nucleation layer improved the crystal quality of the GaN and the n-AlGaN layer of the GaN-based UV LEDs. Hence, the 20-mA output power of UV LEDs with ex situ AlN nucleation layers is higher than that of UV LEDs with GaN nucleation layers. In addition, the enhanced power output of UV LEDs with ex situ AlN nucleation could reach around 52% in magnitude at peak emission wavelengths of 370 nm compared with power outputs of UV LEDs with GaN nucleation layers. Furthermore, UV LEDs with ex situ AlN nucleation show improved reliability. The UV LEDs with ex situ AlN nucleation layer revealed a power output drop of around 9% within 168 hours , which is less than the around 14% power drop of UV LEDs with GaN nucleation layer.

The impact of film thickness and substrate surface roughness on the thermal resistance of aluminum nitride nucleation layers

Thickness dependent thermal conductivity measurements were made on aluminum nitride (AlN) thin films grown by two methods on the (0001) surfaces of silicon carbide (SiC) and sapphire substrates with differing surface roughness. We find that the AlN itself makes a small contribution to the overall thermal resistance. Instead, the thermal boundary resistance (TBR) of 5.1 ± 2.8 m2K/GW between the AlN and substrate is equivalent to 240 nm of highly dislocated AlN or 1450 nm of single crystal AlN. An order-of-magnitude larger TBR was measured between AlN films and SiC substrates with increased surface roughness (1.2 nm vs. 0.2 nm RMS). Atomic resolution TEM images reveal near-interface planar defects in the AlN films grown on the rough SiC that we hypothesize are the source of increased TBR.

Silicon Schottky barrier photodiodes with a thin AlN nucleation layer

PurposeThe purpose of this paper is to present the characteristics of novel silicon Schottky barrier (SB) photodiodes (PDs) with aluminium nitride (AlN) (100 nm) nucleation layer.Design/methodology/approachComparison was made with conventional silicon SB PDs.FindingsIt was found that smaller dark current could be achieved with AlN nucleation layer. It was also found that effective SB height increased from 0.65 to 0.71 eV with the insertion of the AlN layer. The dark leakage current for the Schottky PDs with the AlN layer was shown to be about two orders of magnitude smaller than that for the conventional silicon SB PDs.Research limitations/implicationsIt is possible that the detrimental effect of interface states situated near the metal semiconductor interface was less pronounced for the sample owing to the insertion of the AlN nucleation layer.Originality/valueThere is believed to be no other report on silicon SB PDs capped with an AlN layer in the literature. This paper describes the fabricated silicon SB PDs and reports on the electrical characteristics of the devices with an AlN nucleation layer grown at low temperature.

INFLUENCE OF Al MONOLAYERS ON THE PROPERTIES OF AlN LAYERS ON Si (111)

High-quality aluminum nitride ( AlN ) layers with full width at half maximum (FWHM) values of 11 arcmin were grown by plasma-assisted molecular-beam epitaxy on Si (111) substrates. AlN nucleation layers are being investigated for the growth of GaN on Si . Growth using AlN buffer layers leads to Al -polar films, with surfaces strongly dependent on the flux conditions used. Flat surfaces can be obtained by growing as Al -rich as possible, although Al droplets tend to form. Before starting the AlN growth, a few monolayers of Al are deposited on the substrate to avoid the formation of Si 3 N 4. X-ray diffraction (XRD) techniques were employed to determine the surface and structural quality of the layers. XRD revealed that monocrystalline AlN was obtained. Best AlN films were obtained at high substrate temperatures (875°C) and III/V ratios close to stoichiometry.

Study of buffer and epitaxy technology in two-step growth of aluminium nitride

AlN (aluminium nitride) films were prepared by metalorganic chemical vapor deposition (MOCVD) on c-plane sapphire (α-Al2O3) substrates. By means of studying the traces of in-situ optical reflectivity, it was found that the AlN nucleation layer showed a specific (0001) lattice orientation, which differed from the GaN nucleation layer on (0001) sapphire substrates. The AlN buffer suffered the compressive stress at the initial stage of nucleation. And the compressive strain was relaxed gradually along with the thickness of buffer increasing and consequently annealing. Optical transmission spectra revealed that in the process of growing AlN epilayers, higher V/III ratio could improve the crystal quality but reduce the growth rates. In addition, proper doping of silane (SiH4) could improve the surface morphology of AlN film.