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In this letter, we report the achievement of a high-performance lateral GaN Schottky barrier diode (SBD) on a silicon substrate with a low turn- ON voltage (${V}_{ \mathrm{ON}}$) of 0.35 V and tungsten (W) as the anode. Non-field-plated lateral GaN SBDs with the anode–cathode distances (${L}_{\text {AC}}$) of 6, 10, 15, 20, and $25~\mu \text{m}$ demonstrate the reverse breakdown voltages of 0.6, 1.1, 1.25, 1.5, and 1.9 kV with the differential specific ON-resistances (${R}_{\text{ON}, \text {sp}}$) of 0.38, 0.72, 1.23, 1.87, and 2.61 $\text{m}\Omega \cdot $ cm2, respectively. The power figure-of-merit (FOM) is calculated to be $ {1}\times 10^{ {3}}$ , $ {1.7}\times {10}^{ {3}}$ , $ {1.3}\times {10}^{ {3}}$ , $ {1.2}\times {10}^{ {3}}$ , and $ {1.4}\times {10}^{{3}}$ MW/cm2. To the best of our knowledge, this FOM of ${1.7}\times {10}^{{3}}$ MW/cm2 is the highest among all the lateral GaN SBDs on a Si substrate. Combined with the ~108 current ON/OFF ratio at room temperature, the GaN SBD with the W anode shows a great promise for next-generation power electronics. [ABSTRACT FROM AUTHOR]

We demonstrate that the highly resistive Si substrate in GaN-on-Si RF HEMTs does not act as an insulator, but instead behaves as a conductive ground plane for static operation and can cause significant back-gate-induced current collapse. Substrate ramp characterization of the buffer shows good agreement with device simulations and indicates that the current collapse is caused by charge-redistribution within the GaN layer. Potential solutions, which alter charge storage and leakage in the epitaxy to counter this effect, are then presented. [ABSTRACT FROM AUTHOR]

III-Nitride semiconductors face the issue of localized surface states, which causes fermi level pinning and large leakage current at the metal semiconductor interface, thereby degrading the device performance. In this work, we have demonstrated the use of a Self-Assembled Monolayer (SAM) of organic molecules to improve the electrical characteristics of Schottky barrier diodes (SBDs) on n-type Gallium Nitride (n-GaN) epitaxial films. The electrical characteristics of diodes were improved by adsorption of SAM of hydroxyl-phenyl metallated porphyrin organic molecules (Zn-TPPOH) onto the surface of n-GaN. SAM-semiconductor bonding via native oxide on the n-GaN surface was confirmed using X-ray photoelectron spectroscopy measurements. Surface morphology and surface electronic properties were characterized using atomic force microscopy and Kelvin probe force microscopy. Current-voltage characteristics of different metal (Cu, Ni) SBDs on bare n-GaN were compared with those of Cu/Zn-TPPOH/n-GaN and Ni/Zn-TPPOH/n-GaN SBDs. It was found that due to the molecular monolayer, the surface potential of n-GaN was decreased by ∼350 mV. This caused an increase in the Schottky barrier height of Cu and Ni SBDs from 1.13 eV to 1.38 eV and 1.07 eV to 1.22 eV, respectively. In addition to this, the reverse bias leakage current was reduced by 3–4 orders of magnitude for both Cu and Ni SBDs. Such a significant improvement in the electrical performance of the diodes can be very useful for better device functioning. [ABSTRACT FROM AUTHOR]

Due to its high absorption coefficient and variable bandgap, InGaN is being intensively studied for photovoltaic applications. Growth of thick homogenous InGaN absorbers is challenging due to relaxation, clustering, and transition from 2D to 3D growth. These issues can be avoided by a semibulk multilayer structure. In this work, we analyze InGaN-based semibulk-structured solar cells in detail. We show that for indium content lower than 15%, GaN interlayers’ thickness has no influence on carrier transport due to the low barrier height. A conversion efficiency of 2.4% can be expected for this indium content. However, for higher indium content (15–30%), we show that the thinner the GaN interlayers, the better the conversion efficiency. Beyond 30% of indium, the conversion efficiency is hindered by the barriers’ important height even for very thin thicknesses of GaN interlayers. We show also that, for semibulk structure, both growth direction (N-face and metal-face) have similar impact on efficiency. This theoretical study gives the guidelines for the fabrication of InGaN-based solar cells that can be used as a wide-bandgap top cell in multijunction solar cells. [ABSTRACT FROM AUTHOR]

Coherent In x Al 1−x N (x = 0.15 to x = 0.28) films were grown by metalorganic chemical vapor deposition on GaN templates to investigate if the films obey Vegard’s Law by comparing the film stress-thickness product from wafer curvature before and after In x Al 1−x N deposition. The In composition and film thickness were verified using atom probe tomography and high resolution X-ray diffraction, respectively. Ex-situ curvature measurements were performed to analyze the curvature before and after the In x Al 1−x N deposition. At ∼In 0.18 Al 0.82 N, no change in curvature was observed following InAlN deposition; confirming that films of this composition are latticed matched to GaN, obeying Vegard’s law. The relaxed a 0 - and c 0 - lattice parameters of In x Al 1−x N were experimentally determined and in agreement with lattice parameters predicted by Vegard’s law. [ABSTRACT FROM AUTHOR]

In this work, we have succeeded in growing an approximate 2-inch self-separated thick GaN wafer by hydride vapor phase epitaxy with an introduction of a sacrificial layer of nanoporous GaN. Such nanoporous GaN layer is invented by using the HVPE growth of thin GaN layer on the spin-coating silica nanosphere layer followed by a hydrofluoric acid etching to the silica nanosphere layer. It has been found that the nanoporous GaN layer, enabling a reduction of stickiness between thick GaN films and the substrates, plays a significant role in the self-separation of thick GaN films during the cooling process. However, the thickness of the nanoporous GaN layer is another key issue to achieve good quality self-separated GaN thick films. In our study, we suggest that the nanoporous GaN layer with a thickness of approximately 150–240 nm can best serve as the sacrificial layer in self-separation process. Raman spectroscopy also indicates the self-separated thick GaN films by using the proposed approach are virtually strain-free. [ABSTRACT FROM AUTHOR]

The structures and stability of polar GaN/ScAlMgO 4 ( 0001) interfaces are investigated by performing density-functional calculations. On the basis of the calculated interface energies, we find characteristic features of atomic arrangements depending on the polarity of interface. The interface with Ga-adatom is stabilized over the wide range of Ga chemical potential for Ga-polar GaN, while the interface with N-adatom is always stable for N-polar GaN. Furthermore, the interface resulting in Ga-polar films is found to be more stable than that in N-polar films on ScAlMgO 4 (0001) substrate. The stability of polar GaN/ScAlMgO 4 interfaces is interpreted in terms of the formation of stable bonds and charge neutrality at the interface. [ABSTRACT FROM AUTHOR]

A chemical-etching based method for separating GaN/AlN and AlN epitaxial heterostructures grown on silicon with a silicon-carbide buffer layer and transferring them to substrates of any type is developed. GaN/AlN/SiC and AlN/SiC heterostructures 2.5 μm and 18 μm thick, respectively, are separated and transferred to a glass substrate. It is shown that a silicon-carbide buffer layer on silicon, grown by the substitution method, has a developed subsurface structure which allows easy separation of the film from the substrate and promotes the relaxation of elastic energy caused by a difference in thermal-expansion coefficients of the film and substrate. It is shown that mechanical stresses in the film after its separation from the silicon substrate almost completely relaxed. [ABSTRACT FROM AUTHOR]

Optical characteristics of Mg-ion implanted GaN layers with various fluence ranges were evaluated. Mg ion implantation was performed twice at energies of 30 and 60 keV on n-GaN layers. The first implantation at 30 keV was performed with three different fluence ranges of 1.0 × 10 14 , 1.0 × 10 15 and 5.0 × 10 15 cm −2 . The second implantation at an energy of 60 keV was performed with a fluence of 6.5 × 10 13 cm −2 . After implantation, samples were annealed at 1250 °C for 1 min under N 2 atmosphere. Photoluminescence (PL) spectrum of the GaN layer with the Mg ion implantation at the fluence range of 1.0 × 10 14 cm −2 at 30 keV was similar to the one of Mg-doped p-GaN layers grown by MOVPE (Metal-Organic Vapor Phase Epitaxy) on free-standing GaN substrates and those at the fluence ranges over 1.0 × 10 15 cm −2 were largely degraded. [ABSTRACT FROM AUTHOR]

A study on brittle cracking in GaN films processed by laser lift-off is presented. Two kinds of cracks were found in the N-polar face of GaN after the laser lift-off process, namely perpendicular cracks along the {1-1 0 0} planes and lateral cracks along the (0 0 0-1) plane, respectively. Single-shot laser damage is studied to understand the cracking mechanism. The damage morphology indicates that the GaN material on the edge of the laser ablation area experiences three loading modes: shear stress PS, longitudinal compressive stress PL and transverse tensile stress PT. Under shock PL, lateral cracks likely appear and extend from the illuminated region along the interface in mode I. Furthermore, two different kinds of perpendicular cracks were found, namely shear cracks (PC I) and deflection cracks (PC II). A strongPSgives rise to PC I while a cooperative action of PL andPTresults in PC II. In addition, there exist a critical effective spot sizedPthand a critical ratio of the laser spot size dL to the effective spot size dP, when cracks occur over them. [ABSTRACT FROM AUTHOR]

The recombination processes of excitons in Fe-doped GaN have been characterized by time-resolved photoluminescence measurement. The photoluminescence shape at different excitation powers revealed that the hole capture process by Fe2+ centers has always existed in doped GaN. Decreasing of the fast component in the biexponential decay curves with increasing iron concentration indicates the enhancive contribution of the hole capture process. Furthermore, the structures of an iron-related acceptor and complex bound exciton were confirmed by the dependence of lifetime constants on the localization energy. Also, the extended wave function of the hole from the complex bound exciton will enable spin coupling between isolated iron ions. [ABSTRACT FROM AUTHOR]