Homoepitaxial Layers Research Articles

Correlation between nanopipes formed from screw dislocations during homoepitaxial growth by metal-organic vapor-phase epitaxy and reverse leakage current in vertical p–n diodes on a free-standing GaN substrates

We fabricated p−n diodes under different growth pressures on free-standing GaN substrates of the same quality and observed a noteworthy difference in the reverse leakage current. A large reverse leakage current was generated by nanopipes, which were formed from screw dislocations in the homoepitaxial layer. There were two types of screw dislocation observed in this study. The first type already existed in the substrate and the other was newly generated in the epilayer by the coalescence of edge and mixed dislocations. An increase in the growth pressure suppressed the transformation of screw dislocations into nanopipes, which led to a reduction in the reverse leakage current. To reduce the leakage current further, it is necessary to apply growth conditions that do not transform screw dislocation into nanopipes and to use a free-standing substrate without threading dislocations, that become nanopipes.

Low Defect Thick Homoepitaxial Layers Grown on 4H-SiC Wafers for 6500 V JBS Devices

70-um thick homoepitaxial layers with very low defect density were grown on 6-inch 4° off-axis wafers using hot-wall chemical vapor deposition (CVD). Process optimization resulted in reduction of the density of triangular defects from 1.01 cm-2 to 0.14 cm-2. The treatment of wafer (CMP or selection) was essential. The in-situ etch process was optimized prior to the epitaxial growth. Junction Barrier Schottky diodes fabricated on the epitaxial films presented a typical I–V characteristic and a block voltage of 6500 V.

Cathodoluminescene study of Mg implanted GaN: the impact of dislocation on Mg diffusion

Magnesium (Mg) ion implanted homoepitaxial GaN layers is investigated by cathodoluminescence (CL) and secondary ion mass spectrometry (SIMS). The impact of dislocations on Mg diffusion is clarified by CL monitoring the Mg-related donor-acceptor pair (DAP) emission on novel angle cutting specimen. CL results suggest that: (1) there exist high concentration of nonradiative defects in a Mg implanted layer; and (2) Mg shows pipe diffusion along threading dislocations throughout epilayer to substrate. To achieve successful Mg doping by ion implantation, it is necessary to suppress the formation of a dead region in the Mg implanted layer and the pipe diffusion along threading dislocations.

Phosphorus-doped (113) CVD diamond: A breakthrough towards bipolar diamond devices

Among wide bandgap semiconductors, diamond presents physical properties particularly suited for high performance power electronic devices. Growth and doping of chemical vapor deposited (CVD) diamond have been mainly optimized in the conventional (100) crystal orientation, highly studied on (111) surfaces and recently initiated on (113). This last orientation seems very promising, as is shown for intrinsic and p-type doped diamonds. In this work, we report the growth of CVD phosphorus doped diamond films on (113)-oriented substrates. The (113) homoepitaxial layers present a phosphorus content in the range of 7.2 × 1016 up to 4.5 × 1019 at/cm3 for thicknesses between 0.6 μm and 4 μm. The high quality and the full incorporation of phosphorus into donor sites found for the (113) crystal orientation open new architecture possibilities for bipolar diamond devices.

Thickness of sublimation grown SiC layers measured by scanning Raman spectroscopy

We have grown homoepitaxial high resistivity SiC layers on conducting SiC substrates. We develop a method to determine the thickness of grown layers by scanning confocal Raman spectroscopy (SCRS). We also grow epitaxial graphene on SiC layers to label the top sample surface, and, we correlate the top surface position with Rayleigh scattering (RS). The interface between the high resistivity SiC layer and conductive SiC substrate is probed by the transition from LO phonon to the coupled LO phonon-plasmon Raman mode. The layer thickness measurements are verified by ellipsometry and Secondary Ion Mass Spectroscopy (SIMS). We show that the SCRS method provides superior lateral and vertical resolution, it is robust against errorneous conclusions based on ad-hoc models, and it is easy to implement.

Influence of Surface Orientation on Electrochemical Properties of Boron-Doped Diamond

To study the influence of crystal orientation on the electrochemical properties of boron-doped diamond (BDD), electrodes comprising (100) and (111) homoepitaxial single-crystal layers of BDD were i...

Reduction in residual impurities in semi-polar [formula omitted] and [formula omitted] GaN grown by metalorganic vapor phase epitaxy

We report on residual impurities in semi-polar 303¯1¯ and 202¯1¯ GaN homo-epitaxial layer grown by metal-organic chemical vapor deposition. The 303¯1¯ and 202¯1¯ GaN layer showed atomically smooth surface and clear steps toward 101¯6 and 101¯4, respectively. The residual impurity concentrations of oxygen and carbon were below the detection limit of secondary-ion mass spectroscopy. Low-temperature photoluminescence revealed that 202¯1¯ GaN layer consisted free excitons and Si donor bound excitons, along with two-electron satellite lines and longitudinal optical (LO) phonon coupling transitions. The results indicate semi-polar 303¯1¯ and 202¯1¯ GaN epitaxial layers are promising candidates in obtaining a high quality GaN drift layer for vertical GaN devices.

CVD growth and properties of on-axis vanadium doped semi-insulating 4H-SiC epilayers

Highly resistive homoepitaxial layers of 4H-SiC have been grown on the Si-face of nominally on-axis, n-type substrates using chemical vapor deposition. Vanadium tetrachloride has been used as the V-dopant which is responsible for the high resistivity of the epilayers. 100% 4H-polytype was reproduced in the epilayers using the optimized on-axis growth process. The upper limit of vanadium tetrachloride flow rate was also established to achieve high resistivity epilayers free of 3C polytype inclusion. A resistivity of more than 1 × 105 Ω cm has been achieved in epilayers with a very low concentration of V (1 × 1015 cm−3). Owing to the low concentration of V, superior epilayer structural quality was achieved compared to V-doped and standard high purity semi-insulating bulk grown material of similar resistivity. Epitaxial layers with varying vanadium tetrachloride flow have also been grown to study the influence of V concentration on the polytype stability, structural quality, and optical and electrical properties of epilayers. A clear correspondence has been observed in the flow-rates of vanadium tetrachloride, the atomic concentration of V, and electrical, optical, and structural properties of epilayers.

Anisotropic mosaicity and lattice-plane twisting of an m-plane GaN homoepitaxial layer

We have observed anisotropic mosaicity of an m-plane GaN homoepitaxial layer by X-ray diffraction topography imaging over a wafer and X-ray rocking curves measured at various wafer points.

Editors' Choice—Review—Theory and Characterization of Doping and Defects in β-Ga2O3

Gallium oxide (β-Ga2O3) is an emerging semiconductor with relevant properties for power electronics, solar-blind photodetectors, and some sensor applications due to its ultra-wide bandgap and developing technology base for high quality, melt-based substrate growth and thick, low-doped homoepitaxial layers. Of critical importance for the commercialization of this potentially important material is understanding of doping mechanisms in the monoclinic lattice, where two types of Ga sites and three types of O sites have been identified. A critical literature review of doping and defects of the monoclinic β-phase of gallium oxide is provided in this work. Theoretical fundamentals of both donor and acceptor doping in Ga2O3 are reviewed. Advances in doping of epitaxial Ga2O3 with a focus on molecular beam epitaxy and ion implantation are critically examined. As doping is fundamentally related to defects, particularly in this material, a review of defect characterization by optical and electrical spectroscopic methods is provided as well. P-type doping, one of the fundamental challenges for Ga2O3, is discussed in terms of first-principles calculations and ion implantation of known acceptors such as Mg and N.

Lattice-plane bending angle modulation of Mg-doped GaN homoepitaxial layer observed by X-ray diffraction topography

We have studied the lattice-plane modulation of Mg-doped GaN homoepitaxial layers by X-ray diffraction topography.

Epitaxial <inline-formula> <tex-math notation="LaTeX">$\beta$ </tex-math> </inline-formula>-Ga2O3 and <inline-formula> <tex-math notation="LaTeX">$\beta$ </tex-math> </inline-formula>-(AlxGa1−x)2O3/<inline-formula> <tex-math notation="LaTeX">$\beta$ </tex-math> </inline-formula>-Ga2O3 Heterostructures Growth for Power Electronics

We report on the growth of high quality ${\beta }$ -Ga2O3 films using metal organic chemical vapor deposition (MOCVD). Ga(DPM)3, TEGa, and TMGa metal organic precursors were used as Ga sources and oxygen for oxidation. Films grown from each Ga sources had high growth rates with up to 10 ${\mu }\text{m}$ /h achieved using TMGa. To study the quality homoepitaxial layers, MOCVD was used to grow unintentionally doped (UID) and Si doped ${\beta }$ -Ga2O3 layers with a growth rate between 0.5 and 4.0 $\mu \text{m}$ /h Epitaxial layers with XRD FWHM and RMS roughness ${n\,\,{=}\,\,8{\times }10^{19}}\,\,1$ /cm3 to ~120 cm2/Vs for ${n\,\,{=}\,\,1.6{\times }10^{17}}\,\,1$ /cm3. These values are comparable with the best literature data, despite higher growth rates. For the UID ${\beta }$ -Ga2O3 layers, Si was identified as the major impurity responsible for the free carrier concentration with strong accumulation at the film/substrate interface. The reactor was also used to grow high quality strained ${\beta }$ -(AlxGa1−x)2O3/ ${\beta }$ -Ga2O3 heterostructures and superlattices with Al content of up to 43%. The results suggest that the MOCVD enables growth of device quality ${\beta }$ -Ga2O3 and related alloys at a fast growth rate which is critical for high voltage power devices.

Effect of growth rate on morphology evolution of 4H-SiC thick homoepitaxial layers

In this paper, the surface morphologies of 4H-SiC epilayers with different growth rates were investigated by Candela CS920, atomic force microscope and optical microscope. The investigation of the surface morphologies of the samples showed that an evolution from micro-step to small-step and then back to macro-step occurred on the surface, with the surface roughness increased gradually during this evaluation. It was concluded that the higher growth rate the larger differences of step migration rate. In this case, the steps easily gather together forming greater steps. The gathering effect was enhanced with the increase of the growth rate.

Doped organic single-crystal photovoltaic cells

Abstract Doped rubrene single-crystal photovoltaic cells were fabricated. Whole photocurrent generated in the pn-homojunction with the macroscopic area of 2 mm × 1 mm was confirmed to be collected through the p-doped homoepitaxial layer. A single-crystal substrate collected excitons to the pn-homojunction with the collection efficiency reaching 46%, owing to the long exciton diffusion length of 2.7 μm.

A correlation study of substrate and epitaxial wafer with 4H-N type silicon carbide

A correlation study between substrate and epitaxial wafer of 4H-N Silicon Carbide (SiC) is conducted on five aspects for the first time: thickness and doping concentration uniformity distribution, topography change, surface roughness and crystalline quality. The 4H-N SiC homoepitaxial layer is deposited on the commercial substrates from different manufacturers using the method of Chemical Vapor Deposition (CVD). These data are characterized using these methods of mercury-probe CV measurement, Fourier transform infrared reflectance, atomic force microscope, Flatness Measuring Instrument and X-ray diffraction. It is concluded that the resistivity distribution of SiC substrate has a direct impact on the growth facet of crystal, but has no obvious influence on thickness and doping concentration distribution of epilayer. In the meantime, the relationship between crystalline quality of substrate and epilayer is found. Based on this research, it is necessary that the discuss correlation between defects of substrate and epitaxial wafer.

Study of a new type nominal “washboard-like” triangular defects in 4H-SiC 4° off-axis (0 0 0 1) Si-face homoepitaxial layers

In this work, 4H-SiC epilayers were performed on 4°off-axis Si-face substrates by horizontal hot wall chemical vapor deposition (HWCVD). A new type nominal “washboard-like” triangular defects without particulate located at their apex were observed. The microstructure and formation mechanism were investigated by micro-Raman spectroscopy, electron backscatter diffraction (EBSD) and cross-section transmission electron microscopy (TEM). Characterization results indicate that the triangular defects observed have a 3C-SiC nature. In addition, the phenomenon that a serious of other triangular defects of which the vertices arranged in a row neatly with the new type nominal “washboard-like” triangular defect was observed. Based on these observations and analysis, a model of the formation mechanism of the triangular defect had been proposed. In this model, the 3C-SiC crystal formed by 2D nucleation of adatoms on the terraces is mainly triggered by the scratch in the substrate.

Roughening of GaN homoepitaxial surfaces due to step meandering and bunching instabilities and their suppression in hydride vapor phase epitaxy

In this letter, we have shown that well-known surface instabilities in crystal growth, i.e., in-phase step meandering and step bunching, are the main causes of surface roughening of GaN homoepitaxial layers on vicinal +c-oriented GaN substrates. Both instabilities were effectively suppressed in hydride vapor phase epitaxy (HVPE) under appropriate conditions, which produced highly smooth as-grown surfaces suitable for reproducible device fabrication. Wavy surface morphologies, often observed in homoepitaxial GaN layers grown not only by HVPE but also by metal-organic chemical vapor deposition (MOCVD), were found to be covered by an array of meandered bunched steps consisting of m- and a-oriented sections. Because the bunched steps meandered in an in-phase fashion, facets consisting of m- and a-oriented bunched steps formed narrow macro-steps and wide macro-terraces, respectively, leading to the formation of ridges and grooves in-between the facets. Although the use of a substrate with large off-angles (≥0.4°) effectively suppressed the step meandering, i.e., wavy surface morphology, it induced a strong tendency for step bunching. Only growth on surfaces having relatively small off-angles (0.25°), under conditions providing large degrees of adatom desorption, i.e., at high temperatures or low V/III-ratios, suppressed both the meandering and bunching instabilities simultaneously and produced highly smooth as-grown surfaces. The use of the HVPE method seems better than the use of the MOCVD method in this strategy to increase the surface flatness of GaN homoepitaxial layers because it can maintain a sufficiently high growth rate even with a large degree of adatom desorption.

Lithographically engineered shallow nitrogen-vacancy centers in diamond for external nuclear spin sensing

The simultaneous control of the number and position of negatively charged nitrogen-vacancy (NV) centers in diamond was achieved. While single near-surface NV centers are known to exhibit outstanding capabilities in external spin sensing, trade-off relationships among the accuracy of the number and position, and the coherence of NV centers have made the use of such engineered NV centers difficult. Namely, low-energy nitrogen implantation with lithographic techniques enables the nanoscale position control but results in degradation of the creation yield and the coherence property. In this paper, we show that low-energy nitrogen ion implantation to a 12C (99.95%)-enriched homoepitaxial diamond layer using nanomask is applicable to create shallow NV centers with a sufficiently long coherence time for external spin sensing, at a high creation yield. Furthermore, the NV centers were arranged in a regular array so that 40% lattice sites contain single NV centers. The XY8-k measurements using the individual NV centers reveal that the created NV centers have depths from 2 to 12 nm, which is comparable to the stopping range of nitrogen ions implanted at 2.5 keV. We show that the position-controlled NV centers are capable of external spin sensing with a ultra-high spatial resolution.

High resolution boron content profilometry at δ-doping epitaxial diamond interfaces by CTEM

Ultimate spatial resolution in boron δ-doped homoepitaxial diamond interfaces has been achieved by diffraction contrast technique in Transmission Electron Microscopy. The combination of two reflections with the Howie-Whelan equations allows profiling the boron content of δ-doped diamond homoepitaxial layers by fitting experimentally measured CTEM intensities with the theoretical ones. To validate the method, the obtained doping profiles are compared with that of secondary ion mass spectrometry, obtaining a boron concentration of 1.6·1021 at/cm−3, which is in good agreement with that of SIMS. This approach is capable to perform dopant concentration quantification in a non-destructive way, and provides the possibility of nanometric resolution dopant concentration mapping by TEM.

Growth mode evolution during (100)-oriented β-Ga2O3 homoepitaxy

This work focuses on homoepitaxial growth of β-Ga2O3 on (100)-oriented substrates during molecular beam epitaxy. It provides a comprehensive study on the growth mode by combining in situ with ex situ tools. In situ reflection high-energy electron diffraction (RHEED) indicates 2D layer-by-layer mode accompanied by (1 × 1) surface reconstruction. The homoepitaxial layers are grown pseudomorphic with the substrate without in-plane strain as probed by in-plane azimuthal RHEED and out-of-plane synchrotron-based high resolution x-ray diffraction. In contrast to the substrate, stacking faults and twin domains are present in the layer.