Metalorganic Chemical Vapor Deposition Reactor Research Articles

Demonstration of MOCVD based in situ etching of β-Ga2O3 using TEGa

In this work, we demonstrate an in situ etch technique for β-Ga2O3 inside a metalorganic chemical vapor deposition (MOCVD) reactor using triethylgallium (TEGa) as the etching agent. At sufficiently high substrate temperatures (Tsub), TEGa is introduced into the MOCVD reactor which undergoes pyrolysis, resulting in the deposition of Ga on the β-Ga2O3 surface. These Ga adatoms react with Ga2O3 to form gallium suboxide (Ga2O), which desorbs from the β-Ga2O3 surface resulting in the etching of the epilayer. MOCVD chamber parameters such as TEGa molar flow rate, substrate temperature, and chamber pressure were shown to be key in controlling the etch rate and surface morphology. A wide range of etch rates from ∼0.3 to 8.5 μm/h is demonstrated by varying the etch parameters. In addition, smooth surface morphology on (010) and (001) β-Ga2O3 substrates is also demonstrated. This new etch technique could enable damage free fabrication of 3D structures like fins and trenches, which are key components in many β-Ga2O3 device structures.

Dislocations/Defects analysis in III-V nitrides - a cost effective MOCVD epitaxy solution

In present paper an innovative technique to reproduce the epitaxial growth results through lateral flow metal organic chemical vapor deposition (MOCVD) reactor process at atomistic scale is reported. It includes the equivalent MOCVD reactor geometry architecture of AIXTRON 200/4 RF-S horizontal flow reactor. The gas- and surface phase chemical reaction kinetics and thermodynamics are given due consideration in the present study without use of any continuum or fluid dynamics models. The optimum conditions are extracted by running design of experiments over TNL-EpiGrow simulator to achieve high crystalline quality aluminum nitride (AlN) films over Si (111) substrate. The impact of variation in precursor NH3 flow rates and carrier gas N2 pressure are used to predict the conditions to optimize the improved morphology and quality of the AlN films. The defects densities are characterized in terms of vacancies and dislocation densities. The roughness and lattice parameters are extracted. The growth rates obtained in present studies are compared against reported the similar experiments. The excellent agreement is observed between experimental and simulated results. The dislocation densities in grown samples are also found in good agreement with the similar experimental reported densities in each sample.

Low-thermal-budget synthesis of monolayer molybdenum disulfide for silicon back-end-of-line integration on a 200 mm platform.

Two-dimensional (2D) materials are promising candidates for future electronics due to their excellent electrical and photonic properties. Although promising results on the wafer-scale synthesis (≤150 mm diameter) of monolayer molybdenum disulfide (MoS2) have already been reported, the high-quality synthesis of 2D materials on wafers of 200 mm or larger, which are typically used in commercial silicon foundries, remains difficult. The back-end-of-line (BEOL) integration of directly grown 2D materials on silicon complementary metal-oxide-semiconductor (CMOS) circuits is also unavailable due to the high thermal budget required, which far exceeds the limits of silicon BEOL integration (<400 °C). This high temperature forces the use of challenging transfer processes, which tend to introduce defects and contamination to both the 2D materials and the BEOL circuits. Here we report a low-thermal-budget synthesis method (growth temperature < 300 °C, growth time ≤ 60 min) for monolayer MoS2 films, which enables the 2D material to be synthesized at a temperature below the precursor decomposition temperature and grown directly on silicon CMOS circuits without requiring any transfer process. We designed a metal-organic chemical vapour deposition reactor to separate the low-temperature growth region from the high-temperature chalcogenide-precursor-decomposition region. We obtain monolayer MoS2 with electrical uniformity on 200 mm wafers, as well as a high material quality with an electron mobility of ~35.9 cm2 V-1 s-1. Finally, we demonstrate a silicon-CMOS-compatible BEOL fabrication process flow for MoS2 transistors; the performance of these silicon devices shows negligible degradation (current variation < 0.5%, threshold voltage shift < 20 mV). We believe that this is an important step towards monolithic 3D integration for future electronics.

Manufacturing of Gallium Nitride Thin Films in a Multi-Wafer MOCVD Reactor

Abstract Gallium nitride (GaN) thin films have attracted considerable attention for manufacturing optical and electronic devices. They have wide bandgap and superb performance in these applications. The reliability and durability of optoelectronic devices depend on the quality of the GaN thin films. The metal-organic chemical vapor deposition (MOCVD) process is a common manufacturing technique for fabricating high-quality thin films. By manipulating the operating conditions and the reactor design, one can control the deposition rate and the uniformity of the thin film. In this paper, the manufacturing process for GaN thin films in a multi-wafer MOCVD reactor is simulated based on the three-dimensional computational model of an experimental system which provides data for validation as well as realistic design parameters. The reactor pressure and the flow rate of the precursor, trimethyl-gallium (TMG), significantly affect the deposition rate and film uniformity. The incursion of impurities in the deposition can be reduced by increasing the volumetric ratio of NH3 to TMG (V/III) and reducing the reactor pressure. The deposition rate and quality of the thin film are enhanced using an appropriate mixture of H2 and N2 as the carrier gas. The design of the inlet can also be varied to improve the utilization of metal-organic precursors and increase the deposition rate. This paper presents and discusses results on these aspects for this important manufacturing process. Thus, it leads to a better understanding of the basic mechanisms involved and provides guidelines for obtaining high deposition rates with high film quality in practical chemical vapor deposition reactors.

Nucleation and coalescence of tungsten disulfide layers grown by metalorganic chemical vapor deposition

The nucleation of tungsten disulfide WS2 crystallites and coalescence behaviour of monolayer WS2 films grown on C-plane sapphire have been studied in a commercial AIXTRON close coupled showerhead metalorganic chemical vapor deposition (MOCVD) reactor using tungsten hexacarbonyl and di-tert-butyl sulfide as precursors. The influence of sapphire substrates offcut (both orientation and angle), as well as the substrate annealing conditions and growth temperature, on the nucleation and size of the WS2 domains has been investigated. A higher nucleation temperature combined with increased substrate annealing temperatures was found to promote an increase in the WS2 domain size. The dependence of surface coverage and coalescence behaviour of the WS2 domains on the growth duration has also been determined, allowing monolayer WS2 films with < 10 % bilayer to be obtained. Crystalline quality of the coalesced WS2 films has been assessed by grazing incidence XRD and misorientation mapping using 4D-scanning transmission electron microscopy, showing a slight in-plane misorientation of the crystallites in the WS2 monolayer. The electrical performance of the coalesced WS2 films was assessed using backgated TLM structures demonstrating mobility values of up to 5 cm2/Vs and a high Ion/Ioff ratio greater than 108.

Study on stability of cavity in metal–organic chemical vapor deposition calculation based on neural network method

The computational fluid dynamics (CFD) method is widely used to study the process parameters and internal flow states of reactor chambers based on metal–organic chemical vapor deposition (MOCVD) to guide film growth. Currently, several machine learning models have been used in CFD studies, and the prediction accuracy of such models is positively correlated with the amount of data. Thus, two-dimensional (2D) models are used in CFD studies, while three-dimensional (3D) models contain more information and have been used more widely. Herein, neural network (NN) models for target regions based on a 3D MOCVD reactor are proposed and applied to flow-stability studies using the MOCVD reactor chamber. NN models are used to predict the cavity stability curve, and the range of process parameters can be controlled by the characteristics of the curve. NN prediction results have higher accuracy, after the model is established, which considerably reduces the work of CFD numerical simulation and lays a foundation for MOCVD equipment design and process debugging.

High Performance Planar Antimony-Based Superlattice Photodetectors Using Zinc Diffusion Grown by MBE

In this letter, we report a mid-wavelength infrared (MWIR) planar photodetector based on InAs/InAs1−xSbx type-II superlattices (T2SLs) that has a cut-off wavelength of 4.3 μm at 77 K. The superlattice for the device was grown by molecular beam epitaxy while the planar device structure was achieved by Zinc diffusion process in a metal–organic chemical vapor deposition reactor. At 77 K, the peak responsivity and the corresponding quantum efficiency had the value of 1.42 A/W and 48% respectively at 3.7 μm under −20 mV for the MWIR planar photodetector. At 77 K, the MWIR planar photodetector exhibits a dark current density of 2.0 × 10−5 A/cm2 and the R0A value of ~3.0 × 102 Ω∙cm2 under −20 mV, which yielded a specific detectivity of 4.0 × 1011 cm·Hz1/2/W at 3.7 μm. At 150 K, the planar device showed a dark current density of 6.4 × 10−5 A/cm2 and a quantum efficiency of 49% at ~3.7 μm under −20 mV, which yielded a specific detectivity of 2.0 × 1011 cm·Hz1/2/W.

Effects of indium composition on the surface morphological and optical properties of InGaN/GaN heterostructures

PurposeThis study aims to investigate the effects of indium composition on surface morphology and optical properties of indium gallium nitride on gallium nitride (InGaN/GaN) heterostructures.Design/methodology/approachThe InGaN/GaN heterostructures were grown on flat sapphire substrates using a metal-organic chemical vapour deposition reactor with a trimethylindium flow rate of 368 sccm. The indium composition of the InGaN epilayers was controlled by applying different substrate temperatures. The surface morphology and topography were observed using field emission scanning electron microscope (F.E.I. Nova NanoSEM 450) and atomic force microscopy (Bruker Dimension Edge) with a scanning area of 10 µm × 10 µm, respectively. The compositional analysis was done by Energy Dispersive X-Ray Analysis. Finally, the ultraviolet-visible (UV-Vis) spectrophotometer (Agilent Technology Cary Series UV-Vis-near-infrared spectrometer) was measured from 200 nm to 1500 nm to investigate the optical properties of the samples.FindingsThe InGaN/GaN thin films have been successfully grown at three different substrate temperatures. The indium composition reduced as the temperature increased. At 760 C, the highest indium composition was obtained, 21.17%. This result was acquired from the simulation fitting of ω−2θ scan on (0002) plane using LEPTOS software by Bruker D8 Discover. The InGaN/GaN shows significantly different surface morphologies and topographies as the indium composition increases. The thickness of InGaN epilayers of the structure was ∼300 nm estimated from the field emission scanning electron microscopy. The energy bandgap of the InGaN was 2.54 eV – 2.79 eV measured by UV-Vis measurements.Originality/valueIt can be seen from this work that changes in substrate temperature can affect the indium composition. From all the results obtained, this work can be helpful towards efficiency improvement in solar cell applications.

Numerical Simulation of Thermal Performance of GaAs‐Metal‐Organic Chemical Vapor Deposition Reactor Based on 36 × 4 inches’ Wafers

AbstractCurrently, limited studies on 3D models based on thermal and flow fields have investigated the effects of geometric and process parameters on the metal–organic chemical vapor deposition (MOCVD) process in large square reactors under severe temperatures. To address these problems, this study conducts numerical simulations and experiments for a large square Gallium Arsenide (GaAs) MOCVD reactor. A 3D model based on the MOCVD reactor coupled with fluid flow and heat transfer is developed to analyze the influence of the heating mode and process parameters on the temperature uniformity and heating efficiency. At 800 °C, the heating time is decreased less than 300 s, and a temperature uniformity of 7.9 °C is achieved, thereby realizing improved uniformity and excellent reactor performance. The use of cross and lateral lamps promote the controllability of the reactor temperature. As the gas flow rate increases, the velocity at the edge of the reactor increases, which induces the difference in the heat transfer coefficient between the center and edge increased. The variations in the gas composition influence the heating rate and temperature uniformity. The results of this study are useful for the design of heating modules in MOCVD reactors.

High-speed flow field prediction and process parameters optimization in a vertical MOCVD reactor based on a hybrid RSM-KNN model

Metal-Organic Chemical Vapor Deposition (MOCVD) is an important method of epitaxial growth used to obtain high-quality film and mass production. Computational Fluid Dynamics (CFD) method is widely used to simulate and study the growth process of MOCVD, but the complex process parameters and high computational cost have limited the real-time application. A hybrid Response Surface Methodology–K-Nearest Neighbor (RSM-KNN) model is developed to reach the goal of the high speed of flow field prediction and process parameters optimization. In this paper, a 3-dimensional ZnO-MOCVD model is built and then validated using the experimental and simulation results. The Design of Experiment (DOE) method is used to improve data collection performance. Results of deposition rate and uniformity are combined with the RSM model to analyze the influence of process parameters and to explore the relationship between deposition rate, uniformity and flow state. The results of the flow field are combined with the machine learning method KNN to study and predict the flow field and flow states in the reactor. The hybrid model is also presented and optimized to realize the growth of high deposition rate, and the uniformity is increased by 30% at a steady flow state of plug flow.

(Invited) Prospects for MOCVD Growth of GaN for 10kV Power PN Diodes

GaN wide-bandgap semiconductors have superior electronic material properties compared to Si and even SiC that will enable the foundational diodes and transistors for the next revolution in power management technology. To date, GaN pn diodes with 33 μm thick, lightly n-type doped drift layers have been demonstrated with breakdown voltages of 5 kV. [1] However, applications requiring higher blocking voltages could operate with greater efficiency and higher frequency if GaN based diodes and transistors could be proven. Simulations indicate that GaN pn diodes with blocking voltages of 10 kV require drift layers at least 50 μm thick and with carrier concentration less than 3x1015 cm-3. Achieving such demanding such material requirements presents significant challenges for GaN growth processesHydride Vapor Phase Epitaxy (HVPE) is the growth process of choice for very thick GaN layers due to its high growth rate (>50 μm/hr) and is a prevalent method for producing free-standing N+ GaN substrates. This growth technique and its use of carbon free precursors is a natural choice for growth of 50+ μm thick drift layers needed for 10 kV pn diodes. However, Si from the quartz growth chamber used in conventional hot-wall HVPE system leads to difficulty in controllably achieving low carrier concentrations and thus new materials and equipment designs for the growth chamber are being developed. [2] Furthermore, it is challenging to maintain smooth surface morphology of thick HPVE grown GaN epilayers and to grow p-type GaN epilayers that are needed for continuously grown pn diodes. Anode formation by epitaxial regrowth using Metal-Organic Chemical Vapor Deposition (MOCVD) or Mg implantation and annealing have yet to demonstrate multi-kilovolt diodes with reverse leakage currents equal to the best, continuously grown diodes grown by MOCVD.The low growth rate (< ~5 μm/hr) for MOCVD and the use of carbon containing precursors make it a suspect process for producing the > 50 μm thick, lightly doped (< 3x1015 cm-3) drift layers needed for 10 kV diodes. However, large substrate capacity, high up-time MOCVD reactors running highly-efficient, mature manufacturing processes developed for commercial production of visible LEDs could prove attractive for GaN pn diodes when compared to immature, quartz free HVPE reactors that to date have much lower wafer capacity. Further increasing the growth rate of the HPVE process offers diminishing returns in reducing the overall production cycle time, while modest advances in the growth rate of the MOCVD process would significantly reduce in cycle time.Since the lower growth rate of MOCVD might not be disqualifying, the concern shifts to controlling electron concentration at the low levels (< 3x1015 cm-3) in GaN epilayers where the background carbon concentration is at a similar level due to the use of carbon containing precursors. In this presentation we will discuss MOCVD growth and Si doping of GaN epilayers up to 60 μm thick and the properties of pn diodes with 50 μm thick drift layers. We find that carrier concentration is linear with Si flow down to 1x1015 cm-3, the limit of the mercury probe capacitance voltage system, and that the carrier concentration is independent of epilayer thickness from a few microns to 60 microns showing that the MOCVD process is stable for growth of thick drift layers required for 10 kV diodes. We find that controlling the surface morphology is the greatest challenge to producing 10kV-class pn diode devices and discuss how various elements such as surface mis-cut and substrate vendor affect surface morphology. While more work is needed, our studies suggest that MOCVD growth is capable of producing epilayers required for GaN pn power diodes with breakdown voltages of 10 kV.The information, data, or work presented herein was funded in part by the Advanced Research Projects Agency – Energy (ARPA-E), U.S. Department of Energy under the PNDIODES and OPEN+ programs directed by Dr. Isik Kizilyalli. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525. H. Ohta et al., J. J. Appl. Phys., 57, 04FG09 (2018).H. Fujikura et al., Appl Phys. Lett. 117, 012103 (2020).

Experimental Study of the Effect of Precursor Composition on the Microstructure of Gallium Nitride Thin Films Grown by the MOCVD Process

Abstract Chemical vapor deposition (CVD) is a widely used manufacturing process for obtaining thin films of materials like silicon, silicon carbide, graphene, and gallium nitride that are employed in the fabrication of electronic and optical devices. Gallium nitride (GaN) thin films are attractive materials for manufacturing optoelectronic device applications due to their wide band gap and superb optoelectronic performance. The reliability and durability of the devices depend on the quality of the thin films. The metal-organic chemical vapor deposition (MOCVD) process, which uses compounds that contain metals and organic ligands as precursors in a CVD reactor, is a common technique used to fabricate high-quality GaN thin films. The deposition rate and uniformity of thin films are critical to a successful and useful process. These are determined by the thermal transport processes and chemical reactions occurring in the reactor, and are manipulated by controlling the operating conditions and the reactor geometrical configuration. In this study, the epitaxial growth of GaN thin films on sapphire (Al2O3) substrates is carried out in two commercial MOCVD systems: a vertical rotating disk MOCVD reactor and a close-coupled showerhead MOCVD reactor. The surface morphology and crystal quality of GaN thin films have been examined using atomic force microscopy (AFM) and scanning electron microscope (SEM). This paper focuses on the composition of the precursor and the carrier gases since earlier studies have shown the importance of precursor composition. The results show that the flow rate of trimethylgallium (TMG), which is the main ingredient in the process, has a significant effect on the deposition rate and uniformity of the films. Also, the carrier gas plays an important role in deposition rate and uniformity. Using hydrogen as a carrier gas enhances the quality of the thin film but a lower deposition rate occurs on the wafer surface. On the other hand, a high flow rate of pure nitrogen gas improves the growth rate of the film. However, it decreases the uniformity of the film and promotes carbon contamination on the wafer surface. Thus, the use of an appropriate mixture of hydrogen and nitrogen as the carrier gas can improve the deposition rate and quality of GaN thin films.

Ge doping of β-Ga2O3 by MOCVD

We report on the Ge doping of Ga2O3 using metalorganic chemical vapor deposition (MOCVD) epitaxy. The effects of the GeH4/N2 flow rate, substrate temperature, VI/III ratio, type of Ga precursor, and MOCVD reactor geometry on the incorporation efficiency of Ge into Ga2O3 were explored. The Ge concentration incorporated into the films was quantified using Hall and secondary ion mass spectroscopy measurements. The increase in the GeH4/N2 flow rate, decrease in the substrate temperature, and increase in the VI/III ratio increase the amount of Ge incorporated into Ga2O3. The incorporation of Ge into the lattice of Ga2O3 was found to be strongly dependent on the substrate temperature, i.e., lowering the growth temperature leads to a higher doping concentration. Films with a free carrier concentration ranging from ∼2 × 1016 to ∼3 × 1020 cm−3 and corresponding mobilities ranging from ∼140 to ∼38 cm2/Vs were realized. The incorporation of Ge into the films was also found to be strongly dependent on the metalorganic precursor type used for the growth of the Ga2O3 film. We found that it was more challenging to dope Ga2O3 with Ge using trimethylgallium rather than triethylgallium as a source for Ga. Additionally, we found that Ge doping has a strong memory effect dependent on the reactor geometry. The result highlights the challenges in achieving controllable Ge doping for n-type conductivity despite all the positive indicators from theoretical studies that suggest that Ge is a suitable dopant candidate for Ga2O3 similar to Si and Sn.

Atomic surface control of Ge(100) in MOCVD reactors coated with (Ga)As residuals

Heteroepitaxy of planar, low-defect III-V semiconductor layers on Ge(100) requires a single-domain substrate surface, where dimer rows are aligned in parallel on atomically well-ordered terraces, which are separated by steps of even numbered atomic height. The presence of Ga and As in the sample ambience crucially impacts the preparation of such Ge(100) surfaces. Ga and As are commonly omnipresent, when applying metalorganic chemical vapor deposition (MOCVD), either directly supplied by precursors, in the form of MOCVD reactor residuals, or both. We study the impact of the growth conditions on the Ge(100) surface formation in situ, in dependence on the reactor pre-conditioning, the type of As supply, and/or temperature, utilizing surface-sensitive reflection anisotropy spectroscopy. We benchmark the in situ spectra to in system X-ray photoelectron spectroscopy, low energy electron diffraction and scanning tunneling microscopy. We find that interaction of tertiarybutylarsine (TBAs) with a coating of the inner MOCVD reactor walls by GaAs residuals favors desorption of As from reactor parts resulting in As-dimers on the Ge(100) surface, which are rotated by 90° compared to preparation routes employing TBAs in Ga-free ambience. The optical in situ control enables precise adjustment and switching between distinct Ge(100) surface reconstructions for subsequent III-V heteroepitaxy.

Influence of Precursor Concentration on Crystalline Quality of GaN Thin Films Grown on a Sapphire Wafer

Abstract Chemical vapor deposition (CVD), which involves chemical reactions in gases for deposition on a heated surface, is an extensively used manufacturing technique for obtaining thin films of materials like silicon, graphene, silicon carbide, aluminum nitride, and gallium nitride (GaN). The process is driven by heat and mass transfer, fluid flow, and chemical reactions in the gases and at the surface. GaN is one of the most promising materials for manufacturing optical and electronic devices. However, the reliability and durability of the GaN-based devices depend on the crystalline quality of the thin films used. In this study, the epitaxial growth of GaN thin films on sapphire (Al2O3) wafers is carried out in a vertical rotating disk metalorganic chemical vapor deposition (MOCVD) system. Epitaxial growth refers to the process of growing a crystal of a particular orientation on the top of another crystal, with the orientation being determined by the underlying crystal. MOCVD reactors are CVD systems that use metalorganic compounds that consist of metal and organic ligands, leading to materials like GaAs, AlN, InN, and GaN. The quality of the thin films is largely determined by the choice of operating conditions such as the flowrate, surface temperature, and concentration of the metalorganic precursors that decompose due to heat in the reactor, react, and deposit the desired material on the surface of a wafer or a heated susceptor. In this experimental study, the crystalline quality and surface morphology of GaN thin films are evaluated using atomic force microscopy (AFM), X-ray diffraction (XRD), and Raman spectroscopy. The correlation between the crystalline quality of GaN thin films and the flowrate of the precursors is examined in detail on the basis of an evaluation of the dislocation density. The results indicate that a low concentration (V/III) ratio, where V and III refer to elements in the fifth and third groups of the periodic table, is beneficial for obtaining a high deposition rate since a low value of this ratio implies a high precursor concentration. However, it negatively affects the crystalline quality of the thin film. Similarly, high V/III ratios lead to low deposition rates and better crystalline quality, indicating the need to optimize the process.

Computational fluid dynamics modeling of a new high-pressure chemical vapor deposition reactor design

The design of a new super-atmospheric pressure metal organic chemical vapor deposition (MOCVD) reactor with spatially separated source zones and rotating susceptor is proposed and analyzed using computational fluid dynamics (CFD) techniques to determine fluid transport phenomena and suitability for thin-film synthesis of group III nitrides. This High-Pressure Spatial Chemical Vapor Deposition (HPS-CVD) reactor is designed to permit high-temperature growth of high-indium content group III nitrides. This is made possible by increasing the partial pressure of nitrogen by up to two orders of magnitude in the system thereby increasing decomposition temperatures of the group III nitride thin film. The effects of rector design, chamber height, system pressure, inlet flow rate, and rotational speed are investigated and discussed. Flow instabilities arising from the heated and rotating susceptor traversing separate source zones are minimized. Growth rates of group III nitride materials synthesized in an HPS-CVD reactor are estimated to be enhanced by approximately a factor of 10 compared to an existing super-atmospheric MOCVD reactor due to improved reactor design thereby providing comparable growth rates to current atmospheric MOCVD systems.

Design of Ion-Implanted Junction Termination Extension for Vertical GaN Pin Rectifiers

Gallium-nitride and related materials have become suitable semiconductor platforms for next-generation power electronic devices. This materials system leverages unique properties of wider energy bandgap, higher carrier mobility, and ultrashort carrier recombination lifetime to achieve much improved bipolar switching characteristics when compared to Si- or SiC-based counterparts. In recent years, vertical GaN switches such as PIN rectifiers, junction barrier Schottky (JBS) diodes, and junction field-effect transistors (JFETs) have been actively sought in hopes to achieve low-loss device performance at kilo-volt (kV) operation range. Over the years, significant progresses in low-defect-density substrate preparation and high-quality epitaxial growth using metalorganic chemical vapor deposition (MOCVD) reactors, along with robust fabrication processing techniques helped achieve many impressive GaN-based power device demonstrations. As vertical GaN devices operate at the kV ranges, proper engineering of the electric field is a key to exploiting the ultimate device performance. To this end, several device-level design strategies such as field plates, beveled sidewalls, and junction termination extensions have been studied. In the context of realizing a planar device topology in GaN materials systems, ion implantation into GaN materials systems offer new opportunities to provide precise control of inhomogeneous carrier distribution for the creation of versatile doping profiles and geometries such as selectively doped regions or highly resistive regions at arbitrary locations in GaN devices.In this presentation, we will discuss a study of the floating guard rings (FGRs) designs that utilize a nitrogen-ion implantation isolation technique. The designs can effectively mitigate the electric field crowding effect and enable robust avalanching capability in vertical GaN PIN rectifiers. Using 1.2-kV GaN PIN rectifiers as design examples, a set of numerical simulation study was performed using a TCAD-Sentaurus software package. The results showed that a closely packed FGRs with a gap of adjacent FGRs in the range of 1-3 microns, a width of the FGRs in the range of 4 to 6 microns, along with a variable-width FGR design toward the outer rings can effectively suppress the peak electric field distribution at edge of the main junction and the surface of junction termination extensions. For example, consider a GaN PIN rectifier structure with a drift layer that consists of 6 microns of unintentionally doped (UID) GaN (n= 5×1015 cm-3) and a 4-micron-thick lightly doped GaN (n = 2×1016 cm-3). The FGR structures can be formed by creating highly resistive GaN regions in the epitaxially grown p-GaN layer using an ion implantation technique. In this design, five of the FGRs have 1-micron-wide undoped GaN and a 6-micron-wide p-GaN region in the p-GaN layer. The outermost FGR (the 6th FGR) is designed to have a 2-micron-wide undoped GaN and 5-micron-wide p-GaN extension. The resulting field distribution showed an effective suppression of the field crowding effect at the edge of the main junction (Figure 1(a)) and a smooth electric potential drop along the lateral direction can be achieved (Figure 1(b)). As shown in Figure 2, the electric field distribution at the vertical junction was plotted for two FGR designs with and without a metal plate on top of the p-GaN region. The electric field distribution of the main junction was also plotted for comparison. It is clearly shown that the peak electric field at the vertical junction is effectively reduced with the metal-plated FGRs by >10% when compared to a non-plated FGRs. Reduced peak electric field in typically high-electric-field regions can safeguard the device from experiencing premature breakdown for robust switching operations. We found that 6 FGRs with a total lateral extension of <45 microns from the main pn junction are sufficient to provide effective junction termination for 1.2 kV devices. Such designs could also support for devices with a blocking voltage up to 1.6 kV.FGR designs were implemented in GaN PIN rectifiers for experimental validation. The fabrication processing of vertical GaN PIN rectifiers was grown on n-type free-standing or bulk GaN substrates using a MOCVD reactor. The cathode was formed by depositing Ti/Al-based ohmic contact on the backside of the wafer, and the anode electrode was formed on the topside p-type GaN layer. Nitrogen-ion implantation was employed to create FGR structures and served as a mean of inter-device isolation. Detailed design strategies of the FGRs, device processing and device characterizations will be discussed in the conference. Figure 1

Mid-Infrared InAs/GaSb Superlattice Planar Photodiodes Fabricated by Metal–Organic Chemical Vapor Deposition**Supported by the National Natural Science Foundation of China (Grant Nos. 61874179, 61804161, and 61605236).

Mid-wavelength infrared planar photodiodes were demonstrated, in which both the epitaxy growth of InAs/GaSb superlattices and the thermal diffusion of p-type dopant were performed in production-scale metal–organic chemical vapor deposition reactors. The formation of a planar homojunction was confirmed by secondary ion mass spectroscopy and its I–V characteristics. A cut-off wavelength around 5 μm was determined in 77 K optical characterization, and photo-current as high as 600 nA was collected from a reverse-biased planar diode of 640 μm diameter. These preliminary results were obtained despite the structural degradation revealed by x-ray diffraction, and we attribute the degradation to the concert of thermal annealing and high Zn concentration behind the diffusion front.

A systematic study of MOCVD reactor conditions and Ga memory effect on properties of thick InAl(Ga)N layers: a complete depth-resolved investigation

Thick InAlN layers (In-molar fraction &gt;0.37) on GaN buffer layers were prepared using a close-coupled showerhead metalorganic chemical vapor deposition (MOCVD) reactor.

A Numerical and Experimental Study on the Fabrication GaN Films by Chemical Vapor Deposition

Abstract Computational modeling and simulation are employed to study a rotating susceptor vertical impinging chemical vapor deposition (CVD) reactor to predict GaN film deposition. Many metal-organic chemical vapor deposition reactor manufacturers use prior experience to design and fabricate CVD reactors without a fundamental basis for the process and information on the optimal conditions for the deposition. Through trial and error, they fine tune the gas flow parameters, heater temperatures, chamber pressure, and concentration of species gases for optimal growth. However, expensive raw precursor gas and time are wasted through this method. A computational model is an important step in the CVD reactor design and GaN growth prediction. It can be used to model and optimize the reactor to yield favorable operating conditions. In this paper, a simple geometry consisting of a rotating susceptor and flow guide is considered. The focus is on gallium nitride (GaN) thin films. The study shows how the computational model can benefit reactor design. It also presents comparisons between model prediction results and experimental data from a physical, practical, system. Commercially available software is used, with appropriate modifications, and the results obtained are discussed in detail.