Tawhid Rana

Comparison of 4H Silicon Carbide Epitaxial Growths at Various Growth Pressures Using Dicholorosilane and Silane Gases

SiC epitaxial films grown in an inverted chimney CVD reactor using silane-propane-hydrogen and dichlorosilane (DCS)-propane-hydrogen systems are compared for growth rates and doping concentrations at various growth pressures. Parasitic depositions in the gas injector tube using these precursor gases are also compared for precursor depletion. Virtual Reactor, a commercial software, is employed to predict growth rates and compare them to experimental results for the same growth conditions using DCS and silane gases.

Epitaxial growth of graphene on SiC by Si selective etching using SiF4 in an inert ambient

Epitaxial graphene growth on SiC by Si selective etching using tetrafluorosilane (SiF4) is introduced, where SiF4 in Ar ambient selectively etches Si from the SiC surface at temperatures 1400 °C or above, leaving the C as graphene. Raman spectra of SiC treated in Ar for 60 min at 300 Torr did not show a graphene G-peak. However, with the addition of SiF4, a clear G-peak was observed for the surface treated for only 1 min, demonstrating faster Si removal using SiF4. Si selective etching of SiC is explained by the Gibbs free energy, where Si removal is more favorable compared to C removal by SiF4.

Behavior of Particles in the Growth Reactor and their Effect on Silicon Carbide Epitaxial Growth

Formation of particles and their effect on SiC epitaxial growth in the CVD reactor is investigated. Particle induced defects in the epilayer at different gas decomposition conditions are discussed. A higher number of pits with larger diameters are observed in the epilayer for conditions where gases decompose later in the gas injector tube (i.e. nearer to the substrate). On the other hand, the number and size of these pits reduce for the condition where gas decomposes earlier in the tube. To investigate the effect of particles during the growth, various particles with different size, shape and compositions are intentionally placed on the substrate surface before epitaxial films are grown. Samples are mapped and compared at similar locations in the pre-growth, post growth and post-etch (by molten KOH) conditions. It is found that the nature of particle induced defects depends primarily on size and shape of particles.

Step dynamics in the homoepitaxial growth of 6H-SiC by chemical vapor deposition on 1° offcut substrate using dichlorosilane as Si precursor

Step flow epitaxial growth was achieved on 1° offcut 6H-SiC substrate using dichlorosilane (DCS) as the Si precursor. High crystal quality and polytype uniformity were verified by XRD and Raman spectroscopy. Mirror-like surfaces with very few triangular and carrot defects were obtained over a wide range of C/Si ratios. Surface step bunching and step crossover were observed and rms roughness values were measured to be 2–4 nm. N-type doping was achieved by site-competition epitaxy at low C/Si ratios. Growth rates of 0.5−4 μm/h was obtained over a temperature range of 1470–1550 °C. The surface diffusion length of the adatoms on the step terraces was calculated using a model based on the Burton-Cabrera-Frank theory of epigrowth on stepped surfaces. In the experimental temperature range, the surface diffusion length varied from 5 to 13 nm, which is significantly shorter than those reported in literature for epigrowth using the conventional silane precursor. The short diffusion lengths for DCS imply a strong de...

Interface Trap-Induced Nonideality in As-Deposited Ni/4H-SiC Schottky Barrier Diode

As-deposited Ni/SiC Schottky diodes often show nonideal forward conduction characteristics. The ideality can be improved by the formation of a nickel-silicide/SiC interface by annealing at 650 °C. The nonideal characteristics in as-deposited diodes are generally attributed to Schottky barrier inhomogeneity at the interface. However, recent studies show that highly nonideal characteristics (n 1.2) cannot be explained by the existing inhomogeneity models. In this paper, we report the observation of hysteresis patterns in the I-V and CV characteristics of as-deposited nonideal diodes. It is argued that the existence of evenly distributed slow, donor-like interface traps can explain the hysteresis and the associated Schottky nonideality. A trap density of 108-1010 cm-2 was estimated from the I-V and CV hysteresis.

SiC Homoepitaxy, Etching and Graphene EpitaxialGrowth on SiC Substrates Using a Novel FluorinatedSi Precursor Gas (SiF4)

Tetrafluorosilane (SiF4 or TFS), a novel precursor gas, has been demonstrated to perform three primary operations of silicon carbide-related processing: SiC etching, SiC epitaxial growth and graphene epitaxial growth. TFS etches SiC substrate vigorously in a H2 ambient by efficient Si removal from the surface, where SiC etch rate is a function of TFS gas concentration. In this SiC etching process, Si is removed by TFS and C is removed by H2. When propane is added to a H2 and TFS gas mixture, etching is halted and high-quality SiC epitaxy takes place in a Si droplet-free condition. TFS’s ability to remove Si can also be exploited to grow epitaxial graphene in a controllable manner in an inert (Ar) ambient. Here, TFS enhances graphene growth by selective etching of Si from the SiC surface.

In-Grown Stacking Faults in SiC-CVD Using Dichlorosilane and Propane as Precursors

In-grown stacking faults (IGSFs) were studied in 4H-SiC homoepitaxial growth from a SiH2Cl2-C3H8-H2 system. Most of the IGSFs, start from the epilayer/substrate interface, and exhibit photoluminescence emission peak at 2.58 eV (480 nm) indicating of 8H polytype. The growth parameters, including growth temperature, growth pressure, growth rate, hydrogen etching, et al., varied around the regular growth condition do not show a significant effect on the IGSF generation. Reactor furniture is identified to be a major reason of IGSF formation, especially when the insulation part of the furnace is not completely isolated from the growth zone. Dusting of insulation material is crucial in the formation of IGSFs. When using graphite felt as the insulation material, the IGSF density in the epilayer can be as high at ~104 cm-2. Improvement of the insulation material by using graphite foil reduces the density to 30-100 cm-2. Further reduction of IGSF density to less than 10 cm-2 is achieved by mild pretreatment of the substrate in molten KOH-NaOH eutectic.

High gain bipolar photo-transistor operation in graphene/SiC Schottky interfaces: The role of minority carriers

We propose a new class of semiconductor transistor devices based on graphene/SiC and graphene/Si Schottky junctions that have the potential to be transformative. By using the graphene as collector/emitter in a bipolar transistor (BJT) and not as a channel material, there is relaxation of the tolerances in graphene thickness and quality, simplifying growth, device design and fabrication. This also enables the exploitation of engineered defects in thicker (2-5ML) graphene films for flexible electronics, currently not being considered, as well controlled uniform defects are preferred to localized random defect clusters. We will discuss an SiF4 based growth method that enables temperature programmed defect engineering. We will discuss the use of electron-beam induced current (EBIC) to characterize these materials. Based on recent results at our lab, a graphene/SiC Schottky junction behaves as a collector (GC) and an emitter (GE) in a BJT with common emitter gain, β>50, measured under phototransistor operation mode. The transparent graphene Schottky collector/emitter junction enables opto-electronic applications, minimizes series resistance in the device due to the thin graphene layer, and also minimizes charge storage time (diffusion capacitance), enabling high speed operation. Furthermore, the observation of β>50 with a GE-BJT demonstrates that significant minority carrier injection occurs in these Schottky junctions, contrary to what is commonly assumed. The injection of minority carriers has the ability to induce conductivity modulation in the underlying semiconductor, reducing overall device resistance. The role of minority carriers in Schottky Junctions will be discussed.