The electrical properties of p-type Mg-doped GaN are investigated through variable-temperature Hall effect measurements. Samples with a range Mg-doping concentrations were prepared by metalorganic chemical vapor phase deposition. A number phenomena observed as the dopant density is increased to high values typically used in device applications: effective acceptor energy depth decreases from 190 112 meV, impurity conduction at low temperature becomes more prominent, compensation ratio...

The hole-transport properties of Mg-doped AlGaN/GaN superlattices are carefully examined. Variable-temperature Hall-effect measurements indicate that the use such enhances average hole concentration at a temperature 120 K by over five orders magnitude compared to bulk GaN film (the enhancement room is factor 9). An unusual modulation-doping scheme, which has been realized using molecular-beam epitaxy, yielded high-hole-mobility and conclusively demonstrated pivotal role piezoelectric...

Semi-insulating 6H–SiC crystals have been achieved by using controlled doping with deep-level vanadium impurities. High resistivity undoped and semi-insulating vanadium-doped single-crystals diameters up to 50 mm were grown physical vapor transport an induction-heated, cold-wall system in which high purity graphite materials constituted the hot zone of furnace. Undoped p-type due presence residual acceptor impurities, mainly boron, exhibited resistivities ranging 3000 Ω cm. The behavior is...

High quality Al0.15Ga0.85N/GaN heterostructures have been fabricated on 6H–SiC and sapphire substrates by metalorganic vapor phase epitaxy (MOVPE). A temperature independent mobility, indicative of the presence a two-dimensional electron gas (2DEG), was observed in all samples below 80 K. The highest low 2DEG 7500 cm2/V s, measured AlGaN/GaN grown 6H–SiC; sheet carrier density 6×1012 cm−2. Strong, well resolved, Shubnikov–de Haas oscillations were fields as 3 T persisted to temperatures high...

A novel growth method (carbon molecular beam epitaxy (CMBE)) has been developed to produce high-quality and large-area epitaxial graphene. This demonstrates significantly improved controllability of the graphene growth. CMBE with C60 produces AB stacked graphene, while graphite filament results in non-Bernal layers a Dirac-like electronic structure, which is similar grown by thermal decomposition on SiC (000-1). Detailed facts importance specialist readers are published as "Supporting...

Acceptors present in undoped p-type conducting GaAs have been studied with photoluminescence, temperature-dependent Hall measurements, deep level transient spectroscopy, and spark source mass spectrometry. It is shown that conduction due to presence of the shallow acceptor CAs cation antisite double GaAs. The first second ionization energies determined for are 77 230 meV from valence-band edge.

High quality wurtzite GaN epilayers have been grown on ZnO(0001) substrates by reactive molecular beam epitaxy. Photoluminescence and reflectivity measurements point to high presumably due the near match of both crystal lattice parameter stacking order between ZnO. In addition, good films lack characteristic yellow photoluminescence band. Any misorientation epilayer planes with respect ZnO substrate is not detectable polarized reflectivity. The x-ray double diffraction indicate this much...

Far-infrared magnetospectroscopy on $\mathrm{InAs}/{\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{Sb}$ quantum-well structures has revealed new transitions ($X$ lines) when sufficient holes (in ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{Sb}$) coexist with electrons InAs) and the magnetic field is high enough. The electron-related $X$ line about 3 meV above electron cyclotron resonance, roughly same slope vs field, increases in intensity increasing hole density or...

Twisted graphene is of particular interest due to several intriguing characteristics, such as its the Fermi velocity, van Hove singularities and electronic localization. Theoretical studies recently suggested possible bandgap opening tuning. Here, we report a novel approach producing epitaxial twisted on SiC (0001) observation intrinsic behaviour. The direct deposition C60 pre-grown layers results in few-layer confirmed by angular resolved photoemission spectroscopy Raman analysis. strong...

We have studied the electronic properties of ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}/\mathrm{G}\mathrm{a}\mathrm{N}$ heterostructures by using Shubnikov--de Haas (SdH) measurement. Two SdH oscillations were detected on samples $x=0.35$ and 0.31, due to population first two subbands with energy separations 128 109 meV, respectively. For sample $x=0.25,$ beat each other, probably a finite zero-field spin splitting. The spin-splitting is equal 9.0 meV. also showed...

In this letter we report the molecular beam epitaxial growth and characterization of InAs/GaSb superlattices grown on semi-insulating GaAs substrates for long wavelength infrared detectors. Photoconductive detectors fabricated from showed photoresponse up to 12 μm peak responsivity 5.5 V/W with Johnson noise limited detectivity 1.33×109 cm Hz1/2/W at 10.3 78 K.

Hall effect, deep level transient spectroscopy (DLTS) and optical absorption measurements were employed in concert to determine the position of vanadium acceptor nitrogen doped 6H 4H SiC. effect results indicate that SiC is at 0.80 eV beneath conduction band edge, 0.66 for polytype. The DLTS signature defect polytype showed an ionization energy a capture cross section 1.8×10−16 cm−2. proved levels investigated are related isolated vanadium, therefore level. Based on secondary ion mass data,...

Photoreflectance from semi-insulating GaAs, and GaAs/GaAs interfaces, is discussed in terms of its behavior with temperature, doping, epilayer thickness, laser intensity. Semi-insulating substrates show an exciton-related band-edge signal below 200 K impurity-related photoreflectance above 400 K. At intermediate temperatures the thin GaAs epilayers contains a contribution epilayer-substrate interface. The interface effect depends on epilayer's carrier mobility. broadens by 5--10 meV,...

Abstract Heterostructures consisting of two-dimensional materials have shown new physical phenomena, novel electronic and optical properties device concepts not observed in bulk material systems or purely three dimensional heterostructures. These effects originated mostly from the van der Waals interaction between different layers. Here we report that a platform can be provided by heterostructures 2D graphene with metal oxide (TiO 2 ). Our direct synthesis graphene/TiO heterostructure is...

The transport properties, particularly free carrier density and mobility, of SiC are usually determined by the Hall effect. Raman spectroscopy has been shown to yield parameters similar analysis longitudinal optical plasmon coupled (LOPC) modes in doped provides such information. In case damped plasmons n-type 4H–SiC, changes concentration result a frequency shift LOPC mode, which appears close A1(LO) phonon mode. validity this approach for different concentrations (plasma frequencies)...

Comparisons are made between the carrier concentrations, ionization energies, and electron mobilities in 4H–SiC samples implanted with similar doses of nitrogen or phosphorus annealed at 1300 1700 °C for 10 min argon. The objective research is to determine which element may yield lower resistance 4H–SiC. Ionization energies 53 93 meV measured from phosphorus-implanted 4H–SiC, assigned hexagonal cubic lattice positions respectively. corresponding nitrogen-implanted 42 84 meV, Phosphorus not...

A model is presented which describes the compensation mechanism resulting in semi-insulating 6H silicon carbide by vanadium doping. Undoped 6H–SiC crystals grown physical vapor transport methods frequently contain between 1×1017 and 5×1018 cm−3 uncompensated boron acceptors. Upon addition of vanadium, 3d1 electron donor compensates holes centers. It shown that when present concentrations greater than boron, Fermi level pinned to level. From temperature dependent Hall effect measurements,...

Photoreflectance is used to measure AlxGa1−xAs composition, and determine carrier concentrations in Si-doped AlGaAs epilayers capped with GaAs. Undoped caps are generally depleted, do not show a usual GaAs photoreflectance. However, photoreflectance from the cap/(doped AlGaAs) interface produces broad signal which distorts entire spectrum, making it hard locate band edges precisely. A similar modulation-doped heterostructures apparently associated samples that presence of two-dimensional...

An AlxGa1−xN/GaN two-dimensional electron gas structure with x=0.13 deposited by molecular beam epitaxy on a GaN layer grown organometallic vapor phase sapphire substrate was characterized. X-ray diffraction maps of asymmetric reciprocal lattice points confirmed that the thin AlGaN coherently strained to thick layer. Methods for computing aluminum mole fraction in x-ray are discussed. Hall effect measurements gave sheet concentration 5.1×1012 cm−2 and mobility 1.9×104 cm2/V s at 10 K....

Short-period superlattices consisting of alternating layers GaN:Mg and AlGaN:Mg were grown by low-pressure organometallic vapor phase epitaxy. The electrical properties these measured as a function temperature compared to conventional layers. It is shown that the optical absorption edge can be shifted shorter wavelengths while lowering acceptor ionization energy using short-period superlattice structures instead bulk-like AlGaN:Mg.

Electrical contact properties and graphitic structures of metal/carbon/4H–SiC are investigated. Metals studied include Ni, Co, Cr, NiCr, Ti, W, Mo, Al, Au. Ohmic contacts formed on Ni/C, Co/C, Cr/C, NiCr/C films 4H–SiC with n-type, C-face, a doping concentration 1.8×1019 cm−3 . Only Ni/C Co/C exhibit behavior SiC Si-face, 1.6×1018 cm−3. Ni Co well known as excellent graphitization catalysts. Raman spectra show that the formation carbon is related to in annealed metal/carbon/SiC structures....