Carrier concentration profiles of two-dimensional electron gases are investigated in wurtzite, Ga-face AlxGa1−xN/GaN/AlxGa1−xN and N-face GaN/AlxGa1−xN/GaN heterostructures used for the fabrication field effect transistors. Analysis measured distributions with AlGaN barrier layers different Al concentrations (0.15<x<0.5) thickness between 20 65 nm demonstrate important role spontaneous piezoelectric polarization on carrier confinement at GaN/AlGaN AlGaN/GaN interfaces....

Two dimensional electron gases in AlxGa1−xN/GaN based heterostructures, suitable for high mobility transistors, are induced by strong polarization effects. The sheet carrier concentration and the confinement of two located close to AlGaN/GaN interface sensitive a large number different physical properties such as polarity, alloy composition, strain, thickness, doping AlGaN barrier. We have investigated these undoped silicon doped transistor structures combination resolution x-ray...

The optical properties of wurtzite-structured InN grown on sapphire substrates by molecular-beam epitaxy have been characterized absorption, photoluminescence, and photomodulated reflectance techniques. These three characterization techniques show an energy gap for between 0.7 0.8 eV, much lower than the commonly accepted value 1.9 eV. photoluminescence peak is found to be sensitive free-electron concentration sample. exhibits very weak hydrostatic pressure dependence, a small, anomalous...

High-quality wurtzite-structured In-rich In1−xGaxN films (0⩽x⩽0.5) have been grown on sapphire substrates by molecular beam epitaxy. Their optical properties were characterized absorption and photoluminescence spectroscopy. The investigation reveals that the narrow fundamental band gap for InN is near 0.8 eV increases with increasing Ga content. Combined previously reported results Ga-rich side, versus composition plot alloys well fit a bowing parameter of ∼1.4 eV. direct system covers very...

Infrared reflection experiments were performed on wurtzite InN films with a range of free-electron concentrations grown by molecular-beam epitaxy. Measurements the plasma edge frequencies used to determine electron effective masses. The results show pronounced increase in mass increasing concentration, indicating nonparabolic conduction band InN. We have also found large Burstein-Moss shift fundamental gap. observed effects are quantitatively described...

The fundamental band gap of InN films grown by molecular beam epitaxy have been measured transmission and photoluminescence spectroscopy as a function temperature. edge absorption energy its temperature dependence depend on the doping level. variation Varshni parameters are compared with other group III nitrides. peak is affected emission from localized states cannot be used to determine energy. Based results obtained two samples distinctly different electron concentrations, effect...

Undoped AlGaN/GaN structures are used to fabricate high electron mobility transistors (HEMTs). Using the strong spontaneous and piezoelectric polarization inherent in this crystal structure a two-dimensional gas (2DEG) is induced. Three-dimensional (3-D) nonlinear thermal simulations made determine temperature rise from heat dissipation various geometries. Epitaxial growth by MBE OMVPE described, reaching mobilities of 1500 1700 cm/sup 2//Ns, respectively, For sheet density near 1/spl...

We fabricated a 0.25 μm gate length AlGaN/GaN heterostructure field effect transistor (HFET) with maximum extrinsic transconductance of 27 mS/mm (at room temperature) limited by the source series resistance. The device exhibited an excellent pinch-off and low parasitic output conductance in saturation regime. measured cutoff frequency fT oscillation fmax as 11 35 GHz, respectively. These values are superior to highest reported for transistors based on other wide band-gap semiconductors such...

A series of thin InN films down to 10 nm in thickness were prepared by molecular-beam epitaxy on either AlN or GaN buffers under optimized growth conditions. By extrapolating the fitted curve sheet carrier density versus film zero thickness, a strong excess charge was derived, which must come from surface interface between and its buffer layer. Since metal contacts, including Ti, Al, Ni, Hg probe, can always form an ohmic contact without any annealing, it is determined that at least part...

The effect of an AlN buffer layer on the epitaxial growth InN by molecular-beam epitaxy (MBE) is studied. Using can significantly improve structural and electrical properties InN. With increasing thickness layer, Hall mobility will monotonically increase while electron carrier concentration decreases. surface morphology film also improves. A more than 800 cm2/V s with a 2–3×1018 cm−3 at room temperature be routinely obtained ∼0.1 μm film. More importantly, it found that under optimum...

The pH-sensitivity of GaN surfaces in electrolyte solutions has been determined. For this purpose, field-effect transistors and AlGaN/GaN high-electron-mobility transistor (HEMT) structures were used to measure the response nonmetallized gate regions changes H+-concentration an ambient electrolyte. We found a linear pH between pH=2 pH=12 for both as-deposited thermally oxidized surfaces. Both showed almost Nernstian behavior with sensitivities 57.3 mV/pH GaN:Si/GaN:Mg 56.0 GaN/AlGaN/GaN HEMT...

We report on the dc characteristics and microwave performance of AlGaN/GaN heterostructure field effect transistors in temperature range from 25 to 300 °C. At temperatures above 200 °C, we observe activated shunt conductance which is independent gate voltage (the activation energy 0.505 eV). The cutoff frequency maximum oscillations vary 22 70 GHz at °C 5 4 respectively. leakage current biases −4 +1 V small nearly proportional even 0.88 These results show that deep traps strongly affect...

InN films with free electron concentrations ranging from mid-1017 to mid-1020 cm−3 have been studied using optical absorption, Hall effect, and secondary ion mass spectrometry. The absorption edge covers a wide energy range the intrinsic band gap of about 0.7 1.7 eV which is close previously accepted InN. concentration dependence fully accounted for by Burstein–Moss shift. Results spectrometry measurements indicate that O H impurities cannot account in films.

Energetic particle irradiation is used to systematically introduce point defects into ${\mathrm{In}}_{\mathit{1}\ensuremath{-}x}{\mathrm{Ga}}_{x}\mathrm{N}$ alloys over the entire composition range. Three types of energetic particles (electrons, protons, and $^{4}\mathrm{He}^{+}$) are produce a displacement damage dose spanning five decades. In InN In-rich InGaN free electron concentration increases with increasing but saturates at sufficiently high dose. The saturation due Fermi level...

The dislocation densities, surface morphology, and strain of Ga1−xInxAs/GaAs epitaxial interfaces as a function indium composition layer thickness have been investigated by transmission electron microscopy, medium energy ion blocking, double-crystal x-ray diffractometry. microscopy shows that in the thinnest dislocated films (90 160 nm, x=0.07) 60° α dislocations form first one 〈110〉 direction at interface. Surprisingly, however, an asymmetry residual is not detected these samples,...

Epitaxial growth of InN on (0001) sapphire with an AlN buffer layer was studied by migration-enhanced epitaxy, which is composed alternative supply pure In atoms and N2 plasma. A series samples were prepared different substrate temperatures ranging from 360 to 590 °C. As-grown films characterized x-ray diffraction (XRD), reflective high-energy electron diffraction, atomic-force microscopy (AFM), Hall measurements. Both XRD θ–2θ ω scans show that the full width at half maximum (0002) peak...

We report on the growth of nominally undoped GaN/AlxGa1−xN/GaN (x<0.4) high mobility heterostructures with N-face or Ga-face polarity sapphire substrates by plasma-induced molecular beam epitaxy (PIMBE) and metalorganic chemical vapor deposition in order to study formation electrical transport properties polarization induced two-dimensional electron gases (2DEGs). By depositing a thin AlN nucleation layer before GaN buffer PIMBE, we were able change wurtzite films from N Ga face. The...

We present the results of our experimental and theoretical studies concerning temperature dependence electron mobility in a two-dimensional gas (2DEG) confined at GaN/AlGaN interface. Experimental 2912 cm2 (V s)−1 4.2 K, remains almost constant up to lattice TL = 150 it then decreases rapidly down 1067 300 K. In order compare with theory we use simple analytical formula for low-field based on 2D degenerate statistics 2DEG triangular well. consider acoustic phonon, polar-optical dislocation...

We report optical absorption and photocurrent measurements on a GaN/AlN-based superlattice. The has full width at half maximum of 120 meV takes place an energy 660 (5270 cm−1); this corresponds to wavelength 1.9 μm. While the remained unchanged up room temperature, signal could be observed 170 K. With respect absorption, peak was slightly blueshifted (710 meV/5670 cm−1) had narrower 115 meV. Using quantum-well infrared photodetector, we were able measure spectrum 1.55 μm superluminescent...

Interband photoluminescence (PL) and absorption spectra of $n\text{\ensuremath{-}}\mathrm{In}\mathrm{N}$ samples with Hall concentrations from $3.6\ifmmode\times\else\texttimes\fi{}{10}^{17}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}6\ifmmode\times\else\texttimes\fi{}{10}^{18}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ were studied. Sample thicknesses in the range...

Abstract The InGaN alloy system offers a unique opportunity to develop high efficiency multi‐junction solar cells. In this study, single junction cells made of x Ga 1– N are successfully developed, with = 0, 0.2, and 0.3. materials grown on sapphire substrates by MBE, consisting Si‐doped layer, an intrinsic layer Mg‐doped the top. I – V curves indicate that cell all‐GaN has low series resistance (0.12 Ω cm 2 ) insignificant parasitic leakage. Contact resistances p n contacts 2.9 × 10 –2 2.0...

Crucial photoemission properties of layered III--V semiconductor cathodes are predicted using Monte Carlo simulations. Using this modeling, a GaAs structure is designed to reduce simultaneously the transverse energy and response time emitted electrons. This structure, grown by molecular beam epitaxy activated negative electron affinity, characterized. The measured values quantum efficiency found agree well with Such advanced structures will allow generation short bunches from photoinjectors...

High quantum yield, low transverse energy spread, and prompt response time make GaAs activated to negative electron affinity an ideal candidate for a photocathode in high brightness photoinjectors. Even after decades of investigation, the exact mechanism emission from is not well understood. Here, photoemission such photocathodes modeled using detailed Monte Carlo transport simulations. Simulations show quantitative agreement with experimental results efficiency, distributions emitted...

The wurzite group-III nitrides InN, GaN, and AlN are tetrahedrally coordinated direct band gap semiconductors having a hexagonal Bravais lattice with four atoms per unit cell. As consequence of the noncentrosymmetry structure large ionicity factor covalent metal–nitrogen bond, spontaneous polarization oriented along c-axis is predicted. In addition, highly piezoelectric. strain induced piezoelectric as well polarizations expected to be present govern optical electrical properties GaN based...