Juan Salvador Rojas-Ramirez

InAs hole inversion and bandgap interface state density of 2 x 10(11) cm(-2) eV(-1) at HfO2/InAs interfaces

High-k/InAs interfaces have been manufactured using InAs surface oxygen termination and low temperature atomic layer deposition of HfO2. Capacitance–voltage (C–V) curves revert to essentially classical shape revealing mobile carrier response in accumulation and depletion, hole inversion is observed, and predicted minority carrier response frequency in the hundred kHz range is experimentally confirmed; reference samples using conventional techniques show a trap dominated capacitance response. C–V curves have been fitted using advanced models including nonparabolicity and Fermi-Dirac distribution. For an equivalent oxide thickness of 1.3 nm, an interface state density Dit = 2.2 × 1011 cm−2 eV−1 has been obtained throughout the InAs bandgap.

Structural and optical properties of β-Ga2O3 thin films grown by plasma-assisted molecular beam epitaxy

Epitaxial beta-gallium oxide (β-Ga2O3) has been deposited on c-plane sapphire by plasma-assisted molecular-beam epitaxy technique using two methods. One method relied on a compound Ga2O3 source with oxygen plasma while the second used elemental Ga source with oxygen plasma. A side-by-side comparison of the growth parameters between these two methods has been demonstrated. With various substrate temperatures, pure phase (2¯01) oriented β-Ga2O3 thin films were obtained using both sources. Reflection high energy electron diffraction patterns displayed a threefold reconstruction during the growth. X-ray photoelectron spectroscopy analysis showed a shift in the binding energy of the Ga 2p peaks consistent with a Ga being in a +3 oxidation state. For transparent oxide like β-Ga2O3, it is important to determine the index of refraction (n) and its functional dependence on the wavelength. The Cauchy dispersion relation was employed to evaluate the refractive index, film thickness, roughness values, and extinction ...

Field-Effect Mobility of InAs Surface Channel nMOSFET With Low

Frequency (100 Hz ≤ f ≤ 1 MHz) and temperature (-50 ≤ T 20 °C) characteristics of low interface state density D_it high-κ gate-stacks on n-InAs have been investigated. Capacitance-voltage (C-V) curves exhibit typical accumulation/depletion/inversion behavior with midgap D_it of 2 × 10¹¹ and 4 × 10¹¹ cm^-2 eV^-1 at -50 °C and 20 °C, respectively. Asymmetry of low-frequency C-V curves and C-T dependence for negative voltage showing a sharp transition of ≅-20 dB/decade between low- and high-frequency behavior indicate surface inversion. An inversion carrier activation energy and an InAs hole lifetime of 0.32 eV and 2 ns have been extracted, respectively. Surface channel nMOSFETs with gate length L_g = 1 μm, channel thickness = 10 nm, and equivalent oxide thickness (EOT) 1 ≤ EOT ≤ 1.6 nm have been fabricated. For EOT = 1 nm, a subthreshold swing S = 65 mV/decade, transconductance g_m = 1.6 mS/μm, and ON-current I_ON = 426 μA/μm at an OFF-current I_OFF = 100 nA/μm (supply voltage V_dd = 0.5 V) have been measured. Peak electron field-effect mobilities of 6000-7000 cm²/Vs at sheet electron densities of 2-3 × 10¹² cm^-2 were obtained for EOT as small as 1 nm.

D_{\rm it}

We report the first demonstration of InAs FinFETs with fin width W_fin in the range 25-35 nm, formed by inductively coupled plasma etching. The channel comprises defect-free, lattice-matched InAs with fin height H_fin = 20 nm controlled by the use of an etch stop layer incorporated into the device heterostructure. For a gate length L_g = 1 μm, peak transconductance gm,peak = 1430 μS/μm is measured at V_d = 0.5 V demonstrating that electron transport in InAs fins can match planar devices.

Scaled Gate-Stack

One of the major challenges of high mobility complementary metal-oxide-semiconductor (CMOS) circuits is to meet off-current requirements of <100 pA/μm for low stand-by power (LSTP) operation due to the small bandgap (≤0.5 eV) of the channel material (bandgap limit). In this work, we present experimental proof that the bandgap limit can be overcome at nanometer dimensions leveraging the phenomenon of steady state deep depletion (SSDD). The occurrence of SSDD is investigated using high-k capacitors with 5 and 10 nm InAs channel on a n- or p-type doped lattice matched wide bandgap AlAsSb layer. Absence of charge carriers at the off-state band edge is observed for 5 nm InAs channel layers demonstrating occurrence of SSDD and lifting of the off-state bandgap limit providing a path to meet LSTP requirements for future high mobility CMOS.

InAs FinFETs With

We report on the use of SrTiO3 films on GaAs(001) substrates grown by molecular beam epitaxy (MBE) as intermediate buffer layers for the heteroepitaxial growth of ferromagnetic La0.7Sr0.3MnO3 (LSMO) and room temperature multiferroic (ferroelectric/antiferromagnetic) BiFeO3 (BFO) thin films using the pulsed laser deposition technique. The exchange bias coupling effect in the BFO/LSMO heterostructure has been investigated. The magnetization measurements with field cooling exhibit a surprising increment in the magnetic moment with enhanced magnetic hysteresis squareness. This we believe is the consequence of exchange interactions between the antiferromagnetic BFO and the ferromagnetic LSMO at the interface. The integration of BFO materials with LSMO on GaAs substrates facilitated the demonstration of resistive switching based non-volatile memory (NVM) devices which can be faster with lower energy consumption compared to present commercial technologies. Ferroelectric switching observations using piezoresponse force microscopy show polarization switching demonstrating its potential for read–write operation in NVM devices. The ferroelectric and electrical characterization exhibits strong resistive switching with low set/reset voltages. Furthermore, we demonstrate a prototypical epitaxial field effect transistor based on multiferroic BFO as the gate dielectric and ferromagnetic LSMO as the conducting channel. The device exhibits a modulation in channel conductance with a high ON/OFF ratio. This work also demonstrates the first step towards the development of magneto-electronic devices integrated with a compound semiconductor.

\textrm {H}_{\mathrm {fin}}=20

The growth of high quality epitaxial beta-gallium oxide (β-Ga2O3) using a compound source by molecular beam epitaxy has been demonstrated on c-plane sapphire (Al2O3) substrates. The compound source provides oxidized gallium molecules in addition to oxygen when heated from an iridium crucible in a high temperature effusion cell enabling a lower heat of formation for the growth of Ga2O3, resulting in a more efficient growth process. This source also enabled the growth of crystalline β-Ga2O3 without the need for additional oxygen. The influence of the substrate temperatures on the crystal structure and quality, chemical bonding, surface morphology, and optical properties has been systematically evaluated by x-ray diffraction, scanning transmission electron microscopy, x-ray photoelectron spectroscopy, atomic force microscopy, spectroscopic ellipsometry, and UV-vis spectroscopy. Under optimized growth conditions, all films exhibited pure 2¯01  oriented β-Ga2O3 thin films with six-fold rotational symmetry when...

nm Fabricated Using a Top–Down Etch Process

This study entails a comparison of the broken-gap InAs/GaSb heterojunction system on two different substrates, including Si and native GaSb as a control. Through the use of different integration schemes such as AlSb and SrTiO3 buffer layers, GaSb was grown on miscut Si substrates using solid-source molecular beam epitaxy. The InAs/GaSb p+-i-n+ heterostructures were grown on the GaSb/Si virtual substrates and compared in terms of their surface morphology and crystalline quality. Esaki tunnel diodes were fabricated, and their performance compared across the different integration platforms. The control sample shows the best peak current density of 336 kA/cm2 and a conductance slope of 274 mV/decade compared to the broken-gap junction on SrTiO3/Si and AlSb/Si virtual substrates. These results show the possibility of integrating the InAs/GaSb system in ultralow power tunnel field-effect transistors logic applications with the cost-effectiveness and maturity of the silicon technology.

Lifting the off-state bandgap limit in InAs channel metal-oxide-semiconductor heterostructures of nanometer dimensions

Record setting III-V MOSFETs are reported. For the first time performance better than state-of-the-art HEMTs is demonstrated. For a MOSFET with 10 nm unstrained InAs surface channel and L_g = 130 nm operating at 0.5 V, on-current as high as I_on = 601 μA/μm (at fixed I_off = 100 nA/μm) is achieved. This record performance is enabled by g_{m, ext} = 2.72 mS/μm and S = 85 mV/dec, DIBL = 40 mV/V, resulting from breakthroughs in epitaxy and III-V/dielectric interface engineering. Measured mobility is 7100 cm²/V.s at n_s = 6.7×10¹² cm^-2. Device simulations further elucidate the performance potential of III-V N-MOSFETs.

Integration of BiFeO3/La0.7Sr0.3MnO3 heterostructures with III–V semiconductors for low-power non-volatile memory and multiferroic field effect transistors

β-Ga2O3 thin films were grown on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. The films were grown using an elemental gallium source and oxygen supplied by an RF plasma source. Reflection high-energy electron diffraction (RHEED) was used to monitor the surface quality in real time. Both in situ RHEED and ex situ X-ray diffraction confirmed the formation of single crystal β-phase films with excellent crystallinity on c-plane sapphire. Spectroscopic ellipsometry was used to determine the film thicknesses, giving values in the 11.6–18.8 nm range and the refractive index dispersion curves. UV-Vis transmittance measurements revealed that strong absorption of β-Ga2O3 starts at ∼270 nm. Top metal contacts were deposited by thermal evaporation for I-V characterization, which has been carried out in dark, as well as under visible and UV light illumination. The optical and electrical measurements showed that the grown thin films of β-Ga2O3 are excellent candidates for deep-ultraviolet detection and sensing.