Mark A. Wistey - IEEE Xplore Author Profile

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Models of GeSn and GeCSn quantum well (QW) lasers were compared to predict net gain and threshold for computing applications. GeSn showed weak confinement of electrons in both k-space (directness) and real space, as well as a weak optical confinement factor. Using material parameters from ab-initio calculations, adding 1-2% carbon to Ge or GeSn could provide all three confinements simultaneously, ...Show More
Device models show GeSn lasers are limited by weak electron and photon confinement. Adding carbon offers strong conduction band offsets, freeing SiGeSn layers for separate confinement heterostructures, reducing thresholds. Photoluminescence from recent growths of GeC and GeSnC quantum wells will be presented.Show More
We used ab-initio and finite element strain modeling to explain high threshold current densities in reported tensile Ge lasers. Anisotropic strains improve carrier confinement but reduces optical confinement, and intervalence band absorption still dominates. Strain anisotropy increases Jth compared with simple slab models.Show More
Ab-initio simulations of dilute germanium carbides (Ge:C) using hybrid functionals predict a direct bandgap with <;1%C. Growth of dilute Ge:C shows reduced direct gap consistent with the model, with no structural defects detected. Ge:C may enable lasers and compact modulators on Si.Show More
Core-shell upconverting nanostructures (CSUNs) improve upconversion efficiency by blocking midgap recombination. Consecutive 3-level systems absorb strongly but preserve long carrier lifetime in their final states. Germanium has a nearly-direct bandgap ideal for a CSUN core: strong optical absorption yet slow recombination. Electrons in the indirect conduction band valley absorb a second photon to...Show More
Summary form only given. In this talk, I will review some of the recent development of tunnel field effect transistors (TFETs) at Notre Dame [1-8]. Tunnel FETs are promising replacements of Si-MOSFETs beyond 2020 due to their promise to achieve Ion/Ioff > 103 with Ion > 100 uA/um at low supply voltages (up to 0.5 V). To date we have demonstrated Ion/Ioff ~ 106, Ion ~ 180 uA/um, separately, based o...Show More
Vertical tunnel field-effect transistors (TFETs) in which the gate field is aligned with the tunneling direction have been fabricated using a novel gate-recess process, resulting in record on-current. The tunnel junction consists of InAs/GaSb with a broken band alignment. The gate-recess process results in low drain contact and access resistances; together with the favorable broken gap heterojunct...Show More
Theoretically, 1.4% biaxial tensile strain could produce a direct bandgap in Ge. But high strain can lead to dislocations that reduce radiative efficiency and carrier mobilities. Also, the high circulating power in a laser can lead to damage in real time. In this study, we examined the sensitivity of strained Ge to damage by irradiating it with high-energy electrons and comparing which strain cond...Show More
Vertical n-channel tunnel field-effect transistors (TFETs) with tunneling normal to the gate based on an n+ In∞=0.53->;1GaAs/p+ InP heterojunction have been demonstrated to exhibit simultaneously a high ION/IOFF ratio of 6 × 105, a minimum subthreshold swing (SS) of 93 mV/dec, and an on-current of 20 μA/μm at VDS = 0.5 V and a gate swing of 1.75 V at 300 K, a record TFET performance. The significa...Show More
Nonalloyed ohmic contacts regrown by molecular beam epitaxy were made on InAlN/AlN/GaN/SiC high-electron-mobility transistors (HEMTs). Transmission-line-method measurements were carried out from 4 K to 350 K. Although the total contact resistance is dominated by the $\hbox{metal}/ \hbox{n}^{+}\hbox{-}\hbox{GaN}$ resistance ($\sim$ 0.16 $\Omega\cdot\hbox{mm}$), the resistance induced by the interfa...Show More
The current-voltage characteristics of AlGaSb/InAs staggered-gap n-channel tunnel field-effect transistors are simulated in a geometry in which the gate electric field is oriented to be in the same direction as the tunnel junction internal field. It is shown that this geometry can also support low-voltage operation and low subthreshold swing. In the absence of a simple analytic theory for this tra...Show More
Record high on-current of 78 $\mu\hbox{A}/\mu\hbox{m}$ in a tunnel field-effect transistor (TFET) is achieved at 0.5 V at room temperature. The TFET employs a staggered AlGaSb/InAs heterojunction with the tunneling direction oriented in-line with the gate field. The measured results are consistent with numerical simulation of the device structure. Simulations of optimized structures suggest that s...Show More
Vertical n-channel tunnel field-effect transistors (FETs) based on compound semiconductors, in a new geometry with tunneling normal to the gate, are demonstrated for the first time using an n+ In0.53Ga0.47As/n+ /n+,=0.53- >;1 GaAs/p+ InP heterojunction. At 300 K, the TFETs show an on-current of ~20 μA/μm and a minimum subthreshold swing (SS) of 130 mV/dec using an Al2O3 gate dielectric (EOT ~3.4 n...Show More
Tunnel field-effect transistors (TFETs) are under intense investigation for low-power applications because of their potential for extremely low subthreshold swing (SS) and low off-state leakage [1]. III–V semiconductors with small effective mass and near broken band alignment are considered to be ideal for TFETs in that they promise high on-current and ION/IOFF ratios [2–3]. In this paper, we repo...Show More
III-V FETs are in development for both THz and VLSI applications. In VLSI, high drive currents are sought at low gate drive voltages, while in THz circuits, high cutoff frequencies are required. In both cases, source and drain access resistivities must be decreased, and transconductance and drain current per unit gate width must be increased by reducing the gate dielectric thickness, reducing the ...Show More
We present the effect of active carrier concentration on the specific contact resistivity (ρc) of in-situ molybdenum (Mo) Ohmic contacts to n-type InAs. It is observed that, although the Fermi level pins in the conduction band for InAs, the contact resistivity decreases with the increase in InAs active carrier concentration. The lowest ρc obtained through transmission line model measurements was (...Show More
Abstract-We report Al2O3Zln0.53Ga0.47As MOSFETs having both self-aligned in situ Mo source/drain ohmic contacts and self-aligned InAs source/drain n+ regions formed by MBE regrowth. The device epitaxial dimensions are small, as is required for 22-nm gate length MOSFETs; a 5-nm In0.53Ga0.47As channel with an In0.4sAl0.52As back confinement layer and the n++ source/drain junctions do not extend belo...Show More
We report the effects of UV-ozone oxidation, oxide removal etch chemistry (dilute HCl or concentrated NH4OH), semiconductor doping, and annealing on the contact resistivity (rhoc) of Ti0.1W0.9 refractory alloy to n-type InGaAs. The semiconductor surface was oxidized through exposure to UV-ozone, then subsequently etched by either dilute HCl or concentrated NH4OH before TiW contacts were deposited ...Show More
A scalable, self-aligned In0.53Ga0.47As MOSFET process was developed and enhancement mode device operation was demonstrated. The 0.7 mum Lg device shows a maximum drive current of 0.14 mA/mum at Vgs=4.0 V and Vds=2.5 V. The devices have almost an order of magnitude larger drive current than our previously reported MOSFETs. The channel layer was 5 nm thick InGaAs with InAlAs bottom barrier for vert...Show More
Because of the low electron effective mass and the high resulting carrier velocities, we are developing InGaAs/InP MOSFETs for potential application in VLSI circuits at scaling generations beyond 22 nm. We will report device design, review gate dielectric growth processes, and describe in detail the development of process modules for fabrication of fully self-aligned enhancement-mode devices. Key ...Show More
Because of the low electron effective mass and the high resulting carrier velocities, we are developing InGaAs/InP MOSFETs for potential application in VLSI circuits at scaling generations beyond 22 nm. We will report device design, review gate dielectric growth processes, and describe in detail the development of process modules for fabrication of fully self-aligned enhancement-mode devices. Key ...Show More
We examine the feasibility of developing bipolar transistors with current-gain and power-gain cutoff frequencies of 1-3 THz. High bandwidths are obtained by scaling; the critical limits to such scaling are the requirements that the current density increase in proportion to the square of bandwidth and that the metal-semiconductor contact resistivities vary as the inverse square of device bandwidth....Show More
The first monolithic GaInNAsSb/GaNAs 1550-nm mode-locked lasers are reported on a GaAs substrate. A repetition rate of 5.8 GHz has been realized.Show More
An extremely low in situ metal contacts can be formed to (In,Ga)As on InP. it is also possible to form ultra low resistance ex situ contacts by improved surface treatment. However, unlike in situ contacts, ex situ contacts are very sensitive to surface preparation. Similar contact resistivities to InAs on GaAs were reported by Nittono et al. This is the first time such low metal-semiconductor cont...Show More