Comprehensive comparison and experimental validation of band-structure calculation methods in III\u2013V semiconductor quantum wells

We present and thoroughly compare band-structures computed with density functional theory, tight-binding, k p and non-parabolic effective mass models. Parameter sets for the non-parabolic C, the L and X valleys and intervalley bandgaps are extracted for bulk InAs, GaAs and InGaAs. We then consider quantum-wells with thickness ranging from 3 nm to 10 nm and the bandgap dependence on film thickness is compared with experiments for In0:53Ga0:47As quantum-wells. The impact of the band-structure on the drain current of nanoscale MOSFETs is simulated with ballistic transport models, the results provide a rigorous assessment of III\u2013V semiconductor band structure calculation methods and calibrated band parameters for device simulations

A full-quantum simulation study of InGaAs NW MOSFETs including interface traps

The interaction between strain and border traps in short-channel InGaAs NW MOSFETs is investigated through full-quantum 3D simulations based on a k·p Hamiltonian. Traps induce a sizable degradation of the ON-current, which can be recovered through the application of a suitable strain, provided the quantization effects, which increase by scaling the NW lateral size, do not become too large

Electron transport properties of diarylethene photoswitches by a simplified NEGF-DFT approach

A homemade program called FOXY has been used for the theoretical investigation on the conducting properties of two diarylethene based molecules, which, according to recent literature data, can act as photoswitches. FOXY uses a simplified method relying on NEGF theory coupled to DFT calculations and using a suitable electric field to mimic the bias voltage, together with a simple representation of the electrodes. The results confirm the experimental findings and are rationalized by analyzing the space extension of the pertinent molecular orbitals in the ON and OFF electronic states and confirm the FOXY program as a cheap and reliable code to be used in the field of molecular electronics

Transport properties of binuclear metal complexes of the VIII group using a simplified NEGF-DFT approach

We report on a theoretical study of the electronic transport properties of binuclear complexes of metals of the VIII group bridged by pyrazine. Metal-porphyrazine units have been combined in order to investigate symmetric and non-symmetric species with particular focus on their current rectification properties. Transmission functions and I-V characteristics of the various species have been computed using a Non-Equilibrium Green Function with a simplified treatment of the molecule-lead interaction. The results obtained show an overall moderate asymmetry in the current along the molecules, which is of the donors- acceptor type and follow the trend of the ionization potential of the metals in the binuclear system. The bias-dependent rectification ratio, which is significant in a limited voltage window, can be explained in terms of the alignment of the occupied orbitals of the metallic fragments that contribute to the HOMO and HOMO - 1 of the supermolecule. The possible improvement of the rectification performance of such a class of molecules has also been investigated exploiting suitable substitution by electron-withdrawing groups

Design guidelines for GaSb/InAs TFET exploiting strain and device size

A simulation study exploring the possibility of performance improvements for GaSb/InAs nanowire TFETs under appropriate stress conditions is carried out. It is demonstrated that biaxial tensile strain induces a remarkable enhancement of the on-state current thanks to bandgap reduction; however, a degradation of the ambipolar behavior is observed as well. Some stress intensity values and device geometry configurations are investigated. The best simulated device can achieve an on/off current ratio of about 3 7107 with ION 480.33 mA/\u3bcm at VDD=0.3 V

Impact of strain and interface traps on the performance of III-V nanowire TFETs

The impact of strain and semiconductor/oxide interface traps (ITs) on the turn-on characteristics of a 10x10 nm^2 nanowire (NW) Al0.05Ga0.95Sb/InAs heterojunction n-type tunnel field-effect transistor (TFETs) is carefully investigated using a full-quantum simulator. In order to capture the effect of traps on the device electrostatics in a way consistent with the ballistic approach, the SRH theory has been properly generalized. Our results indicate that the presence of a relatively high IT density can cause a huge current reduction that cannot be recovered exploiting strain. In fact, biaxial tensile strain induces a remarkable current enhancement due to bandgap reduction and tunnel energy alignment at the heterojunction; however, a huge degradation of the ambipolar behavior is also observed

Impact of Traps and Strain on Optimized n- and p-Type TFETs Integrated on the Same InAs/AlGaSb Technology Platform

A simulation study on the impact of interface traps and strain on the I - V characteristics of co-optimized p- and n-type tunnel FETs (TFETs) realized on the same InAs/Al0.05Ga0.95Sb technology platform is carried out, using a full-quantum ballistic simulator. In order to capture the effect of interface/border traps on the device electrostatics consistently with carrier degeneracy and ballistic transport, the classical Shockley-Read-Hall theory has been properly generalized. The effect of an experimental Dit distribution of a high-k gate stacks on InAs has been investigated. Unfortunately, traps induce a significant reduction of the ON-state current. However, it turns out that localized strain at the source/channel heterojunction caused by lattice mismatch is able to induce for the n-type TFET, a performance enhancement with respect to the ideal device even in the presence of traps. On the contrary, for the p-type one, a current degradation \ue2\u89\u83 18 % is observed

Impact of Strain on Tunneling Current and Threshold Voltage in III-V Nanowire TFETs

A simulation study on the effects of different strain configurations on n-type III-V-based nanowire tunnel-FETs is presented, with the aim to determine optimal strain conditions to enhance device performance. We find that both the biaxial tensile and the uniaxial compressive stress shift up the valence band. Biaxial stress, however, lowers the conduction band as well, thus providing the largest reduction of the energy bandgap. Instead, the gap variation is limited for the biaxial compressive and uniaxial tensile strains. Moreover, for these strain conditions, the lowest conduction subband is not connected to the highest valence subband via the imaginary wave vector but to a lower one. This leads to an effective bandgap higher than the expected, which reflects into a large threshold increase and a degradation of the ON-state current

Electron Transport Properties of Diarylethene Photoswitches by a Simplified NEGF-DFT Approach

A homemade program called FOXY has been used for the theoretical investigation on the conducting properties of two diarylethene based molecules, which, according to recent literature data, can act as photoswitches. FOXY uses a simplified method relying on NEGF theory coupled to DFT calculations and using a suitable electric field to mimic the bias voltage, together with a simple representation of the electrodes. The results confirm the experimental findings and are rationalized by analyzing the space extension of the pertinent molecular orbitals in the ON and OFF electronic states and confirm the FOXY program as a cheap and reliable code to be used in the field of molecular electronics