[Paper Review] Quantum Transport Simulation of III-V TFETs with Reduced-Order K.P Method

Jun Huang, Lining Zhang+3 more|arXiv (Cornell University)|Nov 8, 2015

Advancements in Semiconductor Devices and Circuit Design4 citations

TL;DR

This paper presents a reduced-order k⋅p method combined with non-equilibrium Green's function (NEGF) simulations to enable efficient 3D quantum transport modeling of III-V tunneling FETs. The approach achieves high accuracy with significantly reduced computational cost, enabling systematic optimization of InAs homojunction and GaSb/InAs heterojunction nanowire TFETs across channel orientation, doping, strain, and source-pocket engineering, with heterojunctions showing up to 10× higher on-current than homojunctions.

ABSTRACT

III-V tunneling field-effect transistors (TFETs) offer great potentials in future low-power electronics application due to their steep subthreshold slope and large "on" current. Their 3D quantum transport study using non-equilibrium Green's function method is computationally very intensive, in particular when combined with multiband approaches such as the eight-band K.P method. To reduce the numerical cost, an efficient reduced-order method is developed in this article and applied to study homojunction InAs and heterojunction GaSb-InAs nanowire TFETs. Device performances are obtained for various channel widths, channel lengths, crystal orientations, doping densities, source pocket lengths, and strain conditions.

Motivation & Objective

• To address the high computational cost of 3D multi-band quantum transport simulations in III-V TFETs using NEGF with eight-band k⋅p Hamiltonians.
• To develop a reduced-order k⋅p method that maintains accuracy while drastically lowering simulation time for complex nanowire TFET structures.
• To enable systematic performance optimization of III-V TFETs across design parameters such as channel orientation, doping, strain, and heterostructure engineering.
• To validate the method against tight-binding benchmarks and demonstrate its accuracy in predicting I-V characteristics and band structures.
• To explore performance-enhancing strategies like source pockets and strain in GaSb/InAs heterojunction TFETs for low-power applications.

Proposed method

• A multi-point expanded reduced-order k⋅p model is constructed to replace the full eight-band k⋅p Hamiltonian, reducing matrix size and computational load.
• The method employs matrix rotations and discretization in mixed real and spectral space to preserve band structure accuracy near the band gap.
• A spurious band elimination procedure is introduced to remove unphysical bands arising from multi-point expansion, ensuring physical consistency.
• The reduced-order k⋅p Hamiltonian is coupled with the non-equilibrium Green's function (NEGF) formalism for quantum transport simulation.
• Simulations are performed on gate-all-around InAs and GaSb/InAs nanowire TFETs with varying cross-sections, orientations, and device parameters.
• Benchmarking is conducted by comparing band structures and I-V curves against tight-binding simulations to validate accuracy and efficiency.

Experimental results

Research questions

• RQ1 How can the computational cost of 3D multi-band quantum transport simulations in III-V TFETs be reduced without sacrificing accuracy?
• RQ2 What is the optimal crystal orientation ([100], [110], [111]) for maximizing on-current and scaling performance in InAs nanowire TFETs?
• RQ3 How do source-pocket doping and heterojunction engineering affect the on-current and subthreshold swing in GaSb/InAs TFETs?
• RQ4 What is the impact of uniaxial strain on the performance of heterojunction TFETs in different crystal orientations?
• RQ5 Can the reduced-order k⋅p method accurately reproduce the I-V characteristics and band structures of complex TFETs compared to tight-binding methods?

Key findings

• The [111] crystal orientation exhibits the best cross-section scaling ability in InAs homojunction TFETs, enabling superior performance in narrow nanowires.
• Heterojunction GaSb/InAs TFETs achieve approximately 10× higher on-current than homojunction InAs TFETs due to favorable staggered-gap band alignment reducing tunneling barrier height and distance.
• Source-pocket doping improves on-current by up to 200 μA/μm, with an optimal pocket length of around 4 nm beyond which performance saturates or degrades.
• Uniaxial compressive strain enhances on-current most effectively in the [100] orientation, while it degrades performance in [111] due to increased effective mass.
• The reduced-order k⋅p NEGF method achieves high accuracy in band structure and I-V prediction with significantly reduced simulation time compared to full k⋅p or tight-binding approaches.
• The spurious band elimination procedure successfully removes unphysical bands introduced by multi-point expansion, ensuring reliable simulation results.