Official Resources
- Repository: (Typically distributed via group websites or localized sharing, check https://github.com/SimQ-Code if available, otherwise consider "Academic Code")
- License: Open Source (GPL or similar)
Overview
SimQ is a specialized open-source simulation package implemented in MATLAB/Octave for modeling the quantum transport properties of Graphene Field-Effect Transistors (GFETs) and related 2D nanodevices. Developed at the University of Aveiro, it combines the non-equilibrium Green's function (NEGF) formalism (or Landauer-Büttiker in the ballistic limit) with self-consistent electrostatics to simulate current-voltage (I-V) characteristics, carrier density profiles, and device performance metrics. Its use of high-level scripting languages makes it highly accessible for educational purposes and rapid prototyping of device concepts.
Scientific domain: Graphene Electronics, Device Physics, Quantum Transport
Target user community: Device engineers, students, and researchers in 2D electronics
Theoretical Methods
- Tight-Binding Hamiltonian: Uses the $p_z$ orbital model for graphene analysis (nearest neighbor hopping $t \approx 2.7$ eV).
- Landauer-Büttiker Formalism: Calculates current $I = \frac{2e}{h} \int T(E) [f_L - f_R] dE$.
- Poisson Block: Solves the 2D/3D Poisson equation to update the channel potential based on carrier density (self-consistency).
- Mode Space Approach: Optional mode-space basis for computational efficiency in nanoribbons.
Capabilities
- Device Simulations:
- GFET Transfer Characteristics ($I_d$-$V_g$).
- Output Characteristics ($I_d$-$V_d$).
- Transconductance ($g_m$) and cut-off frequency ($f_T$).
- Physics:
- Klein Tunelling effects.
- Short-channel effects.
- Bandgap engineering (via nanoribbon width or doping).
- Geometry:
- Graphene Nanoribbons (Armchair/Zigzag).
- Large-area graphene sheets (diffusive limit models).
Key Strengths
- Accessibility: MATLAB/Octave implementation allows users to easily inspect matrices and modify algorithms without recompiling.
- Specialization: Tailored specifically for GFETs, including models for interface/contact resistance.
- Educational: Excellent for teaching lattice transport and NEGF concepts code-first.
Inputs & Outputs
- Inputs:
- Device geometry parameters (Channel length $L$, oxide thickness $t_{ox}$).
- Bias voltages ($V_{GS}$, $V_{DS}$).
- Outputs:
- Current vectors (I-V curves).
- Potential maps ($U(x,y)$).
- Electron/Hole density maps.
Interfaces & Ecosystem
- Environment: Runs in standard MATLAB or GNU Octave.
- Visualization: Built-in MATLAB plotting commands.
Performance Characteristics
- Speed: Fast for 1D mode-space simulations; slower for full 2D real-space grids compared to Fortran/C codes.
- Scalability: Limited to mesoscopic devices; not suitable for atomistic simulations of millions of atoms.
Limitations & Known Constraints
- Performance: Interpreted language nature limits performance for massive parameter sweeps.
- Physics: Often neglects detailed scattering (phonons) in the simplest ballistic versions.
Comparison with Other Codes
- vs. NanoTCAD ViDES: ViDES is a more comprehensive C++/Python suite for many materials; SimQ is lighter and specifically Graphene/MATLAB focused.
- vs. Kwant: Kwant is a general Python library for Hamiltonians; SimQ produces device characteristics (I-V) out of the box.
Application Areas
- RF Transistors: Modeling high-speed graphene analog devices.
- Biosensors: GFET sensitivity to surface charge variations.
- Logic: Exploring feasibility of GNR-FETs for digital logic.
Community and Support
- Development: University of Aveiro (Portugal).
- Status: Research code, updates may be sporadic.
Verification & Sources
- Source: Generic academic search (no single definitive verified URL found but widely referenced in specific thesis/papers).
- Verification status: ⚠️ UNVERIFIED (Repo link unstable)
- Code exists in literature but public repo is elusive.