Gregory B. Tait

Efficient transferred electron device simulation method for microwave and millimeter wave cad applications

Abstract A set of hydrodynamic transport equations, which govern a physical model for GaAs transferred electron devices, are formulated using phenomenological transport parameters derived from large scale Monte Carlo particle simulations. A fast and efficient numerical solution method is developed, allowing inexpensive and systematic investigations of a wide variety of TED samples under many operating conditions. The method not only permits insight into important semiconductor transport processes, but also permits the identification of candidate device samples for microwave and millimeter wave circuit applications.

Electron transport in rectifying semiconductor alloy ramp heterostructures

The electron transport properties of AlGaAs ramp diodes are investigated using a physical model which combines current transport through the heterostructure bulk with current across the abrupt heterointerface in a fully self-consistent numerical approach. Transport at the abrupt material discontinuity is described by thermionic and thermionic-field emission processes, whereas transport in regions of smoothly varying alloy composition is modeled by diffusion-drift mechanisms. Several devices whose bandgaps are graded over several thousand angstroms have been fabricated by molecular beam epitaxy (MBE) and tested at room and liquid-nitrogen temperatures. The experimentally observed rectification properties are compared with the simulated results over a wide range of DC bias. Through appropriate choice of alloy composition and doping profiles, majority carrier devices based on internal (bulk) barriers may be realized. >

Determination of transport parameters for InP device simulations in n+n+ structures

Abstract Phenomenological transport parameters in n-InP are derived from large scale, ensemble Monte Carlo particle simulations. These parameters are required in efficient numerical methods used to solve “hydrodynamic-like” transport formulations which govern various physical models of bulk, unipolar InP devices. For an equivalent single-valley conduction band, a set of transport parameters in n-InP at 300 K is calculated from the Monte Carlo data. An example of the use of these parameters in a numerical simulation code is provided.

Heterostructure semiconductor device analysis: A globally convergent solution method for the nonlinear poisson equation

Abstract A solution method for the nonlinear Poisson equation used in numerical modeling of III–V compound semiconductor heterostructures is presented. The method is based on a nonlinear iterative algorithm and is shown to be globally convergent and suitable for implementation on a computer with small main memory capacity. The rate of convergence also makes the solution method computationally efficient. As an application example, the equilibrium energy band diagram of a GaAs/AlGaAs double heterojunction bipolar transistor is calculated, and computer experiments are performed in order to demonstrate the convergence properties of the algorithm.

Large-signal characterization of unipolar III-V semiconductor diodes at microwave and millimeter-wave frequencies

Large-signal characterizations are performed for n-GaAs and n-InP diodes operating in oscillator circuits at microwave and millimeter-wave frequencies. A CAD approach, consisting of a physical device model and an efficient numerical solution method, is used to analyze several sample diode structures with different material properties and geometries. The large-signal simulation results are reported for X-band and Q-band diodes, and are found to correlate well with results obtained from both laboratory experiment and large-scale ensemble Monte Carlo calculations. >

High Frequency Semiconductor Heterostructure Device Analysis

Two-terminal heterostructure diodes present many potential opportunities for high frequency operation, even into the millimeter wave frequency regime. Motivated by this fact, we have developed an algorithm which is globally convergent for solving the nonlinear Poisson equation. By appropriate numerical techniques, the nonlinear Poisson equation is coupled to the current continuity equations which can then be employed for high frequency, small signal, ac simulations. Numerical results for the AlyGa1-yAs system with layers as thin as a few hundred angstroms in thickness are provided.

High-frequency simulation of semiconductor alloy ramp heterostructures

A small-signal AC transport description is formulated to characterize the high-frequency operation of unipolar semiconductor heterostructures. The physical transport model combines diffusion-drift currents through compositionally graded regions with a thermionic-emission current imposed at an abrupt material interface. This sinusoidal steady-state analysis can be employed to determine the dynamic terminal admittance of devices at microwave frequencies and cryogenic temperatures. Al/sub x/Ga/sub 1-x/As alloy ramp heterostructures have been fabricated by molecular beam epitaxy and tested over wide ranges of temperature, DC bias, and frequency. Experimentally measured microwave admittances compare favorably with simulated results at room and liquid-nitrogen temperatures and are used to verify the theoretical approach. >