Search

We present a flexible, full-band, 3-D Monte Carlo (MC) modeling software package for charge transport in semiconductor devices. The numerical model can employ both analytical and full-band descriptions of the band structure simultaneously and uses unstructured meshes for device discretization that can be constructed with commonly available meshing tools. A numerical approach is also included to minimize the self-forces resulting from the unstructured mesh. The scattering rates are computed over a tetrahedral mesh, the refinement capabilities of which provide accurate rates near band minima and maxima. The efficient geometrical device discretization enables us to simulate devices that have traditionally been limited to drift-diffusion approaches due to the computational requirements of MC simulations. To highlight the capabilities of this tool, we present two simulation examples, a conical HgCdTe APD and a silicon trench MOS, both run with a superparticle charge of 1e. In addition to simulating the output characteristics of the trench MOS and the gain and excess noise factor of the APD, we investigate the injection location-dependent time response and corresponding diffusion tail.

A novel room-temperature negative differential resistance (NDR) effect is proposed, theoretically analyzed, and quantitatively modeled for short-wave infrared (SWIR) HgCdTe photodiode detectors in dense double-layer planar heterostructure arrays with a 2.5 $\mu \text{m}$ cutoff at 300 K. The predicted NDR results from nonequilibrium minority carrier suppression—with associated Auger suppression and negative luminescence—imposed by dense array geometry under uniform reverse bias. Using three-dimensional quantitative modeling, we evaluate representative dark current–voltage characteristics at different array pitch values. The predicted dark current and NDR resulting from structural variations in junction radius are consistent with the analytic dense array lateral diffusion current suppression model. The NDR effect and its relation to geometric parameters should be considered when attempting to minimize dark current in high-temperature SWIR HgCdTe photodiode arrays.

We discuss, through numerical device simulation, a number of possible design approaches intended for optimizing the internal quantum efficiency (IQE) of light-emitting diodes based on InGaN quantum wells (QWs) grown along the c-axis emitting in the near-ultraviolet region. We study the effects on IQE of thickness, doping, and alloy composition of the electron and hole blocking layers in order to maximize the confinement of both carrier species in the active region. We discuss the selection of the number of QWs to be employed in the active region and their optimum width, and we show the comparatively minor effects of the thickness of the barrier layers. We also compare different strategies for barrier doping, confirming that a p-type doping in all barriers helps to compensate the spontaneous and piezoelectric surface charges and to enhance hole transport. Finally, we evaluate the impact of Auger recombination on IQE and its role in the experimentally observed efficiency droop. Whenever possible, we suggest practical design criteria and provide technologically feasible sets of design parameters.

We present a comprehensive study of the transport dynamics of electrons in the ternary compounds, Al/sub x/Ga/sub 1-x/N and In/sub x/Ga/sub 1-x/N. Calculations are made using a nonparabolic effective mass energy band model. Monte Carlo simulation that includes all of the major scattering mechanisms. The band parameters used in the simulation are extracted from optimized pseudopotential band calculations to ensure excellent agreement with experimental information and ab initio band models. The effects of alloy scattering on the electron transport physics are examined. The steady state velocity field curves and low field mobilities are calculated for representative compositions of these alloys at different temperatures and ionized impurity concentrations. A field dependent mobility model is provided for both ternary compounds AlGaN and InGaN. The parameters for the low and high field mobility models for these ternary compounds are extracted and presented. The mobility models can be employed in simulations of devices that incorporate the ternary III-nitrides.

In this paper, we discuss the complexities that arise in Monte Carlo based modeling of noncubic symmetry semiconductors and their related devices. We have identified three general issues, band structure, scattering mechanisms, and band intersections that require some modification of the Monte Carlo simulator from that for cubic symmetry. Owing to the increased size and number of atoms per unit cell, the band structure is far more complex in noncubic than in zincblende phase semiconductors. This added complexity is reflected by the greater number of bands, smaller Brillouin zone and concomitant increase in the number of band intersections. We present strategies for modeling the effects of band intersections on the carrier dynamics using the Monte Carlo method. It is found that the band intersection points greatly affect the carrier transport, most dramatically in the determination of the impact ionization and breakdown properties of devices and bulk material. Excellent agreement with experimental measurements of the impact ionization coefficients is obtained only when treatment of the band intersections is included within the model.