R.C. Block

Distribution of radial energy deposition around the track of energetic charged particles in silicon

The distribution of radial energy deposition around the track of carbon, aluminum, and iron ions with energy range from 10 MeV to 10 GeV inside silicon was calculated. A simple and direct approach was developed utilizing a corrected semianalytical model. The results of the present work agree very well with Monte Carlo calculations as well as stopping power tables.

Numerical simulation of heavy ion charge generation and collection dynamics

Describes a complete simulation approach to investigating the physics of heavy-ion charge generation and collection during a single event transient in a p-n diode. The simulations explore the effects of different ion track models, applied biases, background dopings and LET (linear energy transfer) on the transient responses of a p-n diode. The simulation results show that ion track structure and charge collection via diffusion-dominated processes play important roles in determining device transient responses. The simulations show no evidence of rapid charge collection in excess of that deposited in the device depletion region in typical funneling time frames. Further, the simulations clearly show that the device transient responses are not simple functions of the ions incident LET. The simulation results imply that future studies should consider the effects of ion track structure and extend transient charge collection times to insure that reported charge collection efficiencies include diffusion-dominated collection processes. >

The effects of ion track structure in simulating single event phenomena

This paper describes a first order model for simulating single event phenomena using a three-dimensional device simulator. The importance of track structure effects and linear energy transfer (LET) in determining device transient current and charge collection is demonstrated.<<ETX>>

High energy heavy-ion-induced single event transients in epitaxial structures

This paper describes numerical and experimental heavy-ion charge collection studies using P/sup +/N junctions on epitaxial layers. The numerical simulations provide insights into the basic mechanisms contributing to transient currents and charge collection in devices on epitaxial layers. This paper also presents charge collection data from /spl sim/2 GeV /sup 127/I ions incident upon P/sup +/N junctions on both bulk silicon and epitaxial layers and compares the experimental data with the simulation results. The experimental data show that charge deposited below the epitaxial layer can be collected. This work is unique and important because this GeV-energy-range /sup 127/I ion more nearly represents a cosmic ray compared to lower energy, heavy-ions in the hundreds of MeV energy range. This paper also discusses the simulation results with respect to the experimental data and charge collection models for epitaxial transistors. Additionally, a shunting model is proposed to model the early transient current responses. >

An extended ambipolar model: Formulation, analytical investigations, and application to photocurrent modeling

An extended development of the ambipolar transport equation is presented with a thorough investigation of the commonly omitted terms and conventional approximations. An analytical technique of integrating the fully inclusive steady‐state ambipolar equation is reported. This technique can yield closed form solutions for the frequently used recombination functions (Shockley–Read–Hall, band‐to‐band, and/or Auger models) that describe electron‐hole recombination in indirect or direct band‐gap semiconductors. The ensuing results are potentially applicable to many areas of current research. One such application is demonstrated by constructing a model for the photocurrent response of the reverse‐biased silicon p‐n junction in the presence of uniformly imposed external generation of excess carriers. The model is found to be in excellent agreement with numerical simulations. The extended ambipolar equation is shown to significantly improve the ability to model the current response due to excess carriers. Terms tha...

A novel approach for measuring the radial distribution of charge in a heavy-ion track

We describe the design and uses of possible semiconductor test structures for measuring the initial radial distribution of charge and subsequent charge transport in a high energy, heavy-ion track. Numerical simulations show how the test structure can resolve different radial distributions of charge within an ion track. The test structure simulations also show the importance of accurately representing ion track structure in single event effects simulations. >

Photocurrent modeling at high dose rates

An analytical steady-state photocurrent model that includes ohmic field effects and treats (nonlinear) ambipolar diffusion and nonlinear recombination effects explicitly is developed. The nonlinear recombination and ambipolar diffusion are solved exactly, and the asymptotic ohmic field is treated as an approximate perturbation with fitted parameters. The model is found to be in good agreement with numerical calculations and with experimental results. Appropriate Taylor series expansions and extensive parametric studies using the model indicate that the superlinear response is largest and occurs at smaller dose rates in relatively high-resistivity materials that have a long excess carrier lifetime and, if the material is n-type, a large tau /sub no// tau /sub po/ ratio. The nonlinearity is more pronounced for infinite-medium devices. For this reason, power devices are expected to exhibit more nonlinear behavior than integrated circuit devices. >

A new method for using /sup 252/Cf in SEU testing (SRAM)

A system using /sup 252/Cf and associated nuclear instrumentation has determined the single-event upset (SEU) cross section versus linear energy transfer (LET) curve for several 2 K*8 static random access memories (SRAMs). The /sup 252/Cf fission fragments pass through a thin-film organic scintillator detector (TFD) on the way to the device under test (DUT). The TFD provides energy information for each transiting fragment. Data analysis provides the energy of the individual ion responsible for each SEU; thus, separate upset cross sections can be developed for different energy and mass regions of the californium spectrum. This californium-based device is quite small and fits onto a bench top. It provides a convenient and inexpensive supplement or alternative to accelerator and high-altitude/space SEU testing. >

High-energy heavy-ion-induced charge transport across multiple junctions

High-energy heavy ion experiments and numerical simulations show that two or more junctions bridged by an ion track respond in a coupled manner. The potential difference across the structure strongly affects the amount of charge collected at each of the junctions. Experiments with 1.7 GeV /sup 197/Au ions indicate that, for emitter biases less than or equal to 0.0 volts and potential differences of 5 or more volts, more charge may be collected at a junction than was initially deposited by the ion. Simulations show that, when an ion track intersects multiple junctions of a device, the responses of the individual junctions cannot be modeled independently of each other. Simulation and experimental results indicate that charge transport in a multiple junction structure cannot be modeled using simple geometry or funneling assumptions.

SEU tests with an improved Cf-252 system

An improved Cf-252 single event upset (SEU) testing system is described. The improved system has a greater range of linear energy transfer (LETs) and has a rotating platform that can test devices at different angles with respect to the beam of fission fragments. The quality of the fission fragment detector is also improved. Better SEU results of a 2k/spl times/8 SRAM have been obtained and confirmed those obtained with an accelerator.<<ETX>>