VeGamen exploring art and history in Venice

To make exploring a locale's heritage a challenging and compelling experience, the Venice Game uses a handheld platform and educational software that leverages video game techniques.     

Using 3D Sound to Improve the Effectiveness of the Advanced Driver Assistance Systems

Future generation cars will be characterized by a wide range of Information Technology (IT) services providing safety and infotainment. This makes the car an information intensive environment where the visual channel is overloaded, putting the safety of drivers and passengers in jeopardy. We propose the use of a 3D auditory display to provide information from the Advanced Driver Assistance Systems. This reduces the eye-off-road time, exploiting the human capability to associate sounds with positions in space. Preliminary lab tests reveal the suitability of this approach. The system still has to be carefully tuned and personalized to achieve usability and reliability, but we think that it provides a complementary channel that is specially useful in low visibility conditions.     

User testing a hypermedia tour guide

Although handheld guides have been proposed as a way to enhance visitors' experience of museums and exhibitions, the authors describe user studies that actually test the theory in a real-world setting.     

Design Criteria for Near-Ultraviolet GaN-Based Light-Emitting Diodes

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.     

Full-Band Monte Carlo Simulation of HgCdTe APDs

A full-band Monte Carlo model has been developed for understanding the carrier multiplication process in HgCdTe infrared avalanche photodiodes. The proposed model is based on a realistic electronic structure obtained by pseudopotential calculations and a phonon dispersion relation determined by ab initio techniques. The calculated carrier–phonon scattering rates are consistent with the electronic structure and the phonon dispersion relation, thus removing adjustable parameters such as deformation potential coefficients. The computation of the impact ionization transition rate is based on the calculated electronic structure and the corresponding wavevector-dependent dielectric function. The Monte Carlo model is applied to investigate key performance figures of long-wavelength infrared (LWIR) and mid-wavelength infrared (MWIR) HgCdTe avalanche photodetectors such as carrier multiplication and noise properties. Good agreement is achieved between simulations and experimental results. The multiplication process in LWIR (λ _c = 9.0 μm at 80 K) and MWIR (λ _c = 5.1 μm at 80 K) devices is found to be initiated only by electrons, as expected from excess noise measurements. This single-carrier multiplication behavior can be traced back to the details of the computed valence-band structure and phonon scattering rates.     

A 2D Full-Band Monte Carlo Study of HgCdTe-Based Avalanche Photodiodes

This work presents a numerical simulation study of HgCdTe-based avalanche photodetectors (APDs). The two-dimensional model used is based on a full-band Monte Carlo approach in which the electronic structure is computed using a nonlocal empirical pseudopotential model with spin–orbit corrections. The carrier–phonon scattering rates have been computed from first principles using a rigid pseudo-ion model. The most attractive feature of these devices is the potential for single-carrier ionization when electrons are used as the primary injection carrier. For this reason, this work focuses on two front-illuminated (electron-injection) device structures: a planar diffused PIN structure and a planar diffused PN photodiode with guard rings. To predict the performance of these APDs, the electron multiplication gain has been studied as a function of the position where photogenerated carriers are injected and as a function of the curvature of the p-type diffusion region. We find that, in the diffused PIN structure, the limited lateral spatial extent of the high-electric-field region leads to a reduction of the multiplication gain from the center of the device to the periphery. Furthermore, the higher the curvature, the more abruptly the gain decreases. For the simple PN structure, we find that the presence of the guard rings removes the high electric field from the surface and induces a more gradual roll-off of the gain from the center of the device to the periphery.     

Design and development of multicolor MWIR/LWIR and LWIR/VLWIR detector arrays

Multicolor infrared (IR) focal planes are required for high-performance sensor applications. These sensors will require multicolor focal plane arrays (FPAs) that will cover various wavelengths of interest in mid wavelength infrared/long wavelength infrared (MWIR/LWIR) and long wavelength infrared/very long wavelength infrared (LWIR/VLWIR) bands. There has been significant progress in HgCdTe detector technology for multicolor MWIR/LWIR and LWIR/VLWIR FPAs.^1–3 Two-color IR FPAs eliminate the complexity of multiple single-color IR FPAs and provide a significant reduction of weight and power in simpler, reliable, and affordable systems. The complexity of a multicolor IR detector MWIR/LWIR makes the device optimization by trial and error not only impractical but also merely impossible. Too many different geometrical and physical variables need to be considered at the same time. Additionally, material characteristics are only relatively controllable and depend on the process repeatability. In this context, the ability of performing “simulation experiments” where only one or a few parameters are carefully controlled is paramount for a quantum improvement of a new generation of multicolor detectors for various applications.     

Intensity distortion induced by cross-phase modulation andchromatic dispersion in optical-fiber transmissions with dispersioncompensation

In dispersion compensated systems, the intensity distortion induced by the interplay between cross-phase modulation and fiber chromatic dispersion can be a primary cause of transmission degradation. This interplay is mostly studied by time-consuming computer simulations. This letter introduces a new model of this interplay in fiber transmissions with dispersion compensation, leading to a linear filter that, applied to the input intensity of a modulated interfering channel, gives the intensity distortion of a continuous-wave probe signal at the receiver. The model can be of significant value in the search for optimized dispersion maps     

Hydrodynamic transport parameters of wurtzite ZnO from analytic- and full-band Monte Carlo simulation

Analytic-band Monte Carlo simulation of electron transport in bulk wurtzite ZnO, validated against the results of a full-band code and available experimental data, is used to determine the main parameters required by drift-diffusion and hydrodynamic models. Steady-state drift velocity, carrier temperature, energy and momentum relaxation time, noise diffusivity, and electron thermal conductivity are calculated, and their dependence on temperature and electric field or average electron energy is approximated by means of a complete set of fitting models suitable for inclusion in commercial device simulation tools.