Showing papers by "Enrico Bellotti published in 2011"
TL;DR: In this article, the authors investigated the combined electromagnetic and electrical response of HgCdTe-based pixel detector arrays with different geometries and computed the propagation of the optical signal in the detector structure by solving Maxwell's curl equations using a finite-difference time-domain approach.
Abstract: We have investigated the combined electromagnetic and electrical response of HgCdTe-based pixel detector arrays with different geometries. We have computed the propagation of the optical signal in the detector structure by solving Maxwell’s curl equations using a finite-difference time-domain approach. From the field distribution inside the device, we have evaluated the optical carrier generation rate. Using this information in a three-dimensional (3D) numerical model based on a drift–diffusion approach, we have computed the quantum efficiency and photoresponse of a number of pixel geometries. Specifically, we have analyzed the response of both mesa-type and planar detector arrays with and without CdZnTe substrate. Furthermore, the electromagnetic response has also been evaluated for different metal contact dimensions and configurations. It is found that, for mesa-type arrays without the substrate, significant reflection effects take place in the device that lead to resonance peaks in the photoresponse.
34 citations
TL;DR: In this paper, a 2D numerical simulation is employed to assess a number of possible design approaches aimed at optimizing the internal quantum efficiency (IQE) of ZnO-based light-emitting diodes (LEDs) grown along the c-axis.
Abstract: 2-D numerical simulation is employed to assess a number of possible design approaches aimed at optimizing the internal quantum efficiency (IQE) of ZnO-based light-emitting diodes (LEDs) grown along the c-axis. First, the relative performance of similar ZnO-based and GaN-based LED structures is compared and discussed. Second, the effects on IQE of thickness, doping, and alloy composition of the MgZnO electron blocking layer (EBL) is studied in order to maximize the carrier confinement in the active region. The optimum number of quantum wells is also addressed, and different strategies for barrier doping are considered, showing that, if the EBL is doped p-type, a similar doping in the barriers is not required to compensate for the spontaneous and piezoelectric interface charges and to enhance hole transport. Different choices of the geometrical and doping parameters of the n-type access region are considered, and the impact of different values of the electron mobility is determined. Finally, the analysis of a ZnO/BeZnO LED structure suggests that the incorporation of BeZnO layers does not provide significant advantages.
30 citations
TL;DR: In this article, band-to-band Auger recombination mechanisms in HgCdTe are investigated as functions of temperature in the small modulation limit by using realistic electronic structures obtained by empirical pseudopotential calculations and their corresponding wavevector-dependent dielectric functions.
Abstract: Band-to-band Auger recombination mechanisms in HgCdTe are investigated as functions of temperature in the small modulation limit by using realistic electronic structures obtained by empirical pseudopotential calculations and their corresponding wavevector-dependent dielectric functions. The calculated Auger lifetimes are compared with the semiempirical Beattie-Landsberg-Blakemore (BLB) model, which has been extensively employed to reproduce experimental data. The Auger-1 lifetime can be fitted well to the BLB model with a constant overlap integral |F
1
F
2| = 0.16, near the lower limit of the range reported in the literature. The role of the Auger-7 process in p-type HgCdTe is also investigated and the ratio γ between the intrinsic Auger-7 and Auger-1 lifetimes is found to be about 10.
22 citations
TL;DR: In this paper, a numerical simulation study of HgCdTe-based avalanche photodetectors (APDs) is presented, where the electronic structure is computed using a nonlocal empirical pseudopotential model with spin-orbit corrections.
Abstract: 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.
8 citations
TL;DR: In this article, the performance of GaN-based avalanche photodetectors using an ensemble Monte Carlo method was analyzed using the full band structure derived from nonlocal empirical pseudopotential calculations.
Abstract: This paper presents a theoretical study of the performance of GaN-based avalanche photodetectors using an ensemble Monte Carlo method. The model includes the details of the full band structure derived from nonlocal empirical pseudopotential calculations. Carrier-phonon and impact ionization scattering rates are obtained from the calculated electronic structure and from a first-principles study of the lattice dynamics. Multiplication gain, noise and bandwidth properties of back- and front-illuminated structures are evaluated by means of full band Monte Carlo simulation for different crystal orientations and multiplication region thicknesses. The simulation results indicate that hole injection in devices grown along the Γ-A direction provides the most favorable operating condition in terms of gain and noise. Finally, gain saturation effects due to electric field screening induced by photogenerated carriers are discussed.
8 citations
10 Oct 2011
TL;DR: In this article, the authors investigated the combined electromagnetic and electrical response of HgCdTe-based pixel detector arrays with different geometries and computed the propagation of the optical signal in the detector structure by solving Maxwell's curl equations using a finite-difference time-domain approach.
Abstract: We have investigated the combined electromagnetic and electrical response of HgCdTe based pixel detector arrays with different geometries. We have computed the propagation of the optical signal in the detector structure by solving Maxwell's curl equations using a finite-difference time-domain approach. From the field distribution inside the device, we have evaluated the optical carrier generation rate. Using this information in a 3D numerical model based on drift-diffusion, we have computed the quantum efficiency and photo-response of a number of pixel geometries. Specifically, we have analyzed the response of both mesa type and planar detector arrays with and without CdZnTe substrate. Furthermore, the electromagnetic response has also been evaluated for different metal contact dimensions and configurations. It is found that for mesa type arrays without the substrate, significant reflection effects take place in the device that lead to resonance peaks in the photo-response.
5 citations
TL;DR: The 13th International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD) was held at the University of British Columbia, Canada and Joachim Piprek, NUSOD Institute, USA.
Abstract: This special issue ofOptical andQuantumElectronics contains a selection of papers that were presented at the 13th International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD) in Vancouver, Canada, August 19–22 2013. NUSOD’13 was chaired by Lukas Chrostowski from the University of British Columbia, Canada and Joachim Piprek, NUSOD Institute, USA. The purpose of the NUSOD Conference is to provide a forum for scientists from research labs around the world to discuss the recent advances in the modelling of optoelectronic devices. This year the main topics included numerical modelling of light emitting diodes, photo-detectors, photonic crystal fibres, propagation of ultra-short optical pulses, photovoltaic and optical integrated devices. The papers collected in this special issue of Optical and Quantum Electronics provide a comprehensive representation of the topics discussed at the conference. The editorswish to thank all contributing authors for careful preparation of themanuscripts and the reviewers for their work and timely response. We now look forward to NUSOD’14 that will take place in Palma de Mallorca, Spain, September 1–4, 2014.
1 citations
01 May 2011
TL;DR: In this article, the subpicosecond kinetics of photoexcited carriers in bulk gallium nitride were studied and the theoretical results were compared with the experimental results of the time-resolved photoluminescence induced by a 100-femtosecond pulse.
Abstract: We present a study of subpicosecond kinetics of photo-excited carriers in bulk gallium nitride. The theoretical results are compared with the experimental results of the time-resolved photoluminescence induced by a 100-femtosecond pulse.