Modeling of InGaAs/AlGaAsSb avalanche photodiodes (APDs) is presented in this work. Based on a drift-diffusion theory, the APD dark- and photo-current and multiplication gain are simulated. The frequency response and bandwidth are also computed based on a derived formalism by following the carrier transit analyses. Modeling results of I-V curves, multiplication gain, breakdown voltage, excess noise factor, -3dB bandwidth and gain-bandwidth product are demonstrated. Some results are compared with the experimental report. The APD performance is further evaluated with respect to two of the key design factors, the multiplication and the absorption layer thickness, respectively.
In this paper, the optical problem of the Vertical Cavity Surface Emitting Laser (VCSEL) is analyzed in details. Taking advantage of the VCSEL layer structure, Maxwell’s equation is discretized on uniform Yee grid, and the rigorous full vectorial Finite Difference Frequency Domain (FDFD) method was used to formulate and solve the complex eigenvalue problem. The full vectorial solver is well suited for the fundamental as well as the higher-order modes and includes different field polarization. The method is demonstrated for advanced VCSEL incorporating the surface reliefs and the oxide layer. In order to compare with the experimental structure, a superposition of the VCSEL modes is used to construct the Linearly Polarized (LP) mode.
Modeling of waveguide AlInAs avalanche photodiodes is reported in this work. Based on beam propagation method analyses, the waveguide design and evanescent coupling are investigated at first. The APD dark- and photo-response and multiplication gain are further simulated based on a drift-diffusion method. The frequency response and bandwidth are also evaluated based on carrier transit analysis formalism. Modeling results of I-V curves, multiplication gain, breakdown voltage, excess noise factor, -3dB bandwidth and gain-bandwidth product are presented with some consistently compared with reported experimental demonstration.
In this work, two-dimensional modeling of planar junction AlInAs avalanche photodiodes is reported. Modeling results of dark/photo current, multiplication gain, breakdown voltage, -3dB bandwidth and gain-bandwidth product, and excess noise etc., are presented. The modeling results of multiplication gain and -3dB bandwidth are consistent with the reported experimental demonstration. Design optimization is also explored for high gain-bandwidth product for such AlInAs avalanche photodiodes.
Three-dimensional (3D) modeling is reported for CMOS active pixel image sensors particularly by comparing front surface and back-surface illumination. The opto-electronic responses are presented versus various power intensity and illumination wavelength. The optical efficiency and quantum efficiency from FDTD modeling are also presented. For appropriately designed sensor structure, it is shown that back-surface illumination pixel could achieve improved sensitivity within certain wavelength range. The presented results demonstrate a methodological and technical capability for 3D modeling optimization of complex CMOS image sensor.
Comprehensive electro-opto and thermal analysis on GaSb-based vertical-cavity surface-emitting lasers (VCSELs)
emitting at 2.6μm are presented. The theoretical models include a 2D/3D drift-diffusion equations for carrier
transport coupled with the optical model which describes the spontaneous noise as the driving force for lasing.
Optical gain is obtained by Fermi’s golden rule and the self-consistent solution of Schrodinger equation. Self-
heating effects of the device are also included self-consistently. These results shed light on the internal device
physics such as carrier transport, temperature ditribution, optical gain and losses etc. Based on the simulation,
we also discuss the areas for future improvements.
Based on Crosslight APSYS, we have made 2D simulation of dual and triple junction solar cells based on CdZnTe and
CdTe material system on Si substrate with tunnel junctions. The basic physical quantities like band diagram, optical
absorption and generation for these solar cells, and external quantum efficiency for individual subcell junctions of triple
junction solar cells are obtained. Current matching analyses and multi-sun concentration simulation are also performed.
The modeling shows efficiency 28.85% (one sun AM1.5G) for CdZnTe/Si dual junction solar cells and efficiency
34.92% (one sun AM1.5G) and maximum 39.09% (multi-sun concentration around 500-700 suns) for CdZnTe/CdTe/Si
triple junction solar cells. The presented results indicate that the dual and triple junction solar cells with II-VI CdZnTe
and CdTe on Si can achieve efficiency comparable to those III-V based compound on Ge substrate.
Based on Crosslight APSYS, single junction ZnTe/CdSe, CdZnTe/CdSe and CIGS/CdS solar cells as well as
CdZnTe(CdSe)/CIGS tandem cells are modeled. Basic physical quantities like band diagrams, optical absorption and
generation are obtained. Quantum efficiency and I-V curves are presented. The results are discussed with respect to the
interface recombination velocity and the related material defect trap states for ZnTe/CdSe single junction solar cells and
the top TCO layer affinity for tandem cells. The projected efficiency obtained is 28% for one of the modeled twoterminal
tandem cells. The modeling results give possible clues for developing CdZnTe(CdSe)/CIGS tandem solar cells
with increased efficiency.
Based on Crosslight APSYS, thin film amorphous Si (a-Si:H)/microcrystalline (μc-Si) dual-junction (DJ) and a-
Si:H/amorphous SiGe:H (a-SiGe:H)/μc-Si triple-junction (TJ) solar cells are modeled. Basic physical quantities like
band diagrams, optical absorption and generation are obtained. Quantum efficiency and I-V curves for individual
junctions are presented for current matching analyses. The whole DJ and TJ cell I-V curves are also presented and the
results are discussed with respect to the top surface ZnO:Al TCO layer affinity. The interface texture effect is modeled
with FDTD (finite difference time domain) module and results for top junction are presented. The modeling results give
possible clues to achieve high efficiency for DJ and TJ thin film solar cells.
In this work, based on the advanced drift and diffusion theory with improved tunneling junction model, two-dimensional
modeling for the GaInP/GaAs/Ge and the inverted-grown metamorphic GaInP/GaAs/GaInAs triple-junction solar cells
are performed by using a commercial software, the Crosslight APSYS. Basic physical quantities like band diagram,
optical absorption and generation are obtained and characteristic results such as I-V curves, current matching, fill factor,
efficiency etc under one-sun and multi-sun illumination are presented. Some of the modeling results generally agree with
the published experimental results for both TJ cells. Comparative analyses are made with these two TJ cells and
optimization approaches are discussed with respect to minority carrier lifetime, front anti-reflection coating, and top
contact grid size and spacing.
In this work, based on the advanced drift and diffusion model with commercial software, the Crosslight APSYS, twodimensional
photoresponsivity behavior for the InP/InGaAs separate absorption, grading, charge and multiplication
avalanche photodiodes have been modeled to analyze suppressing premature edge breakdown. Basic physical quantities
like band diagram, photon absorption, carrier generation and electric field as well as performance characteristics such as
photocurrent, multiplication gain, and breakdown voltage etc., are obtained and selectively presented. Modeling results
indicate that an etched mesa structure with the charge sheet layer can effectively suppress the premature edge breakdown
in the device periphery region. Optimization modeling results with mesa step height are also demonstrated. Approach to
model complex guard ring structure with double diffusion is further explored. Possible combination of Crosslight
CSuprem diffusion profile is also discussed.
Based on Crosslight APSYS, two-dimensional simulations have been performed on Si-based solar cell devices especially
those with V-grooved surface texture. These Si-based solar cells include rear-contacted cells and passivated emitter, rear
totally diffused cells etc. The APSYS simulator is based on drift-diffusion theory with many advanced features. It can
enable an efficient computation across the whole solar spectra by taking into account the effects of multiple layer optical
interference and photon generation. The integrated ray-tracing module can compute optical absorption through the
complex texture surface with multiple antireflection coating layers. Basic physical quantities like band diagram, optical
absorption and generation can be demonstrated. The I-V characteristics with short-circuit current density and open-circuit
voltage agree with the published experimental results and enhanced cell efficiency is shown with the V-grooved
texture. The results are analyzed with respect to surface recombination, antireflection coating, bulk doping/resistivity and
lifetime etc. Modeling capabilities for polycrystalline silicon and amorphous silicon cells are also discussed.
Based on the advanced drift-diffusion simulator, the Crosslight APSYS, InGaAs/AlGaAs resonant cavity enhanced
separate absorption charge and multiplication APDs for high bit-rate operations have been modeled. The APSYS
simulator is based on drift-diffusion theory with many advanced features. Basic physical quantities like band diagram,
optical absorption and generation are calculated. Performance characteristics such as dark current and photocurrent,
multiplication gain, breakdown voltage, photoresponsivity, quantum efficiency, impulse response and bandwidth etc.,
are presented. The modeled results of multiplication gain and bandwidth are comparable to the experimental. The results
are also discussed with respect to some applicable features of Crosslight APSYS.
We extended the theory by Henry  to accurately treat the coupling of spontaneous emission noise with microcavity modes. The
Green's function method is employed to solve the inhomogeneous wave equation including a Langevin force f&comega; which accounts for
spontaneous emission by carriers at angular frequency &comega;. The optical wave equation is coupled with the self-consistent calculations of the material spontaneous emission rate of quantum well/dot using envelope wavefunction method. Finally the carrier transport equations are solved within the framework of 2D/3D drift-diffusion model implemented in the Crosslight Software package APSYS
. The simulation results of a GaN based resonant-cavity light-emitting diode (RC-LED) showed that our models can
be used to predict the characteristics of RC-LED.
In this work, based on the advanced commercial software, the Crosslight APSYS with improved tunnel junction model, two-dimensional (2D) simulation has been performed on the triple-junction (TJ) GaInP/GaAs/Ge solar cell devices. The APSYS simulator solves several interwoven equations including the basic Poisson's equation, and drift-diffusion current equations for electrons and holes. The model of tunnel junction with the equivalent mobility enables an efficient modeling of multi-junction solar cell across the whole solar spectra, where all the spectrum data points are processed by taking into account the effects of multiple layer optical interference and photon generation. Basic physical quantities like band diagrams, optical absorption and generation are demonstrated. The modeled IV characteristics and offset voltage agree well with the published experimental results for TJ GaInP/GaAs/Ge solar cell device. The quantum efficiency spectra have also been computed for the modeled TJ solar cell device. Possible design optimization issues to enhance the quantum efficiency have also been discussed with respect to some applicable features of Crosslight APSYS.
Avalanche photodiodes (APDs) are being widely utilized in various application fields where a compact technology computer aided design (TCAD) kit capable for APD modeling is highly demanded. In this work, based on the advanced drift and diffusion model with commercial software, the Crosslight APSYS, avalanche photodiodes, especially the InP/InGaAs separate absorption, grading, charge and multiplication (SAGCM) APDs for high bit-rate operation have been modeled. Basic physical quantities like band diagram, optical absorption and generation are calculated. Performance characteristics such as dark- and photo-current, photoresponsivity/multiplication gain, breakdown voltage, excess noise, frequency response and bandwidth etc., are simulated. The modeling results are selectively presented, analyzed, and some of results are compared with the experimental. Device design optimization issues are further discussed with respect to the applicable features of the Crosslight APSYS within the framework of drift-diffusion theory.
We report on the design and analysis of a surface-normal coupled-quantum-well (CQW) electro-absorption modulator (EAM) using a simulation software APSYS. The modulator is designed as a p-i-n diode operating at 1.55 um, in which the CQW structure is composed of InGaAs-InAlAs. In this paper, detailed analysis of the internal device physics is investigated, which includes the transition energy and the square of the normalized overlap integrals between confined energy levels for electrons and holes. This analysis reveals the mechanisms in the device that are responsible for the redshift of the absorption spectra for achieving an operating wavelength at 1.55 um, which, in turn, provides researchers with insight in the high performance modulators design. The analysis also explains the dependence of the absorption spectra on wavelength and bias voltage. The simulation model self-consistently solves for wavefunctions and the corresponding quantum states energies and then used for absorption spectra calculations within the 2D/3D drift-diffusion framework.
WS9001: Crosslight Software Inc. Industry Sponsored Workshop: Introduction to Optoelectronic Device Simulation and VCSEL Design
The course introduces design principles of modern optoelectronic devices such as vertical-cavity lasers and nitride light emitters. It includes hands-on exercises and provides basic skills for operating advanced simulation software. Deep insight into micro- and nano-scale physical processes is given using real-world device examples. Key material properties are discussed and strategies for obtaining realistic simulation results are described.