Integrated Systems EngineeringDevelopment, Modeling, and Optimization of MicroelectronicProcesses, Devices, Circuits, and Systems

August 2004 for NUSOD 2004

Dessis for Optoelectronics

Speaker: Wei-Choon Ng

Email: weichoon@ise.com

ISE Inc., San Jose, California.

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• Introduction

• Components of a Laser/LED Simulator

• Highlights of Some Advanced Physics

• Optoelectronics Examples

Overview

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Introduction to OptoelectronicsIntroduction to Optoelectronics

Simulation in Simulation in DessisDessis

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History

• History of electronic simulator– 1993, spinoff from research of Swiss Federal

Institute of Technology, ETH, Zurich– Became industry standard for modeling CMOS

devices, HEMTs, HBTs and high power devices• History of laser simulator

– 1999, added optics, QW, gain and photon rate modules to the electronic simulator

– 2000, VCSEL simulation enabled– 2002, better gain modeling– 2002, photodetector modules added

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History and Future

• History of laser/LED simulator– 2003, ray tracing module enabling LED

simulation– 2004, Full 3D edge emitter simulation– 2004, Noise and AC models for lasers

• The future…research at ETH– Superluminescent LED– Tunable lasers

• The researchers:Bernd Witzigmann, Andreas Witzig, Matthias Streiff, Michael Pfeiffer, Lutz Schneider, Stefan Odermatt, Valerio Laino, Prof. Wolfgang Fichtner

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Physics-based Optoelectronics TCAD

OpticsElectronics

Poisson ϕ,ϕ,ϕ,ϕ,n,p,TL

Continuity ϕ,ϕ,ϕ,ϕ,n,p, TL,G,A

Temperatureϕ,ϕ,ϕ,ϕ,n,p,TL

Heterostructureϕ,ϕ,ϕ,ϕ,n,p,TL,E(k),ψψψψ

MaxwellΑ,Α,Α,Α,n,p,G,νννν

Photon RateS,G,νννν,n,p

Gain ModelG,n,p,TL,νννν

Self-consistent solutions

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Time Scale

Dipole relaxation

Intraband carrierrelaxation

Optical period

Carrier scattering

10-15 10-14 10-910-1010-1110-1210-13 sec

QW carrier capture

Photon lifetimeQW radiative

recombination time

Carrier lifetime

Quantum mechanical treatment of carriers and classical treatment of optics is appled

transportcapture

intraband

escape

recombination

dipole relaxation

optical period

photon lifetime

Mirror

Mirror

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Coupling between Electronics & Optics

Electrical Problem

Poisson equation

Carrier continuity equations

Temperature/Hydrodynamic equations

QW scattering equations

Optical Problem

Helmholtz equation

Gain Calculations

Schrödinger equation

Photon rate equation

Refractive index, absorptionWavelength

Mode, photon lifetime

Material gain

Active region carrier densities

Stimulated and spontaneous emissions

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Optoelectronics Applications

• Benchmark Applications– 2D Edge Emitting Lasers (bulk, QW, Fabry-

Perot, simple DFB)– 3D Edge Emitting Lasers (with varied grating and

sectional design)– VCSELs (including gain guiding and thermal

lensing effects)– Light Emitting Diodes (LED), 2D & 3D– Photo detectors (PD, APD, MSM)– Imaging, CMOS Sensors, CCD, Solar cells

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Components of a Components of a Laser/LED SimulatorLaser/LED Simulator

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• Representation and Material Database

• Electronic Solver

• Optical Solver

• Quantum Well Transport

• Gain Calculations

• Coupling Everything

Components of a Laser Simulator

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Representation of the Problem

• Devise, new and versatile

editor that enables user to

draw 2D and 3D geometries

and intersections easily.

• Finite Box Integration

method applied to every

node of the mesh.

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Material Database

• All III-V compounds used in lasers and LEDs

• Binary, ternary, quadtenary compounds with default set

of parameters

• Users can change any parameter and define the

properties of a new material

• A PMI (Physical Model Interface) allows the user to

implement functions for certain parameters, e.g.

refractive index, bandgap narrowing, etc.

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Electronic Solver

• Poisson, Continuity, Thermodynamic and Hydrodynamic equations

• Different mobility models

• Ionization, quantization, traps, tunneling models

• Different recombination-generation models

• Degradation, radiation models

• Noise and fluctuation analysis

• Monte Carlo used to tune strained CMOS parameters

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Waveguide problem : Helmholtz equationCavity problem : Wave equation

Optical Solvers - Laser

• Finite element method (FEM)(both waveguide & cavity problems, scalar &vectorial)

• Perfectly Matched Layer (PML)(to simulate radiative boundary conditions)

• Standalone Optical Solver(to optimize mode shape and wavelength)

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Optical Solvers - PML

PML layers

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Optical Solvers - PML

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Optical Solvers - LED

LED problem : Wave equation

• Ray Tracing method(for large structures in the millimeter range)

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• Capture into QW based on a scattering process

• Separate continuum and bound states carrier continuity equations

• Drift-diffusion transport in the lateral plane of the QW

• Only bound state carriers contribute to the gain calculations

Quantum Well Transport

QW Bound States

QW Continuum States

TE

TE

SC

TE: Thermionic Emission

SC: Carrier Scattering

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• Simple model using rectangular wells

(polarization dependent optical matrix element)

• Advanced model with k.p method (Schrödinger

coupled with Poisson)

(zinc blende: 4x4, 6x6 or 8x8. wurtzite: 6x6)

• Bandgap renormalization

• Strain

• Gain broadening models

(Lorentzian, Landsberg, Hyperbolic-cosine)

Gain Calculations

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Gain Calculations

• Gain shift due to many-

body effects

(free carrier theory,

screened Hartree-Fock,

2nd Born approximation)

• Piezoelectric charge for

GaN type QWs

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• 1D gain modeling

(for initial design and fast tuning)

• PMI for loading in external table of gain values

(possibly from direct measurements)

• Option to output gain tables

(for calibration of gain parameters)

• Output k.p bandstructures and wavefunctions

Gain Calculations

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Coupling Everything

System of nonlinear equations

Mesh of Device 1

Circuit Level

System of nonlinear equations

Mesh of Device 2

Circuit Element

• Mixed-mode Simulation(combining device simulations with circuit elements self-consistently)

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• Multiple levels and dimensions

(unlimited connectivity)

• Flexible mathematical framework

(add new models easily)

• Solved by Newton and Gummel iterations

• A wide choice of sparse linear and direct solvers

• Enhanced convergence

• Steady state, Transient and AC simulations

Coupling Everything

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Highlights of Some Highlights of Some Advanced PhysicsAdvanced Physics

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Piezoelectric Field and Screening

• Quantum-confined Stark effect– Piezoelectric charge at

material interfaces � tilted quantum-well

– Quantum-well carriers are spatially distributed according to Schrödinger’s equation � separation of Electrons and Holes

– High Quantum-well carrier densities � screening of Piezoelectric charges

• Effect on laser gain– Gain reduction due to

decreased electron-hole overlap � threshold shift

Band diagram and wave functions for bound carriers. Black: no Piezoelectric charge. Red and blue: positive and negative Piezoelectric charge, respectively.

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Optoelectronic Optoelectronic

ExamplesExamples

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AlGaAs/GaAsAlGaAs/GaAs MQW MQW etched mesa VCSELetched mesa VCSEL

simulationsimulation

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Optoelectronics: VCSEL Simulation

• Simulation of Vertical-Cavity Surface-Emitting Laser (VCSEL)

• Finite-Element TypeFull-Vectorial Optical Mode Solver

• Rigorous Simulation of Diffraction Loss and Radiating Waves

• Simulation includes Spatial Hole Burning and Thermal Lensing

Oxide ConfinementBragg Mirrors

Active Region

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VCSEL: Comparison to Measurements

Output Characteristics Wavelength Tuning (includes self-heating and thermal lensing)

Reference: M. Streiff, A. Witzig, M. Pfeiffer, P. Royo, W. Fichtner: “A Comprehensive VCSEL Device Simulator”, IEEE Journal of Selected Topics in Quantum Electronics, vol. 9, no. 3, May/June 2003

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AlGaAs/GaAs MQW VCSELrotational symmetry

top AlGaAs Bragg Mirror (23 pairs)

active part

bottom AlGaAs Bragg Mirror (35 pairs)

GaAs substrate

cathode

anode anode

dielectric aperture

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AlGaAs/GaAs MQW VCSEL

Optical field distribution (HE11 mode) inside VCSEL structures for different structure geometries

Rout=10um, Rin=5um, Rconf=5um

Rout=10um, Rin=5um, Rconf=2.5um

Rout=5um, Rin=2.5um, Rconf=1.5um

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a)

c)

b)

d)

AlGaAs/GaAs MQW VCSEL

Lattice temperature distribution inside VCSEL taken at Va=1.3 V (a), 1.8V (b), 1.9V (c), and 2V (d) bias points

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VCSEL Near-Field Patterns

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Aperture (µm)

2

3

4

5

VCSELs

Typical VCSEL simulation task: Aperture optimization

Device optimization for:• Mode discrimination

• High Output power

• Good Fiber coupling

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LED SimulationLED Simulation

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Light Emitting Diodes (LEDs)

n-doped

p-doped

i-doped

anode

cathode

Optical intensity distribution inside GaN LED at 2 Volts forward bias condition

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2D MQW AlGaAs/InGaAs LED

Ray Trace portraitOptical intensity

Emission power angular distribution

Spontaneous emission in quantum wells or bulk regions is considered as radiation source

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3D MQW AlGaAs/InGaAs LED

Ray Trace portrait:- 289 active vertices

- 68 rays per active vertex

Optical intensity

“Far-field” is represented as output intensity projected to the sphere

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AlGaInPAlGaInP MQW edgeMQW edge--emitting laser on emitting laser on GaAs substrateGaAs substrate

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AlGaInP MQW laser (1)

Device structureDevice structure

active region (2 QW)

GaAs-cap

GaAs-substrate

Mesa

Current blocking layer

cathode

anode

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AlGaInP MQW laser (2)

Perfectly Match Layer (PML) approach has been used to apply the absorption boundary condition at the external boundaries

Real part of the complex optical mode intensity obtained by vectorial optical mode solver Lumi. Mode polarization is indicated by vector

Radiation waves towards the higher refractive index GaAs layers are clearly seen

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AlGaInP MQW laser (3)

Current confinement above the lasing threshold

Laser output power transient response on a current pulse

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3D Edge Emitting Laser 3D Edge Emitting Laser SimulationSimulation

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Optoelectronics: Advanced / Future Features

State-of-the-Art Active Region Models:

• k·p Bandstructure

• Manybody Gain

Full 3D Edge-Emitter Laser SimulationExample: Ridge Waveguide Multi-Section

Sampled-Grating DFB

Longitudinal Axis

Laser Beam

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CMOS SensorCMOS Sensor

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Transient Electric Field

Electric field plotted on DESSIS grid Electric field plotted on EMLAB grid

The fields are simulated in 3D, but only a cross-section is displayed here.

Steady stateMovie

P = 10 W/m2

λ = 500nm

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Power Density and Optical Generation (Movies)

P = 10 W/m2

λ = 600nm

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Charged Coupled DeviceCharged Coupled Device

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Charge Coupled Device (CCD)

CCD cell geometry Doping Profile

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CCD - Simulation Results (EMLAB)

Instantanous Poynting Field Carrier Generation Rate

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CCD –Ray Tracing vs EMLAB

Carrier Generation Rate for λλλλ=0.5 µµµµmRay Tracing EMLAB

Both generators predict the similar carrier generation patterns within the certain wavelength range

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Integrated Systems EngineeringDevelopment, Modeling, and Optimization of MicroelectronicProcesses, Devices, Circuits, and Systems

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