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Simulating GaN Based Devices
Optical and Electrical GaN Device Simulations
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Optical and Electrical GaN Device Simulations
• Background • General device simulator capabilities • Physical models for GaN FET applications • Physical models for GaN optoelectronic applications • Optical application examples
• Random compositional variation effects • Blue LED • Triple quantum well LED • GaN LED on sapphire
• Schottky diode application example • FET application examples
• I-V characteristics • Optimizing field plate design • Self heating effects
• Conclusions
Contents
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Optical and Electrical GaN Device Simulations
• GaN device operation is dominated by Piezo-Electric charges generated by inter-layer stresses and spontaneous polarization
• Often FET devices have no intentional doping so all contacts are Schottky type
• Wurtzite Phase Material System • DIODE, FET and LED are the most common applications
Background
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Optical and Electrical GaN Device Simulations
• Drift-diffusion • Energy balance • Compositionally variant heterojunctions • Self heating • Quantum solutions (Schrodinger – Poisson, NEGF, tunneling) • Optical detection (Ray Trace, FDTD, TMM, BPM) • Optical emitters (Helmholtz, photon rate, gain models) • Reverse ray trace for LEDs • 2D and 3D simulations
General Device Capabilities - Physics
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Optical and Electrical GaN Device Simulations
• Randomized composition or doping variation capability • Interface and bulk traps (can also be used to simulate semi-insulating
substrates) • C-Interpreter for user-defined functions • DC, small signal AC, large signal AC, transient • S, H, Y and Z parameters
• Gains (Ft, Fmax)
• Capacitance – inductance – smith charts • Design of experiments and optimization • Unified structure formats and runtime environment for all simulators
General Device Capabilities - Features
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Optical and Electrical GaN Device Simulations
• Automated calculation of spontaneous and Piezo-Electric polarization • Automated calculation of strain for the whole InAlGaN material system • X and Y composition dependent models for bandgap, electron affinity,
Permittivity, density of state masses, recombination, impact ionization, heat capacity, refractive Index, low and high field mobilities
• GaN specific impact ionization and field/temperature dependent mobility models
• Phonon-assisted tunneling model
Physical Models for GaN FET Applications
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Optical and Electrical GaN Device Simulations
• In addition to the GaN FET models on the previous slide, optoelectronic models for GaN devices include: • Three band parabolic strain dependent quantum k.p. models for gain and spontaneous
recombination • Adachi’s and Sellmeier’s refractive index models with frequency dispersion • Temperature dependent refractive index
Physical Models for Optoelectronic Applications
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Optical and Electrical GaN Device Simulations
• Random compositional variation in quantum wells • User inputs mean and std. deviation of composition fraction or doping
Optoelectronic Examples – Composition Variation
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Three quantum well LED showing user defined randomized x-composition variations in the wells.
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Optical and Electrical GaN Device Simulations
• Effects of random composition on emission spectrum
Optoelectronic Examples – Composition Variation
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The double peak in the optical spectrum resulting from band splitting from random compositional variation.
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Optical and Electrical GaN Device Simulations
• Reverse ray trace and I-V curve for a blue LED
Optoelectronic Examples – Blue LED
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Optical and Electrical GaN Device Simulations
• Resulting emission spectra versus bias for the blue LED
Optoelectronics – Blue LED
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Optical and Electrical GaN Device Simulations
• Triple multi-quantum well LED
Optoelectronics Examples – Multi Quantum Well
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Showing electron and hole populations across the triple well LED.
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Optical and Electrical GaN Device Simulations
• Resulting Spectral Output from Triple Well LED
Optoelectronic Examples – Multi Quantum Well
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Optical and Electrical GaN Device Simulations
• Device Cross Section
Optoelectronic Examples – GaN LED on Sapphire
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GaN N-type conc=3e18
GaN P-type conc=3e17 Anode
Cathode Air
Sapphire
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Optical and Electrical GaN Device Simulations
• Emitted Light Intensity versus Angle For GaN on Sapphire
Optoelectronics Examples – GaN LED on Sapphire
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Optical and Electrical GaN Device Simulations
• Device Cross Section and Band Diagram of a n-GaN Schottky Diode
Schottky Diode Application Example – Reverse IV Characteristics
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Ref P.Pipinis et al, J Appl Physics, 99, 093709 (2006)
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Optical and Electrical GaN Device Simulations
• Reverse I-V Characteristic of a n-GaN Schottky Diode Showing Leakage Current due to Photon Assisted Tunneling versus Temperature
Schottky Diode Application Examples – Reverse IV Characteristics
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Ref P.Pipinis et al, J Appl Physics, 99, 093709 (2006)
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Optical and Electrical GaN Device Simulations
• Current-Temperature Characteristics of a GaN Schottky Diode, Simulated at Different Reverse Bias Voltage With and Without Phonon-Assisted Tunneling Mode
Schottky Diode Application Examples – Reverse IV Characteristics
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Ref P.Pipinis et al, J Appl Physics, 99, 093709 (2006)
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Optical and Electrical GaN Device Simulations
• Typical I-V characteristics
FET Application Examples – IV Characteristics
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Optical and Electrical GaN Device Simulations
• Non Ideal Breakdown Characteristics using Standard Gate Field Plate Design (Breaks down at 150 volts)
FET Application Examples – Optimizing Design
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Optical and Electrical GaN Device Simulations
• After optimizing gate field plate height and over-lap, a 600 volt breakdown was obtained
FET Application Examples – Optimizing Design
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A DOE can be created using ANY parameter in the input file since anything can be made a variable.
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Optical and Electrical GaN Device Simulations
• For GaN FETs on sapphire or silicon carbide substrates, self heating effects are significant. The figures below compares these effects on the resulting I-V and gm curves
FET Application Examples – Self Heating Effects
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Optical and Electrical GaN Device Simulations
• Comparing IdVd curves for a GaN FET on sapphire and silicon carbide substrates respectively
FET Application Examples – Self Heating
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Sapphire Substrate SiC Substrate
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Optical and Electrical GaN Device Simulations
• Many automated models specific to the GaN material system with good default parameters
• Very intuitive and easy to use input file syntax • Industry leading visualization tools for navigating results • Open architecture for propriety in-house model development using
Silvaco’s C-Interpreter model interface • DOE and optimization on any parameter • Virtual Wafer Fab (VWF) split lot runtime environment also available,
running on 64 bit commercial database
Conclusions
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