GeSi Avalanche Photodiode Resonance Cavity Design
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Solution Overview
Problem
GeSi photodiodes experience low absorption efficiency and responsivity when operating beyond the bandgap wavelength, particularly in the 1.55 μm to 1.6 μm range, and high data rates require thin absorbers that further degrade performance.
Innovation Solution
A normal incident avalanche photodiode with a resonance cavity enhanced (RCE) reflector, incorporating an anti-reflection structure with dielectric layers and a heavily doped top contact layer, and a RCE reflector with intrinsic or lightly doped Si multiplication and cavity length compensation layers, optimized for reflectivity and absorption efficiency across 800 nm to 1600 nm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a thin absorber is used to achieve high 3 dB bandwidth for high data rate operation, then the bandwidth is improved, but the responsivity is degraded
Solution Approach 1:
The patent introduces a resonance cavity structure beneath the absorber layer, transforming the problem from a one-dimensional thickness optimization to a multi-dimensional solution involving cavity depth, reflector position, and resonant wavelength tuning. This allows the thin absorber to achieve enhanced light interaction through resonant standing waves without requiring increased thickness
Solution Approach 2:
The patent optimizes multiple parameters including the cavity depth (typically λ/4), the refractive index of cavity layers, the reflector positioning, and the absorber thickness to achieve resonant enhancement. By carefully tuning these parameters, the system achieves high responsivity despite using a thin absorber layer
2Reliability
If the absorber thickness is increased to improve absorption efficiency, then the responsivity is improved, but the 3 dB bandwidth is reduced
Solution Approach 1:
Instead of relying solely on increased absorber thickness, the patent introduces the resonance cavity dimension to enhance light absorption. The cavity creates resonant standing waves that increase the effective interaction length between light and the absorber material without physically increasing the absorber thickness
Solution Approach 2:
The resonance cavity creates periodic standing wave patterns within the cavity structure, causing light to interact repeatedly with the absorber layer at specific resonant wavelengths. This periodic interaction enhances absorption efficiency without requiring a thicker absorber
3Adaptability or versatility
If a normal incident photodiode operates at wavelength beyond the bandgap of its absorber material, then the device can operate in the desired wavelength range, but the absorption efficiency becomes very low
Solution Approach 1:
The patent uses resonance cavity theory to tune the optical response to specific wavelengths beyond the absorber bandgap. By adjusting the cavity depth, refractive indices, and layer thicknesses, the system achieves resonant enhancement at target wavelengths (e.g., 1.55 μm to 1.6 μm) where the absorber material would otherwise have very low absorption
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enhances the performance and responsivity of GeSi photodiodes, enabling high-speed operation by adjusting reflectivity and absorption efficiency, thereby overcoming the limitations of conventional GeSi photodiodes.
Implementation Method 1
an anti-reflection structure... The reflectivity of the anti-reflection structure for top surface reflection may be less than 10%
Implementation Method 2
a RCE reflector... a bottom reflectivity of the RCE structure may depend on a thickness of the BOX layer and a thickness of a sum of the Si multiplication layer, the Si contact layer and the Si cavity compensation layer
Implementation Method 3
a Ge absorption region on which the anti-reflection structure is disposed
Data Source
AI summary
A GeSi avalanche photodiode (APD includes an anti-reflection structure, a Ge absorption region, and a resonance cavity enhanced (RCE) reflector. The anti-reflection structure includes one or more dielectric layers and a top contact layer which is heavily doped with dopants of a first polarity. The RCE reflector includes: an intrinsic or lightly doped Si multiplication layer, a Si contact layer which is heavily doped with dopants of a second polarity opposite the first polarity, a Si cavity length compensation layer, a buried oxide (BOX) layer, and a Si substrate.