Slanted-Incidence Photodetector Structure for Lower Back Reflection

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Solution Overview

Problem

Photonics chips face significant back reflection due to refractive index mismatches between photodetector materials and waveguide materials, leading to reduced responsivity and quantum efficiency.

Innovation Solution

A structure comprising a pad, a waveguide core adjoined to the pad, and a light-absorbing layer on the pad, where the waveguide core's longitudinal axis is inclined relative to the light-absorbing layer's longitudinal axis, effectively reducing back reflection by optimizing the angle of incidence for light absorption.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a photodetector is used with a waveguide, then light detection function is achieved, but back reflection occurs due to refractive index mismatch

Engineering Contradiction:

Improveoptical signal transmission qualityVSAvoidback reflection

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The light-absorbing layer is designed with an asymmetric angled interface rather than a symmetric perpendicular interface. The interface is angled at a specific angle (e.g., 45 degrees) relative to the waveguide axis, creating asymmetry that allows light to pass through while reflecting harmful back reflections away from the waveguide core.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The patent converts the harmful back reflection into a beneficial effect by using the angled interface to redirect reflected light away from the waveguide. The reflection that would normally harm the system is now directed at an angle that prevents it from returning to the waveguide core, effectively converting a harmful factor into a design feature that protects the system.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Ease of manufacture

If the light-absorbing layer interface is perpendicular to the waveguide axis, then alignment is simple, but back reflection is significant

Engineering Contradiction:

Improvealignment simplicityVSAvoidback reflection

Core Design Contradiction:

Ease of manufactureVSObject-generated harmful factors

Solution Approach 1:

The perpendicular interface is replaced with an asymmetric angled interface. This changes the geometry from symmetric (perpendicular) to asymmetric (angled), which eliminates back reflection while maintaining manufacturability through standard semiconductor fabrication techniques such as angled etching or inclined substrate preparation.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The interface angle parameter is changed from 90 degrees (perpendicular) to a specific angled value (e.g., 45 degrees). This parameter change fundamentally alters the optical interaction at the interface, eliminating back reflection while preserving the structural integrity and manufacturability of the device.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If the light-absorbing layer has a larger absorption area, then quantum efficiency increases, but device area increases

Engineering Contradiction:

Improvequantum efficiencyVSAvoidphotodetector area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent transitions from a two-dimensional planar absorption area to a three-dimensional angled absorption path. By introducing an angle into the light-absorbing layer interface, the optical path length is extended without increasing the planar footprint, effectively utilizing the third dimension (depth/angle) to achieve higher quantum efficiency in a compact area.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The angled interface creates a non-linear optical path through the light-absorbing layer. Instead of a straight perpendicular path, light travels along an angled trajectory, effectively increasing the absorption path length within the same planar area, similar to how curved paths can extend travel distance without increasing straight-line distance.

Inventive Principle:

Principle #14Spheroidality (Curvature)

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

The proposed structure enhances the optical path within the light-absorbing layer, increasing responsivity and quantum efficiency while reducing dark current and back reflection.

Implementation Method 1

Photodetectors that convert modulated pulses of light into an electrical signal

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 2

back reflection due to a refractive index mismatch between the material of the photodetector and the material of a waveguide

Methodology Applied

Scientific EffectRefraction: Refraction

Data Source

PatentUS12272758B2Photodetectors and absorbers with slanted light incidence

Publication Date: 2025.04.08 GLOBALFOUNDRIES US INC

AI summary

Structures for a photodetector or light absorber and methods of forming a structure for a photodetector or light absorber. The structure includes a pad, a waveguide core adjoined to the pad, and a light-absorbing layer on the pad. The waveguide core includes a first longitudinal axis, and the light-absorbing layer includes a second longitudinal axis and an end surface intersected by the second longitudinal axis. The end surface of the light-absorbing layer is positioned adjacent to the waveguide core. The first longitudinal axis of the first waveguide core is inclined relative to the second longitudinal axis of the light-absorbing layer and/or the end surface slanted relative to the second longitudinal axis.