Quantum Dot Photodetector Temperature Stability

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Solution Overview

Problem

Photodetecting devices with quantum dot structures face sensitivity degradation at higher temperatures due to increased potential barriers, making it difficult to maintain high sensitivity across a wide temperature range.

Innovation Solution

Incorporating a quantum well structure with a smaller band gap than the embedding layers downstream of the quantum dot structure, which reduces the temperature dependence of the potential barrier, allowing electrons to flow perpendicularly and maintaining sensitivity even at elevated temperatures.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a quantum dot structure is used in the photodetecting section, then the device can detect light incident perpendicularly to the layer surfaces and achieve high sensitivity at low temperatures, but the sensitivity degrades suddenly when the temperature rises

Engineering Contradiction:

Improvephotodetection sensitivityVSAvoidoperating temperature range

Core Design Contradiction:

Measurement precisionVSTemperature

Solution Approach 1:

The patent combines quantum dots and quantum well layers to form a composite structure. The quantum dots provide high sensitivity through their discrete energy levels and efficient carrier capture, while the quantum well layers provide continuous states that facilitate carrier transport at elevated temperatures. This composite approach allows the photodetector to maintain high sensitivity across a wide temperature range by leveraging the complementary properties of both quantum dot and quantum well structures.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent introduces quantum well layers specifically at the downstream position where photoexcited carriers are generated, while maintaining quantum dots in the photodetecting section. This local differentiation allows the quantum well to provide thermal accommodation for carriers without compromising the quantum dot's sensitivity-enhancing properties. The quantum well layers act as a localized solution to the temperature-dependent sensitivity degradation problem.

Inventive Principle:

Principle #3Local quality

2Adaptability or versatility

If quantum well layers are used in the photodetecting section, then infrared light detection is enabled, but the device requires complex optical devices or diffraction gratings to make incident light parallel to layer surfaces

Engineering Contradiction:

Improveinfrared light detection capabilityVSAvoidoptical device complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

Instead of making the incident light parallel to the layer surfaces (conventional quantum well approach), the patent inverts the approach by having carriers flow perpendicular to the layer surfaces. The quantum dots and quantum well layers are arranged such that photoexcited carriers move from the quantum dot layer through the quantum well layers in the vertical direction, eliminating the need for complex optical devices to redirect light.

Inventive Principle:

Principle #13The other way round (Inversion)

3Adaptability or versatility

If quantum well structure is used, then infrared detection is achieved, but dark current increases exponentially with operating temperature requiring cooling

Engineering Contradiction:

Improveinfrared light detection capabilityVSAvoiddark current

Core Design Contradiction:

Adaptability or versatilityVSObject-generated harmful factors

Solution Approach 1:

The composite quantum dot-quantum well structure addresses dark current by using quantum dots with discrete energy levels that provide better carrier confinement. The quantum well layers with continuous states facilitate controlled carrier transport, reducing thermally generated dark current compared to conventional quantum well structures. This allows operation at higher temperatures without excessive cooling requirements.

Inventive Principle:

Principle #40Composite materials

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 solution effectively stabilizes the potential barrier, preventing sensitivity degradation at high temperatures and enabling high-performance photodetection across a wide temperature range.

Implementation Method 1

a photodetecting device having quantum dots... capable of detecting light which is incident perpendicularly to the layer surfaces

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 2

quantum well structure... whose band gap is smaller than those of the second and third embedding layers... reduces the temperature dependence of the potential barrier

Methodology Applied

Scientific EffectBand gap energy transition:

Data Source

PatentUS7399988B2Photodetecting device and method of manufacturing the same

Publication Date: 2008.07.15 FUJITSU LTD

AI summary

A photodetecting device which is capable of performing photodetection with a high sensitivity in a wide temperature range. A quantum dot structure including an embedding layer and quantum dots embedded by the embedding layer is formed. A quantum well structure including embedding layers and a quantum well layer whose band gap is smaller than those of the embedding layers is formed at a location downstream of the quantum dot structure in the direction of flow of electrons which flow perpendicularly to the quantum dot structure during operation of the photodetecting device. This reduces the temperature dependence of the potential barrier of a photodetecting section, which has to be overcome by electrons, whereby it is possible to lower the potential barrier of the embedding layers at high temperature.