Avalanche Heterojunction Phototransistor Layer Stack Design
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Solution Overview
Problem
Existing heterojunction phototransistors face a trade-off between responsiveness and response time, where reducing the thickness of the base and collector layers to improve responsiveness leads to increased response time, and complex structures that enhance quantum efficiency come at the expense of response time.
Innovation Solution
Incorporating an avalanche layer with a high bandgap and a set of semiconductor layers between the collector and base layers, including a graded layer, screen charge layer, avalanche layer, and injection layer, to generate additional avalanche gain without increasing the thickness of the base and collector layers, thereby enhancing responsiveness without prolonging response time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the thickness of the base layer and collector layer is reduced to improve responsiveness, then the response time increases
Solution Approach 1:
The patent divides the semiconductor structure into distinct functional layers: a base layer for light absorption, a collector layer for charge collection, and an intermediate layer with specific doping profile. This segmentation allows each layer to be optimized independently - the base and collector layers can be made thin for fast response, while the intermediate layer compensates for responsiveness without adding transit time penalty.
Solution Approach 2:
The patent applies local quality by creating an intermediate layer with a specific doping profile (gradual transition from base to collector doping levels) located between the base and collector layers. This localized structural modification with distinct electrical properties enables the system to achieve both thin base/collector layers for fast response and sufficient charge collection efficiency for high responsiveness.
2Productivity
If complex resonant phototransistor structures are used to improve quantum efficiency, then the response time is limited
Solution Approach 1:
The patent extracts the essential function of enhancing quantum efficiency from complex resonant structures and implements it through a simpler intermediate layer with optimized doping profile. This intermediate layer, positioned between the base and collector, provides the necessary charge multiplication and field enhancement without the temporal limitations imposed by complex resonant cavity structures.
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 avalanche heterojunction phototransistor achieves improved responsiveness by multiplying the photocurrent through avalanche gain, maintaining the response time without increasing the thickness of the base and collector layers, thus optimizing both performance metrics.
Implementation Method 1
said base layer being configured to absorb light radiation at an energy greater than or equal to said gap of the base layer so as to generate a current called photocurrent
Implementation Method 2
said avalanche layer being configured to generate an avalanche gain M, in addition to the transistor gain β and to the optical/electrical conversion gain Gopt, multiplying the photocurrent
Data Source
Figure 1
Figure 2
AI summary
Avalanche heterojunction phototransistor (HAPT) comprising a stack of semiconductor layers above a substrate (S) comprising a set of successive semiconductor layers (Ens), arranged between the collector layer and the base layer comprising: - a top layer of the set called the N-doped graded layer (Grad); - a layer arranged below the graded layer, called the P+-doped charge-screen layer (Ecr); - a layer arranged below the screen layer, having the same material as the screen layer, called the undoped avalanche layer (Av); - a layer arranged below the avalanche layer, having the same material as the screen layer, called the N+-doped injection layer (Inj), having a thickness at least 10 times less than the thickness of said avalanche layer.