Stacked APD Gain Layer for Temperature-Stable Laser Radar Detection
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Solution Overview
Problem
The performance of avalanche photodiodes (APDs) is severely affected by temperature changes due to variations in breakdown voltage and gain, leading to instability and reliability issues in applications such as pulsed time-of-flight laser radar systems.
Innovation Solution
The APD design incorporates a gain layer with multiple stacked gain units, each comprising a multiplication and charge layer, to create a gain flattening region, which improves temperature stability and reduces gain changes with temperature variations, along with an annular contact structure and anti-reflective coating to enhance signal accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a single multiplication layer is used to achieve high gain, then the gain can reach breakdown point, but temperature stability deteriorates and gain changes sharply with temperature
Solution Approach 1:
The multiplication layer is divided into multiple sub-multiplication layers (first multiplication layer, second multiplication layer, third multiplication layer) with different thicknesses and doping concentrations. Each sub-layer contributes differently to the overall gain, allowing the total gain to reach breakdown point while distributing the temperature sensitivity across multiple layers, thereby improving temperature stability
Solution Approach 2:
Different regions of the multiplication layer are designed with different properties: the first multiplication layer has higher doping concentration and smaller thickness, the second has intermediate properties, and the third has lower doping concentration and larger thickness. This local differentiation allows each region to contribute optimally to gain while compensating for temperature effects
2Power
If the multiplication layer is made thicker to increase gain, then more photo-generated carriers are amplified, but avalanche tunneling occurs prematurely and dark current increases
Solution Approach 1:
The multiplication layer is segmented into multiple thin sub-layers instead of one thick layer. This segmentation allows the electric field to be distributed more evenly, preventing premature avalanche tunneling while still achieving sufficient gain through the cumulative effect of multiple layers
Solution Approach 2:
The doping concentration and thickness parameters are optimized for each sub-multiplication layer. By adjusting these parameters, the electric field strength in each layer is controlled to be sufficient for carrier multiplication but not excessive to cause premature tunneling, thus reducing dark current while maintaining gain
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 improved APD design enhances temperature stability, reduces temperature-induced gain fluctuations, and increases reliability, while also reducing dark current and preventing premature avalanche tunneling, resulting in more accurate and stable electrical signals for applications like laser radar systems.
Implementation Method 1
collision ionization occurs under an action of relatively high electric field strength of the multiplication layer 106, to implement an internal gain
Implementation Method 2
The absorption layer 103 may generate a photo-generated carrier
Implementation Method 3
collision ionization occurs under an action of relatively high electric field strength of the multiplication layer 106, to implement an internal gain
Data Source
AI summary
An avalanche photodiode (APD) includes a first electrode, a substrate layer, a buffer layer, a gain layer, a gradient layer, an absorption layer, a diffusion barrier layer, a contact layer, and a second electrode. The gain layer, the gradient layer, and the absorption layer are arranged vertically in sequence. The gain layer, the gradient layer, and the absorption layer are located between the buffer layer and the diffusion barrier layer. The gain layer includes at least two gain units, and the gain units are arranged in a stacked manner. Each of the gain units includes a multiplication layer and a charge layer that are arranged vertically. A distance between the charge layer and the gradient layer is less than a distance between the multiplication layer and the gradient layer.