Nitride Semiconductor Superlattice Strain Buffer Layer
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Solution Overview
Problem
Nitride semiconductor devices, such as ultraviolet LEDs and HEMTs, face challenges in achieving sufficient current characteristics and light output power due to issues with the flatness and crystallinity of superlattice strain buffer layers, particularly when using GaN or AlGaN layers with low Al content, which affect the quality of the nitride semiconductor layers stacked on them.
Innovation Solution
A nitride semiconductor device is developed with a superlattice strain buffer layer formed by alternately stacking first layers of AlxGa1-xN (0≦x≦0.25) containing p-type impurity and second layers of AlN, on an AlN strain buffer layer, to improve the flatness and crystallinity of the nitride semiconductor layers, thereby enhancing current characteristics and light output power. The p-type impurity, such as Mg, promotes lateral crystal growth, and the thickness of the first layers is optimized to be between 0.1 nm and 3 nm to achieve these improvements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a superlattice strain buffer layer is formed using GaN or AlGaN layers with low Al content, then the flatness of the buffer layer is improved, but the crystallinity of the nitride semiconductor layers stacked on it deteriorates
Solution Approach 1:
The invention changes the compositional parameter by introducing p-type impurity (Mg, Zn, Ca, or Be) into the low-Al-content AlGaN layers of the superlattice strain buffer layer. This impurity doping modifies the crystal structure and growth characteristics, enabling the buffer layer to maintain good flatness while providing a crystalline template that improves the crystallinity of subsequently stacked nitride semiconductor layers.
2Power
If the thickness of low-Al-content GaN or AlGaN layers in the superlattice strain buffer layer is reduced, then the light output power of ultraviolet LEDs is improved, but the flatness of the buffer layer deteriorates
Solution Approach 1:
The invention changes the physical-chemical parameter by doping p-type impurity into the thin low-Al-content AlGaN layers. This impurity incorporation enhances lateral crystal growth and improves surface flatness even when the layer thickness is minimized (0.1-3 nm), thereby maintaining good buffer layer flatness while allowing ultra-thin designs that maximize light output power by reducing light absorption in the buffer layer.
3Stability of the object's composition
If p-type impurity is added to AlxGa1-xN layers with low Al content, then the crystallinity and flatness of the superlattice strain buffer layer are improved, but the device complexity increases
Solution Approach 1:
The invention applies local quality by introducing p-type impurity only in the low-Al-content AlGaN layers (first layers) of the superlattice structure, while keeping the AlN layers (second layers) undoped. This localized doping approach improves the crystallinity and flatness of the buffer layer without requiring complex doping throughout the entire structure, thereby limiting the increase in device complexity to only specific regions where it is most needed.
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 approach results in nitride semiconductor devices with improved current characteristics and high light output power by ensuring good flatness and crystallinity of the nitride semiconductor layers, with the p-type impurity concentration between 5×10^16 cm^-3 and 2×10^19 cm^-3, and thickness optimization of the superlattice strain buffer layer layers, leading to enhanced performance in both ultraviolet LEDs and HEMTs.
Implementation Method 1
the p-type impurity, such as Mg, promotes lateral crystal growth
Implementation Method 2
a superlattice strain buffer layer... is provided between the AlN strain buffer layer and an n-type nitride semiconductor layer, thereby controlling thin-film stress and preventing cracks from generating
Data Source
AI summary
A nitride semiconductor device is provided, in which a superlattice strain buffer layer using AlGaN layers having a low Al content or GaN layers is formed with good flatness, and a nitride semiconductor layer with good flatness and crystallinity is formed on the superlattice strain buffer layer. A nitride semiconductor device includes a substrate; an AlN strain buffer layer made of AlN formed on the substrate; a superlattice strain buffer layer formed on the AlN strain buffer layer; and a nitride semiconductor layer formed on the superlattice strain buffer layer, and is characterized in that the superlattice strain buffer layer has a superlattice structure formed by alternately stacking first layers made of AlxGa1-xN (0≦x≦0.25), which further contain p-type impurity, and second layers made of AlN.