PIN Photodiode Window Layer Thickness Control
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Solution Overview
Problem
Conventional semiconductor photo detecting elements, such as PIN-type photodiodes, face challenges in achieving high quantum efficiency for short wavelength ranges due to surface traps and energy barriers, particularly when integrated with InP electronic devices, limiting their performance in communication systems using 850 nm signals.
Innovation Solution
A PIN-type photo detecting element is designed with a semiconductor substrate and multiple layers, including a window semiconductor layer with specific band gap energies and dopant concentrations, where the window semiconductor layer has a thickness of 5 nm to 50 nm to minimize surface traps and enhance carrier generation, thereby improving quantum efficiency across both short and long wavelength ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional PIN-type photodiode structure is used, then the device can be integrated with InP electronic devices, but the quantum efficiency for short wavelength range (less than 0.92 μm) is reduced due to absorption in the InP protective layer and surface traps
Solution Approach 1:
An InAlAs window layer is introduced as an intermediary between the InGaAs active layer and the InP protective layer. This window layer has a bandgap energy (1.4-1.7 eV) higher than InGaAs (0.75-0.85 eV) but lower than InP (1.35 eV), allowing it to transmit short wavelength light while providing a lattice-matched interface that reduces surface traps. The window layer thickness is controlled at 5-50 nm to minimize absorption loss while maintaining its protective function.
Solution Approach 2:
The bandgap energy parameter is optimized by selecting InAlAs composition with Al content adjusted to achieve 1.4-1.7 eV bandgap. The thickness parameter is precisely controlled at 5-50 nm to balance light transmission and surface trap reduction. These parameter changes enable the window layer to simultaneously achieve high transmittance for short wavelength light and effective surface passivation.
2Reliability
If the thickness of the light-absorbing layer is increased to improve carrier generation, then the quantum efficiency improves, but the control precision of the layer thickness becomes difficult to maintain
Solution Approach 1:
The active layer thickness is optimized within the 2-5 μm range, which provides sufficient volume for carrier generation while remaining within the precise control capability of molecular beam epitaxy (MBE). This parameter optimization ensures that the layer is thick enough to absorb incident light effectively but thin enough to maintain uniform thickness and avoid defects.
3Reliability
If a silicon photodiode is used for 850 nm communication, then the quantum efficiency for short wavelength is improved, but the integration with InP electronic devices becomes difficult due to material incompatibility
Solution Approach 1:
The entire photodetector structure uses Group III-V semiconductor materials (InP substrate, InAlAs window layer, InGaAs active layer) that are lattice-matched and chemically compatible. This material homogeneity enables monolithic integration with InP-based electronic devices such as HBTs and SOAs on the same substrate, achieving both high quantum efficiency and full system compatibility.
4Reliability
If the window semiconductor layer thickness is increased to reduce surface traps, then the surface trap reduction improves, but the absorption loss increases
Solution Approach 1:
The window layer thickness is precisely optimized at 5-50 nm, which is sufficient to passivate surface traps and provide a stable interface with the InP protective layer, yet thin enough to allow most short wavelength light (less than 0.92 μm) to transmit through with minimal absorption. This narrow thickness range achieves the optimal balance between surface protection and light transmission.
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 configuration achieves high quantum efficiency for both short and long wavelength ranges, reducing surface traps and increasing carrier contribution to responsivity, outperforming conventional silicon photodiodes and maintaining reliability with low dark current.
Implementation Method 1
A PIN-type photo detecting element has a semiconductor substrate, a first semiconductor layer, a second semiconductor layer and a third semiconductor layer. The first semiconductor layer is provided on the semiconductor substrate, is lattice-matched to the semiconductor substrate, includes a first conductivity type dopant, and has first band gap energy.
Implementation Method 2
The first semiconductor layer is provided on the semiconductor substrate, is lattice-matched to the semiconductor substrate
Data Source
AI summary
A semiconductor photo detecting element includes a PIN-type photo detecting element and window semiconductor layer. The PIN-type photo detecting element has a semiconductor substrate, a first semiconductor layer, a second semiconductor layer and a third semiconductor layer. The first semiconductor layer is provided on the semiconductor substrate, is lattice-matched to the semiconductor substrate, includes a first conductivity type dopant, and has first band gap energy. The second semiconductor layer is provided on the first semiconductor layer, has the first band gap energy, and has a concentration of the first conductivity type dopant lower than that of the first semiconductor layer or is substantially undoped. The third semiconductor layer is provided on the second semiconductor layer. The window semiconductor layer has second band gap energy larger than the first band gap energy at a light-incoming side with respect to the second semiconductor layer and has a thickness of 5 nm to 50 nm.