Silicon PN-Junction Light Emission via Reverse Bias Avalanche
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Solution Overview
Problem
CMOS silicon semiconductor manufacturing processes are inefficient in generating and coupling light due to insulating silicon dioxide and metal interconnect layers on the top face of integrated circuits, which inhibit and distort light emission, making them unsuitable for high-speed optical communication systems.
Innovation Solution
A light emitting device using an indirect bandgap semiconductor material with a pn-junction configured for reverse biased breakdown mode, where the insulating and interconnect layers are adapted to reflect light towards a secondary face for improved transmission, allowing for efficient coupling of near-infrared light beyond 1 μm wavelength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If standard CMOS silicon semiconductor manufacturing processes are used with forward-biased pn-junctions, then light emission is achieved, but switching speed is limited to a few hundred kHz
Solution Approach 1:
The patent changes the biasing parameter of the pn-junction from forward-bias to reverse-bias operating mode. This parameter change enables the junction to operate in avalanche breakdown mode, achieving GHz switching speeds while maintaining useful light emission in the 350 nm to 1.7 μm wavelength range, particularly around 700 nm peak
2Speed
If reverse-biased avalanching pn-junctions are used, then switching speed increases to GHz levels, but electroluminescent efficiency decreases
Solution Approach 1:
The patent converts the harmful effect of avalanche breakdown (typically associated with high power consumption and heat) into a beneficial light source. By operating the reverse-biased pn-junction in avalanche breakdown mode, the device generates useful photons in the visible and near-infrared range while achieving fast switching speeds, effectively turning the energy-dissipating avalanche effect into a productive electroluminescent source
3Ease of manufacture
If insulating silicon dioxide and metal interconnect layers are present on the top face of CMOS IC, then standard IC manufacturing is enabled, but light out-coupling is inhibited and radiation pattern is distorted
Solution Approach 1:
The patent inverts the conventional light emission approach by orienting the light-emitting pn-junction away from the standard top face (first face) with insulating and metal layers. Instead, light is emitted through the bottom face (other face) of the silicon body, which is naturally transparent to the generated wavelengths. This inversion allows standard CMOS manufacturing processes to be used while enabling efficient light out-coupling through the opposite face
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
Enables efficient light emission and coupling of near-infrared light with high switching speeds, overcoming the inefficiencies of standard CMOS ICs and enabling their use in optical communication systems by enhancing light transmission and radiation patterns.
Implementation Method 1
reverse-biased avalanching silicon pn-junctions emit light in a wide band from 350 nm to 1.7 μm, with a peak at about 700 nm
Implementation Method 2
forward-biased silicon pn-junctions emit light in a narrow band around 1.1 μm
Implementation Method 3
at least part of the configuration may be adapted or processed to reflect emitted light towards the other face
Implementation Method 4
a body of an indirect bandgap semiconductor material having a first face and at least one other face
Data Source
AI summary
A light emitting device (10) comprises a body (12) of a semiconductor material having a first face (14) and at least one other face (16). At least one pn-junction (18) in the body is located towards the first face and is configured to be driven via contacts on the body into a light emitting mode. The other face (16) of the body is configured to transmit from the body light emitted by the at least one pn-junction (18) in the near infrared part of the spectrum and having wavelengths longer than 1 μm.