Interband Cascade Laser Cladding for Lower Threshold Voltage
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Solution Overview
Problem
Current interband cascade laser (ICL) devices face challenges with high threshold voltage and operating voltage due to suboptimal metal contacts and carrier transport issues, particularly when grown on n-type GaSb substrates or semi-insulating silicon substrates, leading to inefficiencies in voltage efficiency and temperature performance.
Innovation Solution
The development of GaSb-based ICLs with a highly doped n+-InAsSb layer as the bottom outer cladding layer, grown on a p-type GaSb substrate or semi-insulating substrate, featuring a metal contact on the highly doped n+-InAsSb bottom cladding layer, which reduces threshold voltage and operating voltage, enhancing voltage efficiency and allowing lasing at higher temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If ICLs are grown on n-type GaSb substrates with n-type InAs/AlSb superlattice cladding layers, then the device structure is established for 3-4 μm wavelength operation, but the metal contact creates extra voltage and causes non-ideal ohmic contact leading to high threshold voltage and poor voltage efficiency
Solution Approach 1:
The patent changes the substrate type from n-type to p-type GaSb, and modifies the cladding layer doping from n-type to highly doped n+ type, fundamentally altering the electrical parameters to achieve low-impedance contact and reduce threshold voltage
Solution Approach 2:
The highly doped n+ InAs/AlSb superlattice cladding layer acts as an intermediary between the p-type substrate and the active region, providing both structural support and excellent electrical contact properties that reduce voltage drop
2Ease of manufacture
If ICLs are grown on semi-insulating silicon substrates to reduce cost and increase size, then device cost is reduced and size is increased, but current injection through the metal contact on the high-resistance cladding layer becomes problematic
Solution Approach 1:
The patent changes the cladding layer from undoped or lightly doped to highly doped n+ type, dramatically reducing electrical resistance and enabling reliable current injection onto semi-insulating substrates
Solution Approach 2:
The highly doped n+ cladding layer serves multiple functions: it provides structural support, enables low-resistance current injection, and maintains optical confinement, making the device compatible with cost-effective semi-insulating substrates
3Ease of manufacture
If the conduction band edge of GaSb is much higher than InAs without proper management, then carrier transport complications arise due to possible variations in layer thicknesses, but proper management is complex
Solution Approach 1:
The patent modifies the doping concentration parameter of the cladding layer to highly doped n+ type, which creates a strong electric field that facilitates carrier transport across the conduction band offset, making the structure tolerant to thickness variations
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
This configuration achieves reduced threshold voltage and current densities, enabling ICLs to lase efficiently at temperatures above 270 K in continuous wave mode and above 400 K in pulsed mode, with improved voltage efficiency and smooth carrier transport.
Implementation Method 1
the current needs to be injected laterally through a metal contact on the cladding layer, which is typically made of an InAs/AlSb SL layer that has a relatively high electric resistance
Implementation Method 2
a multitude of developments have paved the way for this III—V based technology to produce efficient and coherent mid-infrared (IR) light sources
Data Source
AI summary
An ICL has (1) an IC region having a real refractive index, the IC region configured to generate light based on interband transitions, (2) an outer cladding layer formed from a high-doped semiconductor material and having an outer cladding layer real refractive index which is lower than the IC region real refractive index, and (3) a metal contact to the outer cladding region. The ICL may further include an intermediate cladding layer positioned between the IC region and the outer cladding layer, and at least one SCL positioned between the IC region and the intermediate cladding layer. In one non-limiting embodiment the ICL comprises an outer cladding layer positioned on a p-type GaSb substrate, wherein the high-doped semiconductor material comprises n+-type InAsSb doped with silicon and the GaSb substrate is doped with beryllium or zinc. The ICL may instead comprise a semi-insulating substrate such as GaAs, Si, or InP.