VCSEL Tunnel Junction Reduces Voltage Drop
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Solution Overview
Problem
Conventional vertical-cavity surface-emitting lasers (VCSELs) experience higher voltage drops due to the higher resistance of p-type DBRs compared to n-type DBRs, leading to reduced performance and increased optical absorption loss.
Innovation Solution
Incorporating a tunnel junction that replaces some p-type material with n-type material in the VCSEL structure, reducing the voltage drop and enhancing conductivity, thereby improving performance by reducing optical absorption loss and allowing lower doping in the top mirror.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If p-type DBR is used in the VCSEL structure, then the top mirror can be formed with conventional doping, but the voltage drop increases and performance decreases due to higher resistance
Solution Approach 1:
The patent changes the doping parameter from p-type to n-type in the top mirror DBR structure. By forming the top mirror with n-type doping instead of conventional p-type doping, and using a tunnel junction to inject holes into the active region, the resistance is significantly reduced, thereby reducing voltage drop and improving overall VCSEL performance
Solution Approach 2:
The patent substitutes the conventional p-type hole injection mechanism with an n-type electron injection mechanism combined with tunnel junction-based hole generation. The tunnel junction creates hot carriers that generate holes in the active region, replacing the need for p-type DBR hole injection and enabling lower resistance top mirror structure
2Loss of energy
If p-type material is used in the top mirror, then the structure can be simplified, but optical absorption loss increases
Solution Approach 1:
The patent changes the material parameter by using n-type doping instead of p-type doping in the top mirror DBR. This parameter change reduces optical absorption loss because n-type materials have lower optical absorption in the relevant wavelength range, compensating for the increased structural complexity introduced by the tunnel junction
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 tunnel junction reduces the voltage drop across the VCSEL, enhancing its performance by improving electrical and optical confinement, and enabling lower doping in the top mirror, which results in reduced optical absorption loss.
Implementation Method 1
a tunnel junction over the p-type layer, wherein the tunnel junction is to reverse a carrier type of an n-type top mirror
Implementation Method 2
an oxidation layer over the active region, wherein the oxidation layer is to provide optical and electrical confinement of the VCSEL
Implementation Method 3
an oxidation layer over the active region, wherein the oxidation layer is to provide optical and electrical confinement of the VCSEL
Data Source
AI summary
A VCSEL may include an n-type substrate layer and an n-type bottom mirror on a surface of the n-type substrate layer. The VCSEL may include an active region on the n-type bottom mirror and a p-type layer on the active region. The VCSEL may include an oxidation layer over the active region to provide optical and electrical confinement of the VCSEL. The VCSEL may include a tunnel junction over the p-type layer to reverse a carrier type of an n-type top mirror. Either the oxidation layer is on or in the p-type layer and the tunnel junction is on the oxidation layer, or the tunnel junction is on the p-type layer and the oxidation layer is on the tunnel junction. The VCSEL may include the n-type top mirror over the tunnel junction, a top contact layer over the n-type top mirror, and a top metal on the top contact layer.