Monolithic integrated InP distributed bragg reflector (DBR) lasers on (001) silicon

At a Glance

Metadata	Details
Publication Date	2015-01-01
Journal	Ghent University Academic Bibliography (Ghent University)
Authors	Bin Tian, Zhechao Wang, Marianna Pantouvaki, Weiming Guo, P. Absil
Institutions	Imec the Netherlands, Ghent University
Analysis	Full AI Review Included

Monolithic InP DBR Lasers on Silicon: Enabling Next-Generation Photonic ICs

This document analyzes the technical requirements and achievements of the research demonstrating monolithic integrated InP DBR lasers on silicon. 6CCVD positions its specialized Chemical Vapor Deposition (CVD) diamond platforms—particularly Single Crystal Diamond (SCD)—as the essential material solution for overcoming critical thermal limitations and enabling the high-power density scalability required for future Photonic Integrated Circuits (PICs).

Executive Summary

Core Achievement: Demonstration of a room temperature operating, monolithic, integrated in-plane Indium Phosphide (InP) Distributed Bragg Reflector (DBR) laser grown on a standard 300mm silicon substrate.
Integration Method: Utilization of a selective area growth technique (originally for ultrafast transistors) to overcome the major lattice mismatch and thermal expansion differences between III-V materials (InP) and silicon.
Performance Metrics: The device achieved single-mode operation at 931.3 nm, low threshold (77 mW), narrow linewidth (FWHM 1.7 nm), and electrical-to-optical efficiencies exceeding 5%.
Structural Innovation: The process utilized a thin 20 nm buffer layer at the InP-Si interface, significantly thinner than conventional micrometer-thick buffers, enabling superior vertical integration.
6CCVD Value Proposition: While silicon serves as a foundational platform, the thermal bottleneck inherent in high-density PICs necessitates materials with superior heat dissipation. Optical Grade SCD offers thermal conductivity 10x higher than silicon, making it the ideal ultimate substrate or heat spreader for high-power III-V/Silicon hybrid devices.
Manufacturing Capability: The complex fabrication requires extreme material precision (polishing, etching, metalization). 6CCVD provides custom diamond platforms with Ra < 1 nm polishing and specialized metal stacks tailored for bonding and electrical contact requirements.

Technical Specifications

The following key operating parameters and structural dimensions were achieved in the monolithic InP DBR laser device:

Parameter	Value	Unit	Context
Center Wavelength	931.3	nm	Measured single mode operation.
Spectral Linewidth (FWHM)	1.7	nm	Narrow spectral bandwidth, indicating stable operation.
Threshold Power (Peak)	77	mW	Low optical pumping threshold.
External Efficiency	> 5	%	Demonstrated high light-light curve slope efficiency.
Substrate Diameter	300	mm	Standard industry-compatible silicon wafer size (001).
Pump Wavelength	532	nm	Nd:YAG nanosecond pulsed laser used for characterization.
Pump Pulse Duration	7	ns	Temporal characteristic of the excitation source.
InP-Si Buffer Thickness	20	nm	Ultra-thin buffer layer to maintain high crystalline quality.
Bragg Grating Period	165	nm	First order Bragg grating definition.
Bragg Grating Etch Depth	60	nm	Defined via Electron Beam Lithography (EBL) and plasma etching.
Objective Numerical Aperture	0.65	NA	Used for collecting laser emissions (50x objective).

Key Methodologies

The monolithic integration relied on advanced semiconductor fabrication techniques to manage lattice mismatch and integrate the III-V material system onto silicon:

Substrate Preparation: Use of standard 300 mm (001) silicon wafers.
Trench Definition: Implementation of Shallow-Trench-Isolation (STI) methodology to define narrow trenches for selective growth.
Anisotropic Etching: V-groove etching performed to create diamond-shaped cross-sections within the trenches.
Selective Area Growth (SAG): Indium Phosphide (InP) waveguides were grown selectively within the trenches, minimizing the required buffer layer thickness (down to 20 nm) and maintaining high crystalline quality.
Grating Definition: Fabrication of first-order Bragg gratings (165 nm period, 60 nm depth, 50% duty cycle) on top of the InP waveguides using Electron Beam Lithography (EBL) followed by plasma etching.
Optical Field Isolation: Selective dry etch process utilized to completely remove the silicon substrate directly beneath the InP waveguide structure, preventing leakage of the optical field (suspending the InP structure).
Characterization: Optical pumping using 7 ns, 532 nm Nd:YAG pulses, with emission collected and measured via a monochromator to confirm single-mode laser operation.

6CCVD Solutions & Capabilities

6CCVD is an expert supplier of MPCVD diamond platforms, crucial for advanced photonic and electronic integration where thermal and optical purity are paramount. We enable researchers to transition from traditional Si/GaAs platforms to high-power, high-density diamond-based PICs.

Applicable Materials and Thermal Management

The demonstrated InP DBR laser, while functional on Si, is an ideal candidate for integration onto a diamond platform to ensure long-term reliability and scalability for high-power applications.

6CCVD Material Solution	Application Requirement	Material Specification
Optical Grade SCD	Next-generation photonic substrate/heat spreader for III-V integration. Required for high power > 1 W/mm².	Single Crystal Diamond, thickness 0.1 µm - 500 µm. Highly thermal conductive (> 2000 W/mK).
PCD Wafers	Cost-effective, large-area thermal management layers or sacrificial carrier substrates.	Polycrystalline Diamond, up to 125mm in diameter.
Custom Substrates	Direct thermal contact for integrated structures like the suspended InP/DBR section.	Substrates up to 10 mm thickness available for ultimate rigidity.
Metalization Layers	Integration interfaces for laser mounting, electrical contacts, and bonding.	Au, Pt, Pd, Ti, W, Cu layers available. Critical for bonding InP devices.

Customization Potential for Replication and Extension

The complex nature of DBR grating fabrication and selective etching demands substrates with exceptional flatness, purity, and interface preparation capabilities.

Custom Dimensions and Substrate Sizing:
- While the paper used 300 mm Si, 6CCVD can provide custom diamond plates/wafers up to 125 mm (PCD) or large-area SCD mosaics optimized for subsequent selective area growth steps or heterointegration bonding.
Ultra-Precision Polishing:
- The quality of the initial substrate interface is critical for the 20 nm buffer layer and subsequent epitaxy. 6CCVD guarantees Ra < 1 nm polishing on SCD and Ra < 5 nm on inch-size PCD platforms, ensuring optimal surface preparation for III-V deposition.
Advanced Metalization Services:
- Replicating electrically-pumped devices requires custom contact schemes. 6CCVD offers in-house e-beam and sputter deposition of specialized metal stacks (e.g., Ti/Pt/Au for ohmic contacts) tailored for III-V semiconductor integration and bonding processes.
Etch Compatibility:
- Our diamond platforms are highly chemically inert, compatible with the plasma etching (for gratings) and selective dry etch processes mentioned in the research.

Engineering Support

6CCVD’s in-house PhD material science team specializes in optimizing diamond material properties (crystallinity, defects, surface termination) for highly sensitive applications like monolithic integrated lasers and quantum emitters. We can assist your team in selecting the appropriate SCD or PCD grade, thickness, and crystallographic orientation to ensure optimal thermal spreading and minimal stress transfer when integrating complex III-V structures onto diamond for similar Integrated Laser Source projects.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Silicon Photonics more and more is considered as a competitive platform for building complex photonic ICs, applicable in various fields, but the lack of a practical on-chip integrated compact, high-yield and electricallydriven laser source remains a major bottleneck. Due to its indirect bandgap, silicon itself is a poor light emitter. Therefore, new materials such as Germanium, III-V compounds and rare earth doped nanocrystals are being investigated and laser operation from hybrid III-V lasers 1, monolithic Germanium lasers 2 and monolithic IIIV nanowire lasers 3 has been demonstrated. While III-V provides generally better performance, realizing monolithically integrated in-plane lasers that can be integrated with other waveguide circuits remains extremely challenging. In this paper, using a selective area growth technique originally developed for realizing nextgeneration ultrafast electronic transistors, we demonstrate a room temperature operating monolithic integrated inplain InP DBR laser grown on a standard 300mm (001)-silicon substrate. Conventional approaches for growing III-V compounds on silicon require a micrometers-thick buffer to cope with the large lattice mismatch and thermal expansion coefficient difference between silicon and III-Vs. In our work, InP waveguides were selectively grown inside narrow trenches defined by a Shallow-Trench-Isolation (STI) method 4 and V-groove etching. The transmission electron microscope (TEM) image shown in Fig. 1a shows that the InP-material is of high crystalline quality except for the 20nm buffer layer located at the InP-Si interface. Following the epitaxy, we defined first order Bragg gratings (165 nm period, 60 nm etching depth, and 50% Duty Cycle) on top of the diamond-shape InP-waveguides using electron beam lithography (EBL) and plasma etching. Next, the silicon substrate beneath the InP was removed using a selective dry etch process to prevent leakage of the optical field (Fig. 1b). For characterization, 7 ns pump pulses from a 532 nm Nd:YAG nanosecond pulsed laser are delivered to the sample in a uniform rectangular area covering a single cavity. After being scattered by the second order grating located at one end of the DBR laser, the laser emissions is collected by a 50x, 0.65 numerical aperture (NA) objective and measured through a 1⁄4 m monochromator. The single mode spectrum in Fig. 1c and the S-shaped light-light curve convincingly show the devices exhibit indeed laser operation. Efficiencies of more than 5% and high reproducibility of these results over multiple devices and multiple wafers has been demonstrated. The top-down integration process, high yield and high controllability together with the in-plane laser configuration, thin buffer layer and selective area process make this device highly promising as a source for future photonic ICs.

Tech Support

Original Source

DOI: None