Postdoctoral position in Growth, fabrication and characterization of Group III-Nitride microLEDs on Metallic TiN substrate (M/F)

Job Description

Missions

The first part of the postdoc will be dedicated to the MOVPE overgrowth on ordered seed GaN NWs, aiming to form GaN microplatelets on TiN substrates. This will be followed by the optimization of the LED structure growth on these microplatelets, including n-GaN, multiple InGaN quantum-wells, an electron blocking layer and pGaN.
Additionally, the candidate will contribute to the detailed structural and optical characterization of samples, utilizing routine characterization tools such as Scanning Electron Microscopy (SEM), atomic force microscopy, X-Ray Diffraction (XRD), cathodoluminescence(CL) and micro photoluminescence (microPL) . Furthermore, the researcher is expected to actively participate in advanced structural and spectroscopic Transmission Electron Microscopy (TEM) techniques through the ACT-M platform, which offers a unique, cross-linked, and multiscale approach to investigate the structural and interface properties of TiN substrates and III-nitride platelets/thin films and understand the physical properties by measuring internal electric fields in the material.
In a second step the postdoctoral researcher will be responsible for the development of the microLED process flow in a cleanroom environment, with the ultimate goal of demonstrating monolithically integrated RGB GaN-based μ-LEDs on a single wafer.

Activity

The vertical integration of semiconductor devices is a highly attractive strategy to increase the number of devices per unit area. Furthermore, vertical current injection offers several advantages over lateral injection, such as improved current spreading, heat dissipation and contact resistances. This is particularly interesting for the family of group III-nitride semiconductors (i.e., AlN, GaN, InN and their alloys), forming the active regions in commercial light-emitting diodes (LEDs) and high frequency filters.
In this context we propose an original approach through the following project MINT: “Monolithic Integration of Group III-Nitrides on Metallic TiN: A Path Towards Advanced (Opto-)Electronics “, a three-years project in collaboration between CRHEA in Valbonne and the Paul-Drude-Institut für Festkörperelektronik (PDI) in Berlin. The objective is to develop the epitaxial growth of III-nitrides on metallic TiN thin films. The conductive TiN thin films will act as both epitaxial templates and bottom electrodes for Gallium Nitride (GaN)-based micro light-emitting diodes (µLEDs) and Aluminum Nitride (AlN)-based bulk acoustic wave (BAW) devices. This design should drastically simplify the device fabrication: the structure can be vertically powered through the TiN bottom electrode and a top contact while improving heat dissipation and light extraction via back reflection. However, the integration of nitride semiconductors with metallic substrates poses major challenges related to lattice mismatch, chemical incompatibility, and interface defects. Achieving high crystalline quality across the semiconductor-metal interface is thus critical for efficient device operation. The approach proposed in MINT aims to address these challenges:
The originality of this method is to perform lateral overgrowth of GaN nanowires to obtain GaN microplatelets serving as template for microLEDs fabrication. Promising preliminary results have been performed, where GaN platelets were successfully obtained by overgrowing MBE-grown GaN NWs on TiN substrates of variable density (figure shown here). The ohmic contact measured between GaN platelets and TiN underlines the relevance of our approach. Moreover, we aim to control the emission wavelength of the InGaN quantum wells grown on the platelets by tuning their diameter, thus enabling RGB emission from the same wafer.
An additional aspect of the project involves the epitaxial growth of thin AlN films on TiN by allowing full coalescence of AlN nanowires forming an ideal template for epitaxial Bulk Acoustic Wave (BAW) devices. While the focus of the postdoc position is on microLEDs, the researcher will have the opportunity to be involved in this aspect too.

Your Profil

Skills

The different aspects of this work are the epitaxial growth, structural/optical characterization and nanofabrication. A PhD in semiconductor physics or materials science is thus required. A background in III-Nitride materials or LED fabrication would be appreciated but is not mandatory.
The postdoc will participate to regular meeting between CRHEA and PDI. Excellent analytic, organizational and communication skills are thus expected.

Your Work Environment

A postdoctoral position is available at CRHEA within the framework of the MINT project, co-funded by the French National Research Agency (ANR) and the German Research Foundation (DFG). The objective is to develop semiconductor-on-metal platforms for targeted applications in micro-LEDs and Bulk Acoustic Wave (BAW) devices. The selected candidate will be in charge of the epitaxial growth, fabrication and characterization of GaN-based microLEDs on TiN metal substrates using Metal Organic Vapor Phase Epitaxy (MOVPE).
CRHEA (Centre de Recherche sur l'Hétéro-Epitaxie et ses Applications, Université Côte d'Azûr-CNRS): The laboratory is leader on the field of III-nitride semiconductor material epitaxy and has been leading the Labex “GaNeX/t” dedicated to GaN. CRHEA pioneered and contributed to many of the developments in GaN technology, including the growth of GaN platelet on Si and SOI for microLED display . The team has the expertise and the tools necessary for the growth (3 MOCVD reactors for GaN) and device fabrication in clean-room (https://www.crhea.cnrs.fr/en/technology-platform.htm). For structural and optical characterization, CRHEA benefits from the P-CAT facilities (Advanced characterization techniques), with its CRHEACAM platform which specializes in the state-of-the-art characterization (SEM, TEM, PL and CL, XRD, Capacitance-Voltage measurements) of semiconductor materials and crystalline insulating materials. MicroRaman and CL with EBIC measurements will be performed in collaboration with PDI (Berlin) to extract the carrier concentration and assess the electrical contacts.

What We Offer:
Opportunity to work on an international project and on different aspect of materials science: growth, nanofabrication and deep structural characterization. Presentation of the results at national and international conferences.

How to Apply:
Interested candidates should submit their application by sending an email to blandine.alloing@crhea.cnrs.fr and ileana.florea@crhea.cnrs.fr, including a detailed CV, a cover letter explaining their interest and previous background, two reference letters, and a list of publications.

Compensation and benefits

Compensation

Between 3071 € and 4 502 € depending on experience

Annual leave and RTT

44 jours

Remote Working practice and compensation

Pratique et indemnisation du TT

Transport

Prise en charge à 75% du coût et forfait mobilité durable jusqu’à 300€

About the offer

About the CNRS

The CNRS is a major player in fundamental research on a global scale. The CNRS is the only French organization active in all scientific fields. Its unique position as a multi-specialist allows it to bring together different disciplines to address the most important challenges of the contemporary world, in connection with the actors of change.

CNRS

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