Colloquium: Dr. Albert Davydov | NIST
In-Person PHYS 401
Location
Physics : 401
Date & Time
April 16, 2025, 11:00 am – 12:00 pm
Description
TITLE: "CRYSTAL GROWTH AND DOPING OF 2D MATERIALS FOR ADVANCED ELECTRONICS”
ABSTRACT: Layered van-der-Waals 2D materials, such as graphene and metal chalcogenides, are being extensively studied for beyond CMOS scaling limits applications, such as sub-1-nm thick channels for the Front-End-of-Line transistors and complimentary logic devices for the Back-End-of-Line integration. To realize these potentials, multiple material challenges must be overcome, such as wafer-scale fabrication of high-quality 2D layers, reduction of contact resistance, controllable doping, etc. Focusing on the latter, the ability to manipulate electrical properties by controllable doping 2D semiconductors opens a possibility for fabricating ultra-thin p/n junctions and other two- dimensional and hybrid electronic devices. However, reliable processes for reproducible doping of 2D materials are yet to be developed.
ABSTRACT: Layered van-der-Waals 2D materials, such as graphene and metal chalcogenides, are being extensively studied for beyond CMOS scaling limits applications, such as sub-1-nm thick channels for the Front-End-of-Line transistors and complimentary logic devices for the Back-End-of-Line integration. To realize these potentials, multiple material challenges must be overcome, such as wafer-scale fabrication of high-quality 2D layers, reduction of contact resistance, controllable doping, etc. Focusing on the latter, the ability to manipulate electrical properties by controllable doping 2D semiconductors opens a possibility for fabricating ultra-thin p/n junctions and other two- dimensional and hybrid electronic devices. However, reliable processes for reproducible doping of 2D materials are yet to be developed.
This talk will survey various doping approaches of 2D semiconductors from substitutional to electrostatic to charge transfer, followed by the specific example of developing controllable doping of indium selenide (InSe) layers. The n- and p-type substitutional doping of InSe was conducted via single-crystal Bridgman growth using Sn and Zn impurities, respectively. For the n-type case, the concentration of Sn atoms in progressively doped n-type InSe samples varied from tens to hundreds of ppm as estimated from inductively coupled plasma mass spectrometry (ICP-MS). Electrically active dopant concentration was evaluated by van-der-Pauw Hall measurements and compared against the total Sn concentration in the InSe matrix. It was found that the concentration of electrically active Sn dopants was two-to-three orders of magnitude lower than the total Sn content in the InSe matrix. DFT calculations reveal that the relatively low doping efficiency was due to the high ionization energy of substitutional Sn defects in the InSe matrix.
The talk will conclude with utilizing controllable doping of InSe layers to demonstrate a p-InSe/n-InSe homojunction photodetector and gate-tunable n-InSe/p-Si heterojunction tunnel triode.
