Wydarzenia

Seminarium Fizyki Politechniki Wrocławskiej

Scalable 2D Materials for Light Emitting and Light Sensing Devices

Prof. Gerd Bacher

University of Duisburg-Essen, Germany

Abstract:

Two-dimensional (2D) materials represent an ultrathin material class with unique properties. Graphene as the first 2D material reported combines high electrical conductivity and high transparency, whereas transition metal dichalcogenides (TMDCs) exhibit efficient light absorption and emission. Although a wide variety of optoelectronic devices based on 2D materials are reported, most of them lack scalability from both a material as well as a device architecture point of view. In this contribution we report on wafer-scale 2D materials and their implementation in scalable light emitting and light sensing devices.

Graphene has been grown by CVD in an AIXTRON Black Magic reactor by a plasma-enhanced (PE) growth procedure. The PECVD growth was first developed for Cu foils [1], and then adapted to metal-free substrates like Ge [2] and GaN [3] to avoid complex transfer processes during device implementation. As a proof-of-concept, we demonstrate integration of directly grown graphene as a transparent electrode in GaN-based light emitting devices for the visible [3] and for the UV spectral range. Pronounced lateral current spreading, and a reduced turn-on voltage indicate the suitability of our concept.

The potential of ultrathin TMDCs for light emitting devices in the red spectral range is demonstrated by embedding MOCVD grown WS2 monolayers in a vertical device design, where inorganic and organic injection layers are used for electron and hole injection, respectively. Large area red electroluminescence stemming from the TMDC layer with a turn-on voltage as low as 2.5 V has been achieved for both, rigid [4] as well as flexible substrates [5]. This concept has recently been adapted for realizing self-powered light sensing devices. In a further step, 2D materials heterostructures were directly grown on a sapphire substrate to enable the fabrication of photodetectors without involving any transfer process. We demonstrate an enhancement of the responsivity by more than 5 orders of magnitude in a WS2-MoS2 heterostructure device as compared to a single layer reference [6]. In photosensors that combine a MOCVD-grown WS2 monolayer as light sensitizer with CVD-grown graphene as a highly conductive channel, we have been able to shed light on the widely varying values of responsivity reported in literature for such devices. A multicolor optical pump – electrical probe technique enables us to disentangle adsorbate effects and intrinsic photoresponse in 2D heterostructure photodetectors [7].

References
[1] B. Bekdüz et al., Nanotechnology 29 (2018), 455603
[2] B. Bekdüz et al., Sci. Reports 10 (2020) 12938
[3] J. Mischke et al., 2D Materials 7 (2020) 035019
[4] D. Andrzejewski et al., ACS Photonics 6 (2019) 1832
[5] D. Andrzejewski et al., Adv. Opt. Mat. 8 (2020) 2000694
[6] U. Hutten et al., 2D Materials 8 (2021) 045015
[7] Y. Beckmann et al., ACS Appl. Mat. Interf. 14 (2022) 35184