Prof. Sunkook Kim's (Department of Advanced Materials Science and Engineering) Develops Nanoporus IGZO Applicable to Visible-to-NIR detecting photo transistor

Professor Sunkook Kim’s research team (Department of Advanced Materials Science and Engineering) proposed an approach for detecting wide spectral range using indium gallium zinc oxide (IGZO) phototransistors. IGZO phototransistors have limited applicability in broad spectral range detection; to solve this many research had been done using external photo-absorber. Our team developed nanoporous IGZO phototransistors, which can detect near infrared (NIR) without using any absorber.

IGZO is optically transparent due to a bandgap of nearly 3–4 eV; thus, to extend the light detection range of IGZO, a laminated approach that introduces secondary materials has been suggested in previous reports. An additional optical absorption layer with a narrower bandgap on the IGZO thin film has been investigated in various studies.  These absorption layers include CdSe, CdS, and PbS quantum dots; graphene dots; metal nanoparticles; and films of selenium. Heterojunctions of two-dimensional MoS₂, graphene, and perovskite (CsPbl_xBr_3-x) with IGZO films have also been investigated.

To solve this problem, Sunkook Kim’s research team investigated the performance of nanoporous IGZO phototransistors. The nanopores throughout the entire thickness of ~ 30 nm in (IGZO) created by block co-polymer lithography. The process of creating a nonporous morphology is sophisticated and is accessed using a wafer-scale phototransistor array. See-through nanopores have edge functionalization with vacancies, which leads to a large subgap states within the conduction band minima and valence band maxima. These subgap states further contribute to detect NIR by employing photogating effect. 

The performance of the phototransistors is assessed in terms of photosensitivity (S) and photoresponsivity (R); both are of high magnitudes (S = 8.6×10⁴ at _ex = 638 nm and P_inc = 512 mW cm⁻²; R = 120 A W⁻¹ at P_inc = 2 mW cm⁻² for the same _ex). 

Additionally, the 7 × 5 array of 35 phototransistors is effective in sensing and reproducing the input image by responding to selectively illuminated pixels.

Prof. Kim said, “This study is significant for developing IGZO phototransistors for visible -NIR detection without using photo-absorber”.

This study was supported by the SKKU Research Fellowship Program of Sungkyunkwan University and in part by the Basic Science Research Program through the National Research Foundation of Korea 

(NRF-2021R1A2B5B02002167, 2021M3H4A1A02056037, 2021R1I1A1A01060065, and 2021R1I1A1A01060078) 

and published on 13^th June 2022 in ACS Nano (I.F:18.03)

Paper name: Probing the Efficacy of Large-Scale Nonporous IGZO 

for Visible-to-NIR Detection Capability: An Approach toward High-Performance Image Sensor Circuitry

DOI: https://doi.org/10.1021/acsnano.2c01773

Article by Sen Anamika