Growth and characterization of Ga2O3 and ZnMgO thin films for solar-blind ultraviolet applications (2020-2023)

Project leader Ramūnas Nedzinskas

Agreement No 1.1.1.2/16/I/001

Research application No 1.1.1.2/VIAA/3/19/442

Deep ultraviolet (UV) photodetectors based on wide-bandgap semiconductors can be used in a variety of applications in defense, astronomy, flame detection, biomedicine, chemical sensing water purification, etc. The concept of this project is to extensively verify the applicability of emerging wide bandgap (WBG) semiconductor Ga2O3 along with the novel pseudobinary system of ZnO-MgO for the needs of ultraviolet (UV) sensor applications, with a particular interest in p-type doping of both materials. Indeed, since a bandgap of beta-Ga2O3 is 4.6­­–4.9 eV, and a tunable bandgap of recently developed ZnMgO can be taylored within 3.3–7.8 eV, both materials are very attractive for their solar-blind nature.

In this project we seek to achieve new insights into the most perspective UV sensing materials by investigation of beta-Ga2O3 and ZnMgO semiconductor thin film structures, exclusively produced in Latvia, as a result of advanced technology transfer from Taiwan. The project includes the number of inbound and outbound training with further activities sweeping from technological growth, fundamental (optical and electrical) characterization, and theoretical modelling to sensor device fabrication and its prototype realization. We believe this project will be beneficial to the society of Baltic countries, owing to the advanced technology and novel engineering systems established.

The project will be implemented at the Institute of Solid State Physics, University of Latvia from 01.06.2020 until 31.05.2023. The total cost of the project is 133’805.88 EUR.


Project progress

09.12.2020

According to the implementation plan of the Project, in the 3rd quarter of 2020, a WP2 was set:
Advanced WBG semiconductor technology transfer from National Sun-Yat Sen University, (NSYSU; Kaoshiung, Taiwan) to ISSP UL (Latvia) through training. In particular, an extensive outbound training in the cleanroom course, epitaxial growth, and structural characterization of wide bandgap semiconductor thin films was planned in the NSYSU laboratories.

However due to the pandemic covid-19 situation, the training in NSYSU is postponed to the earliest possible time window. Accordingly, alternative mobility actions/training were and are being implemented in the largest scientific research centers in Vilnius, Lithuania - Center for Physical Sciences and Technology (FTMC; Partner institution) and Vilnius University (VU; non-Partner institution)

The main purpose of the secondment at FTMC (20.09.2020.-03.10.2020) was to gain new knowledge on optical sample characterization techniques to be used once the ZnMgO and Ga2O3 thin films will be grown. The techniques learned-to-operate: optical microscopy (Olympus SC50) for microstructural observation of the surface quality of the samples, FTIR spectroscopy (Nicolet 8700) to determine the properties of phonon system, optical absorption spectroscopy (Shimadzu UV-3600) to investigate the characteristic bandgap of the material.

The main purpose of the short secondment at VU (04.10.2020.-10.10.2020) was to gain new technological knowledge on the maintenance and programming of the MOCVD reactor (Aixtron MOCVD CCS 3x2 FT), which is similar to the MOCVD reactor (AIX-200RF) at ISSP UL (the latter is currently under maintenance). The routine-cleaning of the shower-head was performed and a general set of the programming commands was learned.

Currently in Thin films laboratory, ISSP UL, after the Mg target was purchased recently, thin films are being sputtered first as pure ZnO and MgO to obtain the critical growth parameters. Afterwards, different ZnxMg1-xO thin films with diverse material compositions will be grown and studied using the optical and electrical characterization equipment in ISSP UL, and if necessary, additionally in FTMC (Lithuania).
Furthermore, since first attempts to sputter Ga2O3 were not successful due to nearly room temperature (~30 oC) melting point of Ga and poor Ga adhesion to stainless steel target holder, a new design of target holder was implemented and is being produced.


10.09.2020

The initial period of the post-doctoral (PD) literature study of beta-Ga2O3 (beta-GO) and ZnMgO wide-bandgap materials. In particular, gallium-oxide is a rather new topic for a PD fellow, an extensive literature overview was carried out. Currently the presentation slides are being prepared for the seminar in ISSP UL (the seminar time was postponed to the 4th month due to a remote work). Optical low-temperature photoluminescence and modulation spectroscopy setup at Partner institution FTMC (Center for Physical Sciences and Technology, Vilnius,Lithuania) was adjusted for the UV-A (315-400 nm),UV-B (280-315 nm) and UV-C (200-280 nm) spectral ultraviolet (UV) windows, relevant for the beta-GO and ZnMgO (ZMO) thin film structures to be studied. Moreover, UV-VIS-NIR (ultraviolet-visible-near infrared) spectroscopy setup at FTMC is learned-to-operate. Currently, an extensive inbound training (supervised by dr. Mārtiņš Zubkins) on magnetron sputtering of WO(3-x) and Ga2O3 materials in Thin films laboratory, ISSP UL and the subsequent characterisation by X-Ray Fluoresence Spectrometer in Laboratory of spectroscopy,ISSP UL is being carried out.