Synthesis, characterization and study of semiconducting materials for energy conversion, sensors, electronics and medical applications

Project leaders

Matteo Bosi, Miklos Serenyi

Agreement

UNGHERIA - HAS (MTA) - Accademia Ungherese delle Scienze

Call

CNR/HAS (MTA) 2016-2018

Department

Engineering, ICT and technologies for energy and transportation

Thematic area

Engineering, ICT and technologies for energy and transportation

Status of the project

New

Research proposal

This proposal aims to continue the joint work done on previous years in the framework of the bilater projects led by dr. Cesare Frigeri, now retired but associated to IMEM and still part of this proposal. The joint activity has produced several publications and conference communications, and we are motivated to go on with the common research topics highlighted in the following points.

1) Amorphous hydrogenated Ge (a-Ge:H): effect of heat treatments

Amorphous Ge (a-Ge) is used in several devices such as photovoltaic solar cells and IR detectors for medical applications. In solar cells a-Ge is used to form electrical junctions with a-Si, either by itself or alloyed with Si to form SiGe and hence a-Si/a-SiGe junctions. In these applications a-Ge must be hydrogenated because H passivates the Ge dangling bonds, thus improving the electrical performance of a-Ge. Devices under operation often heat up, especially if highly selective coatings are applied, and/or must be annealed in order to recover the Staebler-Wronski effect. For a-Si it is known that heat treatments cause modifications of the Si-H bonding configuration and severe morphological degradation. To our knowledge only a very few reports exist on the effect of annealing in a-Ge:H. The aim of this activity is to investigate this issue.
The a-Ge will be deposited on Si substrates by RF sputtering with different H contents and then annealed in Ar at different temperatures and times. Their morphology will be investigated by SEM and AFM, while the H incorporation will be determined by ERDA (elastic recoil detection analysis). FTIR (Fourier transform IR) spectroscopy will be used to evaluate the Si-H bonds present in the samples and their evolution with annealing temperature, time and initial H content. Since H can diffuse into the substrate during annealing and the stretching modes of Ge-H are very close to the ones of the Si-H, the a-Ge will also be sputtered on GaAs and ZnSe, because with the latter substrates the mentioned overlapping of the stretching modes should not occur



2) Epitaxial growth and characterization of Ga2O3

Semiconducting sesquioxides, especially beta-Ga2O3, recently gathered attention because large single crystals and high-quality homo- and hetero-epitaxial layers became available. The possibility of grow high-quality crystals and films paved the way to two new application areas such as substrates for GaN-based LEDs and high-power transistors.
Parma University and IMEM started a joint activity on deposition and study of b-Ga2O3 on c-oriented sapphire, using MOVPE reactor with water as oxidizing agent. The reactor can be used for a standard MOVPE process or, by switching between the oxygen and gallium sources, for atomic layer deposition (ALD). Using the latter techniques Ga2O3 films were grown at lower temperature with respect of MOVPE



3) Optimisation cubic SiC (3C-SiC) films for sensors and electronics

Cubic silicon carbide (3C-SiC) epilayers deposited on Si substrates have several technological applications in microelectromechanical structures (MEMS). Such applications rely on the use of SiC resonators and cantilevers. It is important to control the release of elastic strain naturally present in the SiC epilayers because of the high lattice and thermal mismatch of SiC to the Si substrate.
The joint MFA-IMEM activity on SiC permitted to characterize the layers from the point of view of deformation (with Makyoh) and crystal quality (with transmission electron microscopy, TEM).
The activity will concern the further optimization of the 3C-SiC growth, with focus on parameters such as buffer layer deposition, temperature and the use of chlorinated precursors such as metyltrichloro silane (MTS).
Makyoh topography will be used to study their surface properties and deformations caused by internal stresses.
For the use of 3C-SiC in electronics and power devices the defect density should be lowered enough to reduce leakage currents and minimize doping incorporation. Studies with TEM, correlated with the growth parameters, will permit to go beyond the current IMEM state of the art and to further optimize the growth process.



4) SiC and SiC/SiO2 core shell nanowires: irradiation effects

The combination of distinctive SiC properties and the possibility to synthesize SiC nanowires (NW) make this material an excellent candidate for the fabrication of nanodevices. The functionalization of SiC NWs may also have notable application in sensing and biosensing.
Nevertheless, nanostructured materials may show different behaviour than bulk material in nanofabrication and characterization (SEM, ion and electron beam lithography, FIB processing, local doping by implantation, etc.) and applications operating in radiative environments. Conspicuous examples are the enhanced radiation resistance of nanowires, enhanced sputtering of nanoparticles, bending of nanowires under FIB processing, and deformation of nanocages under electron irradiation. In case of bulk SiC irradiation-induced crystalline to amorphous transition leads to a density reduction of 20-30% leading to significant swelling. This effect has not been studied yet for SiC NWs. Also, the recrystallization of amorphized SiC NWs by annealing is essential question since a similar process in bulk SiC turned to be challenging.
SiC and SiC/SiO2 core/shell NWs, prepared in CNR-IMEM will be processed and investigated at MTA EK MFA. Irradiation of substrates covered with NWS will be performed by ion implanters. Nanoscale processing - local irradiation and amorphization, swelling, sputtering, bending experiments - can be carried out with a focused ion beam (FIB)/FESEM setup equipped with nanomanipulator arms for positioning. Irradiation-induced amorphization and annealing experiments will be done on SiC and SiC/SiO2 NWs and the results will be compared. Characterization will be carried out with FESEM, TEM, and RBS techniques.

Research goals

1)
TTo understand the formation/rupture mechanism of the GeH2 bonds and formation of surface blisters, to determine the best annealing conditions that avoid blisters formation.
Determination of: activation energy for the formation of the surface blisters; FTIR stretching modes of a-Ge through calibration of the FTIR results with ERDA measurements. No such calibration has ever been reported in literature.

2)
Growth and characterization of Ga2O3, with emphasis on the films grown by ALD. Correlation between X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and growth parameters.
Information about the stoichiometry, layer thickness, and crystalline quality of beta-Ga2O3 and on the epitaxial properties, e.g., the quality of the interface with Rutherford backscattering spectrometry combined with channeling (RBS/C). The presence of defects (point defects, external defects, strain) can be analyszed as a function of depth in the Ga2O3 layer.


3)
The aim is to obtain stress-free SiC layers and minimal wafer warp. Elimination or reduction of the wafer warp will make easier and more successful the use of the photolithographic More detailed information on the crystallographic defectivity will be achieved by transmission electron microscopy with the aim to understand the elastic strain release mechanisms.

4)
We aim to study the effect of irradiation and annealing on SiC NW structures

Last update: 25/04/2024